2019-02-19

IMERG降水产品主要来源于GMI和DPR。GSMap产品由JAXA 开发的一款高时空分辨率卫星降水产品。GSMap算法中，红外数据和被动微波数据的结合将高分辨率和高精度同时实现，其主要产品为GSMap_MVK和GSMap_Gauge。GSMap_Gauge产品是在GSMap_MVK基础上，引入地面数据对其进行改进，一定程度上提高了GSMap_Gauge产品的准确度及产品质量。
TMI/PR combined instrument (TCI)
TRMM Microwave Radiometer (TMI)
precipitation radar (PR)
TRMM Multi-satellite Precipitation Analysis (TMPA)
the real-time TMPA (TMPA-RT)
the Integrated MultisatellitE Retrievals for GPM (IMERG).

The Version 7 TRMM product 3B42 is being computed with the TMPA after real time, and
constitutes the research-grade archive of TMPA estimates. Note that the version numbering for
the TMPA-RT and official TRMM products are not necessarily related, although both are currently numbered 7. The post-real time computation allows several improvements in 3B42 compared to 3B42RT:

1. Data are processed starting with the first full month of TRMM data, which begins 1 January 1998.
2. The IR calibration period is the calendar month in which the observation time falls, rather
   than a trailing 30-day accumulation.
3. The TRMM Combined Instrument product (2B31) is used as the calibrating standard monthto-
   month, which should give better estimates than the climatological calibration used in the RT.
4. For each grid box, the individual 3B42 3-hourly precipitation values are scaled to sum to a
   combination of monthly 3B42 and gauge analysis, which is TRMM product 3B43.

3B42, ”TRMM and Other Sensors - 3-Hourly”, provides precipitation estimates in the
TRMM regions that have the mean of the ”TRMM Combined Instrument” precipita-
tion estimate and the dense sampling of high-quality microwave data with fill-in using
microwave-calibrated infrared estimates. The 3-hourly satellite estimates are then rescaled
to the monthly precipitation gauge data. The granule size is 3 hours. The following sec-
tions describe the structure and contents of the format.

Dimension definitions:
nlat 400 Number of 0.25o grid intervals of latitude from 50o N to 50o S.
nlon 1440 Number of 0.25o grid intervals of longitude from 180o W to 180o E.