Large IR Detector Arrays For Space Applications - A User Standpoint

Earth Observation from Space calls for new sensors with ever improved performances afforded by advanced technology. The recent concepts of space-borne optical imagers are for most of them based on the push-broom imaging principle whereby each line of the image is electronically scanned by an array of integrated solid-state detectors. The deployment of the push-broom principle in the visible part of the spectrum has come recently in the realm, as illustrated by the SPOT-HRV camera, the German MOMS or the Japanese MOS-1 instrument which represent second generation in space optical instrumentation for Earth observation. The advent of multi-element, self-scanned arrays or IR detectors makes it feasible to extrapolate the push-broom concept towards short, medium and longwavelength infrared, since observation in these bands is highly desirable to complement visible, near IR imagery. However, practical implementation on a space platform entails specific constraints which are sometimes overlooked. More specifically, the potential dwell time advantage afforded by the electronically scanned arrays over the discrete detectors used in conjunction with a mechanical scanner cannot be easily exploited in several cases. This paper emphazises on the most critical difficulties to be overcome, namely interfacing with optics, cooling of large detector arrays, signal processing requirements and in-flight calibration. Suitability of existing devices is discussed with respect to the presently foreseen space applications.