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You are here: GES DISC Home Precipitation Documentation TRMM_README Readme for TRMM Product 3B42 (V7)

Readme for TRMM Product 3B42 (V7)

Data Access for
TRMM and Other Satellites Precipitation Product


Contents of TRMM and Other Satellites Precipitation Product 3B42


The purpose of the 3B42 algorithm is to produce TRMM-adjusted merged-infrared (IR) precipitation and root-mean-square (RMS) precipitation-error estimates. The algorithm consists of two separate steps. The first step uses the TRMM VIRS and TMI orbit data (TRMM products 1B01 and 2A12) and the monthly TMI/TRMM Combined Instrument (TCI) calibration parameters (from TRMM product 3B31) to produce monthly IR calibration parameters. The second step uses these derived monthly IR calibration parameters to adjust the merged-IR precipitation data, which consists of GMS, GOES-E, GOES-W, Meteosat-7, Meteosat-5, and NOAA-12 data. The final gridded, adjusted merged-IR precipitation (mm/hr) and RMS precipitation-error estimates have a daily temporal resolution and a 0.25-degree by 0.25-degree spatial resolution. Spatial coverage extends from 50 degrees south to 50 degrees north latitude.

For more details of the algorithm, go to

Data Flow Description

The data flow of 3B42 and the rest of the products are found in

Data Set Description

Data Characteristics

TRMM 3B42 Characteristics
Temporal Coverage Start Date: 1998-01-01; Stop Date: -
Geographic Coverage Latitude: 50°S - 50°N; Longitude:180°W - 180°E
Temporal Resolution 3-Hourly
Horizontal Resolution 0.25° x 0.25°; nlat = 400, nlon = 1440
Average File Size Compressed: ~0.71 MB; Original: ~11 MB
File Type HDF

Data Format Structure

Further information on the contents and structure of this product can be found in File Specifications for TRMM Products - Version 7.00

Data Format Structure for 3B42
Name Type Record
Dim Size/
# of Records
Range Unit Description
ECS Core Metadata Char Attribute 10,000  - - - - ECS Core Metadata
PS Metadata Char Attribute 10,000  - - - - Product Specific Metadata
Grid Structure Char Attribute 5,000  - - - - The specification of the grid geometry
precipitation Float SDS nlat*nlon - 0.0 - 100  mm hr-1 TMPA precipitation estimate
relativeError Float SDS nlat*nlon - 0.0 - 200 mm hr-1 TMPA random error estimate
satPrecipitationSource Integer SDS 2 nlat*nlon -     Flag to show source of data at each 0.25 x 0.25 degree box.
HQprecipitation Float SDS 4 nlat*nlon  - 0.0 - 100 mm hr-1 Pre-gauge-adjusted microwave precipitation estimate at each 0.25 x 0.25 degree box.
IRprecipitation Float SDS 4 nlat*nlon  - 0.0 - 100 mm hr-1 Pre-gauge-adjusted infrared precipitation estimate at each 0.25 x 0.25 degree box.
satObservationTime Integer SDS 1 nlat*nlon  - -90 - 90 minute Satellite observation time minus the time of the granule at each 0.25 x 0.25 degree box.
Note: nlat =  400: number of 0.25° latitude grids from 50°S - 50°N;
          nlon = 1440: number of 0.25° longitude grids from 180°W - 180°E;
          Missing data are given the value of -9999.9
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Last updated: Mar 18, 2013 03:39 PM ET