Satellite Instrument Calibration Issues: experience gained from SSMIS

Following the launch of F16 SSMIS in October 2003, a number of instrumental biases have been investigated by the extended Cal/Val team. For the lower atmospheric temperature sounding channels, where radiometric performance is most critical for NWP data assimilation applications, the two most significant instrumental biases are associated with solar intrusions into the warm calibration load and thermal emission from the main reflector. Strategies have been developed at the Met Office and elsewhere to deal with these problems either through flagging or by correcting the measured brightness temperatures. A conservative Day 1 strategy has been implemented at the Met Office which involves flagging and subsequently rejecting intrusion affected observations, and correcting for reflector emission as part of a pre-processor. Pre-processed radiances for the low atmospheric sounding channels give global innovations in the range 0.2 0.3 K, and relatively stable biases, based on a short monitoring period (August October 2005).