Scatterometer Climate Record Pathfinder
PR on TRMM Gridded Image Product Users Notes

The Precipitation Radar (PR) on the Tropical Rain Measurement Mission (TRMM) has very high spatial resolution (4.5 km) over a narrow (250 km) swath. TRMM orbits in an low-inclination equitorial orbit and so has coverage o nly up to approximately 30 deg latitude. The PR operates at Ku-band, like SASS, NSCAT, and QuikSCAT but makes measurements only at incidence angles less than 20 deg. It thus compliments the scatterometer observations which are at 17 deg incidence and higher. Unlike the scatterometers, PR has vertical resolution. However, only non-raining surface backscatter values are used in the images produced here.

Because of the high intrinsic resolution of PR, only non-enhanced, gridded images are generated. They are generated on a compatible grid in the same projection as the scatterometer regions. The grid resolution is 8.9 km/pixel. This is coarser than the the intrinsic resolution to ensure that sufficent measurements are combined into each grid to support linear regression of sigma-0 versus incidence angles. Only incidence angles greater than 5 deg are included. The incidence angle of normalization is 11 deg. The narrow swath requires 30 days to ensure multiple passes at each location so data from multiple orbit passes are combined. Each image is generated from 30 days of data, with one image generated every 15 days.

Raw TRMM PR 2A21 Version 6 was obtained from the Goddard DAAC. No recalibration has been applied. More information about TRMM and the TRMM PR are available from the Goddard DAAC.

Though the images are NOT resolution enhnaced, the image files are produced in the BYU .SIR file format, using the standard naming scheme. The files are gzipped to minimize storage and transfer requirements. The standard images are designed for land observation and so are landmasked. However, .SIR format land mask files (containing 0 for ocean and 1 for land) are available for each standard region. .SIR format images containing "images" of the latitude and longitude of each pixel for each region are also available.