Recent work by the proposal team has utilized measurements from the TRMM satellite to develop and improve microwave rain rate retrievals over land for the Goddard Profiling Algorithm (GPROF). Significant progress has been accomplished through our previous participation on the PMM and AMSR-E science teams and these improvements are continuously incorporated into the TRMM 2A12 and AMSR-E L2 facility algorithms. Due to its physical robustness and its portability to different microwave sensors, the GPROF framework has become the standard microwave algorithm that has been adopted by the scientific community as we enter into the GPM era. Despite the great advances made in GPROF, further research is needed in order to vastly improve the algorithm over land, in particular, to expand its utility beyond the warm season regime. This will be accomplished by developing a diverse array of hydrometeor profiles that are representative of global precipitation regimes. The GPM microwave imager (GMI) will include high frequency channels that will greatly enhance the ability to measure light rain and falling snow. Also, the GPM dual-frequency precipitation radar (DPR) will provide detailed microphysical information on light rain and snow. Recent work with the NOAA Advanced Microwave Sounding Unit (AMSU) has utilized measurements at 89, 150 and 183 GHz to develop an operational precipitation retrieval algorithm that has shown improved sensitivity to light rain over land. An important issue with the current GPROF algorithm over land is the identification of precipitation and its differentiation from other surface features. This 'screening module' is grossly outdated and needs improvement. The high frequency channels offer the ability to sense precipitation over land without strong surface emissivity effects. Also, the weighting functions of these water vapor channels reach their maximum at different altitudes, offering the potential to delineate the vertical distribution of hydrometeors. If GPM is to meet its requirement of global 3-hourly precipitation, the use of sounders such as AMSU will likely be needed. Our proposed work is to utilize the traditional imager channels in conjunction with high frequency observations from AMSU and SSMIS, cloud resolving models and advanced radiative transfer models to:
- Improve the current GPROF surface screening to remove ambiguity between precipitation and other surface signatures that resemble precipitation,
- Study the effects of hydrometeors on the 10-183 GHz radiances and the Bayesian precipitation retrieval from this database. We will examine the comprehensiveness of the hydrometeor data base for regimes outside the tropics and the adequateness of radiative transfer calculations for the pertinent hydrometeors,
- Investigate the potential of incorporating microwave sounding channels (50-60 GHz and 183 GHz) to the hydrometeor profile retrieval.
Based on our findings, we will make recommendations and modifications to the database and the radiative transfer models to improve the precipitation retrieval using all the GMI channels. Studies will also be conducted to determine the ability of the various GPM constellation satellites (including sounders) to perform land based precipitation retrievals, and determine proxy data sets that can be used for those sensors that lack the proper channels. We plan to collaborate with other researchers on the PMM team and leverage their work to advance our understanding to improve the use of GPROF beyond the tropics.
