NASA has just released its newest and most comprehensive estimate of rain and snow covering nearly 20 years. Version 6 of NASA's IMERG -- the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (GPM) -- combines information from a constellation of satellties are operating in Earth orbit, at a given time, to estimate precipitation over the majority of the Earth's surface. This algorithm is particularly valuable over the majority of the Earth's surface that lacks precipitation-measuring instruments on the ground. What is new in Version 6 IMERG is that the algorithm can now fuse the early precipititation estimates collected in 2000-2014 during the operation of the TRMM satellite with more recent precipitation estimates collected during operation of the GPM satellite. The longer the record, the more valuable it is, as researchers and application developers will attest. TRMM and GPM are two satellites specially designed to provide the most reliable space-based estimates of preciptiation, and both satellites are joint missions between NASA and the Japan Aerospace Exploration Agency (JAXA).
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 22.214.171.124.0