Abstract
The National Aeronautics and Space Administration’s (NASA) Precipitation Measurement Missions (PMMs) include two earth satellite missions, namely, the Tropical Rainfall Measuring Mission (TRMM, 1997–2015) and the Global Precipitation Measurement (GPM, 2014-present). To generate a consistent multi-decadal brightness temperature (Tb) record that spans the TRMM and GPM eras, it is highly desirable to perform a comprehensive intercalibration of the TRMM Microwave Imager (TMI) and the GPM Microwave Imager (GMI) Tb measurements. Unfortunately, GMI and TMI share a limited common operational period of only 13 months. Fortunately, the WindSat polarimetric radiometer (2003-present) has been shown to be well calibrated and radiometrically stable relative to TMI for a period of over 5 years. Therefore, this paper describes the use of overlapping WindSat Tb measurements as the calibration bridge to achieve a seamless transfer joining the TMI and GMI Tb time series. Also, the development of the Tb measurement uncertainty estimation model is presented, which incorporates all relevant sources of uncertainty. Afterwards, this model was applied to three intercalibration processes: TMI to GMI, TMI to WindSat, and WindSat to GMI, and results are presented that quantify the corresponding Tb channel measurements biases and associated uncertainties associated with the merged TMI-GMI Tb record. This is an important accomplishment because this study can enable improved future Earth Science and global climate change investigations by making a long-term Tb record with estimated uncertainty available.
Highlights
The Tropical Rainfall Measuring Mission (TRMM), launched on November 27, 1997, was a jointEarth Science satellite mission between the National Aeronautics and Space Administration (NASA)and the Japan Aerospace Exploration Agency (JAXA)
Since WindSat provides the calibration bridge between Global Precipitation Measurement (GPM) Microwave Imager (GMI) and TRMM Microwave Imager (TMI) Tb records, the TMI/WindSat intercalibration uncertainties for the six individual years are shown in Figure 7 for the three major uncertainty sources by radiometer channel
Earth Science investigations and global climate change studies require consistent long-term precipitation data as input, which increases the need for a long-term unified brightness temperature record
Summary
The Tropical Rainfall Measuring Mission (TRMM), launched on November 27, 1997, was a joint. The new version of TMI Tbs has improvements on several issues over the old V7 including geolocation, emissive antenna correction, hot load correction, multi-scan calibration, and radio frequency interference [14,15,16,17] With these results, the derived Tb biases after the composite intercalibration (XCAL) offsets can be applied to the TMI 17-plus years legacy Tb product, to create a consistent multi-decadal TRMM-GPM Tb record. Tb measurement errors and long-term radiometric calibration stability of the TMI/GMI time series This requires systematic analysis and consistent methods of incorporating Tb uncertainty estimations into its downstream precipitation product that is significant for global climate change assessments. This process will provide uncertainties for the TMI/GMI Tb time series
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