The Role of Combination Techniques in Maximizing the Utility of Precipitation Estimates from Several Multi-Purpose Remote-Sensing Systems

Multi-purpose remote-sensing products from various satellites have proved crucial in developing global estimates of precipitation. Examples of these products include low-earth-orbit and geosynchronous-orbit infrared (leo- and geo-IR), Outgoing Longwave Radiation (OLR), Television Infrared Operational Satellite (TIROS) Operational Vertical Sounder (TOVS) data, and passive microwave data such as that from Special Sensor Microwave/Imager (SSM/I) and Microwave Sounding Unit (MSU). Each of these datasets has served as the basis for at least one useful precipitation estimation scheme, however each has regions around the globe in which it provides little or no information on precipitation. In this paper we review the regional and temporal availability of these individual datasets and discuss combination techniques which take advantage of the characteristics of the various data sets in each region and time period. In cases where the sampling of the two datasets differs, either leo and geo or two different leo platforms, we emphasize collecting coincident data between the two for performing intercalibration. As well, we incorporate regional calibration by raingauge analyses in the combination schemes to anchor the products to "real" data to the extent possible. Examples will be drawn from the algorithms the authors have developed over the past decade on various time scales: monthly (both for Global Precipitation Climatology Project, GPCP, and Tropical Rainfall Measuring Mission, TRMM), daily (for GPCP), and 3-hourly (for TRMM). Current developments, data availability, and prospects for the future, including the Global Precipitation Mission, will be discussed.