The entire DISR instrument worked well during descent and even after landing, returning 600 images from the 3 camera channels. A number of dark frames were received between 260 K and 240 K. Early images from the haze can be profitably used to upgrade the flat field matrices.
Figure 3 (left) provides a plot of the CCD temperature throughout the operation. The CCD was passively cooled by a radiator that rapidly cools from 260 K to 170 K providing excellent operation conditions. The bulk of the images (and particularly the most interesting ones below 30 km where the cloud region was mostly passed) were taken with almost no dark charge components since the detector was cold enough and the exposure times were comparatively short (7-50 ms).
Flat fielding requires calibration of the hexagonal "chicken wire" pattern introduced by the fiber bundles along with singular deviations from fiber elements with degraded transmission. The resulting effect can be widely removed even though the pattern location varies slightly over temperature.
M i s s i o n T i m e , min L i n e E n u m e r a t i o n
Figure 3. (left) CCD temperature and (right) column average dark charge at 260 K.
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