The Mission Index:
A Way to Find Rain Events in the TRMM Data Set

Outline

Introduction

Download the Mission Index Data Files

How to use the Mission Index

Additional Information

• TSDIS Orbit Viewer
• Contact Address

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Introduction

The TRMM Mission Index is a way to find a rain event observed by the TRMM satellite when you are interested in a particular location in the tropics. Developed by TSDIS in November of 2000, this index is particularly helpful when you looking for storms in semi-arid regions where it might only rain only a few times a year. The index can also help you find unusually intense storms in regions with frequent rain. In short, the Mission Index helps you to choose which TRMM orbit to order. You can then order the full resolution data for that orbit from TSDIS (if you are a TSDIS Science User) or from the Goddard DAAC.

To use the TRMM Mission Index, you must download one of the data files listed in the Download section of this document and then download the TSDIS Orbit Viewer from Here.

The TRMM Mission Index summarizes the 6 terabytes of TRMM Microwave Imager (TMI) and Precipitation Radar (PR) rain products, 2A12 and 2A25, produced since January, 1998. Based on the 3G68 algorithm, this index consists of daily average rain rate on a 1x1 degree grid with an overlay of the satellite track and orbit numbers. When a scientist rubber-bands a region, the Orbit Viewer immediately calculates a time series of rain rate for that year in that region. By clicking on a peak in the time series, the scientist can create a low-resolution image of heavy rain on a particular day.

The TRMM data used in the examples on this web page were provided by NASA / NASDA / CRL.

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Download the Mission Index Files

There is one Mission Index file for each year for each of the following two surface rain algorithms: the 2A12 algorithm for the TRMM Microwave Imager (TMI) and the 2A25 algorithm for the Precipitation Radar (PR). The compressed versions of the files are each only 1.5 megabytes for easy downloading. If you are unable to uncompress gzip files, you may download the uncompressed versions, which are each 11 megabytes.

There are two ways to download the index files. One way is to download them directly from the list below. If your web browser does not allow that, you can use anonymous FTP.

To download with FTP, start an FTP session on ftp-tsdis.gsfc.nasa.gov using "anonymous" as the username and your e-mail address as the password. Then, move to the following directory: [pub/TSDISorbitViewer/mission_index_gz]. Download the files in that directory.

To download a mission index file using a web browser, click on one of the following link with the right mouse button. In the menu that pops up, select "save link as" or "save target as." Year Data 1998 PR TMI 1999 PR TMI 2000 PR TMI 2001 PR TMI 2002 PR TMI 2003 PR TMI 2004 PR TMI 2005 PR TMI 2006 PR TMI 2007 PR TMI 2008 PR TMI

These files were compressed with the gzip program. Use the "gzip -d" command to uncompress the files if you are on a UNIX system. If you are on a Microsoft Windows system, use WinZip or some other uncompression program that can work with gzip files. If you cannot uncompress gzip files, then follow this link to download the uncompressed version of the files: Uncompressed Version.

After you download one of the data files, download the TSDIS Orbit Viewer. The Orbit Viewer is installed in a directory named "orbit". The best place to put Mission Index files in in a directory named "orbit/data/average/." When you select the View-> Mission_Summary-> Mission_Index menu option, the Orbit Viewer will first search the contents of the orbit/data/average/ directory for any Mission Index files.

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How to Use the Mission Index

The example shown below uses the 2A25.1999.day.HDF which contains an index to Precipitation Radar (PR) surface rain rate from 1999. The first step is to open this file in the Orbit Viewer.

Once you have opened the file, select the avg_rain_rate variable from the list at the left side of the main window, and then select a zoom region by clicking on the map of the tropics at the bottom of the main window.

Once you select a zoom region, a new window will appear to display a time series of the rain rate observed by TRMM in that region during that year (Figure 1).

Figure 1. Time Series for TRMM Observations
of Rain Over New Mexico in 1999

[click here for a larger image]

To make a low resolution image of any day of the year, click on that point in the time series. A sample image is shown in Figure 2. The image has sufficient resolution for a scientist to decide which orbit to order from the Goddard DAAC or from TSDIS. Since the heavest rain is in orbit 8175 in Figure 2, the scientist would order data from that orbit.

Figure 2. Low resolution image for April 30, 1999

[click here for a larger image]

If you wish to refine the region in the time series, use the "Select Region" item in the File menu of the time series window. In the Select Region window that appears, type in the latitude and longitude boundaries of the region of interest, and then click the "Apply" button. Alternatively, click on the box next to the words "Select region with cursor." Then rubber band a region in the zoom image. Once you choose a region, the time series is recalculated, so that it shows the average rain rate in just that region.

Using the information you have gathered from these images, you can order individual orbits of the full resolution data, each of which may be 140 to 250 megabytes. From that full-resolution data, you can make images of the same region using the Orbit Viewer (Figure 3).

Figure 3. High resolution image for orbit #8175
on April 30, 1999

[click here for a larger image]

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Additional Information

The TRMM Mission Index is displayed with the TSDIS Orbit Viewer, which can be downloaded for free from the following web page: Orbit Viewer.

If you have questions about the TRMM Mission Index or if you discover an error, please contact the TSDIS / PPS Helpdesk at the following address.

TSDIS / PPS Helpdesk
helpdesk@pps-mail.nascom.nasa.gov
301-614-5060