The Global Precipitation Measurement (GPM) started as an international project and a follow-on and expansion of the
Tropical Rainfall Measuring Mission (TRMM). The GPM mission consists of two different categories of satellites. One
is a TRMM-like core satellite carrying both active and passive microwave instruments, jointly developed by Japan and
the US. The other is a constellation of satellites carrying passive microwave sensors and provided by partner agencies.
A Dual-frequency Precipitation Radar (DPR) for the GPM core satellite is being developed by JAXA and NICT, and
consists of Ku- and Ka-band precipitation radars to measure light rainfall and snowfall as well as moderate-to-heavy
rainfall. One major objectives of GPM is to contribute to operational utilization, and frequent and accurate precipitation
products, at less than 3-hour intervals, will be produced by combining multi-satellite microwave radiometers and
geostationary IR information. DPR will provide accurate rainfall database to microwave radiometers, and enhance their
algorithms, which will be used to make frequent rainfall map.
The DPR L1 algorithms are being developed by JAXA. Collaboration activities between Japan and the US have started
to develop L2/3 rainfall algorithms for DPR, and DPR/GMI combined products. Research activities to develop
algorithms for rainfall map products have been underway both in Japan and the US. Validation activities in JAXA will
be focused on contributions to algorithm development before and after the launch, as well as evaluation of the quality of
rainfall products. Pre-launch validation will include ground-based campaigns and utilization of synthetic data produced
by numerical models.