Near-real-time global rainfall map using multi-satellite data by JAXA and its validation

Japan Aerospace Exploration Agency (JAXA) has developed and operated near-real-time data processing system with passive microwave radiometer (PMW) data (i.e., TRMM TMI, Aqua AMSR-E, and DMSP SSM/I and SSMIS) and GEO IR data and distributed rainfall products via the Internet (http://sharaku.eorc.jaxa.jp/GSMaP/). Core algorithms of the system are based on the algorithm developed under the Global Satellite Mapping of Precipitation (GSMaP) project. Horizontal resolution of GSMaP_NRT is 0.1-degree latitude/longitude grid and temporal resolution is 1 hour. The datasets are provided in near real time (about four hours after observation). The PMW-IR blended products of the GSMaP are the GSMaP_NRT for the near-real-time purpose and the GSMaP_MVK. The GSMaP_MVK estimates are achieved by the temporal interpolation of PMW retrievals using a PMW-IR blended algorithm composed of a morphed technique (Joyce et al., 2004) and a Kalman filter (Ushio et al., 2009) using IR information. For computation of the PMW retrievals, estimates from the PMW imagers are retrieved by a TRMM/PR-consistent advanced microwave radiometer algorithm by the GSMaP Project (Aonashi and Liu 2000; Kubota et al. 2007; Aonashi et al. 2009). The retrievals from the SSMIS instruments on the DMSP F16 and F17 have been merged in the GSMaP_NRT since June 2010. Rainfall estimates from the NOAA AMSU-B are not used in the GSMaP_NRT now (Aug. 2010), but they will be merged in near future. In the current plan, we will use the retrievals from the GSMaP_AMSU algorithm (Shige et al., 2009) over ocean and the NOAA Microwave Surface and Precipitation Products System (Zhao and Weng 2002; Ferraro et al. 2005) over land and coast. Kubota et al. (2009) analyzed satellite estimates in terms of data sources and surface types around Japan with reference to a ground-radar dataset calibrated by rain gauges provided by the Japan Meteorological Agency from January through December 2004. They demonstrated effective performance by the merger of PMW sounders over the ocean was verified by radar validation, in addition to the best results of the PMW imagers. In the GSMaP_MVK algorithm, rainfall features are propagated via IR data both forward and backward, while they are only propagated forward in GSMaP_NRT, the merit of which is a faster processing time. Daily product of the GSMaP is utilized for the International Precipitation Working Group (IPWG) satellite precipitation validation/intercomparison studies. Currently GSMaP_NRT, as well as other satellite-based rainfall products, are compared to regional ground rain gauge and radar network data in near-real-time basis over United States (University of Maryland), South America (University of Maryland), Australia (Bureau of Meteorology), and Japan (Kyoto University).