Observing with the ISOCAM detector arrays

Given the memory and transient effects after changes of the illumination, it is most of the time necessary to leave out, for stabilization purpose, the first exposures of an observation. After that the S/N ratio increases normally as . But there are three types of limitations:

1. a low frequency noise, when the observation time gets long
2. the flat-field error, which limits the accuracy of the background substraction.
3. the noise of the dark frame to be substracted from the measurement

The flat-field error becomes the dominant performance limiting factor whenever the background contribution to the signal is large. This can be the case for a large PFOV, a wide band pass filter or in the longer wavelength part of the spectral range of the camera. In a single pointing observation, once the flat-field error becomes dominant nothing is gained in increasing the observation time, beam-switching or micro-scanning are required.

Figures to provide the performances, in some particular cases, for the filters and the CVF's. Detailed instructions for using these figures are given for each AOT, but the easiest way to determine the observation time of a measurement is to use the ISOCAM simulator software (see section ).