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TRMM Microwave Imager L1A (TRMM 1A11)

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Explanation: The Dataset or Sensor Guide Document you are accessing is no longer actively maintained. The Dataset Guide Documents were created for earlier versions of the NASA EOSDIS system. The content of these documents, particularly with regard to characteristics of the data or technical descriptions of a sensor, is likely still accurate. However, information such as contact names, phone numbers, mailing addresses, email addresses, software programs, system requirements, and data access procedures may no longer be accurate. We therefore recommend searching for updated information from other sites to insure that reliable and current information is obtained.



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 1A product file (1A11) is a concatenation of the Level 0 data with a header record and, as such, is reversible to Level 0. The header record contains information pertaining to orbit times, orbit number, times of the first scan and number of scans, among other things. The Level 0 data contain the actual channel data expressed as "sensor counts." A file contains data for a single orbit with a file size of about 7 MB (uncompressed). There are 16 files of TMI 1A11 data 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

Goddard DAAC
Hydrology Data Support Team, Code 610.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771

301-614-5224 voice
301-614-5268 fax


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 Information

Document Revision Date:Fri May 17 10:10:05 EDT 2002
Document Review Date: Wed May 15 10:24:19 EDT 2002
Document Author: Hydrology Data Support Team

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Last updated: Jul 18, 2013 02:37 PM ET