| Abstract: |
The Tropical Rainfall Measurement Mission (TRMM) was a joint effort between the NASA and the Japan Aerospace Exploration Agency (JAXA) that was launched in November 1997 for a 3-year mission to study the statistics of rainfall from the tropical and subtropical regions of the Earth. Fortunately, the satellite and instruments performed flawlessly for 17-plus years, thereby providing a legacy of microwave radiometric data from the TRMM Microwave Imager (TMI). The Global Precipitation Measuring (GPM) mission is the follow-on mission to TRMM, launched in February 2014, and like TRMM, GPM is a remote sensing satellite mission designed to unify and advance precipitation measurements from a constellation of research and operational microwave radiometers that will provide scientifically valuable observations for studying the Earth’s water and energy cycles.
GPM operates in non-sun-synchronous orbit, which results in regular daily coincident overpasses with all of the sun-synchronous polar-orbiting spacecraft. As a result, the GPM Microwave Imager (GMI) performs as a brightness temperature (Tb) calibration standard for the intersatellite radiometric calibration (XCAL) for the other constellation members, and before GPM was launched, TMI was the XCAL standard. Thus, radiometric calibration between TMI to GMI is necessary for generating a consistent multi-decadal Tb data record that spans the TRMM and GPM eras; however, the TMI and GMI share only a 13-month common operational period (2014 – 2015). Fortunately, the Naval Research Lab’s WindSat radiometer, launched in 2003 and continuing today provides a means to extend the GMI/TMI intercalibration and to provide the calibration bridge to achieve a seamless transfer between the TMI and GMI Tb time series.
This paper presents results of the 3-way XCAL of GMI/TMI/WindSat for their joint overlap period and of the TMI/WindSat XCAL for their >12 years period (2003-2015), which demonstrate the exceptional long-term radiometric stability of TMI (relative to WindSat). Thus, a multi-decadal oceanic Tb dataset will be created that ensures a consistent long-term precipitation record that covers TRMM and GPM eras. Moreover, an important feature of this dataset is a quantitative estimate of the Tb uncertainty. The model used to provide this estimate will be described and results will be presented for both XCAL processes. |
