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Japan Aerospace Exploration Agency (JAXA) has addressed the water issues by conducting the Global Precipitation Measurement (GPM) Mission. GPM core satellite carries Dual-frequency Precipitation Radar (DPR). DPR can observe 3-dimensional precipitation with high accuracy, whereas the observation swath is narrow, and observation is not so frequent. To achieve the high frequent precipitation observation, we developed the multi-satellite precipitation product called Global Satellite Mapping of Precipitation (GSMaP) under the collaboration with international GPM constellation satellite. GSMaP provides hourly global precipitation distribution by 0.1 x 0.1 degrees latitude/longitude, and its utilization is spread especially over the Asian countries and used in various fields. As one of the future precipitation observation missions discussed in JAXA, there is the concept of small precipitation radar constellation. This can improve the quality of GSMaP if realized. In this study, the impact on accuracy of GSMaP caused by the increase of radar observation is evaluated over Japan area. Japan Meteorological Agency provides highaccurate and high-resolution ground precipitation radar data calibrated by rain gauges. This ground observation data is assumed as future precipitation radar data and inserted to the GSMaP processing in some temporal intervals. The sampling errors are taken into consideration. The relationship between temporal interval of insertion (assumed as radar observation frequency) and improvement of accuracy is verified and discussed.
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