Algorithm Information

The Integrated Multi-satelliE Retrievals for GPM (*IMERG*) is the unified U.S. algorithm that provides the multi-satellite precipitation product for the U.S. GPM team.

This document describes the algorithm and processing sequence for the Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement (GPM) mission (IMERG). This algorithm is intended to intercalibrate, merge, and interpolate “all” satellite microwave precipitation estimates, together with microwave-calibrated infrared (IR) satellite estimates, precipitation gauge analyses, and potentially other precipitation estimators at fine time and space scales for the Tropical Rainfall Measuring Mission (TRMM) and GPM eras over the entire globe.

The algorithm for the Integrated Multi-satellitE Retrievals for GPM (IMERG) has now been upgraded to Version 07.  IMERG V07 involves a wide range of changes to all aspects of the algorithm, many of which are implemented in response to feedback on V06, which was the first time the IMERG record spanned the TRMM-GPM eras.  IMERG V07 is being reprocessed for the entire TRMM-GPM record and thus supersedes all prior IMERG versions, as well as superseding the prior TRMM-based TMPA products (3B42, 3B43).

The L3GPROF algorithm provides monthly and daily mean precipitation and related retrieved parameters from the Level 2 GPROF precipitation profiling algorithm for the GPM core and constellation satellites.

Each L3GPROF product contains global 0.25o x 0.25o gridded monthly/daily unconditional means and pixel counts. Monthly product filenames start with 3A-MO or 3A-CLIM-MO, and daily product filenames start with 3A-DAY or 3A-CLIM-DAY.

This Level 3 GPROF Version 07 release involves the following changes from the previous
(Version 05) release:

1. Product format change:
Added dimension variables such as lat, lon, layer, lat_bnds, lon_bnds, layer_bnds. Removed
cloudIce variable but added graupel and latentHeating variables.
2. Total number of precipitation pixels (npixPrecipitation):
In Version 05, pixels with pixelStatus=0 and surfacePrecipitation > 0 are counted as
precipitation pixels. In Version 07, pixels with pixelStatus=0, surfacePrecipitation > 0 and

GPROF V05 is the rainfall algorithm used in TRMM V8. It matches in all ways the algorithm from the retrieval for GPM GMI and other satellites in the constellation. The Goddard Profiling Algorithm is a Bayesian approach that nominally uses the GPM Combined algorithm to create it's a-priori databases. Given the importance of these databases to the final product, they are worth reviewing before discussing particular changes to the algorithm. GPROF V03 was implemented at the launch of the GPM mission and thus had no databases from the GPM satellite itself.

This document describes the data file formats for all GPM products. Metadata is described in Metadata for GPM Products. The purpose of this file specification document is to define the file content and format for the GPM data products. The file specifications have been reviewed by the algorithm developers. Formats are expected to change for each processing cycle.

Version 7.16 TKIO 3.100

This document contains a comprehensive list of all data products produced by the NASA Precipitation Processing System, including their Document Object Identifiers (DOIs)

This document describes the file naming conventions that will be used to name data products produced by the Precipitation Processing System (PPS) for the Global Precipitation Measurement (GPM) Mission. These file naming conventions are also intended to apply to files produced or reprocessed from the Tropical Rainfall Measuring Mission (TRMM) satellite during the period of GPM operations.

The purpose of this file specification document is to define the file content and format for the TRMM data products.