A Comparison of GOES and AMSU based Total Precipitable Water Retrievals

Satellite-derived total precipitable water (TPW) is being assimilated in NCEP's Eta Model. GOES TPW is assimilated directly while radiance information is being considered from passive microwave sensors like the DMSP SSM/I and the NOAA Advanced Microwave Sounding Unit (AMSU). Additionally, the GOES TPW uses 12-hour forecast TPW as a first guess. The GOES and microwave retrievals are "complimentary" in the sense that the GOES TPW obtainable under clear conditions only (land and ocean) while the SSM/I and AMSU retrievals can be obtained under almost all weather conditions (but restricted to ocean only).

The assimlation process minimizes the differences in a variety of data sources, in this case, satellite and radiosonde fields. An alternative method would be to derive a "blended" TPW product which minimizes the errors of the satellite retrievals prior to the assimilation cycle. This product would not only be of potential use to NWP assimilation, but as a stand alone product for NWS field office use. As a first step in the development of such a product, a thorough understanding of the differences between the various satellite products is needed. It is the purpose of this study to intercompare the TPW derived from the GOES, SSM/I and AMSU for a test period during June and July 2000. Results will be stratified by region and will include the Pacific Ocean, Gulf of Mexico, and Atlantic Ocean.