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TRMM PR Reflectivities (TRMM 1C21)

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The TRMM Precipitation Radar (PR), the first of its kind in space, is an electronically scanning radar, operating at 13.8 GHz that measures the 3-D rainfall distribution over both land and ocean, and defines the layer depth of the precipitation.

The 1C21 calculates the effective radar reflectivity factor at 13.8 GHz without any propagation loss (due to rain or any other atmospheric gas) correction (Zm). Therefore, the Zm value can be calculated just by applying a radar equation for volume scatter with PR system parameters. The noise-equivalent Zm is about 21 dBZ. Through the subtraction of the system noise, the Zm value as small as 16 or 18 dBZ are still usable although the data quality is marginal. In 1C21, all echoes stored in 1B21 are converted to "dBZ" unit. This is not relevant for "non-rain" echo; however, this policy is adopted so that the 1B21 and 1C21 product format should be as close as possible except for the following points:

  • Radar quantity is Zm in dBZ unit instead of received power (dBm).
  • Data at echo-free range bins judged in 1B21 are replaced with a dummy value.

The data are stored in the Hierarchical Data Format (HDF), which includes both core and product specific metadata applicable to the PR measurements. A file contains a single orbit of data with a file size of about 139 MB (uncompressed). The HDF-EOS "swath" structure is used to accommodate the actual geophysical data arrays. There are 16 files each of PR 1C21 produced per day.

Spatial coverage is between 38 degrees North and 38 degrees South, owing to the 35 degree inclination of the TRMM satellite. There are, in general, 9150 scans along the orbit, with each scan consisting of 49 rays. The scan width is about 220 km.


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 10:10:24 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 02:40 PM ET