Geolocation Error Analysis of the Special Sensor Microwave Imager/Sounder

Geolocation errors in excess of 20-30 km have been observed in the special sensor microwave imager/sounder (F-16 SSMIS) radiometer observations when compared with accurate global shoreline databases. Potential error sources include angular misalignment of the sensor spin axis with the spacecraft zenith, sample timing offsets, nonuniform spin rate, antenna deployment offsets, spacecraft ephemeris, and approximations of the geolocation algorithm in the Ground Data Processing Software. An analysis methodology is presented to automate the process of quantifying the geolocation errors rapidly in terms of partial derivatives of the radiometer data in the along-scan and along-track directions and is applied to the SSMIS data. Angular and time offsets are derived for SSMIS that reveal the root cause(s) of the geolocation errors, while yet unresolved, are systematic, correctable in the ground processing software, and may be reduced to less than 4-5 km (1-sigma).