Space Telescope Science Institute   4.5.5 SBC Flatfield  4.6 SBC Bright-Object Limits

4.5.6 SBC Nonlinearity


Global

The MAMA detector begins to experience nonlinearity (photon impact rate not equal to photon count rate) at global (across the entire detector) count rates of 200,000 counts/second. The nonlinearity reaches 10% at 360,000 counts/second and can be corrected for in post-observation data processing at the price of a loss of photometric reliability. Additionally, the MAMA detector plus processing software are not able to count reliably at rates exceeding 285,000 counts/second. For this reason, and to protect the detectors, observations beyond this rate are not allowed (see Section 4.6).

Local

The MAMA detector remains linear to better than 1% up to ~22 counts/second/pixel. At higher rates, it experiences local (at a given pixel) nonlinearity. The nonlinearity effect is image dependent-that is, the nonlinearity observed at a given pixel depends on the photon rate affecting neighboring pixels. This property makes it impossible to correct reliably for the local nonlinearity in post-observation data processing. In addition, MAMA detectors are subject to damage at high local count rates (see Section 4.6).


 4.5.5 SBC Flatfield  4.6 SBC Bright-Object Limits
Space Telescope Science Institute
http://www.stsci.edu
Voice: (410) 338-1082
help@stsci.edu