Global rainfall products of high spatial and temporal resolutions have been provided using combined data from passive microwave (PMW) sensors in low Earth orbit and infrared (IR) radiometers in geostationary Earth orbit (GEO). This study compared six satellite rainfall estimates around Japan with reference to a ground-radar dataset calibrated by rain gauges provided by the Japan Meteorological Agency (JMA) from January through December 2004. Validation results tended to be better for the products with temporal interpolation based upon the morphed technique using GEO IR information. Satellite estimates were poor for light rainfall during the warm season and for very heavy rainfall.
  Further analyses of satellite estimates were conducted in terms of data sources and surface types. 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. Overall, validation results over the ocean were best, and results over mountainous regions were worst. Performance was poor over coasts and small islands, due to the problem of PMW retrievals. This study focused on hydrometeor profiles of orographic heavy rainfall over the Japanese Archipelago, which could be related to the poor performance of satellite estimates in very heavy rainfall.