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Coded Aperture Imaging in High-Energy Astronomy banner


Status: April 14, 1995
Prepared by:
Jean in 't Zand (Los Alamos National Lab, NM, USA),
Gerry Skinner (University of Birmingham, UK),
Rob Rideout (University of Birmingham, UK)

The following list concerns 296 papers that deal with the principle and details of coded aperture imaging (i.e., aperture designs, camera configurations, reconstruction designs and related subjects), as well as have sideways references to coded aperture imaging.

If you have a preprint of a paper on coded-aperture imaging, I'd appreciate it very much if you send me a copy!

Ables, J.G.: 1968, Proceedings of the Astronomical Society of Australia, 1,172
Fourier Transform Photography: A New Method for X-Ray Astronomy
In comparison with all other branches of astronomy, X-ray astronomy suffers from a relative dearth of image forming devices. No X-ray lens is known and image formation by reflection requires glancing incidence optics which have small fields of view and are extremely difficult to fabricate, even for small apertures (about 2 cm;2) now employed. The only other imaging device which has been successfully employed is the simplest of all, the pinhole camera. Pinhole cameras with resolutions better than 10;-3~rad are easily constructed, but the apertures are very small--not greater than about 10;-4 cm;2. The new instrument described here is closely related to the pinhole camera and may be viewed as an attempt to overcome the aperture restrictions of this simple device.

Aitken, G.J.M.,Corteggiani, J.P.,Gay, J.: 1981, Journal of the Optical Society of America, 71,759
Partially Redundant Apertures for Infrared Stellar Imaging

Akimov, V.V.,Blokhintsev, I.D.,Leikov, N.G.: 1988, Space Science Reviews, 49, 139
Characteristics of the Telescope Gamma-1 in the Coded Aperture Mode

Antweiler, M.,Bomer, L.: 1990, Electronics Letters, 26,2068
Merit Factor of Chu and Frank Sequences

Antweiler, M.,Bomer, L.: 1991, Electronics Letters, 27,777
Merit Factor of Chu and Frank Sequences - Reply

Antweiler, M.F.M.,Bomer, L.,Luke, H.D.: 1990, IEEE Transactions On Information Theory, 36,696
Perfect Ternary Arrays

Antweiler, M.,Luke, H.D.: 1994, Frequenz, 48,58
Mismatched Filtering for Periodical Binary Arrays
The crosscorrelation function of a two-dimensional binary array with a mismatched filter array is an ideal impulselike signal. A measure for the loss of the signal-to-noise ratio compared to matched filtering is the filter efficiency of the binary array. The paper derives three methods for the construction of binary arrays with a high filter efficiency. Furthermore, a method for searching the best binary arrays with certain dimensions is introduced. Two tables comprise the best results obtained by the search and constructive methods for arrays with up to 40 and 256 elements, respectively. Applications of the arrays lie in the field of two-dimensional signal processing, e.g. group coding or coded aperture imaging.

Arefev, V.A.,Bugrov, V.P.,Volchanskii, A.V.,Gurov, A.Y.,Korotkova, E.V.,Perkov, A.I.,Fedotov, S.N.,Sharak, M.P.: 1990, Instruments and Experimental Techniques, 33,776
Gamma-Telescope With One-Dimensional Coded Aperture
A one-dimensional scintillation gamma telescope with a coded aperture is described that permits real-time monitoring of the space-energy distributions of gamma sources with energies of 0.5-5 MeV. The telescope has an angular resolution of 1.9-degrees-3.2-degrees and an arc of vision of 26-degrees-50- degrees.

Badiali, M.,Cardini, D.,Emanuele, A.,Ranieri, M.,Soggiu, E.: 1985, Astronomy and Astrophysics, 151,259
Hard X-Ray-Imaging With a Rotating Wide Field Coded Mask Telescope - An Inflight Test

Barber, H.B.,Barrett, H.H.,Wild, W.J.,Woolfenden, J.M.: 1983, Journal of Nuclear Medicine, 24,P25
Development of Small Gamma-Ray Imaging Probes for Invivo Use

Barret, D.,Laurent, P.: 1991, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 307, 512
Calibration of Detectors for Soft Gamma-Ray Astronomy - The Monte-Carlo Approach Applied to the Sigma-Telescope
The general problem of calibrating soft gamma-ray (100 keV-1 MeV) detectors is illustrated in the case of the SIGMA experiment. Particularly, the advantage of coded mask experiments for spectroscopy and the related specific calibration difficulties are considered. It is shown that a Monte Carlo simulation can separate in the spectrum the components due to the experiment itself and those due to the scattering in the environment and permits to take into account experimental configuration modifications after the calibrations. A very detailed geometrical description of the SIGMA telescope is proposed and its in-flight energy response is estimated from Monte Carlo simulations.

Barrett, H.H.,DeMeester, G.D.: 1974, Applied Optics, 13,1100
Quantum Noise in Fresnel Zone Plate Imaging
A Fresnel zone plate, used as a coded aperture, offers a great advantage in geometric collection efficiency over a conventional pinhole or collimator. We present a detailed analysis of the signla-to-noise ratio (SNR) of a quantum- limited zone plate camera. The magnitude and spatial distribution of the noise field and its dependence on the source distribution and the characteristics of the optical processing system are derived. It is shown that the largest SNR advantage occurs for a point source, while for very large, uniform sources there may be a slight net disadvantage using a zone plate. It is also shown that optical processing does not give the highest possible SNR.

Barrett, H.H.,Horrigan, F.A.: 1973, Applied Optics, 12,2686
Fresnel Zone Plate Imaging of Gamma Rays; Theory
The use of a Fresnel zone plate as a coded aperture for imaging incoherent radiation such as gamma rays has been previously reported. The coded image is in many respects similar to a hologram and can be decoded or reconstructed with a coherent optical system. In this paper, the general theory of coded-aperture imaging is presented, first for an arbitrary code and the for an on-axis zone plate, an off-axis zone plate, and a one-dimensional zone plate (or linear chirp). With the on-axis plate, a matched imaging condition is suggested as a guide to optimizing image contrast. With the off-axis zone plate and the linear chirp, it is necessary to use a half-tone screen to spatially heterodyne the object spectrum into the passband of the aperture. In all three cases, expressions for the resolution, depth of field, field of view and relative efficiency are derived. A simplified noise analysis is presented, and some practical system constraints are discussed.

Bassani, L.,Butler, R.C.,Caroli, E.,Dicocco, G.,Natalucci, L.,Spizzichino, A., Stephen, J.B.: 1989, Astrophysical Letters & Communications, 27,321
Simulated Observations of Low-Energy Gamma-Ray Sources
A series of Monte-Carlo simulated observations of gamma ray sources has been obtained for the Zebra telescope, using recent observational data. The results of the simulations are analyzed in order to assess both the sensitivity and imaging capability of the instrument during a typical balloon flight. It is shown that sources like the Crab nebula, the quasar 3C273, and the Seyfert galaxy NGC4151 will be observable over the entire energy range of the instrument (0.2-10 MeV) at the few tens of sigma confidence level and will be located with an accuracy of the order of a few arcminutes. Furthermore, the simulations furnish an estimate of the capability of the telescope to resolve complex structured sources such as SS433 or crowded regions of the sky like that of the Galactic Center.

Bedrosian, S.D.: 1986, Proceedings of the IEEE, 74,1040
Nonuniform Linear Arrays - Graph-Theoretic Approach to Minimum Redundancy

Bignami, G.F.,Dean, A.J.,Durouchoux, P.,Hurley, K.,Lund, N.,McBreen, B., Schonfelder, V.,Swanenburg, B.N.,Tomaschek, G.,Winkler, C.: 1988, Space Science Reviews, 49,157
The GRASP Telescope

Bignami, G.F.,Dean, A.J.,Durouchoux, P.,Lund, N.,McBreen, B.,Ramsden, D., Staubert, R.,Taylor, B.G.,Vedrenne, G.: 1987, IEEE Transactions On Nuclear Science, 34,31
GRASP - Gamma-Ray Astronomy With Spectroscopy and Positioning

Boella, G.,Bussini, A.,Butler, R.C.,Caroli, E.,Caralambous, P.M.,Dean, A.J., Dicocco, G.,Donati, S.,Graham, G.,Holder, S.M.,Mastropietro, M.,Perotti, F., Santambrogio, R.,Traci, S.,Ubertini, P.,Villa, G.,Younis, F.A.: 1986, IEEE Transactions On Nuclear Science, 33,755
The Basic Unit of the Imaging Plane of the Zebra Low-Energy Gamma-Ray Telescope

Bomer, L.,Antweiler, M.: 1990, IEEE Transactions On Information Theory, 36,411
2-Dimensional Perfect Binary Arrays With 64 Elements

Bomer, L.,Antweiler, M.: 1993, Signal Processing, 30,1
Optimizing the Aperiodic Merit Factor of Binary Arrays
The merit factor of an array specifies the ratio of the energy of its autocorrelation function mainlobe to the energy of its autocorrelation function sidelobes. The merit factor of both the periodic and the aperiodic autocorrelaton function of binary arrays is investigated. The merit factor for the periodic autocorrelation function is computed for known classes of binary arrays, such as perfect arrays, shift-register arrays, Legendre arrays, Calabro- Wolf arrays, Lempel arrays, difference set arrays and product arrays. By applying invariance operations to these arrays, the merit factor of the aperiodic autocorrelation function is increased and the sidelobes of the aperiodic autocorrelation function are decreased. The resulting maximal merit factors and minimal sidelobes are tabulated.

Bomer, L.,Antweiler, M.,Schotten, H.: 1993, Frequenz, 47,190
Quadratic Residue Arrays
In this paper, a new construction method for synthesizing two- and higher- dimensional quadratic residue arrays is introduced. The construction is mainly based on addressing the elements of an m-dimensional array by the elements of Galois Field GF(p(m)), where p denotes an odd prime and m denotes an integer. With a following mapping, the elements of the m-dimensional array, except the leading element, are set to either + 1 or - 1. The dimensions of the resulting m-dimensional arrays have the size p. It is shown that the periodic autocorrelation function of these quadratic residue arrays are two- or three- level, depending on whether the number of elements is N = 1 mod 4 or N = 3 mod 4. With these quadratic residue arrays, new classes of two- and higher- dimensional pseudonoise and Legendre arrays are obtained.

Borozdin, K.,Gilfanov, M.,Syunyaev, R.,Churazov, E.,Loznikov, V.,Yamburenko, N., Skinner, G.K.,Patterson, T.G.,Willmore, A.P.,Emam, O.,Brinkman, A.C.,Heise, J., In 't Zand, J.J.M.,Jager, R.: 1990, Soviet Astronomy Letters, 16,804
KS1947+300 - A New Transient-X-Ray Source in Cygnus
While observing the transient x-ray source GS 2023 + 338 on June 1989 with the TTM telescope aboard the Kvant module on the Mir space station, we detected a new transient source, KS 1947 + 300 (Skinner, 1989). On the first day it was observed, the flux from this object in the 2-27 keV band was 70 +/- 10 mCrab. The flux subsequently declined, and on 19 August, the 3-sigma upper limit on the flux was 10 mCrab.

Braga, J.,Covault, C.E.,Grindlay, J.E.: 1989, IEEE Transactions On Nuclear Science, 36,871
Calibration and Performance of the Energetic X-Ray-Imaging Telescope Experiment

Braga, J.,Covault, C.E.,Manandhar, R.,Grindlay, J.E.: 1990, Revista Mexicana De Astronomia Y Astrofisica, 21,633
Hard X-Ray Arcmin Imaging With the EXITE Telescope
In this paper we describe the Energetic X-ray Imaging Telescope Experiment (EXITE) and show the first results obtained. We discuss the coded-aperture technique for imaging of cosmic X-ray sources, used by EXITE.

Braga, J.,Villela, T.,Jayanthi, U.B.,D'Amico, F.,Neri, J.A.: 1991, Experimental Astronomy, 2,101
A New Mask-Antimask Coded-Aperture Telescope for Hard X-Ray Astronomy
A new imaging balloon-borne telescope for hard X-rays in the energy range from 30 to 100 keV is described. The imaging capability is provided by the use of an extended URA-based coded mask. With only one motor and suitable stop bins, we can rotate a carbon-fibre wheel with most of the mask elements attached to it by 180 deg, and a bar, which is also part of the mask pattern and is allowed to rotate freely over the wheel, by 90 deg; this combined rotation creates an antimask of the original mask, except for the central element. This is a novel and elegant manner of providing an antimask without additional weight and complex mechanical manipulations. We show that the use of antimasks is a very effective method of eliminating systematic variations in the background map over the position sensitive detector area. The expected sensitivity of the instrument for the 30-100 keV range is of the order of 7X10;-5 photons cm;-2 s;-1 keV;-1, for an integration time of 10;4 seconds at a residual atmosphere of 3.5 g cm;-2. This telescope will provide imaging observations of bright galactic hard X-ray sources with an angular resolution of ~2 deg. in a 10 deg by 10 deg FOV, which is defined by a collimator placed in front of the detector system. We are particularly interested in the galactic center region, where recent imaging results in X-rays have shown the presence of an interesting source field. Results of computer simulations of the imaging system are reported.

Brown, C.M.: 1972, Ph.D. Thesis, University of Chicago
Multiplex Imaging With Random Arrays
The signal-to-noise ratio in the image from a pinhole camera can be improved by replacing the single pinhole with many pinholes. Pictures from such cameras are subjected to a posteriori interpretation (postprocessing) which collects the images from all the pinholes into a single, stronger image. When the images from individual pinholes overlap on the film, we say they are multiplexed; advantages can then accrue both from better utilization of information gathering and storage resources and from nonlinear detector response. While the latter effect is best explored experimentally, the linear phenomena in such a system may be treated theoretically. The system is an example of a multiplexing system using correlation coding and decoding methods. Multiplexing systems have in common the goal of increasing the rate in a noisy channel by sending through it a superposition of several encoded messages. The imaging process is equivalent to encoding and decoding messages by correlation with binary arrays. In the absence of a priori information about the messages to be sent, this coding can induce a loss of information, an uncertainty inherent to the technique. Promising methods for synthesis of code arrays inducing low uncertainty are reviewed, and no better two-dimensional codes are found for aperiodic correlation than random arrays whose characteristics have been improved slightly by iterative methods. In the imaging application, the coding induces uncertainty in the form of two kinds of intensity inaccuracies: one of low and one of high spatial frequency. The usual postprocessing technique (optical matched filtering) is unsatisfactory in multiplexing systems. Although it has some optimal noise-rejection properties, in multiplexing it can cause an unacceptable amount of low spatial frequency inaccuracy. Two new postporcessing schemes are introduced (mismatched filtering and pseudomatched filtering involving image subtraction) which can remove this low spatial frequency inaccuracy, at the same time lessening the inaccuracies of high spatial frequency. Detailed models of the inherent uncertainty are developed for the three postprocessing schemes. The uncertainty produced by correlation coding methods is modelled as a quasi- statistical nosie process whose amplitude is proportional to the signal strength. Two common physical processes, proportional to the square root of the signal and independent of the signal, are mentioned and their effects evaluated. The most promising coding schemes (nonmultiplexing, aperiodic correlation coding, psuedoperiodic correlation coding with multiplexing) are compared using an expression which includes the effects from all the noise processes. The conditions are found under which each scheme is to be preferred. Multiplexing is known to yield and advantage if signal-independent noise is dominant; it is found that in the imaging system, multiplexing can yield an advantage even if other forms of noise are dominant. Technniques are illustrated and qualitative and quantitative predictions of the theory are tested.

Brown, C.: 1974, Journal of Applied Physics, 45,1806
Multiplex Imaging With Multiple-Pinhole Cameras
When making photographs in x rays or gamma rays with a multiple-pinhole camera, the individual images of an extended object such as the sun may be allowed to overlap; then the situation is in many ways analogous to that in a multiplexing device such as a Fourier spectroscope. Some advantages and problems arising with such use of the camera are discussed, and expressions are derived to describe the relative efficacy of three exposure/postprocessing schemes using multiple- pinhole cameras.

Brunol, J.,de Beaucoudrey, N.,Fonroget, J.: 1979, Optics Communications, 29,31
Sur La Statistique Et L'imagerie Dans Les Processus De Poission Codes Bidimensionnel: Application a L'imagerie Nucleaire

Butler, R.C.,Caroli, E.,Dicocco, G.,Maggioli, P.P.,Spizzichino, A.,Charalambous, P.M.,Dean, A.J.,Drane, M.,Gil, A.,Stephen, J.B.,Perotti, F.,Villa, G.,Badiali, M.,Lapadula, C.,Polcaro, F.,Ubertini, P.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,41
An Evaluation of the Background Introduced from the Coded Aperture Mask in the Low-Energy Gamma-Ray Telescope Zebra
The background which arises from the presence of a coded aperture mask is evaluated. The major contributions which have been considered here are the interactions with the mask of the isotropic gamma ray background, a parallel gamma ray beam, neutrons and the effect of the mask element profile. It is shown that none of these factors contribute to a significant excess or modulation in the background counting rate over the detection plane. In this way the use of a passive rather than an active coded aperture mask is seen to be suitable for use in a low energy gamma ray telescope.

Byard, K.: 1992, Nuclear Instruments & Methods in Physics Research Section A- Accelerators Spectrometers Detectors and Associated Equipment, 322,97
On Self-Supporting Coded Aperture Arrays
Two new constructions for fully self-supporting coded aperture arrays are presented, which produce apertures having equivalent imaging properties to those of the pseudo noise product (PNP) arrays. These two constructions, called the M- P and M-M constructions, increase the number of available self-supporting coded aperture patterns by between 80% and 187% for unit pattern orders up to 10000.

Byard, K.: 1992, Nuclear Instruments & Methods in Physics Research Section A- Accelerators Spectrometers Detectors and Associated Equipment, 313,283
An Optimized Coded Aperture Imaging-System
A new coded aperture system design for use with circular detectors is discussed, whereby square element coded aperture unit patterns are mosaiced onto a circular detector with a view to maximising the size of the unambiguous field of view for any given detector radius. The results for these optimum configurations are presented for all 50% transparency URA and MURA unit patterns of order v < 600. Improvements in the FOV size over standard rectangular mosaicing are presented with the available increase being found to be around 23% for large values of v.

Byard, K.: 1992, Experimental Astronomy, 2,227
Square Element Antisymmetric Coded Apertures
This paper describes a method for constructing square element coded aperture patterns which possess 90 deg antisymmetry. The resulting patterns now make possible the removal of systematic detector background noise from a square pixel detector by means of 'antimask' imaging using a single aperture, and without requiring full 180 deg aperture rotation

Byard, K.: 1993, Electronics Letters, 29,2011
Family of Binary Sequences With Useful Correlation-Properties
A method for the synthesis of an infinite family of binary sequences with perfectly flat cross-correlation sidelobes is presented. The corresponding postprocessing arrays are similarly two-valued, and so the sequences may be particularly suited to applications in high noise environments.

Byard, K.: 1993, Nuclear Instruments & Methods in Physics Research Section A- Accelerators Spectrometers Detectors and Associated Equipment, 336,262
Synthesis of Binary Arrays With Perfect Correlation-Properties -Coded-Aperture Imaging
A new method for the synthesis of binary arrays which have perfect cross- correlation properties is presented. The arrays, which are discussed with an emphasis on coded aperture imaging, may also be of use in a number of other applications, including signal processing, telecommunications and radio antenna design. The new coded aperture configurations which are made available offer a wider choice of possible aperture parameters, and conveniently fill a gap in the system parameters that are currently available. The increased freedom of system choice, which can be made for both one- and two-dimensional systems, includes the size of the aperture array and its throughput value. The new two-dimensional apertures have the further advantage of being fully self-supporting.

Byard, K.,Dean, A.J.,Goldwurm, A.,Hall, C.J.,Harding, J.S.J.,Lei, F.: 1990, Astronomy and Astrophysics, 227,634
Imaging Using HURA Coded Apertures With Discrete Pixel Detector Arrays
Hexagonal URA (HURA) coded apertures have important properties for gamma-ray imaging and they have been successfully used in conjunction with an Anger camera for astronomical gamma-ray observations. However, when coupled to a detector plane constructed from discrete pixels an inherent systematic noise due to the non-perfect overlap between mask elements and detector pixels can cause degradation of the image quality. Here we presents the results of computer simulations designed to evaluate the basic performance of a system employing a rotating HURA mask and two discrete detector pixel geometries: a square pixel detector (SPD) and a hexagonal pixel detector (HPD). Intrinsic systematic noise has been found to affect the quality of the system point spread function for both detector geometries. The noise varies with the mask orientation, the detector resolution and the source position, and is highly magnified by the background level. Special configurations for the HPD geometry have been identified for which a nearly perfect overlap of mask elements with detector pixels occurs at two mask orientations. Under these conditions the systematic noise is completely absent.

Byard, K.,Ramsden, D.: 1994, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 342, 600
Coded-Aperture Imaging Using Imperfect Detector Systems
The imaging properties of a gamma-ray telescope which employs a coded aperture in conjunction with a modular detection plane has been investigated. Gaps in the detection plane, which arise as a consequence of the design of the position sensitive detector used, produce artifacts in the deconvolved images which reduce the signal to noise ratio for the detection of point sources. The application of an iterative image processing algorithm is shown to restore the image quality to that expected from an ideal detector. The efficiency of image processing has enabled its subsequent application to a general coded aperture system in order to gain a significant improvement in the field of view without compromising the angular resolution.

Cannon, T.M.,Fenimore, E.E.: 1978, IEEE Transaactions On Nuclear Science, NS-25, 184
A Class of Near Perfect Coded Apertures

Cannon, T.M.,Fenimore, E.E.: 1979, Applied Optics, 18,1052
Tomographical Imaging Using Uniformly Redundant Arrays
No abstract

Cardini, D.,Badiali, M.,Emanuele, A.,Farina, G.,Gianni, G.,Ranieri, M.,Catanesi, M.G.,Maggi, G.,Selvaggi, G.,Waldner, F.: 1983, Astronomy and Astrophysics, 127, 169
A Hard X-Ray-Imaging Experiment Using a Coded Mask Telescope Prototype

Caroli, E.,Butler, R.C.,Di Cocco, G.,Maggioli, P.P.,Natalucci, L.,Spizzichino, A.: 1984, Il Nuovo Cimento, 7,786
Coded Masks in X- And Gamma-Ray Astronomy: The Problem of the Signal-To-Noise Ratio Evaluation
Coded-mask telescopes are presently considered as one of the best solutions for producing images of the sky in hard X-ray and gamma-ray astronomy, because they can posses optimum signal-to-noise ratio (SNR), which is crucial in an energy range in which the expected fluxes are generally low compared with the background. For a given field of the sky, the values of the SNR, associated with each pixel of the reconstructed image, depend on both the mask design and the decoding technique employed. The expressions for the SNR of a variety of replicated masks are derived for the cases of the inversion and the correlation methods, in different conditions of background and source fluxes. For the inversion method, the SNR is found to be simply inversely proportional to the square root of the trace of the matrix associated with the mask, but generally in the case of the correlation method the SNR is limited by an additional systematic term due to the cross-talk between sources in the field of view. The effect of this term can be avoided by choosing a uniformly redundant array pattern.

Caroli, E.,Stephen, J.B.,Di Cocco, G.,Natalucci, L.,Spizzichino, A.: 1987, Space Science Reviews, 45,349
Coded Aperture Imaging in X- And Gamma-Ray Astronomy
Coded aperture imaging in high energy astronomy represents an important technical advance in instrumentation over the full energy range over X-rays till gamma-rays and is playing a unique role in those spectral ranges where other techniques become ineffective or impracticable due to limitations connected to the physics of interactions of photons with matter. The theory underlying this method of indirect imaging is of strong relevance both in design optimization of new instruments and in the data analysis process. The coded aperture imaging method is herein reviewed with emphasis on topics of mainly practicle interest along with a description of already developed and forthcoming implementations.

Carter, J.N.,Charalambous, P.,Dean, A.J.,Stephen, J.B.,Butler, R.C.,Dicocco, G., Morelli, E.,Spada, G.,Spizzichino, A.,Barbareschi, L.,Boella, G.,Perotti, F., Villa, G.,Badiali, M.,Lapadula, C.,Polcaro, F.,Ubertini, P.: 1982, Nuclear Instruments & Methods in Physics Research, 196,477
A Position-Sensitive Detector for a Gamma-Ray Imaging Telescope

Carter, J.N.,Ramsden, D.,Frye, G.M.,Jenkins, T.L.,Koga, R.: 1982, Monthly Notices of the Royal Astronomical Society, 198,33
High-Resolution Gamma-Ray Telescope Using a Coded Aperture Mask and Drift Chamber

Charalambous, P.M.,Dean, A.J.,Engel, A.R.,Simnett, G.: 1984, Proceedings of the Society of Photo-Optical Instrumentation Engineers, 445,394
An Imaging Telescope for Gamma-Ray Astronomy - Tigar

Charalambous, P.M.,Dean, A.J.,Stephen, J.B.,Young, N.G.S.: 1984, Applied Optics, 23,4118
Aberrations in Gamma-Ray Coded Aperture Imaging
Laboratory test have been performed to investigate the quality of gamma-ray images which may be obtained using the coded aperture mask technique. A number of potential sources of image defects are examined both theoretically and experimentally, and the methods in which these may be minimized eliminated are studied. It is shown that good quality gamma-ray images may be produced by efficient design and control of the imaging system.

Charalambous, P.M.,Dean, A.J.,Stephen, J.B.,Young, N.G.S.,Gourlay, A.R.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,56
Aberrations in Gamma-Ray Imaging-Systems
The aberrations present in a coded aperture imaging system have a fundamentally different origin to those found in a focused optical instrument. A series of laboratory tests is described in which masks with carefully controlled defects were employed to generate non-perfect gamma-ray images, so that the magnitude of the aberrations introduced could be quantitively investigated. The results of these test are presented and the extend to which they affect the design of a practical gamma-ray imaging system is discussed.

Chen, Y.W.,Miyanaga, N.,Yamanaka, M.,Nakai, M.,Tanaka, K.,Nishihara, K., Yamanaka, T.,Nakai, S.: 1990, Journal of Applied Physics, 68,1483
3-Dimensional Imaging of Laser Imploded Targets

Chen, Y.W.,Yamanaka, M.,Miyanaga, N.,Azechi, H.,Ishikawa, S.,Yamanaka, T.,Nakai, S.,Tamura, S.: 1989, Optics Communications, 73,337
Measurement of D-D Burn Region Using Proton Penumbral Coded Aperture Imaging

Chen, Y.W.,Yamanaka, M.,Miyanaga, N.,Yamanaka, T.,Nakai, S.,Yamanaka, C.,Tamura, S.: 1989, Optics Communications, 71,249
3-Dimensional Reconstruction of Laser-Irradiated Targets Using URA Coded Aperture Cameras

Chou, C.: 1984, Proceedings of the Society of Photo-Optical Instrumentation Engineers, 454,457
Fourier Coded Aperture Imaging in Nuclear-Medicine

Chou, C.: 1994, IEE Proceedings-Science Measurement and Technology, 141,179
Fourier Coded-Aperture Imaging in Nuclear-Medicine
A Fourier aperture (FA) is composed of two sinusoidal gratings in contact. When the two gratings rotate on the same axis in equal angles but opposite directions a clear pattern of difference moire fringes is formed, the moire frequency depending on the angle between the two gratings. This aperture of moire fringes is used as a variable frequency grating which is able to scan the object spectrum in the frequency domain. The summation-filtered back projection algorithm with three different apodising functions was introduced in the reconstruction. A Tc-99m gamma ray source and a 1 in-diameter NaI scintillation detector were used in the experiment. The thyroid phantom images showed that spatial resolution of FA agrees with the theoretical prediction. Three dimensional image capability is also discussed. The matrix inversion algorithm was used in the computer simulation of 3-D images. Although the depth resolution of a FA is limited by the restricted view angle of the detector, two plane objects free from noise at different depths were reconstructed.

Chou, C.,King, H.J.: 1984, Proceedings of the Society of Photo-Optical Instrumentation Engineers, 454,465
Gamma-Ray Imaging By Single Grating Aperture

Chou, C.,King, H.J.: 1994, Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers, 33,2072
Quantum-Noise of Fourier-Coded Aperture Imaging-System
The single-grating aperture (SGA) and Fourier aperture (FA) both behave as variable frequency gratings to record the object spectrum directly in a Fourier domain when quantum noise is originally generated in this region. This is in contrast to a stationary coded aperture in which the noise appears in the space domain in the shadow-casting images. The noise properties of SGA and FA imaging systems, using the summation filtered backprojection reconstruction algorithm, have been determined. They are proportional to the square root of the intensity distribution of the object. From the theoretical calculations, signal-to-noise ratios of SGA and FA show the same performance as the SNR of a pinhole camera for small objects. However, for larger objects, SGA and FA show better performance than the pinhole camera. The calculated SNRs of a point and a disc object agree with the experimental results.

Cook, W.R.,Finger, M.,Prince, T.A.,Stone, E.C.: 1984, IEEE Transactions On Nuclear Science, 31,771
Gamma-Ray Imaging With a Rotating Hexagonal Uniformly Redundant Array

Cook, W.R.,Grunsfeld, J.M.,Heindl, W.A.,Palmer, D.M.,Prince, T.A.,Schindler, S.M.,Stone, E.C.: 1991, Astrophysical Journal, 372,L75
Coded-Aperture Imaging of the Galactic-Center Region At Gamma-Ray Energies
The first coded-aperture images of the Galactic center region at energies above 30 keV have revealed two strong gamma-ray sources. One source has been identified with the X-ray source 1E 1740.7-2942, located 0.8-degrees away from the nucleus. If this source is at the distance of the Galactic center, it is one of the most luminous objects in the galaxy at energies from 35 to 200 keV. The second source is consistent in location with the X-ray source GX 354 + 0 (MXB 1728-34). In addition, gamma-ray flux from the location of GX 1 + 4 was marginally detected at a level consistent with other post-1980 measurements. No significant hard X-ray or gamma-ray flux was detected from the direction of the Galactic nucleus (Sgr A*), or from the direction of the recently discovered gamma-ray source GRS 1758-258.

Cook, W.R.,Palmer, D.M.,Prince, T.A.,Schindler, S.M.,Starr, C.H.,Stone, E.C.: 1988, Astrophysical Journal, 334,L87
An Imaging Observation of SN1987a At Gamma-Ray Energies

Cook, W.R.,Palmer, D.M.,Prince, T.A.,Schindler, S.M.,Starr, C.H.,Stone, E.C.: 1989, IAU Symposia,,581
Gamma-Ray Imaging of the Galactic-Center Region

Cordier, B.,Paul, J.,Mandrou, P.,Roques, J.P.: 1994, Nature, 368,698
Earth Occultation or Coded Mask

Covault, C.E.,Grindlay, J.E.,Manandhar, R.P.: 1992, Astrophysical Journal, 388, L65
Hard X-Ray-Imaging of the Galactic Black-Hole Candidate GX339-4
Imaging and spectral observations in the energy range 20-250 keV of the black hole candidate GX 339-4 have been obtained with the Energetic X-ray Imaging Telescope Experiment (EXITE). Observations were made during a balloon flight from Alice Springs, Australia on UT 1989 May 8-10. A single source of nearly 6- sigma significance is detected near the center of the 3.4-degrees field of view with a position consistent with GX 339-4. This is the first imaging observation of GX 339-4 at hard X-ray energies. Our result confirms previously reported results from nonimaging experiments showing significant hard X-ray flux up to greater-than-or-similar-to 60 keV, with a power-law spectral fit similar to other black hole candidates such as Cygnus X-1. The source may have been in an outburst state similar to that recently detected with BATSE on GRO.

Covault, C.E.,Grindlay, J.E.,Manandhar, R.P.,Braga, J.: 1991, IEEE Transactions On Nuclear Science, 38,591
Techniques for Removing Nonuniform Background in Coded-Aperture Imaging On the Energetic X-Ray-Imaging Telescope Experiment
The coded-aperture technique for reconstructing images for a position-sensitive detector looking through a stationary URA mask requires that the background illumination be distributed uniformly across the surface of the detector. Non- uniformities in the background are typical of balloon and space-borne detectors, and introduce large artifacts into the reconstructed image, with a subsequent loss of signal-to-noise. Here we describe a technique, employed for the Energetic X-ray Imaging Telescope Experiment (EXITE) to remove the systematic effects of non-uniform background. We explore the time dependence of intensity and two-dimensional shape of the background detector image during the flight. We construct a "flat field" image from observations where x-ray sources were absent from the field of view. We demonstrate that this technique can successfully reduce RMS fluctuations to within a few percent of ideal Poisson statistics.

Dallas, W.J.: 1979, Optics Communications, 30,155
Artifact-Free Region-Of-Interest Reconstruction from Coded Aperture Recordings

Dallas, W.J.,Linde, R.: 1983, Optica Acta, 30,1561
X-Ray Coded-Aperture Image-Reconstruction Using an Array of Kinoforms

Dean, A.J.,Badiali, M.,Chiappetti, L.,Caroli, E.,Court, A.,Dicocco, G.,Maggioli, P.,Perotti, F.,Soggiu, E.,Spizzichino, A.,Stephen, J.B.,Ubertini, P.,Villa, G., Yearworth, M.: 1987, IEEE Transactions On Nuclear Science, 34,62
Laboratory Gamma-Ray Images Using the Zebra Telescope

Dicke, R.H.: 1968, Astrophysical Journal, 153,L101
Scatter-Hole Cameras for X-Rays and Gamma Rays
A pinhole camera for which the entrance area, covered with a very large number of randomly distributed pinholes, is 50% open is shown to be a very effective way of forming images of a complex of X-ray stars. A simple statistical trick is used to reduce the multidunious overlapping images into a single image. Less than forty detected photons are needed to form an image of a star. Dicocco, G.,Butler, R.C.,Morelli, E.,Spada, G.,Spizzichino, A.,Villa, G., Barbareschi, L.,Boella, G.,Perotti, F.,Ubertini, P. (1981): The use of coded aperture masks in low energy gamma-ray astronomy. In: Proceedings of the 17th International Cosmic Ray Conference - Paris. Vol. 9. (: ) Commissariat a l'Energie Atomique, Gif-sur-Yvette, France, 1-4. (AE(CNR, Laboratorio di Tecnologie e Studio delle Radiazioni Extraterrestri, Bologna, Italy) AI(CNR, Istituto de Fisica Cosmica, Milan, Italy) AJ(CNR, Istituto di Astrofisica Spaziale, Frascati, Italy))

Ducros, G.,Ducros, R.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,49
Statistical-Analysis for Coded Aperture Gamma-Ray Telescope
We have developed a statistical analysis of the image recorded by a photon sensitive detector associated with a coded mask for the French gamma ray telescope SIGMA, in the energy range 20-2000 keV. The aperture of the telescope is not limited to the size of the mask. In the first part, we describe the principle of the image analysis based on the least squares method with a fit function generated and tested term after term. The statistical test is performed on the F distribution followed by the relative improvement of chi;2 when the fit function has an additional term. The second part deals with digital processing aspects: the adjustment on the method to reduce computation time, and the analysis results of two simulated images.

Dunphy, P.P.,McConnell, M.L.,Owens, A.,Chupp, E.L.,Forrest, D.J.,Googins, J.: 1989, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 274,362
A Balloon-Borne Coded Aperture Telescope for Low-Energy Gamma-Ray Astronomy

Durouchoux, P.,Bignami, G.,Dean, A.,Lund, N.,McBreen, B.,Schonfelder, V., Swanenburg, B.,Vedrenne, G.,Winkler, C.: 1989, IAU Symposia,,633
Mapping the Galactic-Center Region With GRASP

Dyer, S.A.,Harms, B.K.,Park, J.B.,Johnson, T.W.,Dyer, R.A.: 1989, Applied Spectroscopy, 43,435
A Fast Spectrum-Recovery Method for Hadamard-Transform Spectrometers Having Nonideal Masks
Ekstrom, M.P.,Woods, J.W. (1974): Application of digital image restoration in X- ray astronomy. In: . (: ),, . (Proceedings EASCON '74; Electronics and Aerospace Systems Convention, Washington, D.C.; 640-645; N) (Lawrence Livermore National Lab., CA.)

Emanuele, A.,Badiali, M.,Cardini, D.,Ranieri, M.,Catanesi, M.G.,Maggi, G., Selvaggi, G.,Waldner, F.: 1984, Astronomy and Astrophysics, 132,33
Detection and Localization of a Hard X-Ray Solar-Burst With a Balloon-Borne Coded Mask Telescope

Epstein, R.,Skupsky, S.: 1990, Journal of Applied Physics, 68,924
Anticipated Improvement in Laser-Beam Uniformity Using Distributed Phase Plates With Quasirandom Patterns

Ervin, A.,Barrett, H.H.,Gindi, G.R.,Paxman, R.G.,Gmitro, A.F.,Giles, C.L.: 1982, Journal of the Optical Society of America, 72,1803
Hybrid Coded-Aperture Pinhole Imaging-System for Nuclear-Medicine
(Rotating slit compared with pinhole)

Eyles, C.J.,Skinner, G.K.,Willmore, A.P.,Bertram, D.,Harper, P.K.S.,Herring, J.R.H.,Ponman, T.J.: 1987, Journal of the British Interplanetary Society, 40, 159
Spacelab 2 Coded Mask X-Ray Telescope
The X-ray imaging telescope built by the University of Birmingham for flight on the Spacelab 2 mission is described in detail. The instrument comprises dual coded mask telescopes having angular resolutions of 3 and 12 arcmin and which respond to X-rays with photon energies in the range 2. 5-30 keV. The telescopes are mounted on an independent pointing system so that observations of targets of interest can be made regardless of the Orbiter's attitude. An attitude measurement system comprising a low light level TV camera and a 35 mm film camera, both of which record the images of optical stars, and a gyro pack enables the pointing direction of the telescopes to be determined to an accuracy of approximately 30 arcsec. (Author abstract) 3 refs.

Eyles, C.J.,Watt, M.P.,Bertram, D.,Church, M.J.,Ponman, T.J.,Skinner, G.K., Willmore, A.P.: 1991, Astrophysical Journal, 376,23
The Distribution of Dark Matter in the Perseus Cluster
We report on the analysis of spatially resolved spectral images of the Perseus cluster obtained with a coded-mask X-ray telescope flown as part of the Spacelab 2 mission. The data allow the temperature and density profiles of the intracluster gas to be measured. From these the cluster potential and hence the cluster mass as a function of radius can be traced. The results show that there is significantly less dark matter in the cluster than implied by virial mass estimates based on the galaxies. The mass-to-light ratio within 1.3h50 Mpc of the cluster center is found to be approximately 100(M./L.). The dark matter is more centrally condensed than the X-ray - emitting gas and probably more so than the galaxies, contrary to expectations from most cosmogonic scenarios. We show that the conclusions are rather robust and insensitive to different parameterizations and assumptions about the X-ray structure and argue that they favor models in which the dark matter is baryonic.

Fenimore, E.E.: 1978, Applied Optics, 17,3562
Coded Aperture Imaging: Predicted Performance of Uniformly Redundant Arrays
URA's have autocorrelation functions with perfectly flat sidelobes. The URA combines the high transmission characteristics of the random array with the flat sidelobe advantage of the non-redundant pinhole arrays. A general expression for the SNR has been developed for the URA as a function of the type of object being imaged and the design parameters of the aperture. The SNR expression is used to obtain and expression for the optimum aperture transmission. Currently, the only 2-D URAs known have a transmission of 1/2. This, however, is not a severe limitation because the use of the non-optimum transmission of 1/2 never causes a reduction in the SNR of more than 30%. The predicted performance of the URA system is compared to the images obtainable from a single pinhole camera. Because the reconstructed image of the URA contains virtually uniform noise regardless of the original object's structure, the improvement over the single pinhole camera is much larger for the bright points than it is for the low intensity points. For a detector with high background noise, the URA will always give a much better image than the single pinhole camera regardless of the structure of the object. In the case of a detector with low background noise, the improvement of the URA relative to the single pinhole camera will have lower limit of ~2f;-1/2, where f is the fraction of the field of view that is uniformly filled with object.

Fenimore, E.E.: 1980, Applied Optics, 19,2465
Coded Aperture Imaging: The Modulation Transfer Function for Uniformly Redundant Arrays
Coded aperture imaging uses many pinholes to increase the SNR for intrinsically weak sources when the radiation can be neither reflected nor refracted. Effectively, the signal is multiplexed onto an image and then decoded, often by computer, to form a reconstructed image. We derive the modulation transfer function (MTF) of such a system employing URAs. We show that the MTF of a URA system is virtually the same as the MTF of an individual pinhole regardless of the shape or size of the pinhole. Thus, only the location of the pinholes is important for optimum multiplexing and decoding. The shape and the size of the pinholes can then be selected based on other criteria. For example, one can generate self-supporting patterns, useful for energies typically encountered in the imaging of laser driven compressions or in soft X-ray astronomy. Such patterns contain holes all of the same size, easing the etching or plating fabrication efforts for the apertures. A new reconstruction method is introduced called delta-decoding. It improves the resolution capabilities of a coded aperture system ny mitigating a blur often introduced during the reconstruction step.

Fenimore, E.E.: 1983, Applied Optics, 22,826
Large Symmetric Pi-Transformations for Hadamard Transforms
No abstract

Fenimore, E.E.: 1986, Applied Optics, 26,2760
Time-Resolved and Energy-Resolved Aperture Images With URA-Tagging
Coded aperture imaging with URAs is the standard technique for imaging above the limit of grazing incident X-ray telescopes. It is an ideal technique for high- energy astrophysics because it has a high throughput, excellent performance on point sources, and the ability to simultaneously measure signal and background. However, many sources of interest in high-energy astrophysics are time variable or require detailed energy spectra. Until now, to obtain a single time (or energy) sample, the photons from the particular time (or energy) interval must be formed into an encoded pattern, then processed to obtain an image for that sample. Therefore, massive computations are required to cover the entire time and energy parameter space. We present a new method of coded aperture analysis called URA-tagging, which provides time and/or energy resolved histories of sources with known positions without using a correlation operation. It can easily reduce the computation time by orders of magnitude compared to the next fastest method, the fast delta Hadamard transform. URA-tagging can also correct for improperly encoded images or motion blurred images. Whereas previous methods for quantifying performance have not taken into account the finite resolution or the quantized sampling, URA-tagging provides a SNR equation that includes all such effects. URA-tagging analysis explains why delta-decoding has a somewhat poorer SNR than balanced correlation: naively, one would expect the better resolution to yield a better SNR. In addition, we show that complementary URAs (exchanged opaque and transparent elements) have different properties, and those with an even number of transparent elements should be preferred.

Fenimore, E.E.: 1987, Applied Optics, 26,2760
Time-Resolved and Energy-Resolved Coded Aperture Images With Ura Tagging

Fenimore, E.E.,Blake, R.L.: 1980, Rev. Sci. Instrum., 51,445
Random Array Grid Collimators
X-ray collimators using grid patterns which are random offer several significant advantages over collimators using periodic grids. In particular, random array grid collimators (RAGC's) eliminate the requirement that there be very closely spaced grids if a wide field of obscuration outside the central peak is desired. The RAGC should be less susceptibel to systematic off-axis leaks, and the RAGC has a better high energy response than a periodic grid collimator. The random array technique can also be used to produce converging or diverging collimators. A general theory is presented which predicts the angular response of a RAGC. It is shown that pure random arrays have two problems: there are strong wings in the response function and the patterns are not self-supporting. Restrictions on the randomness of the pattern are suggested which eliminate these problems but at the price of putting an upper limit on the available throughput. However, even in the worst case, the upper limit for a two-dimensional collimator is as high as 23%. In other cases, throughputs the order of 40% are possible with two- dimensional collimators and of 50% with one-dimensional collimators with a large collecting area. Suggestions are presented for easing the fabrication effort of the grids.

Fenimore, E.E.,Cannon, T.M.: 1978, Applied Optics, 17,337
Coded Aperture Imaging With Uniformly Redundant Arrays
URA's have autocorrelation functions with perfectly flat sidelobes. The URA combines the high transmission characteristics of the random array with the flat sidelobe advantage of the non-redundant pinhole arrays. This gives the URA the capability to image low-intensity, low-contrast sources. Furthermore, whereas the inherent noise in random array imaging puts a limit on the obtainable SNR, the URA has no such limit. Computer simulations show that the URA with significant shot and background noise is vastly superior to random array techniques without noise. Implementation permits a detector which is smaller than its random array counterpart.

Fenimore, E.E.,Cannon, T.M.: 1981, Applied Optics, 20,1858
Uniformly Redundant Arrays - Digital Reconstruction Methods
Several new digital reconstruction techniques for coded aperture imaging are developed which are especially applicable to URAs. The techniques provide improved resolution without upsetting the artifact-free nature of URAs. Two new techniques are described; one which allows self-supporting arrays and one which avoids (or at least mitigates) a blur which has been associated with previous correlation analyses. Each of the methods and their resolution improvements are demonstrated with reconstruction of a laser-driven compression. Particular emphasis has been placed on the special sampling required of the encoded picture and the decoding function if artifacts are to be avoided. For large URAs, it is known that another new digital technique, periodic decoding, is much faster. Periodic decoding does produce artifacts, but they usually are negligible.

Fenimore, E.E.,Cannon, T.M.,Miller, E.L.: 1978, SPIE Proceedings, 149,232
Comparison of Fresnel Zone Plates and Uniformly Redundancy Arrays
Several imaging systems in laser fusion, e-beam fusion, and astronomy employ a Fresnel zone plate (FZP) as a coded aperture. The recent development of URAs promises several improvements in these systems. The first advantage of URA is the fact that its modulation transfer function (MTF) is the same as the MTF of a single pinhole, whereas the MTF of an FZP is an erratic function including some small values. This means that if inverse filtering is used, the URA will be less susceptible to noise. If a correlation analysis is used, the FZP will produce artifacts whereas the URA has no artifact (assuming planar sources). Both the FZP and URA originated from functions which had flat MTFs. However, practical considerations in the implementation of the FZP detracted from its good characteristics whereas the URA was only mildly affected. The second advantage of the URA is that it better utilizes the available detector area. With the FZP, the aperture should be smaller than the detector in order to obtain the full angular resolution corresponding to the thinnest zone. The cyclic nature of the URA allows one to mosaic it in such a way that the entire detector area collect photons from all of the sources within the field of view while maintaining the full angular resolution. If the FZP is as large (or larger) than the detector, all parts of the source will not be resolved with the same resolution. The FZP does have some advantages, in particular its radial symmetry eases the alignment problem; it has a convenient optical decoding method; and higher diffraction order reconstruction might provide better spatial resolution.

Fenimore, E.E.,Cannon, T.M.,Van Hulsteyn, D.B.,Lee, P.: 1979, Applied Optics, 18,945
Uniformly Redundant Arrays Imaging of LAser Driven Compressions: Preliminary Results

Fenimore, E.E.,Weston, G.S.: 1981, Applied Optics, 20,3058
Fast Delta-Hadamard Transform
In many fields (e.g. spectroscopy, imaging spectroscopy, photo-acoustic imaging, coded aperture imaging) binary bit patters known as m sequences are used to encode (by multiplexing) a series of measurements in order to obtain a larger throughput. The observed measurements must be decoded to obtain the desired spectrum (or images in case of coded aperture imaging). Decoding in the past has used a technique called the fast Hadamard transform (FHT) whose chief advantage is that it can reduce the computational effort from N;2 multiplies to NlogN additions or subtractions. However, the FHT has the disadvantage that it does not readily allow one to sample more finely than the number of bits used in the m sequence. This can limit the obtainable resolution and cause confusion near the sample boundaries (phasing errors). We have developed both 1-D and 2-D methods (called fast delta Hadamard transforms, FDHT) which overcome both the above limitations. Applications of the FDHT are discussed in the context of Hadamard spectroscopy and coded aperture imaging with URAs. Special emphasis has been placed on how the FDHT can unite techniques used by both of these fields into the same mathematical basis.

Fiddy, M.A.,Brames, B.J.,Dainty, J.C.: 1983, Optics Letters, 8,96
Enforcing Irreducibility for Phase Retrieval in 2 Dimensions

Fienup, J.R.,Idell, P.S.: 1988, Optical Engineering, 27,778
Imaging Correlography With Sparse Arrays of Detectors

Fleming, J.S.,Goddard, B.A.: 1982, Medical & Biological Engineering & Computing, 20,7
Comparison of Techniques for Stationary Coded Aperture Imaging in Nuclear- Medicine

Fleming, J.S.,Goddard, B.A.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,242
An Evaluation of Techniques for Stationary Coded Aperture 3-Dimensional Imaging in Nuclear-Medicine

Flynn, M.J.,Neumann, D.R.,Wake, R.H.,Wiener, S.N.: 1982, Journal of Nuclear Medicine, 23,P59
A Hybrid Coded-Aperture Parallel-Plate Collimator for Multiview Cardiac Imaging

Galper, A.M.,Lazarev, S.A.,Luchkov, B.I.,Zerov, I.V.,Prilutskii, O.F.: 1981, Kosmicheskie Issledovaniia, 19,947
Calculation of the Characteristics of a Gamma-Ray Telescope With a Coded Aperture
A theoretical analysis shows that the aperture coding technique makes it possible to substantially improve the angular resolution of a gamma-ray telescope. Even in a system where the coding mask is relatively close to the detector, the improvement in angular resolution is at least six-fold. However, this improvement is accompanied by the loss of the telescope's ability to isolate faint discrete sources above the isotropic background. (In Russian).

Garcia, M.R.,Grindlay, J.E.,Burg, R.,Murray, S.S.,Flanagan, J.: 1986, IEEE Transactions On Nuclear Science, 33,735
Development of the EXITE Detector - A New Imaging Detector for 20 - 300 KeV Astronomy

Gehrels, N.,Cline, T.L.,Huters, A.F.,Leventhal, M.,MacCallum, C.J.,Reber, J.D., Stang, P.D.,Teegarden, B.J.,Tueller, J.: 1985, Proc Nth Cosmic Ray Conference; OG9.2, OG9.2,303
A Coded Aperture Imaging System for Hard X-Ray and Gamma-Ray Astronomy

Giles, A.B.: 1981, Applied Optics, 20,3068
Self-Supporting Perfect Masks for 2-D Infrared and X-Ray-Imaging

Gilfanov, M.,Churazov, E.,Sunyaev, R.,Grebenev, S.,Pavlinsky, M.,Dyachkov, A., Kovtunenko, V.,Kremnev, R.,Goldwurm, A.,Ballet, J.,Laurent, P.,Paul, J., Jourdain, E.,Schimtzfraysse, M.C.,Roques, J.P.,Mandrou, P.: 1993, Advances in Space Research, 13,695
Hard X-Ray Spectral Properties and Discovery of Narrow Annihilation Line in the Spectrum of Nova-Muscae
The observations of X-ray Nova in Musca (GRS1124-684) by two coded mask telescopes on board GRANAT observatory provided spectral data in broad 3 - 1300 keV band. During these observations, spanned over a similar to year, the Nova was detected in a three apparently different spectral states, corresponding to different epochs of the soft X-ray light curve: (1) A spectrum with two distinct components (soft, below similar to 8 keV and hard power law tail with slope similar to 2.5, detected up to similar to 300 keV). The soft emission changed gradually with characteristic decay time around 30 days, while power law component exhibited strong variability on the time scales of several hours and decreased much more slowly. (2) A soft spectrum (without hard power law tail), observed during the ''kick'' of the soft X-ray light curve. (3) A hard power law spectrum with slope similar to 2.2. Thus, while the 3 - 300 keV luminosity decreased by more than order of magnitude, the source passed through all spectral states known for galactic black hole candidates (Cyg X-1, GX339-4, 1E1740.7-2942, GRS1758-258 etc.). On January 20-21 1991, the SIGMA telescope aboard GRANAT detected a relatively narrow variable emission line near 500 keV (Fig.l,2) with net flux x 6 10(-3)phot/s/cm(2), most probably related with electron-positron annihilation processes, occurring in the source /1-4/. Additional excess above power law continuum, centered around similar to 200 keV, was found during this observation.

Gilfanov, M.,Syunyaev, R.,Churazov, E.,Loznikov, V.,Efremov, V.,Kaniovskii, A., Kuznetsov, A.,Yamburenko, N.,Melioranskii, A.,Skinner, G.K.,Alemam, O., Patterson, T.G.,Willmore, A.P.,Brinkman, A.C.,Heise, J.,In 't Zand, J.J.M.,Jager, R.,Voges, W.,Pietsch, W.,Doebereiner, S.,Englhauser, J.,Truemper, J.,Reppin, C., Oegelman, H.,Kendziorra, E.,Mony, B.,Maisack, M.,Staubert, R.,Parmar, A.N., Smith, A.: 1989, Soviet Astronomy Letters, 15,291
Observations of X-Ray Pulsars With the Roentgen Observatory On the Kvant Module

Gindi, G.R.,Arendt, J.,Barrett, H.H.,Chiu, M.Y.,Ervin, A.,Giles, C.L.,Kujoory, M.A.,Miller, E.L.,Simpson, R.G.: 1982, Medical Physics, 9,324
Imaging With Rotating Slit Apertures and Rotating Collimators

Gindi, G.R.,Barrett, H.H.,Paxman, R.G.: 1982, Journal of the Optical Society of America, 72,1737
Can a 3-Dimensional Object Be Derived from a 2-Dimensional Coded Image

Gindi, G.R.,Paxman, R.G.,Barrett, H.H.: 1984, Applied Optics, 23,851
Reconstruction of an Object from Its Coded Image and Object Constraints

Golay, M.J.E.: 1971, Journal of the Optical Society of America, 61,272
Point Arrays Having Compact, Non-Redundant Autocorrelations

Goldwurm, A.,Byard, K.,Dean, A.J.,Hall, C.J.,Harding, J.S.J.: 1990, Astronomy and Astrophysics, 227,640
Laboratory Images With HURA Coded Apertures
In this paper we consider the possibility of using hexagonally uniformly redundant array (HURA) coded apertures for high energy gamma ray telescopes where discrete pixel detectors with low positional resolution are generally used. Results of laboratory tests carried out to study the performance of a coded aperture system using both a stationary and rotating HURA mask with a discrete pixel detector are presented and compared to computer simulations. The tests confirm the simulation results indicating that such a system, when the standard cross-correlation deconvolution is applied, suffers from an intrinsic systematic noise due to the asymmetrical mismatch between the mask elements and the detector pixels. To reduce this coding error which is inherent to the system two techniques have been developed and tested. For a stationary mask, a special configuration using hexagonal pixel detector has been identified for which mask elements are binned nearly exactly by the pixels and no coding error is present. An efficient and fast algorithm, based on mean count subtraction and weighted deconvolution, has also been developed in order to reduce the coding error when a proper design of the system is infeasible or when a rotating mask is used. Both of the above techniques have been proved to be effective, the second being more suitable for rotating masks for which the coding error is smoothed in the convolution stage by the mask rotation.

Gorenstein, P.,Helmken, H.,Gursky, H.: 1976, Astrophysics and Space Science, 42, 89
Localization of Gamma-Ray Bursts With Wide Field Multiple Pinhole Camera System in Near Earth Orbit
A multiple pinhole camera system has been designed and proposed for a small satellite of the SAS type for the detection and localization of gamma-ray bursts. The instrument consists of a three unit array of detectors each of which includes a semi-cylindrical collimator surrounding a two-dimensional position- sensitive detector. The collimator contains slits of 1 mm width that are cut parallel to the axis of the cylinder. The slits are randomly arranged in azimuth around the cylinder. X-rays may enter the counter through several surfaces. The point at which photoelectric interaction takes place is determined in two dimensions in a plane perpendicular to the cylinder axis. Each unit of the system determines the position of a burst to a great circle. An intersection of two (or three) great circles provides the precise positions. The field of view of the instrument is 2.7pi ster, essentially the entire region of the sky not occulted by the Earth. It is designed to operate in 20-100 keV. An instrument sized to fit a SAS spacecraft has a sensitivity of better than 10;-erg cm;-2 for bursts whose intense phase occur in less than a total of three seconds. For stronger bursts (larger than 10;-5 erg cm;-2) the location precision is better than a minute of arc.

Gottesman, S.R.,Fenimore, E.E.: 1989, Applied Optics, 28,4344
New Family of Binary Arrays for Coded Aperture Imaging
We introduce a new family of binary arrays for use in coded aperture imaging which are predicted to have properties and sensitivity (SNR) equal to that of the URA. The new arrays, called MURA (modified URA), have decoding coefficients all of which are unimodular, resulting in a reconstructed image with noise terms completely independent of image-source structure. Although the new arrays are derived from quadratic residues, they do not belong to the cyclic difference set or set of pseudo-noise sequences and consequently are constructable in configurations forbidden for those designs, thus providing the user with a wider selection of aperture patterns to match his particular needs. With the addition of MURAs to the family of binary arrays, all prime numbers can now be used for making optimal coded apertures, increasing the number of available square patterns by more than a factor of 3.

Gottesman, S.R.,Schneid, E.J.: 1986, IEEE Transactions On Nuclear Science, 33, 745
PNP - A New Class of Coded Aperture Arrays
We report on a new class of coded aperture arrays which has all the desirable imaging characteristics of the URA, yet is constructible in dimensions which are forbidden to that design. In addition, the new arrays (called PNP arrays, for pseudo-noise product) are of self-supporting geometry, simplifying fabrication and making them ideal candidates for situations where active collimators are employed, as for example in high-energy gamma-ray imaging. A unique and important feature of all PNP arrays is the ability to produce reconstructed images whose noise is uniform regardless of the original source structure. A comparison of the predicted performance of the PNP, URA, GEOMETRIC, and PINHOLE designs is presented.

Gourlay, A.R.,Stephen, J.B.: 1983, Applied Optics, 22,4042
Geometric Coded Aperture Masks

Gourlay, A.R.,Stephen, J.B.,Young, N.G.S.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,54
Geometrically Designed Coded Aperture Mask Arrays

Gourlay, A.R.,Young, N.G.: 1984, Applied Optics, 23,4111
Coded Aperture Imaging - A Class of Flexible Mask Designs
A general class of coded aperture masks woth certain perfect decoding properties are described. These masks are flexible in design in terms of both their shape and openness ratio.

Grindlay, J.E.,Covault, C.E.,Manandhar, R.P.: 1993, Astronomy & Astrophysics Supplement Series, 97,155
EXITE Observation of the Galactic-Center - A New Transient
The balloon-borne Energetic X-ray Imaging Telescope Experiment (EXITE) observed the galactic center on May 9, 1989. Within the 3.4-degrees (FW H M) field of view, imaged with 22' resolution at 20-250 keV, two sources were detected: the 'Einstein source' (1E1740.7-2942) and a possible second source approximately 40' West (EXS1737.9-2952). This source was detected significantly at both 20-30 keV and 83-111 keV, suggesting a double-backscattered 511 keV line source at 102 keV and a soft excess, perhaps from a black hole candidate undergoing a transient outburst.

Grindlay, J.E.,Garcia, M.R.,Burg, R.I.,Murray, S.S.: 1986, IEEE Transactions On Nuclear Science, 33,750
The Energetic X-Ray-Imaging Telescope Experiment (EXITE)

Grindlay, J.E.,Murray, S.S.: UNKNOWN YEAR, Aip Conference Proceedings, 1982,477
Proposed Hard X-Ray-Imaging and Gamma-Ray Burst Studies for Xte

Groh, G.,Hayat, G.S.,Stroke, G.W.: 1972, Applied Optics, 11,931
X-Ray and Gamma-Ray Imaging With Multiple-Pinhole Cameras Using a Posteriori Image Synthesis

Groh, G.,Stroke, G.W.: 1970, Optics Communications, 1,339
Information Retrieval from Coded Images Formed By Generalized Imaging Systems

Gunson, J.,Polychronopulos, B.: 1976, Monthly Notices of the Royal Astronomical Society, 177,485
Optimum Design of a Coded Mask X-Ray Telescope for Rocket Applications
The paper considers an X-ray telescope based on a two-step imaging technique that involves the formation of a shadowgram of the X-ray source by means of a coded mask built up from opaque and transparent elements. With this technique, the shadowgram is recorded on a suitable position-sensitive detector, and the recording is processed by computer to reconstruct the desired image of the source. These procedures are analyzed, technical problems are discussed, and it is shown that periodic masks with convolution patterns completely free from spurious peaks are optimum. Theoretical as well as practical design considerations are examined for rocket applications of an X-ray telescope system utilizing one- or two-dimensional optimum masks. An autocollimating mask is described in detail, the effect of photon noise on image quality is evaluated, and mask parameters are computed which give the best discrimination against noise for a given set of viewing conditions. A computer simulation of a shadowgraph and source image is provided as an example. It is concluded that coded-shadowmask telescopes are useful in noisy situations only if the field of view under observation is sparsely populated with point sources or extended sources of small angular spread.

Gurker, N.: 1985, X-Ray Spectrometry, 14,74
X-Ray Mapping Using a New Coded Irradiation Technique

Gurov, A.Y.,Fedotov, S.N.: 1990, Instruments and Experimental Techniques, 33, 1060
Comparison of Gamma-Telescope Sensitivities in the Energy-Range of 1-5 MeV
The sensitivities of a Compton gamma telescope (CGT) and a coded-aperture telescope (CAT) in the range of gamma-quantum energies of 1-5 MeV are compared. The effects of the energy resolution of the detectors for the CGT and of the finite transparency of the coded mask for the CAT are taken into account in the calculations. Sensitivity calculations are performed for various measurement times and background levels. The sensitive area of the instruments is assumed to be 10(4) cm2. The sensitivities of the telescopes are compared with the sensitivity of a collimated total-absorption spectrometric detector.

Haaker, P.,Klotz, E.,Koppe, R.,Linde, R.,Moller, H.: 1985, Medical Physics, 12, 431
A New Digital Tomosynthesis Method With Less Artifacts for Angiography

Haberl, F.: 1984, - Thesis, MPI-Garching
Untersuchungen an Einer Kodierten Lochkamera Fuer Astronomische Messungen Im Harten Roentgenbereich

Hammersley, A.P.: 1986, Ph.D. Thesis, University of Birmingham
The Reconstruction of Coded Mask Data Under Conditions Realistic to X-Ray Astronomy Observations

Hammersley, A.P.: 1991, Computer Journal, 34,362
Efficient 2-Dimensional Fast Fourier-Transform Subroutines for Real-Valued or Hermitian Data

Hammersley, A.,Ponman, T.,Skinner, G.: 1992, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 311,585
Reconstruction of Images from a Coded-Aperture Box Camera
Methods for the reconstruction of images from coded-aperture box cameras are discussed. A fast reconstruction method for unbiased reconstruction is presented and examples of its application to simulated and real data are given. An interative procedure to further reduce coding noise is proposed and its effectiveness quantified.

Hammersley, A.P.,Skinner, G.K.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,45
Data-Processing of Imperfectly Coded Images
The theory of mask coding is well established for perfect coding systems, but imperfections in practical situations produce new data processing problems. The Spacelab 2 telescopes are fully coded systems, but some complications arise as parts of the detector are obscured by a strengthening cross. The effects of this sort of obscuration on image quality and ways of handling them will be discussed.

Hanson, C.G.,Skinner, G.K.,Eyles, C.J.,Willmore, A.P.: 1989, Monthly Notices of the Royal Astronomical Society, 240,P1
Coded Mask X-Ray Images of the Large Magellanic Cloud - Hard X-Ray-Emission from EXO 053109-6609.2

Hanson, C.G.,Skinner, G.K.,Eyles, C.J.,Willmore, A.P.: 1990, Monthly Notices of the Royal Astronomical Society, 242,262
Coded Mask X-Ray Images of the Virgo Cluster .1. Hard X-Rays from the Seyfert- Galaxy Ngc-4388

Harper, P.K.S.,Skinner, G.K.,Eyles, C.J.,Wilmore, A.P.,Bertram, D.,Herring, J.R.H.,Peden, J.C.M.,Pollock, A.M.T.,Ponman, T.J.: 1987, Journal of the British Interplanetary Society, 40,163
Flight of the Spacelab X-Ray Telescope
The hard X-ray imaging telescope built at the University of Birmingham and described elsewhere in this issue flew on the Spacelab 2 mission in July/August 1985. The instrument was primarily designed to study the diffuse X-ray emission from clusters of galaxies. During the mission, observations were successfully made of six clusters, a supernova remnant, and the region around the Galactic Centre. This paper describes the preparations for the telescope's flight, and the mission operations. (Author abstract) 3 refs.

Harvey, J.E.,Kotha, A.: 1994, Optics Communications, 106,178
Sparse Array Configurations Yielding Uniform Mtfs in Reciprocal Path Imaging Applications
A method is presented for constructing both one-dimensional and two-dimensional configurations of sparse subaperture arrays which result in uniform spatial frequency response with arbitrarily high spatial resolution for reciprocal path imaging applications (i.e., imaging laser radar applications).

Harvey, J.E.,Rockwell, R.A.: 1988, Optical Engineering, 27,762
Performance-Characteristics of Phased-Array and Thinned Aperture Optical Telescopes
Harwit, M.,Sloane, N.J.A. (1979): Hadamard Transform Optics. 1st ed. Academic Press, New York.

Heindl, W.A.,Cook, W.R.,Grunsfeld, J.M.,Palmer, D.M.,Prince, T.A.,Schindler, S.M.,Stone, E.C.: 1993, Astrophysical Journal, 408,507
An Observation of the Galactic-Center Hard X-Ray Source, 1E 1740.7-2942 With the Caltech Coded-Aperture Telescope
The Galactic center region hard X-ray source 1E 1740.7-2942 has been observed with the Caltech Gamma-Ray Imaging Payload (GRIP) from Alice Springs, Australia, on 1988 April 12 and on 1989 April 3 and 4. We report here results from the 1989 measurements based on 14 hr of observation of the Galactic center region. The observations showed 1E 1740.7-2942 to be in its normal state, having a spectrum between 35 and 200 keV characterized by a power law with an exponent of -2.2 +/- 0.3 and flux at 100 keV of (7.0 +/- 0.7) x 10(-5) cm-2 s-1 keV-1. No flux was detected above 200 keV. A search for time variability in the spectrum of 1E 1740.7-2942 on one hour time scales showed no evidence for variability.

Herring, J.R.H.,Skinner, G.K.,Emam, O.: 1991, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 310,341
A Cylindrical Surface MWPC for All-Round X-Ray Vision
We describe the design, construction and performance of a novel type of position sensitive multiwire proportional counter intended for use in a proposed coded mask all-sky X-ray monitor. The sensitive volume is in the form of a cylindrical shell inside a tubular carbon fibre window. The electronic system uses multichannel preamplifier chips developed at CERN, and includes logic and digitising circuits for direct readout to a computer.

Hogge, C.B.,Schultz, J.F.,Mason, D.B.,Thompson, W.E.: 1988, Applied Optics, 27, 5127
Physical Optics of Multiaperture Systems

Hudson, H.S.: 1982, Advances in Space Research, 2,307
The Pinhole/Occulter Facility
The Pinhole/Occulter Facility concept uses a remote occulting mask to provide high resolution observations of the solar corona and of astronomical X-ray sources. With coded-aperture and Fourier-transform techniques, the Pinhole/ Occulter makes images at a resolution of 0.2 arc sec for 2-120 keV X-rays, using a 50-m boom erected from the payload bay of the Space Shuttle or mounted on a free-flying platform. The remote occulter also creates a large shadow area for solar coronal observations; the Pinhole/Occulter concept includes separate optical and ultraviolet telescopes with 50-cm apertures. These large telescopes will provide a new order of resolution and sensitivity for diagnostic observations of faint structures in the solar corona. The Pinhole/Occulter is a powerful and versatile tool for general-purpose X-ray astronomy, with excellent performance in a broad spectral band complementary to that accessible with AXAF. The large collecting area of 1.5 sq m results in a 5 sigma detection threshold of about 0.02 microJy for the 2-10 keV band.

Indebetouw, G.: 1986, Optics and Laser Technology, 18,268
Scanning Heterodyne Reconstruction of Coded Aperture Images

Indebetouw, G.,Shing, W.P.: 1981, Journal of the Optical Society of America, 71, 1627
Optical Reconstruction of Coded Aperture Images

Indebetouw, G.,Shing, W.P.: 1981, Applied Optics, 20,3996
Optical-Scanning Reconstruction of Fresnel Zone Plate Coded Images

Indebetouw, G.,Shing, W.P.: 1982, Applied Physics B-Photophysics and Laser Chemistry, 27,69
Scanning Optical Reconstruction of Coded Aperture Images

In 't Zand, J.J.M.: 1992, Ph.D. Thesis, University of Utrecht
A Coded-Mask Imager As Monitor of Galactic X-Ray Sources

In 't Zand, J.J.M.,Heise, J.,Jager, R.: 1994, Astronomy and Astrophysics, 288, 665
The Optimum Open Fraction of Coded Apertures With an Application to the Wide Field X-Ray Cameras of SAX
We consider issues that concern the mathematical description of coded aperture patterns. Primarily this involves the relation between the open fraction of such patterns and the signal-to-noise ratio of imaged point sources. A refinement of the corresponding theory is introduced, taking into account the spatial response of the coded aperture camera. From this we predict that patterns with an open fraction of less than 0.5 can enhance the performance of coded aperture cameras to bright sources, as opposed to what was previously thought. As an application of the refined theory, we tested candidate open fractions in the instrumental configuration of two identical, wide field, coded aperture X-ray cameras (1.8-30 keV), that will be part of the X-ray satellite SAX (to be launched in late 1995). These tests consisted of numerical simulations of several types of observations, and show that open fractions between 0.25 and 0.33 are to be favored for the SAX cameras. The improvement in signal-to-noise ratio with respect to the commonly used open fraction of 0.5 is up to 30%. WHenever telemetry limits the data coverage, this profit may well be larger. We also address additional aperture constraints as applied to the SAX cameras, such as the aperture geometry and pattern. From this analysis we propose a new type of coded aperture pattern for the SAX cameras with an open fraction equal to 0.33, which possesses near-ideal mathematical properties.

In 't Zand, J.J.M.,Pan, H.C.,Bleeker, J.A.M.,Skinner, G.K.,Gilfanov, M.R., Sunyaev, R.A.: 1992, Astronomy and Astrophysics, 266,283
The Spectral Variability in 2-28 Kev of GS2023+338 During Its 1989 Outburst
The X-ray transient GS2023+338 (=V404 Cyg in the optical band), a close binary containing a black hole candidate, was observed with the coded mask X-ray camera TTM of the Rontgen observatory on the Kvant module of Mir during June-August 1989, when it was in outburst. We report here the results of an analysis of these observations, which mainly addresses the SPECTRAL variability of the transient on time scales between minutes and months. The spectral signatures of this variability were found to consist of a fluctuating low-energy absorption with a time scale of approximately 1 1/2 h, whose amplitude decreased on a time scale of approximately 1 month, and a slowly decreasing Compton-reflected component, on top of a power-law spectrum with essentially a constant photon index of 1.6-1.7. The fluctuating low-energy absorption could be satisfactory modeled by a varying column density of cold matter, with a dynamical range of at least a factor of - 40 and ranging up to N(H) almost-equal-to 4.5 x 10(23) H cm- 2. This variability most probably originated in dynamical processes. Apart from spectral variability, a wavelength-independent variability is apparent, which had time scales down to at least minutes, on top of a general decay with an e- folding decay time of 32 days. The long-term trends suggest that the environment of the compact object became progressively more transparent by accretion of the circumstellar matter onto the compact object. The total mass transferred to the compact object during the complete outburst was, through equivalence with the radiated energy during the total outburst, found to be approximately 2 x 10(-9) (D/1 kpC)2 M. This is equivalent to an average mass transfer rate from the companion during the quiescent stage since the last outburst of the optical counterpart of (4-12) x 10(15) (D/1 kpc)2 g s-1, which is similar to that observed in other transient low-mass X-ray binaries, as long as D < 3 kpc. In many of its spectral aspects, GS2023+338 resembles the galactic black hole candidate Cyg X-1 in its 'hard' state.

Islam, M.K.,Fitzgerald, L.T.,Bova, F.J.,Mauderli, W.: 1993, Physics in Medicine and Biology, 38,1403
A Coded-Aperture Device for Online Imaging With Megavoltage Photon Beams
A prototype coded aperture device based upon a liquid-filled strip ion chamber has been investigated as an on-line imaging unit for portal imaging of megavoltage photon beams. The strip ion chamber was used to collect integrated data for a series of pixels along a line across the field of view. By translating the detector, in equal steps in a direction perpendicular to its length, the data for a complete projection of the image were collected. Multiple-projection data, corresponding to different angular views, were collected by sequentially rotating the detector in equal angular steps and then translating through the field. The portal image was reconstructed from the multiple-projection data by a convolution-filtered back-projection algorithm. The phantom images taken with a cobalt-60 radiation source were found to be of similar contrast to film images. The signal-to-noise ratio, including the noise propagation of the reconstruction process for an image of 101 x 101 pixels, was 207:1. For a translational step of 2 mm the spatial resolution of the system was found to be 4.2 mm, as determined from the full width at half maximum of the point spread function.

Jacroux, M.,Notz, W.: 1983, Annals of Statistics, 11,970
On the Optimality of Spring Balance Weighing Designs

Jager, R.,Heise, J.,In 't Zand, J.J.M.,Brinkman, A.C.: 1993, Advances in Space Research, 13,315
Wide-Field Cameras for Sax
SAX is an Italian X-ray satellite with a Dutch contribution that will be placed in orbit in 1994. The prime scientific object of SAX is to cover an energy bandwidth that ranges from 0.1 keV upto 200 keV. Among other instruments, SAX will consist of two X-ray Wide Field Cameras built by the Space Research Organisation Netherlands at Utrecht. The WFCs are based on the coded mask principle, the reconstruction of the image takes place on ground. The field of view is 20 degrees square full width at half maximum (FWHM), the angular resolution 5 arcminutes (FWHM) and the energy band ranges from 1.8 to 30 keV with a resolution of 18% at 6 keV. The sensitive area is 200 cm(2) at 6 keV. The mask pattern is based on a pseudo random array with 255 x 257 elements of 1 mm(2), 50% of which are transparent.

Jayanthi, U.B.,Braga, J.: 1991, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 310,685
Physical Implementation of an Antimask in Ura Based Coded Mask Systems
X- and gamma-ray astronomy experiments which employ rectangular URA coded masks alone show artifacts in the images reconstructed due to nonuniform background levels in the detector plane. The employment of a separate antimask in addition to the mask in observations is useful to eliminate this problem. We propose here a method to implement the antimask with the same mask, utilizing the antisymmetric properties in the mask pattern, thereby avoiding the need for a separate antimask in an experiment. Simulations performed with this mask- antimask system are presented to show its advantages.

Jedwab, J.,Mitchell, C.: 1988, Electronics Letters, 24,650
Constructing New Perfect Binary Arrays

Jedwab, J.,Mitchell, C.J.: 1990, Electronics Letters, 26,294
Infinite Families of Quasiperfect and Doubly Quasiperfect Binary Arrays

Jedwab, J.,Mitchell, C.,Piper, F.,Wild, P.: 1994, Discrete Mathematics, 125,241
Perfect Binary Arrays and Difference Sets
A perfect binary array is an r-dimensional array with elements +/- 1 such that all out-of-phase periodic autocorrelation coefficients are zero. Such an array is equivalent to a Menon difference set in an abelian group. We give recursive constructions for four infinite families of two-dimensional perfect binary arrays, using only elementary methods. Brief outlines of the proofs were previously given by three of the authors. Although perfect binary arrays of the same sizes as two of the families were constructed earlier by Davis, the sizes of the other two families are new. Jenkins, T.L.,Frye, G.M.,Owens, A.,Carter, J.N.,Ramsden, D. (1981): Accelerator test of the coded aperture mask technique for gamma-ray astronomy. In: Proceedings of the 17th International Cosmic Ray Conference - Paris. Vol. 9. (: ) Commissariat a l'Energie Atomique, Gif-sur-Yvette, France, 283-286. (Case Western Reserve University, Cleveland; Southampton, University, Southampton, England)

Jenkins, T.L.,Frye, G.M.,Owens, A.,Carter, J.N.,Ramsden, D.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,278
A Gamma-Ray Telescope With Arc Minute Resolution

Jimenez, J.,Olmos, P.,Depablos, J.L.,Perez, J.M.: 1991, Applied Optics, 30,549
Gamma-Ray Imaging Using Coded Aperture Masks - A Computer-Simulation Approach
The gamma-ray imaging using coded aperture masks as focusing elements is an extended technique for static position sensitive detectors. Several transfer functions have been proposed to implement mathematically the set of holes in the mask, the uniformly redundant array collimator being the most popular design. A considerable amount of work has been done to improve the digital methods of deconvolve the gamma-ray image, formed at the detector plane, with this transfer function. Here we present a study of the behavior of these techniques when applied to the geometric shadows produced by a set of point emitters. Comparison of the shape of the object reconstructed from these shadows with that resulting from the analytical reconstruction is performed, defining the validity ranges of the usual algorithmic approximations reported in the literature. Finally, several improvements are discussed.

Johansson, A.,Beron, B.L.,Campbell, L.,Eichler, R.,Hofstadter, R.,Hughes, E.B., Wilson, S.,Gorodetsky, P.: 1980, IEEE Transactions On Nuclear Science, NS-27, 375
The Use of an Active Coded Aperture for Improved Directional Measurements in High Energy Gamma-Ray Astronomy
The coded aperture, a refinement of the scatter-hole camera, offers a method for the improved measurement of gamma-ray direction in gamma-ray astronomy. Two prototype coded apertures have been built and tested. The more recent of these has 128 active elements of the heavy scintillator BGO. Results of tests for gamma-rays in the range 50-500 MeV are reported and future application in space discussed.

Johnson, T.W.,Park, J.B.,Dyer, S.A.,Harms, B.K.,Dyer, R.A.: 1989, Applied Spectroscopy, 43,746
An Efficient Method for Recovering the Optimal Unbiased Linear Spectrum-Estimate from Hadamard-Transform Spectrometers Having Nonideal Masks

Jorgenson, M.B.,Fattouche, M.,Nichols, S.T.: 1991, IEE Proceedings - H Microwaves Antennas and Propagation, 138,441
Applications of Minimum Redundancy Arrays in Adaptive Beamforming
It is shown, through analysis and simulation, that the use of a minimum redundancy array (MRA) in conjunction with an adaptive beamformer results in performance superior to that attained by a comparable system based on an array with uniformly spaced elements, or uniform array (UA) in terms of rejecting interferences located in close angular proximity to the look direction. Further, it is demonstrated that choosing the adaptive elements of a thinned adaptive array (TAA) based on a minimum spatial redundancy criterion, rather than spacing them uniformly, results in improved rejection of main lobe interferences, with negligible degradation in sidelobe interference rejection capabilities.

Jourdain, E.,Bassani, L.,Roques, J.P.,Mandrou, P.,Ballet, J.,Laurent, P.,Lebrun, F.,Paul, J.,Finogenov, A.,Churazov, E.,Gilfanov, M.,Sunyaev, R.,Dyatchkov, I., Khavenson, N.,Novikov, B.,Kuleshova, N.: 1993, Advances in Space Research, 13, 705
The Observations of AGNs in the 40-1300 KeV Energy-Range By the Sigma-Telescope
SIGMA telescope realizes images of the sky in the hard X-ray domain (40 keV-1.3 MeV) through a coded mask system. The extragalactic study was one of the main objectives and has brought new results in our knowledge of the Active Galactic Nuclei behavior at high energy. In fact, the variability in the most important factor as all these objects have been showed to display strong evolution in intensity or/and spectral shape. Moreover, the discovery of a new hard X-ray source close to 3C273 and probably strongly absorbed below 40-50 keV could have many consequences in the extragalactic field.

Jupp, I.D.,Byard, K.,Dean, A.J.: 1994, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 345,576
An Improved Sampling Configuration for a Coded-Aperture Telescope
The sensitivity of a gamma-ray coded aperture telescope has been studied in order to investigate the trade-off between angular resolution and the reconstructed image signal to noise ratio (SNR) that occurs when a discrete pixel detector is used. Without fine sampling of the coded mask by the detector plane, the reconstructed SNR is seriously compromised if the source under observation lies close to sky pixel boundaries, falling to as low as 25% of the maximum SNR. Fine sampling partially restores the image SNR, but at the expense of the telescope angular resolution. However, it is shown that the use of a non- integer fine sampling value, for example 1.5 X 1.5 detector pixels per mask element, can be used to achieve high image SNR whilst retaining good angular resolution.

Kelly, J.G.,Stalker, K.T.: 1981, Transactions of the American Nuclear Society, 38,379
Status of the Coded Aperture Imaging Fuel Motion System (Cais)

Kendziorra, E.,Kretschmar, P.,Pan, H.C.,Kunz, M.,Maisack, M.,Staubert, R., Pietsch, W.,Trumper, J.,Efremov, V.,Sunyaev, R.: 1994, Astronomy and Astrophysics, 291,L31
Evidence for Cyclotron Line Features in High-Energy Spectra of A0535+26 During the March/April-1989 Outburst
The X-ray pulsar A 0535+26 has been observed during its March/April 1989 outburst with the Coded Mask Telescope TTM and the High Energy X-ray Experiment HEXE on board the Mir space station at energies between 4 and 156 keV. Pulsed emission (P=103.26 s for JD 244 7626) has been detected up to at least 100 keV. Above 20 keV the time averaged pulse profiles show a clear double peak structure with an asymmetric main pulse and a more symmetric secondary pulse. The spectrum of the main pulse is significantly harder than that of the secondary pulse. The phase resolved spectra can only be fitted by a power law with exponential cutoff modified by two absorption lines around 50 and 100 keV. We interpret these features as the fundamental and first harmonic cyclotron resonances. The corresponding strength of the magnetic field of the neutron star is 4.3 x 10(12) Gauss.

Klemperer, W.K.: 1974, Astronomy & Astrophysics Supplement Series, 15,449
Very Large Array Configurations for the Observaions of Rapidly Varying Sources

Klotz, E.,Weiss, H.: 1974, Optics Communications, 11,368
Three Dimensional Codewd Aperture Imaging Using Nonredundant Point Distributions
A nonredundant distribution of ten point sources is used for coded aperture imaging. The coded image of a three dimensional X-ray object is decoded by means of an incoherent projection system in all its layers. This decoding process avoids all the adjustement problems of coherent processing systems.

Kohman, T.P.: 1989, Review of Scientific Instruments, 60,3396
Coded-Aperture X-Ray or Gamma-Ray Telescope With Least-Squares Image- Reconstruction .1. Design Considerations

Kohman, T.P.: 1989, Review of Scientific Instruments, 60,3410
Coded-Aperture X-Ray or Gamma-Ray Telescope With Least-Squares Image- Reconstruction .2. Computer-Simulation

Kopilovich, L.E.: 1984, Optica Acta, 31,1409
Non-Redundant Aperture Mask Systems for Interferometric Image Synthesis - A Regular Method of Construction

Kopilovich, L.E.: 1988, Optics Communications, 68,7
Construction of Nonredundant Masks Over Square Grids Using Difference Sets

Kopilovich, L.E.: 1988, Electronics Letters, 24,566
On Perfect Binary Arrays

Kopilovich, L.E.: 1988, Radiotekhnika I Elektronika, 33,1918
Optimization of Two-Dimensional Aperture Synthesis Systems

Kopilovich, L.E.: 1989, Cybernetics, 25,153
Difference Sets in Noncyclic Abelian-Groups

Kopilovich, L.E.: 1992, IEE Proceedings-F Radar and Signal Processing, 139,365
New Approach to Constructing 2-Dimensional Aperture Synthesis Systems
The problem of constructing aperture synthesis (AS) systems which cover a given rectangular domain of spatial frequencies with a minimum of receiving elements is considered. A method for obtaining two-dimensional AS systems by multiplying linear minimum redundancy AS systems is proposed. On the basis of difference sets, AS systems for large domains are suggested. The redundancy of such systems reaches 32-33%, whereas that of T systems for square domains is 50% and for rectangular domains not less than The general estimates of the minimum-41%. redundancy two-dimensional AS systems indicate that the construction suggested in this work can be regarded as a step towards optimal AS systems.

Kopilovich, L.E.,Sodin, L.G.: 1989, Radiotekhnika I Elektronika, 34,2059
Linear Aperiodic Antenna-Arrays Based On Difference Sets

Kopilovich, L.E.,Sodin, L.G.: 1991, IEE Proceedings - H Microwaves Antennas and Propagation, 138,233
2-Dimensional Aperiodic Antenna-Arrays With a Low Sidelobe Level
A method for the synthesis of two-dimensional aperiodic antenna arrays with a low sidelobe level is suggested and studied. It extends Leeper's approach to the synthesis of linear arrays based on cyclic difference sets. The method reported here is based on a new combinatorial construction called generalised two- dimensional difference sets. Ways of constructing such sets and the basic features of the antennas obtained are considered.

Kopilovich, L.E.,Sodin, L.G.: 1993, Astronomy Letters, 19,457
Synthesis of Coded Masks for X-Ray and Gamma-Ray Telescopes
We suggest that coded masks for x-ray and gamma-ray telescopes be synthesized using two-dimensional difference sets in square and rectangular apertures. In comparison to the constructions now used, this considerably expands the possibilities for choosing mask dimensions and the fraction of ''open'' sections, i.e., for improving the telescope resolution and sensitivity, without any degradation of image quality. We also point out the possibility of developing masks based on generalized two-dimensional difference sets, additionally augmenting the set of feasible versions.

Kopilovich, L.E.,Sodin, L.G.: 1994, Radiotekhnika I Elektronika, 39,380
Synthesis of 2-Dimensional Nonequidistant Antenna-Arrays Using Difference Set- Theory

Kopilovich, L.E.,Sodin, L.G.: 1994, Monthly Notices of the Royal Astronomical Society, 266,357
Synthesis of Coded Masks for Gamma-Ray and X-Ray Telescopes
We propose the synthesis of coded masks for gamma-ray and X-ray telescopes with square or rectangular apertures, using two-dimensional difference sets. Compared with masks employed at present, these facilitate a significant increase in the capability to choose both the size and the fraction of the 'open' pixels, i.e. the telescope resolution and sensitivity. We also point out the possibility of constructing masks on the basis of two-dimensional generalized difference sets, which considerably increases the number of feasible variants.

Kujoory, M.A.,Miller, E.L.,Barrett, H.H.,Gindi, G.R.,Tamura, P.N.: 1980, Applied Optics, 19,4186
Coded Aperture Imaging of Gamma-Ray Sources With an Off-Axis Rotating Slit

Laudet, P.,Roques, J.P.: 1988, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 267, 212
Correction for Detector Uniformity of a Gamma-Ray Telescope Using Coded Aperture Imaging

Laudet, P.,Roques, J.P.: 1988, Applied Optics, 27,4226
Resolution of Strong Sources for a Gamma-Ray Telescope Using Coded Aperture Imaging
Laudet, P.,Roques, J.P.: 1989, Applied Optics, 28,755
Iterative Algorithm to Improve the Separating Power On Coded-Aperture Images

Lefkopoulos, D.,Danet, B.,Guilhem, J.B.,Morucci, J.P.,Guiraud, R.: 1983, Proceedings of the Society of Photo-Optical Instrumentation Engineers, 312,188
Attainment of 3-D Images in Nuclear-Medicine By Coded-Aperture Devices

Lempel, A.: 1979, Applied Optics, 18,4064
Hadamard and M-Sequence Transforms Are Permutationally Similar

Linebarger, D.A.: 1992, IEEE Transactions On Antennas and Propagation, 40,1109
A Fast Method for Computing the Coarray of Sparse Linear Arrays
A fast algorithm for computing the coarray of sparse linear arrays is presented. Deriving linear minimum redundancy arrays or linear minimum hole arrays involves huge searches over candidate arrays to determine which arrays have the desired coarray characteristics. Since the number of candidate arrays grows very large with increasing numbers of sensors, it is important to be able to check each array's coarray quickly so that the search does not take too long. The method presented herein for computing coarrays is considerably faster than existing methods. This algorithm is well suited to implementation on a digital computer- it exploits the fact that integer multiplication is equivalent to convolution of the integer's representations.

Linebarger, D.A.,Sudborough, I.H.,Tollis, I.G.: 1993, IEEE Transactions On Information Theory, 39,716
Difference Bases and Sparse Sensor Arrays
Difference bases are discussed and their relevance to sensor arrays is described. Several new analytical difference base structures that result in near optimal low-redundancy sensor arrays are introduced. Algorithms are also presented for efficiently obtaining sparse sensor arrays and/or difference bases. Lastly, new bounds, related to arrays that have both redundancies and holes in their coarray are presented. Also, some extensions to the idea of difference bases that may yield useful results for sensor array design are discussed.

Liu, L.: 1982, Applied Optics, 21,2817
Quasi-Interferometry With Coded Correlation Filtering

Luke, H.D.: 1988, IEEE Transactions On Aerospace and Electronic Systems, 24,287
Sequences and Arrays With Perfect Periodic Correlation

Luke, H.D.,Bomer, L.,Antweiler, M.: 1989, Signal Processing, 17,69
Perfect Binary Arrays

Lum, K.S.K.,Manandhar, R.P.,Eikenberry, S.S.,Krockenberger, M.,Grindlay, J.E.: 1994, IEEE Transactions On Nuclear Science, 41,1354
Initial Performance of the EXITE2 Imaging Phoswich Detector Telescope for Hard X-Ray Astronomy
We have developed, tested, and flown a large-area imaging phoswich detector/ telescope for hard X-ray astronomy. This second-generation Energetic X-ray Imaging Telescope Experiment (EXITE) is designed to detect and image cosmic X- ray sources in the 20-600 keV energy range from a high-altitude balloon. Imaging is accomplished via the coded-aperture technique. Laboratory tests have shown that the detector achieves 14% (FWHM) energy resolution and approximately 10 mm (FWHM) spatial resolution at 60 keV, and that the pulse-shape discrimination (PSD) circuit effectively distinguishes between NaI(T1) and CsI(Na) events from approximately 40-400 keV. The first flight of the instrument was from Palestine, Texas, on 13-14 June 1993. In this paper, we present details of the laboratory performance of the system and some flight results.

Maggioli, P.P.,Caroli, E.,Natalucci, L.,Spizzichino, A.: 1984, Nuclear Instruments & Methods in Physics Research, 221,82
A Numerical Method for Recognition of Virtual Images in Coded Mask Telescopes
A Numerical Method for Recognition of Virtual Images in Coded Mask Telescopes" A problem with telescopes utilizing replicated structure coded masks is the possible occurrence of virtual images. A numerical method to discriminate virtual from real images, and to determine their correct location in the field of view, is described. The performance and reliability of this method, based on eight "ad hoc" modifications of the coding array, have been investigated by Monte Carlo simulations.

Maggioli, P.P.,Caroli, E.,Natalucci, L.,Spizzichino, A.,Badiali, M.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,82
A Numerical-Method for Recognition of Virtual Images in Coded Mask Telescopes

Maisack, M.,Kendziorra, E.,Pan, H.C.,Skinner, G.K.,Pietsch, W.,Reppin, C., Efremov, V.,Sunyaev, R.: 1994, Astronomy and Astrophysics, 283,841
Thermal Comptonization in 4U1700-377
We present results of a broad band X-ray observation of the high-mass X-ray binary 4U 1700-377 (HD 153919) with the Kvant observatory in the energy range 4- 100 keV. We find that a simple bremsstrahlung spectrum, which has been suggested by previous hard X-ray observations, is not a good description of the 4-100 keV spectrum. We suggest thermal Comptonisation of blackbody photons by a hot plasma on the sur-face of the neutron star as the emission mechanism. The parameters of the plasma are kT almost-equal-to 30 keV and optical depth tau almost-equal-to 2. The spectral shape of this model gives a good fit to the data and can explain why observations at slightly different energy ranges mimic bremsstrahlung spectra of different temperatures, since its shape can be approximated by bremsstrahlung spectra of different temperatures in different energy intervals.

Marthon, P.,Bon, P.,Bruel, A.: 1983, Proceedings of the Society of Photo-Optical Instrumentation Engineers, 312,148
Numerical-Method of Adapted Deconvolution - Application to the Tomography By Coded Aperture

McConnell, M.L.,Dunphy, P.P.,Forrest, D.J.,Chupp, E.L.,Owens, A.: 1987, Astrophysical Journal, 321,543
Gamma-Ray Observations of the Crab Region Using a Coded-Aperture Telescope

McConnell, M.L.,Forrest, D.J.,Chupp, E.L.,Dunphy, P.P.: 1982, IEEE Transactions On Nuclear Science, 29,155
A Coded Aperture Gamma-Ray Telescope
A gamma ray telescope is being developed to operate in the energy range 100 keV to 5 MeV utilizing coded aperture imaging. The design incorporates a mask pattern based on a Uniformly Redundant Array (URA), which has been shown to have ideal imaging characteristics. A mask anti-mask procedure is used to eliminate the effects of any possible systematic variations in detector background rates. The detector array is composed of 35 elements of the high-Z material Bismuth Germanate (BGO). Results of laboratory testing of the imaging properties will be presented. A southern hemisphere balloon flight is planned for 1982 with the goal of observing the 0.511 MeV radiation from the Galactic Center. Computer calculations show that a point source of this radiation can be located to within +/- 1 degree.

McConnell, M.L.,Forrest, D.J.,Owens, A.,Dunphy, P.P.,Vestrand, W.T.,Chupp, E.L.: 1989, Astrophysical Journal, 343,317
Gamma-Ray Observations of Cygnus-X-1 and Cygnus-X-3 Using a Coded-Aperture Telescope

Miyamoto, S.: 1977, Space Science Instrumentation, 3,473
Hadamard Transform X-Ray Telescope
A Hadamard transform X-ray telescope is a type of Dicke's random hole X-ray camera for observing the X-ray sky. Instead of making a random pattern mask, a cyclic Hadamard matrix or PN sequence is used to make the mask pattern for this telescope. With this mask and a position sensitive X-ray detector, one can get Hadamard transformed image data of the X-ray sky and easily reconstruct the X- ray sky image from the observed data. The Hadamard matrix can be used to make one dimensional X-ray telescope as well as two-dimensional telescopes. In the case that spurious counts on the detector are predominant over image counts and background counts, the SNR advantage of this telescope is sqrtN/2 compared to the slat type X-ray telescope of the same angular resolution, where N is the number of position sensitive detector cells and N+1 is the order of the cyclic Hadamard matrix employed to make this mask.

Miyamoto, S.,Tsunemi, M.,Tsuno, K.: 1981, Nuclear Instruments & Methods in Physics Research, 180,557
Some Characteristics of Hadamard Transform X-Ray Telescopes
The characteristics of the Hadamard transform X-ray telescope (HTXT) are investigated and the following results are obtained: (1) the statistical error of the image, reconstructed by the HTXT, is uniform all over the image, which is different from the case of a pinhole camera. (2) The SNR of the HTXT is much better than that of the pinhole camera in the case that spurious counts are predominant over the counts due to the X-ray image. (3) The statistical error of the image, which is obtained by summing of several image elements of an HTXT of a finer angular resolution to get a fixed angular resolution is worse that obtained by the HTXT which is designed to the final angular resolution beforehand. (4) Even in the case that data of some detector cells are lost, the image can be reconstructed. (5) All detector cells of the HTXT must see the same X-ray image through the Hadamard mask, otherwise the error due to the fluctuating number of mask holes is introduced. (6) The image reconstructed by the HTXT becomes obscure by the amount of the positional resolution of the X-ray detector in the case that the positional resolution is larger than the cell of the detector. (7) The Hadamard transform imaging system described in this paper is also applicable to other fields such as plasma and a medical diagnoses with slight alteration of the system and is expected to have the same characteristics as the HTXT.

Nelson, E.D.,Fredman, M.L.: 1970, Journal of the Optical Society of America, 60, 1664
Hadamard Spectroscopy
The basic concept of Hadamard spectroscopy is presented. General methods are given for the construction of cyclic measurement matrices. A new algorithm, which permits adaptation of the fast HAdamard transform to the calculation of spectral intensities when the measurement matrices are cyclic, is introduced. Some applications are also briefly discussed.

Neumann, D.R.,Flynn, M.J.,Gottschalk, S.,Wiener, S.N.: 1983, Journal of Nuclear Medicine, 24,P25
Comparative Tomographic Imaging Performance of a Hybrid Coded-Aperture Parallel- Plate Stationary Collimator and a Rotating Camera

Nottingham, M.R.: 1993, Ph.D. Thesis, University of Birmingham (UK)
X-Ray Observations of the Galactic Centre Utilising a New Analytical Technique
A new technique for the analysis of data from coded mask telescopes is introduced. It is shown that this new technique called 'Maximum Likelihood Fitting' (MALF), has several advantages over conventional techniques espacially in the reduction of coding noise from the 'box cameras' design of coded mask telescopes. The new technique is then used with data obtained by the TTM coded mask instrument when the instrument was pointing in the direction of the galactic centre region. Using the MALF technique it was possible to solve for the intensity (in different energy channels) of the small scale (1 degree) diffuse emission which is seen emanating from the galactic nucleus. This would be the first time that accurate spectral measurements of this source have been obtained, however no spatial information could be obtained as an assumed distribution had to be used. All of the point sources which were in the field of view of the instrument during the observations of the galactic centre were also analysed using a variaty of spectral models to try and obtain as much information about individual sources and also to investigate the differences observed between the various groups of X-ray binaries.

Nottingham, M.R.,Skinner, G.K.,Willmore, A.P.,Borozdin, K.N.,Churazov, E., Sunyaev, R.A.: 1993, Astronomy & Astrophysics Supplement Series, 97,165
Observations of the Galactic-Center With the TTM Instrument
A new technique has been developed for the analysis of data from the TTM instrument coded mask telescope. Preliminary spectral results are presented for diffuse emission and point sources in the galactic centre.

Nugent, K.A.: 1987, Applied Optics, 26,563
Coded Aperture Imaging - A Fourier Space Analysis
Coded aperture imaging is analyzed in Fourier space and the conditions for obtaining artifact-free 3-D images are obtained. It is deduced that an infinite square array of coding apertures will obey these conditions. A finite array is considered and it is shown that, after a certain coordinate transformation has been performed, the finite aperture acts to bandlimit the spatial frequencies in the image. This results is used to deduce a sampling theorem for coded apertures which places limits on the artifact-free 3-D information that may be obtained. It is thus deduced that 3-D information with a resolution greater than the limits placed here may only be obtained by extrapolating the data to larger viewing angles.

Nugent, K.A.: 1987, Optics Communications, 62,305
Maximum-Entropy Analysis of Coded Images

Nugent, K.A.: 1988, Review of Scientific Instruments, 59,1658
Coded Imaging of Thermonuclear Neutrons

Nugent, K.A.,Lutherdavies, B.: 1984, Optics Communications, 52,287
The Use of a Regular Array of Apertures in Penumbral Imaging

Nugent, K.A.,Lutherdavies, B.: 1986, Applied Optics, 25,1008
Potential and Limitations of Penumbral Imaging

Ohyama, N.,Endo, T.,Honda, T.,Tsujiuchi, J.,Matumoto, T.,Iinuma, T.A.,Ishimatsu, K.: 1984, Applied Optics, 23,3168
Coded-Aperture Imaging-System for Reconstructing Tomograms of Human Myocardium

Ohyama, N.,Honda, T.,Tsujiuchi, J.: 1981, Optics Communications, 36,434
Tomogram Reconstruction Using Advanced Coded Aperture Imaging

Ohyama, N.,Honda, T.,Tsujiuchi, J.,Matumoto, T.,Iinuma, T.A.,Ishimatsu, K.: 1983, Applied Optics, 22,3555
Advanced Coded-Aperture Imaging-System for Nuclear-Medicine

Olmos, P.,Cid, C.,Bru, A.,Oller, J.C.,Depablos, J.L.,Perez, J.M.: 1992, Applied Optics, 31,4742
Design of a Modified Uniform Redundant Array Mask for Portable Gamma Cameras
Uniform redundant-array masks have been reported as good lenses to form the image of gamma sources, with the correlation between the mask-aperture matrix and, the shadows projected on a static position-sensitive detector. We present a modified uniform redundant-array configuration suitable for portable and small- size gamma-cameras; its ability to reconstruct the image of several sources is analyzed. We have carried out a Montecarlo simulation of the gamma interactions in the mask, defining the expected response of the correlation process and comparing it with that achieved with the usual uniform redundant-array configurations.

Owens, A.: 1990, Nuclear Instruments & Methods in Physics Research Section A- Accelerators Spectrometers Detectors and Associated Equipment, 292,706
Limiting Sensitivities of Coded-Aperture Telescopes for Gamma-Ray Astronomy - Balloon-Borne Fixed-Mask Systems

Palmer, D.M.,Schindler, S.M.,Cook, W.R.,Grunsfeld, J.M.,Heindl, W.A.,Prince, T.A.,Stone, E.C.: 1993, Astrophysical Journal, 412,203
Gamma-Ray Continuum and Line Observations of SN 1987a
The Caltech gamma-ray imaging telescope observed the hard X-ray and gamma-ray emission from SN 1987A as it evolved between 1987 May and 1989 April, in a series of four balloon flights from Alice Springs, NT, Australia. Observations of the Crab Nebula and Pulsar provided in-flight data on pointing accuracy and instrument function for each flight. Results presented here include our measurements on 1987 November 18 (D268) and 1988 April 12 (D414) of both line emission at 847 and 1238 keV from the decay of Co-56, and Compton-scattered continuum above 50 keV. Upper limits for both line and continuum emission were obtained on 1987 May 20 (D86) and 1989 April 4 (D771). For the D268 and D414 continuum measurements, our results are best-fit by a differential power law of the form dN/dE = kappaE(-gamma)(cm-2 s-1 keV-1) for the energy range 50-800 keV. Our corresponding line measurements were fit with Gaussian profiles, containing additional terms for the underlying continuum. We compare our flux measurements and upper limits to those from other experiments and to predictions of theoretical models.

Palmieri, T.M.: 1974, Astrophysics and Space Science, 28,277
Multiplex Methods and Advantages in X-Ray Astronomy
The multiplex advantage is defined and applied in considering various techniques presently used in X-ray astronomy. It is concluded that the multiplex advantage will be useful in evaluating future techniques to be used in X-ray astronomy.

Palmieri, T.M.: 1974, Astrophysics and Space Science, 26,431
An X-Ray Telescope Sensitive At High Energies
A telescope is described which is capable of producing images of point sources of x-rays without recourse to reflection optics. A mathematical approach to the operation and to the SNR properties of the telescope is presented. This is followed by several examples of its response and a discussion of detectors that could be used with the device.

Pan, H.C.,In 't Zand, J.J.M.,Skinner, G.K.,Borozdin, K.N.,Gilfanov, M.R.,Sunyaev, R.A.: 1993, Astronomy & Astrophysics Supplement Series, 97,273
Observations of X-Ray Transient Source GS2023+338 With the TTM Coded Mask Telescope
We present results from TTM observations in which we monitored the bright X-ray transient source GS2023+338 (= V404 Cyg) in the period 1989 June-August.

Park, J.B.,Johnson, T.W.,Dyer, S.A.,Harms, B.K.,Dyer, R.A.: 1990, Applied Spectroscopy, 44,219
On the Mean-Square Error of Various Spectrum-Recovery Techniques in Hadamard- Transform Spectrometry

Pasedach, K.,Haase, E.: 1981, Optics Communications, 36,423
Random and Guided Generation of Coherent 2-Dimensional Codes

Patterson, T.G.: 1990, Ph.D. Thesis, University of Birmingham
A Survey of the Galactic Bulge, Large Magellanic Cloud and Cygnus Region With A Simple Configuration Coded Mask X-Ray Telescope

Paul, J.,Lebrun, F.,Mandrou, P.,Roques, J.P.: 1993, Acta Astronautica, 30,261
2 Years of Successful Operations of the Coded-Mask Telescope Sigma for Hard X- Ray and Soft Gamma-Ray Astronomy
At the beginning of the previous decade, it was recognized that a possible means of improving existing hard X-ray and gamma-ray telescopes, where focusing techniques are totally impracticable, is the incorporation of the coded-aperture technique to actually image celestial sources. The primary advantage of such a technique is to maintain the angular resolution of a single pinhole camera, while increasing the overall effective area of the instrument. Moreover, the coded-mask principle includes the simultaneous measurement of the sky and detector background, systematic effects due to temporal variations in the background are removed. This paper reports on the French SIGMA telescope, the first coded-aperture telescope sensitive to radiation in the energy range from 35 KeV to 1.3 MeV to be operated in space. The SIGMA telescope is one of the main devices on board the astronomy satellite GRANAT, successfully launched on December 1, 1989 from Baikonour, Kazakhstan. After a comprehensive description of the instrument, a report is given on the most relevant inferences which can be drawn from two years of successful in-orbit operations, in order to better define the next generation of gamma-ray instruments.

Paxman, R.G.,Barrett, H.H.,Smith, W.E.: 1985, Acta Polytechnica Scandinavica- Applied Physics Series,,285
Object Dependent System-Design in Coded-Aperture Imaging

Paxman, R.G.,Barrett, H.H.,Smith, W.E.,Milster, T.D.: 1985, Journal of the Optical Society of America A-Optics Image Science and Vision, 2,501
Image-Reconstruction from Coded Data .2. Code Design

Paxman, R.G.,Gindi, G.R.,Barrett, H.H.: 1982, Journal of the Optical Society of America, 72,1737
Tomography With Coded Apertures - The Case for Continuous Objects

Paxman, R.G.,Smith, W.E.,Barrett, H.H.: 1984, Journal of Nuclear Medicine, 25, 700
2 Algorithms for Use With an Orthogonal-View Coded-Aperture System

Pearson, D.,Pillai, S.U.,Lee, Y.J.: 1990, IEEE Transactions On Information Theory, 36,1280
An Algorithm for Near-Optimal Placement of Sensor Elements

Ponman, T.J.,Bertram, D.,Church, M.J.,Eyles, C.J.,Watt, M.P.,Skinner, G.K., Willmore, A.P.: 1990, Nature, 347,450
The Distribution of Iron in the Perseus Cluster

Ponman, T.J.,Hammersley, A.P.,Skinner, G.K.: 1987, Nuclear Instruments & Methods in Physics Research, A262,419
Error Analysis for a Noncyclic Imaging System
The imaging properties of the `coded aperture box camera', a noncyclic coded mask system in which mask and detector are the same size, are investigated under the assumption of random positioning of the mask holes. Each source in the field of view generates noise due to the imperfect coding, in addition to the Poisson and detector noise present in a cyclic coded mask imager. Equations are presented for the magnitude and spatial variation of each of these three sources of noise, and their validity is confirmed by simulations. For a small number of sources the coding variance from each can simply be superposed to a good approximation. In the case of many sources the coding variance is less than the superposition value. The box camera has advantage over a collimated cyclic imager, particularly for wide field imaging, provided that coding errors are not too large compared to Poisson and detector noise.

Proctor, R.J.,Skinner, G.K.,Willmore, A.P.: 1979, Monthly Notices of the Royal Astronomical Society, 187,633
The Design of Optimum Coded Mask X-Ray Telescopes
Considerations involved in the construction and operation of an optimum coded- mask X-ray telescope are discussed. The coded-mask imaging technique is described, along with mask design and construction, telescope geometry, the detector in a coded-mask telescope, attitude determination and control, and data analysis. Specific attention is given to the SL 1501 coded-mask telescope and results obtained with that instrument. It is shown that all the problems associated with the design of coded-mask telescopes are soluble and that X-ray images can be produced at wavelengths shorter than those that can be handled with grazing-incidence optics.

Ranieri, M.,Badiali, M.,Cardini, D.,Emanuele, A.,Auriemma, G.: 1981, Journal of the British Interplanetary Society, 34,135
Coded Aperture Telescopes for Hard X-Ray Astronomy
The coded aperture signal processing reconstruction technique, and its application to a balloon-borne hard X-ray and gamma-burst telescope useful for high-resolution mapping where numerous X-ray sources are present, are described. The coded mask principle, telescope design, background noise, and detector specifications are discussed, as are the results of a Monte Carlo computer simulation of the system.

Ress, D.,Bell, P.M.,Bradley, D.K.: 1993, Review of Scientific Instruments, 64, 1404
A Time-Resolved X-Ray Ring Coded-Aperture Microscope for Inertial Confinement Fusion Applications
For energetic x rays (hv greater-than-or-equal-to 3 keV), ring coded-aperture imaging gives better signal-to-noise ratio than equivalent-resolution pinhole cameras for inertial confinement fusion (ICF) targets. We have created a time- resolved ring coded-aperture microscope by combining a 4 X 3 array of annular apertures with a gated microchannel-plate x-ray imager. The new instrument can produce 500-ps duration sequences of images with a temporal resolution of 80 ps and a spatial resolution of 5 to 6 mum. In demonstration experiments, coded images of imploded targets directly driven by the Omega laser at the Laboratory for Laser Energetics showed the formation and dissolution of the target cores with improved detail. Contour plots of the images indicate that the laser illumination pattern is imprinted in the imploded core region. The gated ring- aperture microscope will be useful in detailed studies of ICF target hydrodynamics.

Rogers, W.L.,Adller, R.S.: 1982, Applied Optics, 21,324
Time-Coded Aperture Design for Nuclear-Medicine Imaging - A Study of Signal-To- Noise Ratio

Roques, J.P.: 1987, Applied Optics, 26,3862
Fast Decoding Algorithms for Uniformly Redundant Arrays
Coded mask aperture imaging techniques are now used in various fields, in particular in X-ray and gamma-ray astronomy. With such systems it is possible to construct apertures which have autocorrelation functions with perfectly flat sidelobes. For quadratic residue arrays (URAs), we have developed fast deconvolution algorithms based on conventional decoding methods but taking advantage of the mathematical properties of the decoding matrices. Balanced decoding, delta decoding, and finely sampled decoding are discussed.

Ruf, C.S.: 1993, IEEE Transactions On Antennas and Propagation, 41,85
Numerical Annealing of Low-Redundancy Linear Arrays
An algorithm is developed that estimates the optimal distribution of antenna elements in a minimum redundancy linear array. These distributions are used in thinned array interferometric imagers to synthesize effective antenna apertures much larger than the physical aperture. The optimal selection of antenna locations is extremely time consuming when large numbers of antennas are involved. This algorithm uses a numerical implementation of the annealing process to guide a random search for the optimal array configuration. Highly thinned low-redundancy arrays are computed for up to 30 array elements. These arrays are equivalent to the optimal solutions that are known for up to 11 elements. The arrays computed for 12-30 elements have the least redundancies reported to date.
Rothschild, R.E., Matteson, J.L., Heindl, W.A., et al.: 1995 SPIE
The Continuous Hard X-ray Imager for Astrophysics (CHIP) (proposed coded aperture imaging mission between 2 and 100 keV with CdZnTe detectors and an array of flat coded apertures)

Salotti, L.,Ballet, J.,Cordier, B.,Lambert, A.,Bonazzola, S.,Mereghetti, S., Mandrou, P.,Roques, J.P.,Sunyaev, R.,Gilfanov, M.,Churazov, E.,Chulkov, I., Kuznetsov, A.,Dyachkov, A.,Khavenson, N.,Novikov, B.: 1992, Astronomy and Astrophysics, 253,145
Soft Gamma-Ray Observations of Cygnus X-1 With the Coded-Aperture Sigma Telescope
The galactic black-hole candidate Cygnus X-1 was observed by the soft gamma ray orbiting SIGMA telescope during March 23/24, 1990. This coded-aperture instrument records images of the sky in the 35 keV-1.3 MeV energy range. Data have been collected in imaging mode and in fast-timing mode. In about one day of image accumulation the source has been detected up to almost-equal-to 500 keV with high statistical significance. The derived photon spectrum has been fitted with various analytical shapes. The best fit corresponds to a Comptonized model with an electron temperature of kT(e) = 62.3 +/- 4.5 keV and an optical depth tau = 2.02 +/- 0.13. Our flux value at 100 keV, combined with simultaneous X-ray measurements, suggests that the source was in a typical gamma-2 state. Timing data, which benefit from the millisecond resolution, have been analysed in order to confirm the variability down to short timescales (80 ms) already detected by HEAO-1 (Nolan et al. 1981b). Shot-noise behaviour has been detected even for E > 80 keV.

Seidler, P.: 1981, Electronics Letters, 17,96
Mismatched Filtering for Coded Aperture Imaging With Minimum Sidelobes

Sembay, S.,Gehrels, N.: 1990, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 295, 477
Design Criteria for Small Coded Aperture Masks in Gamma-Ray Astronomy

Silva, R.,Rogers, G.L.: 1981, Optica Acta, 28,1125
Coded Aperture Imaging - A Noncoherent Optical Approach

Silva, R.,Rogers, G.L.: 1981, Pattern Recognition, 14,3
Coding and Decoding Pictures in Nuclear-Medicine

Silva, R.,Rogers, G.L.: 1982, Optica Acta, 29,257
Tomographical Possibilities in Coded Aperture Imaging Optical Simulations

Sims, M.: 1981, Ph.D. Thesis, University of Leicester
A Wide Field Camera for X-Ray Astronomy

Sims, M.,Turner, M.J.L.,Willingale, R.: 1980, Space Science Instrumentation, 5, 109
A Wide Field X-Ray Camera
A Wide Field of View Camera based on the Dicke or Coded Mask principle is described. It is shown that this type of instrument is more sensitive than a pinhole camera, or than a scanning survey of a given region of sky for wide field conditions. The design of a practical camera is discussed and the sensitivity and performance of the chosen design are evaluated by means of computer simulations. The Wiener Filter and Maximum Entropy Methods of deconvolution are described and these methods are compared with each other and cross-correlation using data from the computer simulations. It is shown that the analytic expressions for sensitivity used by other workers are confirmed by the simulations, and that ghost images caused by incomplete coding can be substantially eliminated by the use of the Wiener Filter and the MAximum Entropy Method, with some penalty in computer time for the latter. The cyclic mask configuration is compared with the simple mask camera. It is shown that when the diffuse X-ray background dominates, the simple system is more sensitive and has the better angular resolution. When sources dominate the simple system is less sensitive. It is concluded that the simple coded mask camera is the best instrument for wide field imaging of the X-ray sky.

Sims, M.,Turner, M.J.L.,Willingale, R.: 1985, Nuclear Instruments & Methods in Physics Research, 228,512
The Influence of Disturbing Effects On the Performance of a Wide Field Coded Mask X-Ray Camera
The coded aperture telescope, or Dicke camera, is seen as an instrument suitable for many applications in X-ray and gamma ray imaging. In this paper the effects of a partially obscuring window mask support or collimator, a detector with limited spatial resolution, and motion of the camera during image integration are considered using a computer simulation of the performance of such a camera. Cross correlation and the Wiener filter are used to deconvolve the data. It is shown that while these effects cause a degradation in performance this is in no case catastrophic. Deterioration of the image is shown to be greatest where strong sources are present in the field of view and is quite small (~10%) when diffuse background is the major element. A comparison between the cyclic mask camera and the simple mask camera is made under various conditions and it is shown that the simple mask camera has a moderate advantage particularly when imaging a wide field of view.

Sims, M.R.,Willingale, R.,Turner, M.J.L.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,77
Computer-Simulations of the Performance of Practical Designs of Coded Aperture Cameras
The coded aperture camera is an instrument suitable for many applications in X- and gamma-ray imaging. In this paper the effect of a partially obscuring window support is considered using a computer simulation technique. This allows the signal to noise in the decoded image to be evaluated for practical designs of camera, a process which is difficult to carry out using an analytical approach. The sensitivity of simple and cyclic forms of camera is determined for real celestial X-ray source distributions under both source and diffuse background dominated conditions. The image obtained is shown to be degraded but not destroyed by the interference of the window support, and the simple form of camera is shown to be more sensitive than the cyclic form for wide fields of view.

Skinner, G.K.: Sept. 1980, Journal of the British Interplanetary Society, 33, 333
Imaging of Cosmic X-Ray Sources Using Coded Mask Telescopes
Mask designs which can be used for coded mask telescopes are discussed, and methods of recovering the image are considered. The paper compiles information from different fields and shows how the data is useful in the construction and application of telescopes for X-ray astronomy. The description of a large dual telescope system which is being constructed for flight on the Spacelab 2 mission of the Space Shuttle is included.

Skinner, G.K.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,33
Imaging With Coded-Aperture Masks
Coded-MAsk imaging systems may be considered as generalizations of the pinhole camera in which the `coding-plane' contains a carefully chosen pattern of transparent and opaque regions instead of a single pinhole. A variety of instruments result from selecting different coding patterns and from simple geometrical variations on the theme. The various schemes which have been proposed and used and the methods of interpreting the data obtained with them are reviewed and compared. Emphasis is placed on systems for X-ray astronomy.

Skinner, G.K.: 1988, Scientific American, 259,84
X-Ray-Imaging With Coded Masks

Skinner, G.K.,Eyles, C.J.,Willmore, A.P.,Bertram, D.,Church, M.J.,Herring, J.R.H.,Ponman, J.,Watt, M.P.: 1988, Astrophysical Letters & Communications, 27, 199
The Spacelab-2 X-Ray Telescope - Coded Mask Imaging in Orbit

Skinner, G.K.,Foster, A.J.,Willmore, A.P.,Eyles, C.J.: 1990, Monthly Notices of the Royal Astronomical Society, 243,72
Localization of One of the Galactic-Center X-Ray Burst Sources

Skinner, G.K.,Grindlay, J.E.: 1993, Astronomy and Astrophysics, 276,673
Coded Masks With 2 Spatial Scales
A new design is proposed for masks for wide-band coded aperture X-ray/gamma-ray telescopes. The masks contain both elements with a coarse spatial scale, which are opaque at all energies at which the telescope is to operate, and elements with finer structure which provide good angular resolution at low energies but which become transparent in the upper part of the energy range. It is shown that patterns exist which have very satisfactory imaging properties and that the sensitivity which is sacrificed to obtain the improvement in angular resolution is very small, even at intermediate energies where the fine mask is partially absorbing.

Skinner, G.K.,Harper, P.K.S.,Herring, J.R.H.,Ramsey, B.D.: 1988, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 273,682
The Spacelab 2 Xrt Xenon-Filled Position-Sensitive Proportional-Counters

Skinner, G.K.,Nottingham, M.R.: 1993, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 333,540
Analysis of Data from Coded-Mask Telescopes By Maximum-Likelihood
Coded mask telescopes have proved of great utility in X- and gamma-ray astronomy. A coded mask telescope of a non-cyclic ''box-camera'' design can in some circumstances have a sensitivity advantage over an optimally coded cyclic configuration, but images reconstructed by a simple correlation technique are subject to various imperfections. A new method, maximum likelihood fitting (MALF), for the analysis of data from non-cyclic coded mask telescopes is presented. MALF avoids artifacts due to strong sources and handles in an optimum way data affected by small-number statistics, by partial coding and by aspects of real systems such as finite detector depth and obscurations of parts of the detector.

Skinner, G.K.,Pan, H.C.,Maisack, M.,Staubert, R.,Borozdin, K.N.,Brinkman, A.C., Englhauser, J.,Gilfanov, M.R.,Kaniovsky, A.C.,Pietsch, W.,Sunyaev, R.A.,In 't Zand, J.J.M.: 1991, Astronomy and Astrophysics, 252,172
The Spectrum and Position of the Hard Galactic-Center Source 1E1740.7-2942
The remarkable hard X-ray and gamma-ray source close to the galactic centre, 1E 1740.7-2942, was observed with two of the instruments of the Rontgen Observatory on the Kvant module of MIR. We present observations made with the TTM coded-mask imager and the HEXE phoswich instrument which together provide spectral coverage from approximately 2 to 200 keV. The spectrum can be well described by a hard power-law with a high energy cut-off and absorption at low energies. Similarities with the spectra of Cyg X-1 and other black hole candidates suggest that 1 E1740.7-2942 may, too, be a black hole binary. With a view to establishing the counterpart of this source in other wavebands, the position of this source was determined with an uncertainty of 12", a significant improvement on the precision of earlier measurements. We consider constraints on the nature of the source imposed by limits on optical and near IR objects within the new error circle.

Skinner, G.K.,Ponman, T.J.: 1987, Journal of the British Interplanetary Society, 40,169
Coded Mask Telescopes for X-Ray Astronomy
The Department of Space Research has made extensive use of coded mask techniques, many aspects of which were pioneered in Birmingham. We describe here the technique and some instruments using it. (Author abstract) 8 refs.

Skinner, G.K.,Ponman, T.J.: 1994, Monthly Notices of the Royal Astronomical Society, 267,518
On the Properties of Images from Coded-Mask Telescopes
We consider coded-mask telescopes with cyclic mask patterns that are 'optimum', i.e. patterns that are based on uniformly redundant arrays (URAs), which can be derived using cyclic difference sets. The properties of images obtained with different reconstruction arrays are compared to find the best options. In the usual case where the detector background is imperfectly known, it is easily shown that, although the elements of an image reconstructed by any of the usual algorithms are nearly independent of each other and of the detector background, they cannot be perfectly so. The correlation between image elements that results is evaluated for various reconstruction algorithms and the circumstances in which it may be important are discussed. Although the effect is small when point sources are considered, it may be significant where sources of emission cover an appreciable fraction of the field of view. Masks based on 'modified URAs' lead to slightly worse interdependence of image pixels.

Skinner, G.K.,Ponman, T.J.,Hammersley, A.P.,Eyles, C.J.: 1987, Astrophysics and Space Science, 136,337
Techniques for the Analysis of Data from Coded-Mask X-Ray Telescopes
Several techniques useful in the analysis of data from coded-mask telescopes are presented. Methods of handling changes in the instrument pointing direction are reviewed and ways of using FFT techniques to do the deconvolution considered. Emphasis is on techniques for optimally-coded systems, but it is shown that the range of systems included in this class can be extended through the new concept of 'partial cycle averaging'.

Skinner, G.K.,Willmore, A.P.,Eyles, C.J.,Bertram, D.,Church, M.J.,Harper, P.K.S.,Herring, J.R.H.,Peden, J.C.M.,Pollock, A.M.T.,Ponman, T.J.,Watt, M.P.: 1987, Nature, 330,544
Hard X-Ray Images of the Galactic-Center

Skinner, G.K.,Willmore, A.P.,Eyles, C.J.,Bertram, D.,Church, M.J.,Harper, P.K.S.,Herring, J.R.H.,Peden, J.C.M.,Pollock, A.M.T.,Ponman, T.J.,Watt, M.P.: 1987, Nature, 330,544
Hard X-Ray Images of the Galactic-Center

Smith, W.E.,Barrett, H.H.: 1988, Journal of the Optical Society of America A- Optics Image Science and Vision, 5,315
Linear-Estimation Theory Applied to the Evaluation of A-Priori Information and System Optimization in Coded-Aperture Imaging

Smith, W.E.,Barrett, H.H.,Paxman, R.G.: 1983, Optics Letters, 8,199
Reconstruction of Objects from Coded Images By Simulated Annealing

Smith, W.E.,Barrett, H.H.,Paxman, R.G.: 1984, Journal of Nuclear Medicine, 25, P55
The Consequences of Multiplexing and Limited View Angle in Coded-Aperture Imaging

Smith, W.E.,Paxman, R.G.,Barrett, H.H.: 1985, IEEE Transactions On Nuclear Science, 32,758
Application of Simulated Annealing to Coded-Aperture Design and Tomographic Reconstruction

Smith, W.E.,Paxman, R.G.,Barrett, H.H.: 1985, Journal of the Optical Society of America A-Optics Image Science and Vision, 2,491
Image-Reconstruction from Coded Data .1. Reconstruction Algorithms and Experimental Results

Stalker, K.T.,Kelly, J.G.: 1981, Proceedings of the Society of Photo-Optical Instrumentation Engineers, 294,135
Design of a Coded Aperture Imaging-System for Simulated Reactor Accident Experiments

Steer, D.G.,Dewdney, P.E.,Ito, M.R.: 1984, Astronomy and Astrophysics, 137,159
Enhancements to the Deconvolution Algorithm Clean

Steinbach, A.,Macovski, A.: 1979, Journal of Physics D, 12,2079
Improved Depth Resolution With One Dimensional Coded Aperture Imaging

Stephen, J.B.,Caroli, E.,Dicocco, G.,Maggioli, P.P.,Natalucci, L.,Spizzichino, A.: 1987, Astronomy and Astrophysics, 185,343
The Identification of Vignetted Sources in Coded Aperture Imaging
The next generation of gamma-ray telescopes will utilize the technique of coded apertures in order to provide high resolution images of the celestial sphere. This method, however, suffers from a disadvantage wherein vignetted sources are reconstructed in false positions with incorrect intensities. Most techniques of identifying these sources involve the use of time consuming iterative computer algorithms. One recent suggestion, however, allows fast decoding which is also accurate when there are a limited number of sources in the field of view and a high background level, as is the case for contemporary low energy gamma-ray instruments. This method has been examined in detail by means of Monte Carlo simulation in order to assess its accuracy and sensitivity.

Stroke, G.W.: 1968, Physics Letters, 28A,252
A New Class of Optical Imaging Systems Achieving 'Aperture Synthesis' from Non- Conventional Optics By a Posteriori Lensless Fourier Transform Holography

Stroke, G.W.,Hayat, G.S.,Hoover, R.B.,Underwood, J.H.: 1969, Optics Communications, 1,138
X-Ray Imaging With Multiple-Pinhole Cameras Using a Posteriori Holographic Image Synthesis

Sunyaev, R.,Churazov, E.,Gilfanov, M.,Terekhov, O.,Dyachkov, A.,Khavenson, N., Kovtunenko, V.,Kremnev, R.,Claret, A.,Lebrun, F.,Goldwurm, A.,Paul, J.,Pelaez, F.,Atteia, J.L.,Mandrou, P.,Vedrenne, G.: 1993, Astronomy & Astrophysics Supplement Series, 97,85
A Search for Weak Gamma-Ray Bursts With Granat/Sigma
During more than two years of GRANAT mission, the Gamma Ray Burst (GRB) cell of the narrow-aperture coded mask telescope SIGMA was operated for approximately 5300 hours (see Sunyaev et al., 1992a for more details). The coding system of SIGMA is capable of localizing to within arcmin accuracy the GRB events detected in the 18.1-degrees by 16.8-degrees coded field of view. Inspite of the high sensitivity of the cell to the on-axis events (3 x 10(-8) and 8 x 10(-8) erg/cm2 in the 40-90 keV band for 0.25 and 2.0 sec integration time) no bursts were actually found within the coded field of view. For about 950 hours SIGMA was pointed towards the Galactic Center (GC) and more than 1.5 x 10(10) M. of Galactic matter was within the telescope coded FOV. For an object placed at 8.5 kpc distance, the threshold burst luminosity in the 40-90 keV band (approximately 3 X 10(38) erg/sec) is comparable with the Eddington limit for a neutron star. The absence of weak GRB events from the GC direction indicates that either the luminosity of a typical GRB is below approximately 10(38) ergs/ sec and GRB are of local origin or, alternatively, that the luminosity is as high as approximately 10(40) ergs/sec or greater and most of GRB come from a massive Galactic ''hale or are of cosmological origin. The lack of weak GRB events observed by SIGMA from all directions is inconsistent with an extrapolation of the KONUS data if the integral GRB counts slope is -3/2.

Sunyaev, R.,Kaniovsky, A.,Efremov, V.,Gilfanov, M.,Churazov, E.,Grebenev, S., Kuznetsov, A.,Melioranskiy, A.,Yamburenko, N.,Yunin, S.,Stepanov, D.,Chulkov, I.,Pappe, N.,Boyarskiy, M.,Gavrilova, E.,Loznikov, V.,Prudkoglyad, A.,Rodin, V., Reppin, C.,Pietsch, W.,Engelhauser, J.,Trumper, J.,Voges, W.,Kendziorra, E., Bezler, M.,Staubert, R.,Brinkman, A.C.,Heise, J.,Mels, W.A.,Jager, R.,Skinner, G.K.,Alemam, O.,Patterson, T.G.,Willmore, A.P.: 1987, Nature, 330,227
Discovery of Hard X-Ray-Emission from Supernova-1987a

Sunyaev, R.A.,Kaniovsky, A.S.,Borozdin, K.N.,Efremov, V.V.,Arefev, V.A., Melioransky, A.S.,Skinner, G.K.,Pan, H.C.,Kendziorra, E.,Maisack, M., Doebereiner, S.,Pietsch, W.: 1993, Astronomy and Astrophysics, 280,L1
Broad-Band X-Ray Observations of the GRO-J0422+32 X-Ray Nova By the Mir-Kvant Observatory
Observations of GRO J0422+32 X-Ray Nova with the instruments of the ''Mir- Kvant'' observatory show that the X-ray spectrum is similar to that of the well- known black-hole candidate Cyg X-1 in its ''low'' state. In the standard 2-20 keV X-ray range both have power law spectra with no strong soft component while at energies higher than 100 keV an exponential cutoff is clearly seen in the spectrum in both cases. Such cutoffs are typical of thermal comptonization of low-frequency photons in the high-temperature plasma of accretion disks.

Syunyaev, R.A.,Arefev, V.A.,Borozdin, K.N.,Gilfanov, M.R.,Efremov, V.V., Kaniovskii, A.S.,Churazov, E.M.,Kendziorra, E.,Mony, B.,Kretschmar, P.,Maisack, M.,Staubert, R.,Dobereiner, S.,Englhauser, J.,Pietsch, W.,Reppin, C.,Trumper, J.,Skinner, G.K.,Nottingham, M.R.,Pan, H.,Willmore, A.P.: 1991, Soviet Astronomy Letters, 17,409
Broad-Band X-Ray-Spectra of Black-Hole Candidates, X-Ray Pulsars, and Low-Mass Binary-X-Ray Systems - Kvant Module Results
The broadband spectra of the brightest x-ray sources obtained by the TTM, Hexe, and Pulsar X-1 instruments of the Kvant module demonstrate differences in the hardness of the spectrum of the weak magnetic field neutron star Sco X-1, the x- ray pulsars A 0535 + 26, Vela X-1, and LMC X-4, and the blackhole candidates Cyg X-1, GS 2023 + 338, GS 2000 + 25, and 3C 273.

Syunyaev, R.,Gilfanov, M.,Churazov, E.,Loznikov, V.,Yamburenko, N.,Skinner, G.K.,Patterson, T.G.,Willmore, A.P.,Emam, O.,Brinkman, A.C.,Heise, J.,In 't Zand, J.J.M.,Jager, R.: 1990, Soviet Astronomy Letters, 16,59
The New X-Ray Transient Burster KS1731-260

Syunyaev, R.,Gilfanov, M.,Churazov, E.,Loznikov, V.,Yamburenko, N.,Skinner, G.K.,Patterson, T.G.,Willmore, A.P.,Emam, O.,Brinkman, A.C.,Heise, J.,In 't Zand, J.J.M.,Jager, R.: 1990, Soviet Astronomy Letters, 16,55
X-Ray Observations of the Large Magellanic Cloud By the TTM Telescope On Board the Kvant Module from November 1988 to June 1989

Syunyaev, R.A.,Gilfanov, M.R.,Churazov, E.M.,Yamburenko, N.S.,Brinkman, A.C., Heise, J.,In 't Zand, J.J.M.,Jager, R.,Skinner, G.K.,Alemam, O.,Patterson, T.G., Willmore, A.P.: 1988, Soviet Astronomy Letters, 14,296
Stabilization of Mir-Kvant - The TTM X-Ray Data

Syunyaev, R.A.,Gilfanov, M.R.,Churazov, E.M.,Yamburenko, N.S.,Brinkman, A.C., Heise, J.,In 't Zand, J.J.M.,Jager, R.,Skinner, G.K.,Alemam, O.,Patterson, T.G., Willmore, A.P.: 1988, Soviet Astronomy Letters, 14,252
Upper Limits On the 2-32 Kev Emission of Supernova-1987a in June August 1987

Syunyaev, R.A.,Kaniovskii, A.,Efremov, V.,Gilfanov, M.,Churazov, E.,Grebenev, S.A.,Kuznetsov, A.V.,Melioranskii, A.S.,Yamburenko, N.S.,Yunin, S.,Stepanov, D., Chulkov, I.,Pappe, N.,Boyarskii, M.N.,Gavrilova, E.A.,Loznikov, V.M., Prudkoglyad, A.,Rodin, V.G.,Reppin, C.,Pietsch, W.,Engelhauser, J.,Trumper, J., Voges, W.,Kendziorra, E.,Bezler, M.,Staubert, R.,Brinkman, A.C.,Skinner, G.K., Alemam, O.,Patterson, T.G.,Willmore, A.P.,Heise, J.,Mels, W.A.,Jager, R.: 1987, Soviet Astronomy Letters, 13,431
Detection of Hard X-Rays from Supernova 1987a - Preliminary Mir-Kvant Results

Teegarden, B.J.,Cline, T.L.,Gehrels, N.,Porreca, G.,Tueller, J.,Leventhal, M., Huters, A.F.,MacCallum, C.J.,Stang, P.D.: 1985, Proc Nth Cosmic Ray Conference; OG9.2, OG9.2,307
The Gamma-Ray Imaging Spectrometer (GRIS): A New Balloon-Bornne Experiment for Gamma-Ray Line Astronomy

Ubertini, P.: 1993, Astronomy & Astrophysics Supplement Series, 97,389
X-Ray Monitor On Integral - Astrophysics in the 4-100 Kev Band
The X-Ray Monitor on INTREGAL will provide images with arcminute angular resolution in the 4-100 keV band, simultaneously with the main gamma ray instruments. The limiting sensitivity for a typical 10(5) second observation will be better than one millicrab. The baseline photon detection system is a high pressure imaging proportional counter behind a coded mask (focal length 4 meters; FOV 6 degrees FWHM to match the other instruments). In addition to its support role on INTEGRAL (providing fine imaging and simultaneous X-Ray flux measurements) the spectral resolution and sensitivity are sufficient to make it a useful stand-alone instrument. In particular it will be able to monitor the iron lines seen in both Galactic and extra-Galactic sources, and relate these to the behavior of the hard continuum, seen in the other instruments. It will also enable the study of hard X-Ray continua of many Galactic and extra-Galactic sources: specifically the search for cyclotron lines in Galactic binaries, Compton 'humps', and other features in AGN spectra, perhaps evidence for pair processes. Because of its high sensitivity it will be used to scan the Galactic plane once every few days to detect the onset of transients (potential 'hard tail' objects), which can then be observed in detail by the Gamma ray instruments.

Vangiessen, J.W.,Viergever, M.A.,Degraaf, C.N.: 1986, IEEE Transactions On Medical Imaging, 5,222
Time-Coded Aperture Tomography - Experimental Results

Vertatschitsch, E.J.,Haykin, S.: 1991, IEEE Transactions On Antennas and Propagation, 39,576
Impact of Linear-Array Geometry On Direction-Of-Arrival Estimation for a Single Source
The impact of the linear array geometry on the direction of arrival estimation accuracy is examined assuming a single source of illumination and additive white Gaussian system noise. The analysis was conducted using the Cramer-Rao lower bound (CRLB), simulation and performance modeling of maximum likelihood estimation (MLE). Particular attention is paid to the implementation of the MLE, the threshold signal-to-noise ratio (SNR), probability of outlier and high SNR mean-squared error (MSE) performance which are evaluated and compared for uniform and nonuniform arrays. The conditions under which trade-offs exist in choosing a particular geometry and their significance are determined.

Villa, G.,Bussini, A.,Perotti, F.,Santambrogio, R.,Rampini, A.,Dicocco, G., Butler, R.C.,Caroli, E.,Stephen, J.B.,Traci, A.,Donati, A.,Ubertini, P., Lapadula, C.,Mastropietro, M.,Patriarca, R.,Dean, A.J.,Court, A.J.,Younis, F.A., Maggioli, P.,Yearworth, M.,Graham, G.: 1987, IEEE Transactions On Nuclear Science, 34,26
The Structure of the Zebra Telescope, the Integration Tests and the 1st Calibration Results

Villela, T.,Braga, J.,Damico, F.,Jayanthi, U.B.,Neri, J.A.: 1994, Astrophysics and Space Science, 214,161
A Balloon-Borne Imaging Telescope for High-Energy Astrophysics
We describe an imaging telescope for observations of celestial sources in the energy range between 30 keV and 1.8 MeV onboard stratospheric balloons. The detector is a 41 cm diameter, 5 cm thick NaI(Tl) crystal coupled to 19 photomultipliers in an Anger camera configuration. It is surrounded by a plastic scintillator 15 cm thick on the sides, 0.2 cm thick at the top and 20 cm thick at the bottom. The imaging device is based upon a 19 x 19 element square MURA (Modified Uniformly Redundant Array) coded mask mounted in an one-piece mask- antimask configuration. The detector's spatial resolution is about 10 mm at 100 keV. This is the first experiment to use such a mask pattern and configuration for astrophysical purposes. The expected 3sigma sensitivity for an on-axis source observed for 104 s at a residual atmosphere of 3.5 cm-2 is 1.44 x 10(-5) photons cm-2 s-1 keV-1 at 100 keV and 1.00 x 10(-6) photons cm-2 s-1 keV-1 at 1 MeV. The angular resolution is approximately 14 arcminutes over a 13-degrees field of view. The instrument is mounted in an automatic platform with a capability for pointing and stabilization in both azimuth and elevation axis with 2 arcmin accuracy.

Wagner, R.F.,Brown, D.G.,Metz, C.E.: 1981, Proceedings of the Society of Photo- Optical Instrumentation Engineers, 314,72
On the Multiplex Advantage of Coded Source Aperture Photon Imaging

Watt, M.P.,Ponman, T.J.,Bertram, D.,Eyles, C.J.,Skinner, G.K.,Willmore, A.P.: 1992, Monthly Notices of the Royal Astronomical Society, 258,738
The Morphology and Dark Matter Distribution of the Coma Cluster of Galaxies from X-Ray Observations
The analysis of a spectral image of the Coma cluster obtained with a coded mask telescope flown as part of the Spacelab 2 mission is presented. The main cluster emission is elongated east-west and extends to a radius of at least 50 arcmin, while an additional region of X-ray emission is detected approximately 50 arcmin to the south-west of the cluster centre. The energy range of the instrument and its imaging capabilities allow the temperature and density of the intracluster gas to be determined as a function of radius, and thus allow the total cluster mass profile to be determined. We find that the gas temperature profile is consistent with an isothermal model, and derive a cluster binding mass of 4.2- 5.2 x 10(14) h50(-1) M. within 1 h50(-1) Mpc (24 arcmin) of the cluster centre, the most accurate determination to date. We find no evidence for variation of metallicity with radius. This result differs from that obtained for the Perseus cluster; we suggest that the two clusters have different evolutionary histories, and that the Coma cluster has recently undergone a merger which has disrupted the pre-existing cluster conditions.

Weiss, H.: 1981, Ntz Archiv, 3,329
Imaging With Coded Aperture

Wild, P.: 1988, Electronics Letters, 24,845
Infinite Families of Perfect Binary Arrays

Wild, W.J.: 1983, Optics Letters, 8,247
Dilute Uniformly Redundant Sequences for Use in Coded-Aperture Imaging

Wild, W.J.: 1987, Sky and telescope,,126
A Gamma-Ray Pinhole Camera

Wild, W.J.,Barber, H.B.,Barrett, H.H.,Woolfenden, J.M.: 1982, Journal of the Optical Society of America, 72,1814
Medical Coded-Aperture Imaging With a Miniature Probe
(15 or 31 element coded aperture rotated and moved axially;single NaI detector with fibre-optic link)

Willingale, R.,Sims, M.R.,Turner, M.J.L.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,60
Advanced Deconvolution Techniques for Coded Aperture Imaging
The standard deconvolution technique for coded aperture imaging is cross correlation with the relevant mask pattern. In practice such an imaging system is imperfect, giving incomplete coding, and direct cross correlation with the mask introduces `ghosting' and enhanced noise fluctuations. This paper describes the application of image processing techniques such as the Wiener Filter and Maximum Entropy Method to deconvolve the recorded shadow pattern and illustrates the advantage of such methods using a computer simulation of a wide field camera for X-ray astronomy.

Willmore, A.P.,Bertram, D.,Watt, M.P.,Skinner, G.K.,Ponman, T.J.,Church, M.J., Herring, J.R.H.,Eyles, C.J.: 1992, Monthly Notices of the Royal Astronomical Society, 258,621
Image Correction in a Coded Mask X-Ray Telescope
A large coded mask telescope was flown on the Spacelab 2 mission in 1985. This was the first time that large amounts of data from such an instrument had been obtained and much effort was devoted to optimizing the methods of reducing detector background effects and of correcting and co-adding images. An unexpected problem was encountered in that small errors in energy calibration led to a large apparent detector background in the presence of bright sources. To provide background information for the scientific results from this instrument, and also because of their relevance to the analysis of data from other coded mask telescopes, we describe the data processing procedures adopted. They have led to an overall performance for the instrument which is close to that theoretically achievable.

Willmore, A.P.,Eyles, C.J.,Skinner, G.K.,Watt, M.P.: 1992, Monthly Notices of the Royal Astronomical Society, 254,139
Hard X-Ray-Emission from the Vela Supernova Remnant
We report the first hard (2.5-25 keV) X-ray images of the Vela supernova remnant (SNR), resulting from observations with the University of Birmingham coded mask telescope flown on the Spacelab 2 mission in 1985. The emission from the region around the pulsar is resolved; the diffuse emission extends approximately 1- degrees to the north-east and south-west, roughly aligned along the direction of the pulsar spin axis, and produces about 48 per cent of the total emission in the 4-25 keV band. We suggest that this region, which overlaps the peak of the Vela-X radio source, is a synchrotron nebula. The power required to produce the relativistic electrons in the nebula is estimated to be 75 per cent of the rotational energy loss of the pulsar. Emission from a number of bright knots in the shell is also detected; whilst these generally correlate with bright features in the lower energy Einstein Observatory and the H-alpha-images, the features at different wavelengths are not coincident, suggesting the presence of blobs of material at a wide range of temperatures.

Willmore, A.P.,Skinner, G.K.,Eyles, C.J.,Ramsey, B.: 1981, Space Science Reviews, 30,601
A Pseudo Random Mask Telescope for Spacelab

Willmore, A.P.,Skinner, G.K.,Eyles, C.J.,Ramsey, B.: 1984, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment, 221,284
A Coded Mask Telescope for the Spacelab-2 Mission
A dual coded mask telescope for the Spacelab 2 mission is now in the final stages of preparation at Birmingham University. It is due for launch in late 1984/early 1985 and will be by far the largest and most sophisticated such instrument to be flown in this time-frame. The design and capabilities of the telescope will be described.

Winkler, C.,Laurance, R.J.,Tomaschek, G.: 1988, ESA Bulletin,,31
GRASP - Gamma-Ray Astronomy With Spectroscopy and Positioning

Winkler, C.,Tomaschek, G.,Bignami, G.F.,Villa, G.,Dean, A.J.,Ramsden, D., Durouchoux, P.,Hurley, K.,Vedrenne, G.,Lund, N.,McBreen, B.,Schonfelder, V., Swanenburg, B.N.: 1988, Space Science Reviews, 49,173
Mission Aspects of GRASP, ESAs Prospective Gamma-Ray Astronomy Satellite

Yamanaka, C.,Yamanaka, M.,Niki, H.,Yamada, A.,Yamamoto, Y.,Yamanaka, T.: 1984, IEEE Transactions On Nuclear Science, 31,490
A URA Coded Aperture Camera for the Inertial Confinement Fusion Experiments

Zhang, S.N.,Fishman, G.J.,Harmon, B.A.,Paciesas, W.S.: 1994, Nature, 368,698
Earth Occultation or Coded Mask - Reply

Zirker, J.B.: 1989, Solar Physics, 120,253
Interferometric Imaging .2. Two-Dimensional Non-Redundant Arrays

Zirker, J.B.,Brown, T.M.: 1986, Journal of the Optical Society of America A- Optics and Image Science, 3,2077
Phase Recovery With Dual Nonredundant Arrays

Zoltowski, M.D.,Silverstein, S.D.,Mathews, C.P.: 1993, IEEE Transactions On Signal Processing, 41,2502
Beamspace Root-Music for Minimum Redundancy Linear Arrays
Beamspace Root-MUSIC is a computationally efficient beamspace implementation of Root-MUSIC developed recently for use in conjunction with a uniformly spaced linear array (ULA). Computationally efficient methods for employing beamspace Root-MUSIC in conjunction with a minimum redundancy linear array (MRLA) for both the narrow-band and wide-band cases are developed. The MRLA is attractive in that it offers enhanced detection performance and enhanced resolution capability relative to a ULA having the same number of elements.

These pages have been compiled by Jean in 't Zand. They are intended to provide general information for those interested in coded aperture imaging. Any citations should reference original papers as noted in the bibliography, and requests for further information about any of the papers should be directed to the authors thereof.

December 21, 1995