For single pointing measurements with one FCS measurement per detector no attempt is made to correct for long term responsivity drifts. It is assumed that the detector responsivity is stable during the execution time of an AOT.
For raster pointing observations and sparse maps, the average of the two bracketing responsivity values is used, provided both have neither a real time problem nor are outside the validity range of the FCS heating power (see Section 10.4).
However, investigations of long measurements have shown that the responsivity is not stable but exhibits a non-linear drift. An exponential behaviour is observed due to switch-on effects. Detailed models of the detector behaviour or baseline fits would be required for optimum correction.
Caveat: PHT OLP does not correct for PHT-P and PHT-C long term detector drifts within an AOT. In case of maps with bracketing FCS measurements only the average responsivity value is used.