Space Telescope Science Institute   4.5.1 SBC Scheduling Policies  4.5.3 MAMA Darks

4.5.2 MAMA Overflow of the 16 Bit Buffer


The MAMA is a photon-counting detector: as each photon is recorded, it is placed into buffer memory. The buffer memory stores values as 16 bit integers; hence the maximum number it can accommodate is 65,535 counts per pixel in a given ACCUM mode observation. When accumulated counts per pixel exceed this number, the values will wrap. As an example, if you are counting at 25 counts/second/pixel, you will reach the MAMA "accumulation" limit in ~44 minutes.

One can keep accumulated counts per pixel below this value by breaking individual exposures into multiple identical exposures, each of which is short enough that fewer than 65,535 counts are accumulated per pixel. There is no read noise for MAMA observations, so no penalty is paid in lost signal-to-noise ratio when exposures are split. There is only a small overhead for each MAMA exposure (see Section 8.2).

Keep the accumulated counts per SBC pixel below 65,535 by breaking single exposures into multiple exposures, as needed.


 4.5.1 SBC Scheduling Policies  4.5.3 MAMA Darks
Space Telescope Science Institute
http://www.stsci.edu
Voice: (410) 338-1082
help@stsci.edu