Developments of Climate Data Records from Special Sensor Microwave Imager (SSM/I) using Simultaneous Overpassing Technique

Satellite measurements from the Defense Meteorological Satellite Program's (DMSP), Special Sensor Microwave/Imager (SSM/I) is the longest time series of satellite microwave imager in existence today, beginning in July 1987 and continuing today (20 years of continuous data). 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. This long time series of SSM/I sensors has to be well calibrated for intersensor bias, sensor degradations, and diurnal variations, in order to generate a high quality and self-consistent climate data records (CDRs).

In this study, we will present an SSM/I cross-calibration algorithm using a simultaneous conical overpassing (SCO) data set from a pair of DMSP satellites. The double difference method is used to calibrate all the SSM/I data to the F13 satellite which is used as a reference sensor. This cross-calibration algorithm has improved the consistency of the monthly SDR's time series from different SSM/I sensors. Total precipitable water biases between sensors are reduced by 75% over the global ocean and 20% over the tropical ocean, respectively. The TPW climate trend is 1.59% per decade (or 0.34 mm decade-1) for the global ocean and 1.39% per decade (or 0.63 mm decade-1) for the tropical ocean, indicating a related trend decrease of 38% and 54% respectively from the uncalibrated SDRs.