Preparations for Global Precipitation Measurement (GPM) ground validation

The Global Precipitation Measurement (GPM) program is an international partnership led by the National Aeronautics and Space Administration (NASA) and the Japan Aerospace Exploration Agency (JAXA). GPM will improve climate, weather, and hydrometeorological forecasts through more frequent and more accurate measurement of precipitation across the globe. This paper describes the concept and the preparations for ground validation within the GPM program. Ground validation (GV) plays a critical role in the program by investigating and quantitatively assessing the errors within the satellite retrievals. These quantitative estimates of retrieval errors will assist the scientific community by bounding the errors within their research products. The two fundamental requirements of the GPM ground validation program are: (1) error characterization of the precipitation retrievals and (2) continual improvement of the satellite retrieval algorithms. These two driving requirements determine the measurements, instrumentation, and location for ground observations. This paper describes GV plans for estimating the systematic and random components of retrieval error and for characterizing the spatial and temporal structure of the error. This paper describes the GPM program for algorithm improvement in which error models are developed and experimentally explored to uncover the physical causes of errors within the retrievals. GPM will ensure that information gained through ground validation is applied to future improvements in the space-borne retrieval algorithms. This paper discusses the potential locations for validation measurement and research, the anticipated contributions of GPM´s international partners, and the interaction of ground validation with other GPM program elements.