Special Sensor Microwave Imager (SSM/I) Cross Calibration and Impact on Water Vapor, Precipitation and Climate Trend

The Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave and Imager (SSM/I) series provide the longest time series of satellite microwave measurements from July 1987 to present. These observations are being followed with a nearly identical sensor, the Special Sensor Microwave Imager/Sounder (SSMIS), which will continue to operate for at least the next decade. The long records of consistent measurements from multi-sensors are extremely important in generating the climate data records (CDRs). However, these different sensors must be carefully calibrated in order to produce the consistent and high quality CDRs for climate analysis and reanalysis.

This presentation will first describe the NOAA SSM/I sensor data record (SDR) intersensor calibration scheme based on the simultaneous conical overpass (SCO) technique to correct the intersensor biases by using F13 as the reference satellite. The impact of this calibration procedure on the SSM/I-based water vapor and precipitation retrievals and their climate trends will be analyzed. Results demonstrate that this scheme produces consistent monthly SDRs from different SSM/I sensors. The scheme has also significantly positive impacts on the retrieved water vapor, surface precipitation and the associated trends. For example, the mean bias of SSM/I monthly precipitation is reduced by 12% with this intersensor calibration procedure against the matched rain products from Tropical Rainfall Measuring Mission (TRMM). The mean total precipitable water path (TPW) intersensor bias is reduced by 75% (20%) over the global (tropical) ocean with the calibration, while the calibrated TPW climate trend is about 1.59% (1.39%) per decade for the global (tropical) ocean. Finally, we will discuss the preliminary results on the SSM/I intersensor calibrations using the Joint Center for Satellite Data Assimilation (JCSDA) Community Radiative Transfer Model (CRTM) simulations as the reference.