Calibrating Array Detectors

The development of sensitive large format imaging arrays for the infraredpromises to provide revolutionary capabilities for space astronomy. Forexample, the Infrared Array Camera (IRAC) on SIRTF will use four 256 x 256arrays to provide background limited high spatial resolution images of the skyin the 3 to 8 micron spectral region. In order to reach the performance limitspossible with this generation of sensitive detectors, calibration proceduresmust be developed so that uncertainties in detector calibration will always bedominated by photon statistics from the dark sky as a major system noisesource. In the near infrared, where the faint extragalactic sky is observedthrough the scattered and reemitted zodiacal light from our solar system,calibration is particularly important. Faint sources must be detected on thisbrighter local foreground. We present a procedure for calibrating imaging systems and analyzing suchdata. In our approach, by proper choice of observing strategy, informationabout detector parameters is encoded in the sky measurements. Proper analysisallows us to simultaneously solve for sky brightness and detector parameters,and provides accurate formal error estimates. This approach allows us to extract the calibration from the observationsthemselves; little or no additional information is necessary to allow fullinterpretation of the data. Further, this approach allows refinement andverification of detector parameters during the mission, and thus does notdepend on a priori knowledge of the system or ground calibration forinterpretation of images.Comment: Scheduled for ApJS, June 2000 (16 pages, 3 JPEG figures