Summary

Description

The Tropical Rainfall Measuring Mission (TRMM) http://disc.gsfc.nasa.gov/precipitation/trmm_instr.shtml is a joint U.S.-Japan satellite mission to monitor tropical and subtropical precipitation and to estimate its associated latent heating. The Level 1B product file (1B11) contains calibrated brightness temperatures and auxiliary geolocation information for each pixel in the scan. The structure of the Level 1B data file is based on the Wentz format for the SSM/I data. The Level 1B data are stored in the Hierarchical Data Format (HDF), which includes both core and product specific metadata applicable to the TMI measurements. A file contains a single orbit of data with a file size of about 14 MB (uncompressed). The HDF-EOS "swath" structure is used to accommodate the actual geophysical data arrays. As in the case of the Level 1A data, there are 16 files of TMI 1B11 data produced per day. Antenna temperatures are derived from the Level 1A sensor counts by applying a linear relationship of the form: Tb = a + b * count. The resultant temperatures are corrected for cross-polarization and spill-over to produce the brightness temperatures found in the Level 1B product. However, no antenna beam pattern correction or ample-to-pixel averaging has been applied to these brightness temperatures. In the Level 1B data, geolocation and channel data are written out for each pixel along the scan, whereas the time stamp, scan status (containing scan quality information), navigation, calibration coefficients, and satellite zenith angle are specified on a per-scan basis. There are, in general, 2991 scans along the orbit, with each scan consisting of 208 high resolution (85 GHz) pixels, and 104 low resolution pixels (all other channels). The scan width is about 760 km. Spatial coverage is between 38 degrees North and 38 degrees South owing to the 35 degree inclination of the TRMM satellite. This orbit provides extensive coverage in the tropics and allows each location to be covered at a different local time each day, enabling the analysis of the diurnal cycle of precipitation.