Statistics of TRMM Data Archive and Distribution at the Goddard DAAC

The Tropical Rainfall Measuring Mission (TRMM) is a joint mission of the National Aeronautics and Space Administration (NASA) and the National Space Development Agency (NASDA) of Japan to monitor and study tropical and subtropical rainfall systems. TRMM has been acquiring data from shortly after its launch on November 28, 1997 to the present. All TRMM standard products are processed by the TRMM Science Data and Information System (TSDIS) and archived and distributed by the Goddard Distributed Active Archive Center (GDAAC). In addition to the standard products (accessible via http://lake.nascom.nasa.gov/data/dataset/TRMM/index.html), the GDAAC generates and/or maintains a set of derived TRMM products (e.g., satellite coincidence subsets, parameter subsets, resampled gridded subsets, GIS-compatible files) to facilitate use of TRMM data by the general public. TRMM data are reprocessed with improved science algorithms approximately once per year, currently at version 5. The average operating altitude for TRMM was moved from 350 kilometers to 403 kilometers during the period from August 7 to 24, 2001, which will significantly extend the mission lifetime for TRMM. The GDAAC stores archive and distribution information on TRMM standard and derived products in a database. In order to better understand the data usage patterns and requirements of TRMM users, statistics are routinely derived from the database for the entire TRMM data set or for specific groups of data products. For example, the total cumulative distribution and archive of TRMM satellite standard products (as of August 2001) are 2,722,479 and 420,573, respectively, in terms of file numbers; and 64.5 TB and 11.4 TB, respectively, in terms of file volumes. The Utilization Rate (UR), defined as the ratio of the number of distributed files to the number of archived files, of these satellite products is 6.5 (not including anonymous ftp distribution). Overall, the UR has increased steadily as TRMM progressed, and the trend is continuing. As measured by the UR, the most frequently requested satellite orbital data products are TMI brightness temperature, and PR and TMI rain profiles, with UR above 12. Most of the satellite gridded data products have a UR above 10, with a few above 20. Because some of the gridded products can also be accessed via anonymous ftp, the statistics of which are not included here, their UR is actually even higher. The complete, detailed statistics and their analysis will be presented. These statistics not only help the GDAAC to better serve its TRMM users, but also are useful inputs to the design of future satellite data support systems, such as those of the TRMM follow-on mission, the Global Precipitation Mission (GPM).