Abstract: 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 rainfall measuring 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-adjusted merged-infrared (IR) 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 iIR 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-degree by 0.25-degree spatial resolution. Spatial coverage extends from 50 degrees south to 50 degrees north latitude.
The data are stored in the Hierarchical Data Format (HDF), which includes both core and product specific metadata. The file size is about 0.74 MB (compressed).
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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Information and data access for all of the Goddard DAAC's hydrology data holdings, including TRMM data from the TMI, Precipitation Radar (PR) and Visible and Infrared Scanner (VIRS) instruments, the Ground Validation (GV) radar data, and ancillary and correlative data products.
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. For more, see, ftp://meso-a.gsfc.nasa.gov/pub/trmmdocs/3B42_3B43_doc.pdf
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, 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.