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The TRMM Microwave Imager (TMI) is a nine-channel passive microwave radiometer, which builds on the heritage of the Special Sensor Microwave/Imager (SSM/I) instrument flown aboard the Defense Meteorological Satellite Program (DMSP) platforms. Microwave radiation is emitted by the Earth's surface and by water droplets within clouds. However, when layers of large ice particles are present in upper cloud regions - a condition highly correlated with heavy rainfall - microwave radiation tends to scatter at frequencies above 19 GHz. The TMI detects radiation at five frequencies chosen to discriminate among these processes, thus revealing the likelihood of rainfall. The key to accurate retrieval of rainfall rates by this method is the deduction of cloud precipitation consistent with the radiation measurement at each frequency. The TMI frequencies are 10.65, 19.35, 37 and 85.5 GHz (dual polarization), and 21 GHz (vertical polarization only).
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 sample-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.
Contacts for Data Access Information
Hydrology Data Support Team, Code 610.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Data Center Identification
Goddard Space Flight Center Distributed Active Archive Center, NASA
File Specifications for TRMM Products - Version 7.00 Document contains file specifications for each algorithm written by PPS. This document replaces the previous Volumes 3 and 4 Interface Control specifications for Level 1, 2 and 3 TRMM products.
Document Revision Date:Fri May 17 10:10:14 EDT 2002
Document Review Date: Wed May 15 10:24:19 EDT 2002
Document Author: Hydrology Data Support Team