Daily TRMM and Others Rainfall Estimate (3B42 V7 derived)Entry ID: GES_DISC_TRMM_3B42_daily_V7
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/space scales should be progressively less affected. [This is the reason the lack of AMSU went undiscovered; the merger system copes very reasonably with missing data.] Nonetheless, users are urged to switch to the newest Version 7 data sets. The newest runs may be identified by the file names: V.7 3B42/43 suffix of "7A.HDF" for January 2000 - September 2010 V.7 3B4xRT suffix of "7R2.bin" for 1 March 2000 - 6 November 2012 It continues to be the case that the Version 7 3B42/43 is some 4% higher than the calibrating data set (2B31) over oceans, which is still under study. However, the initial conclusion is that it results from the sampling mismatch between the (very sparse) TCI and the (much denser) microwave constellation. At the large scales this offset seems to be nearly a proportional constant.
TMPA Restarted with October 2014: On October 07, 2014, routine production ended for the TRMM PR precipitation estimates. Since PR is no longer available, the TMI/PR combined instrument (TCI) estimates are also no longer available. As products 3B42/3B43 use the TCI estimates as the satellite calibrator, September 2014 is the last month these products were produced in this way. In an effort to continue 3B42/3B43 available and usable, the real time TMPA (TMPA-RT) climatological calibrations/adjustments have been adapted for use in the 3B42/3B43. October 2014 is the first month of the climatologically calibrated/adjusted 3B42/3B43. Users should note there will be a discontinuity in the record as a result. Each individual user must determine the most appropriate use of the climatologically calibrated/adjusted 3B42/3B43 products.
The two-month latency for 3B42/3B43 remains the same with this new calibration. The delayed release for October 2014 reflects both development work and a problem with the input IR data. The previously released "provisional" data set is now considered obsolete and should not be used (although in many areas it is identical to this official release). As well, a (different) problem with the input IR for November 2014 is not yet resolved, so that data set is still in provisional status. We expect to have updated November 2014 IR data in the very near future, and thereafter run on the usual schedule.
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Data Set Citation
Dataset Originator/Creator: Tropical Rainfall Measurement Mission Project (TRMM)
Dataset Title: Daily TRMM and Others Rainfall Estimate (3B42 V7 derived)
Dataset Publisher: Goddard Space Flight Center Distributed Active Archive Center (GSFC DAAC)
Version: 7Online Resource: http://disc.gsfc.nasa.gov/datacollection/TRMM_3B42_daily_V7.shtml
Start Date: 1997-12-31
Latitude Resolution: 0.25 degree
Longitude Resolution: 0.25 degree
Horizontal Resolution Range: 10 km - < 50 km or approximately .09 degree - < .5 degree
Vertical Resolution: Surface
Temporal Resolution: Daily
Temporal Resolution Range: Daily - < Weekly
ISO Topic Category
Quality Random error estimates (mislabeled “relative error” for historical reasons) are provided for each 0.25 x 0.25 degree box. The quality of the 3B42 product is highly sensitive to the quality of the input data: TMI (product 2A12), TRMM Combined Instrument (TCI; product 2B31), and the other input datasets listed in the Summary. If the quality of the input data is less than anticipated, then the quality of 3B42 will also be less.
Access Constraints None
Data Set Progress
Distribution Media: FTP
Distribution Size: file size: 2304 kb
Distribution Format: Binary
Email: George.J.Huffman at nasa.gov
NASA Goddard Space Flight Center Mailstop 612
Province or State: MD
Postal Code: 20771
Role: TECHNICAL CONTACT
Email: gsfc-help-disc at lists.nasa.gov
Goddard Earth Sciences Data and Information Services Center Code 610.2 NASA Goddard Space Flight Center
Province or State: MD
Postal Code: 20771
Role: DIF AUTHOR
Email: Zhong.Liu-1 at nasa.gov
NASA Goddard Space Flight Center Mailstop 610.2
Province or State: MD
Postal Code: 20771
Product Readme: ftp://meso-a.gsfc.nasa.gov/pub/trmmdocs/3B42_3B43_doc.pdf
File Specifications for TRMM Products: http://pps.gsfc.nasa.gov/Documents/filespec.TRMM.V7.pdf
Metadata for TRMM Products: http://pps.gsfc.nasa.gov/Documents/filespecMeta.TRMM.V7.pdf
TRMM V6 vs. V7 Major Data Format Changes: http://pps.gsfc.nasa.gov/Documents/formatChangesV7.pdf
TMPA Restarted with October 2014: ... http://pmm.nasa.gov/sites/default/files/imce/3B42_3B43_TMPA_restart...
Huffman, G.J., 1997: "Estimates of Root-Mean-Square Random Error for Finite Samples of Estimated Precipitation," J. Appl. Meteor., 1191-1201.
Huffman, G.J., R.F. Adler, P. Arkin, A. Chang, R. Ferraro, A. Gruber, J. Janowiak, A. McNab, B. Rudolph, and U. Schneider, 1997: "The Global Precipitation Climatology Project (GPCP) Combined Precipitation Dataset," Bul. Amer. Meteor. Soc., 78, 5-20.
Huffman, G.J., R.F. Adler, B. Rudolph, U. Schneider, and P. Keehn, 1995: "Global Precipitation Estimates Based on a Technique for Combining Satellite-Based Estimates, Rain Gauge Analysis, and NWP Model Precipitation Information," J. Clim., 8, 1284-1295.
Huffman, G.J., R.F. Adler, D.T. Bolvin, G. Gu, E.J. Nelkin, K.P. Bowman, Y. Hong, E.F. Stocker, D.B. Wolff, 2007: The TRMM Multi-satellite Precipitation Analysis: Quasi- Global, Multi-Year, Combined-Sensor Precipitation Estimates at Fine Scale. J. Hydrometeor., 8(1), 38-55. PDF available at ftp://meso.gsfc.nasa.gov/agnes/huffman/papers/ TMPA_jhm_07.pdf.gz
Huffman, G.J., R.F. Adler, D.T. Bolvin, E.J. Nelkin, 2010: The TRMM Multi-satellite Precipitation Analysis (TMPA). Chapter 1 in Satellite Rainfall Applications for Surface Hydrology, F. Hossain and M. Gebremichael, Eds. Springer Verlag, ISBN: 978-90-481-2914-0, 3-22.
Extended Metadata Properties
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Creation and Review Dates
DIF Creation Date: 2011-07-19
Last DIF Revision Date: 2016-01-20