|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.