Imaging: Saturation and Sky Counts

Note that saturation magnitudes (the brightest point source that can be observed at the shortest possible exposure time for each mode) are very seeing dependent.

A saturated frame has a typical pattern as shown below. An exposure consists of a single global reset followed by two or more reads of array where the four quadrants are read out in parallel, from the outer corner towards the center. The output image is the difference between the reads so that the interval between reads is constant across the array. The center of the array is always exposed longer in this read mode and hence in the case of a high background the center will saturate sooner than the outer regions; a saturated NDSTARE frame has a characteristic pattern with a strong gradient in counts across the frame, as shown in the image below.