In this Section the detector performance data used for sensitivity calculations have been derived from calibration observations collected in-flight during ISO's performance verification phase and during subsequent routine calibrations.
By the time of writing of this document the general performance description of the instrument has not been finalized. Nevertheless it is found that both the responsivity and sensitivity of the detectors are seriously affected by the presence of ionizing radiation in orbit.
The actual values for the detector read-out noise and NEP at a given time in the mission is observed to depend on the rate of both high and low energy particles hitting the detectors. The particle hit rate varies during a revolution and can vary from one revolution to the other. Consequently, the sensitivity figures quoted in this Section are subject to uncertainties of order 100-200% and should be considered as best nominal values.
In addition, the presence of detector responsivity drifts after flux steps (see section 2.9 of the IOM3.1) have shown to be one of the most important sources of photometric uncertainty.