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, 1997 at 4:27 PM (EST) from the Tanegashima Space Center in Japan.

The TRMM Precipitation Radar (PR), the first of its kind in space, is an electronically scanning radar, operating at 13.8 GHz that measures the 3-D rainfall distribution over both land and ocean, and defines the layer depth of the precipitation.

The primary objective of the 3A26 is to compute the rain rate statistics over 5 degree (latitude) x 5 degree (longitude) x 1 month space-time regions. The output products include the estimated values of the probability distribution function of the space-time rain rates at 4 &apos;levels&apos; (2 km, 4 km, 6 km, and path-averaged) and the mean, standard deviation, and probability of rain derived from these distributions. Three different rain rate estimates are used for the high resolution rain rate inputs to the algorithm: (1) the standard Z-R (or 0th-order estimate having no attenuation correction), (2) the Hitschfeld-Bordan (H-B), and (3) the rain rates taken from 2A25. (Fits based on the high resolution inputs from the surface reference technique are output to the diagnostic file for evaluation).

This algorithm is based on a statistical procedure. Although the radar team believes that a statistical method of this type should be implemented for TRMM, the method is relatively new and the testing has been carried out only on simulated data and on preliminary TRMM data. Caution on the use of the results is well warranted.

Spatial coverage is between 40 degrees North and 40 degrees South, owing to the 35 degree inclination of the TRMM satellite.

The data are stored in the Hierarchical Data Format (HDF), which includes both core and product specific metadata applicable to the PR measurements. A file consists of arrays of rain rate data and supporting information, each of dimension 72 x 16, for three fixed heights (2, 4, and 6 km) and the path-averaged rain rates.  The file size is about 16 MB (uncompressed). The HDF-EOS &quot;swath&quot; structure is used to accommodate the actual geophysical data arrays. There is 1 file of PR 3A26 data produced per month.