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Precipitation Radar (PR) on TRMM Gridded Image Products (prtr)

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 only 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.

Further information is available in the PR on TRMM gridded image users notes.

Available Gridded Images
all passes prtr

Images 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 prtr gridded images are designed for comparison to scatterometer products for land observation. Data over the ocean is generally not useful. However the distributed images are not land masked. .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.