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The TRMM Visible and Infrared Scanner (VIRS) is a five-channel visible/infrared radiometer, which builds on the heritage of the Advanced Very High Resolution Radiometer (AVHRR) instrument flown aboard the NOAA series of Polar-Orbiting Operational Environmental Satellites (POES). The VIRS detects radiation at 1 visible, 2 near infrared and 2 thermal infrared wavelengths, allowing determination of cloud coverage, cloud top height and temperature, and precipitation indices. The central wavelengths for the VIRS channels are 0.63, 1.60, 3.75, 10.8, and 12.0 microns. All channels are in operation during the daytime, but only channels 3, 4 and 5 operate during the nighttime.
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. There are 16 files each of PR 1B01 produced per day.
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 10:10:10 EDT 2002
Document Review Date: Wed May 15 10:24:19 EDT 2002
Document Author: Hydrology Data Support Team