New Wavelet Methods for Flatfielding Coded Aperture Images

Grindlay, J. E.; Barret, D.; Lum, K. S. K.; Manandhar, R. P.; Robbason, B.; Vance, S. E.

doi:10.1007/978-94-011-0407-4_31

Cited by 3 publications

(3 citation statements)

References 5 publications

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“…Although for sufficiently long observations or combinations of observations, these systematic errors will inevitably become important, many methods are available to reduce them [33][34][35][36][37][38][39][40][41][42][43]. Typically these involves fitting and subtracting bright sources or otherwise taking them into account, and carefully modeling background non-uniformities.…”

Section: Introductionmentioning

confidence: 99%

“…The ghost images and other imaging artifacts that arise from partial coding, from non-uniform background, or from other effects present in real instruments can be alleviated provided one has a good understanding of the instrument and adequate computing resources. Although for sufficiently long observations or combinations of observations, these systematic errors will inevitably become important, many methods are available to reduce them [33][34][35][36][37][38][39][40][41][42][43]. Typically these involves fitting and subtracting bright sources or otherwise taking them into account, and carefully modeling background non-uniformities.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of coded mask telescopes

Skinner

2008

Appl. Opt.

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Simple formulae are often used to estimate the sensitivity of coded mask X-ray or gamma-ray telescopes, but these are strictly only applicable if a number of basic assumptions are met. Complications arise, for example, if a grid structure is used to support the mask elements, if the detector spatial resolution is not good enough to completely resolve all the detail in the shadow of the mask or if any of a number of other simplifying conditions are not fulfilled. We derive more general expressions for the Poisson-noise-limited sensitivity of astronomical telescopes using the coded mask technique, noting explicitly in what circumstances they are applicable. The emphasis is on using nomenclature and techniques that result in simple and revealing results. Where no convenient expression is available a procedure is given which allows the calculation of the sensitivity. We consider certain aspects of the optimization of the design of a coded mask telescope and show that when the detector spatial resolution and the mask to detector separation are fixed, the best source location accuracy is obtained when the mask elements are equal in size to the detector pixels.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sensitivity of coded mask telescopes

Skinner

2008

Appl. Opt.

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“…Even if the detector response is well-measured or modeled, it is likely that intrinsic uncertainties in position-sensitive response or gain will always be present, and usually changing (even if only slowly). Although flat-fielding methods 12,13 will partially compensate for background or detector non-uniformities, these are also limited in their usefulness and achievable dynamic range. Although dithering the pointing direction has been used (and is now incorporated on INTEGRAL and will be on Swift), this does not compensate for systematic effects which include multiplicative uncertainties (e.g.…”

Section: Scanning Coded Aperture Imagingmentioning

confidence: 99%

Optimizing wide-field coded aperture imaging: radial mask holes and scanning

Grindlay

Hong

2004

SPIE Proceedings

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Imaging at hard X-ray energies (~10-600 keV) over very large fields of view (~60 o per telescope) is required to conduct a high sensitivity all-sky and all-time survey for black holes. The proposed Energetic X-ray Imaging Survey Telescope (EXIST) could achieve the high sensitivity required for the mission science objectives by scanning an array of widefield coded aperture telescopes with aperture mask holes radially aligned to minimize auto-collimation by the thick (~7mm) masks required for high energy imaging. Simulation results from a preliminary design study are reported which quantify the improvement in off-axis imaging sensitivity vs. the conventional case with mask holes all perpendicular to the mask. Such masks can be readily constructed from a stacked laminate of thin (1mm) laser-etched W sheets. An even more dramatic increase in coded aperture imaging sensitivity, and dynamic range, for a realistic telescope and imaging detector with typical systematic errors can be achieved by continuously scanning the field of view of the telescope over the source region to be imaged. Simulation results are reported for detectors with systematic errors 1-10%, randomly distributed but unknown in each detector pixel. For the simplified case of a 1-D coded aperture telescope scanning along its pattern, the systematics are removed identically. Results are also presented for the 2-D case with both 1-D and partial 2-D scanning which demonstrate the feasibility of a coded aperture scanning telescope with systematic errors achieving nearly Poisson-limited sensitivity for signal/background ratios S/B ~ 10 -4 , in constrast to limits typically ~10-100X worse that have been actually achieved by pointed or dithered coded aperture telescopes flown (or proposed) previously.

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