Scanning Approach

The image below shows a graphical representation of the scanning approach. The instrument utilizes a rotating scan mirror to allow the telescope to view a 51° cross-track nadir strip, an internal blackbody target, and Space, every 2.1 seconds with a nadir resolution of 60m. The 5-day revisit requirement necessitates a wide swath, which is realized by the scan method. The scan mirror sweeps the image of the focal plane across a 51° swath perpendicular to the spacecraft motion. Each point in this strip is sampled by detectors in all 8 spectral channels. The sweep rate is such that, as the spacecraft moves, the full 51° swath is sampled, with a small overlap between strips. The relatively fast sweep rate requires a fast frame-rate focal plane.

The system uses a push-whisk approach where instead of sweeping a few detectors across the scene a detector array (256x256) is swept across the scene. This allows the scan speed to be reduced and a continually rotating mirror. This avoids problems seen with paddle or flyback mirrors where the mirror scans the scene then flies back to the start position to do another scan. It also allows the calibration targets, e.g. blackbody and deep space to be viewed on the remainder of the scan.