Summary

Description

The Tropical Rainfall Measuring Mission (TRMM) is a joint U.S.-Japan satellite mission to monitor tropical and subtropical precipitation. The Level 1B product file (1B01) contains calibrated radiances and auxiliary geolocation information for each pixel in the scan. The Level 1B data are stored in the Hierarchical Data Format (HDF), which includes both core and product specific metadata applicable to the VIRS measurements. A file contains a single orbit of data with a file size of about 87 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 VIRS 1B01 data produced per day. For channels 1 and 2, Level 1B radiances are derived from the Level 1A sensor counts by computing calibration parameters (gain and offset) derived from the counts registered during space and solar and/or lunar views. New calibration parameters are produced every 1 to 4 weeks. Bands 3, 4, and 5 are calibrated using the internal blackbody and the space view. These two data points, together with a quadratic term determined pre-launch, are used to generate a counts vs. radiance curve for each band, which is then used to convert the earth-view pixel counts to spectral radiances. For 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/ solar geometry are specified on a per-scan basis. There are in general 18026 scans along the orbit with each scan consisting of 261 pixels. The scan width is about 720 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.