Daily TRMM and Others Rainfall Estimate (3B42 V7 derived) V7Entry ID: TRMM_3B42_daily
Abstract: This daily accumulated rainfall product, in mm/day, is derived from the original 3-hourly TRMM 3B42 product. It is not from the suite of the official TRMM products, and is generated at NASA GES DISC as a value added product primarily for visualization purposes in Giovanni, even though the data are also available for download.
The daily files are generated in bulk once a month, usually with ... 2-month latency. For every data-day, eight 3B42 files are simply accumulated and the result is scaled so that the resulting units are mm/day. For every data day, the first of the eight 3-hourly accumulated 3B42 files has starting time 22:30:00 (hh:mm:sec) UTC on the day before, and the last 3B42 file has the ending time 22:29:59 UTC on the data day.
The file size is about 2.25 MB (uncompressed). The data are stored in flat binary, as 4-byte floating numbers. Users who download these data will need to execute byte swapping if working on a little endian machine. These data have the first grid cell at (0.125,-49.875) (lon,lat), and data are stored in rows of 1440 longitudes. The first row is at -49.875 latitude. In standard matrix notation, the grid is sized (400,1440) (rows, columns).
The Tropical Rainfall Measuring Mission (TRMM) is a joint U.S.-Japan satellite mission to monitor tropical and subtropical precipitation and to estimate its associated latent heating. TRMM was successfully launched on November 27, at 4:27 PM (EST) from the Tanegashima Space Center in Japan. The precipitation-relevant instruments on the TRMM satellite include the Precipitation Radar (PR), an electronically scanning radar operating at 13.8 GHz; TRMM Microwave Image (TMI), a nine-channel passive microwave radiometer; and Visible and Infrared Scanner (VIRS), a five-channel visible/infrared radiometer.
The purpose of the 3B42 algorithm is to produce TRMM- and raingauge-adjusted multi-satellite precipitation rate (in mm/hr) and root-mean-square (RMS) precipitation-error estimates. The algorithm combines multiple independent precipitation estimates from the TMI, Advanced Microwave Scanning Radiometer for Earth Observing Systems (AMSR-E), Special Sensor Microwave Imager (SSMI), Special Sensor Microwave Imager/Sounder (SSMIS), Advanced Microwave Sounding Unit (AMSU), Microwave Humidity Sounder (MHS), and microwave-adjusted merged geo-infrared (IR). All input microwave data are intercalibrated to TRMM Combined Instrument (TCI) precipitation estimates (TRMM product 3B31); the IR estimates are computed using monthly matched microwave-IR histogram matching; then missing data in individual 3-hourly merged-microwave fields are filled with the IR estimates. After the preprocessing is complete, the 3-hourly multi-satellite fields are summed for the month and combined with the monthly accumulated Global Precipitation Climatology Centre (GPCC) rain gauge analysis using inverse-error-variance weighting to form a monthly best-estimate precipitation rate, which is TRMM Product 3B43. The final step is to scale all the 3-hourly estimates for the month to sum to the monthly value (for each gridbox separately). The final 3B42 precipitation (in mm/hr) estimates have a 3-hourly temporal resolution and a 0.25�x0.25� spatial resolution. The spatial coverage is the latitude band 50�S to 50�N.
Important Changes: After the initial Version 7 processing, it was discovered that AMSU data were neglected in the first retrospective processing of both the Version 7 TMPA (3B42/43) and TMPA-RT (3B40/41/42RT) data series, which created an important shortcoming in the inventory of microwave precipitation estimates used during 2000-2010. In addition, a coding error in the TMPA-RT replaced the occasional missings in product 3B42RT with zeros. Accordingly, both product series were retrospectively processed again. The main impact in both series was to improve the fine-scale patterns of precipitation during 2000-2010 (and for 3B4xRT into late 2012). Averages over progressively larger time/sp...
Data Set Citation
Start Date: 1997-12-31
ISO Topic Category
Data Set Progress
Extended Metadata Properties
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