Since the 1970s, Geographic Information Systems have been able to display two dimensional images and vector data. Since the 1990s, several data formats have become commonly used for transferring data between different GIS applications. A geotiff file is a tiff image file that contain geographic information in its header. Some GIS applications can display geotiff files. In addition, some GIS applications can display a variety of image files (tiff, png, etc.) as long as they are accompanied by a "world file" that contains the necessary geographic information. The compressed directories that can be downloaded below contain both geotiff and png images with world files. These compressed directories were created with the UNIX zip command and can be uncompressed under UNIX, Windows XP, and Mac OS X. These zip file also contain some vector data that is stored in the shapefile format.
The observations in these files were made by the Tropical Rainfall Measuring Mission
(TRMM)
satellite.
Download Data
This section describes four severe weather events for which you can download a zip file containing geotiff and shapefiles of TRMM data. The names of the zip files are listed in the following table.
Severe weather events
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On June 19, 1998, severe convective storms passed through eastern
Oklahoma and were observed by the TRMM satellite. During the summer, the central United States periodically has severe storms that can cause damage due to lightning strikes, large hail, tornadoes, flash floods, or fast surface winds. According to NOAA's
Storm Event Database,
Oklahoma felt many of these effects from the series of severe storms that blew through on June 19, 1998. One of these storms was among most intense ever observed by the TRMM satellite [Zipser et al., 2006, Bulletin of the Am. Meteor. Soc.;
NASA
Press Release, 2006/10/26].
The zip file contains data from
one of these Oklahoma storms that was observed about a hundred miles southeast of Tulsa at 0129 UT. The zip file can be
downloaded by clicking here:
Oklahoma zip file.
|
Severe storm over Oklahoma
19 June 1998
|
The zip file for the Oklahoma contains 11 different data sets. There are multiple files for each data set. The files are summarized below for the Oklahoma zip file, but the zip files for the other severe weather events contain an analogous set of files.
GIS files for the Oklahoma squall line
| File Name |
File Extension |
Description |
| color_bar |
png, pngw |
A color bar describing the units used in the other images. |
| squall_cloud |
image (1) |
Cloud top temperatures from the TRMM Visible and Infrared Scanner (VIRS). |
| squall_land |
image (1) |
The land-ocean mask. |
| squall_landDetail |
image (1) |
A detailed land-ocean mask at the location of the TRMM satellite overflight of the storm. |
| squall_rain48hr |
image (1) |
Rain accumulation (mm) over the past 48 hours calculated from the TRMM 3B42 gridded 3 hour accumulation files. There is also a "squall_rain48hr_float" file that contains the floating point values instead of 1-byte color-coded values. |
| squall_rainPR |
image (1),
shape (2) |
The image files contain high resolution gridded rainfall rates for a single overflight of the TRMM Precipitation Radar. The shape file contains a vector-based representation of the same rainfall rates. The shape file contains a more accurate representation of the location of each instrument pixel containing significant rain rate. |
| squall_rainTMI |
image (1),
shape (2) |
Same as for squall_rainPR except that it contains data from a single overflight of the TRMM Microwave Imager (TMI). |
| squall_edge |
shape (2) |
This shapefile outlines the data swath edges of the TRMM Precipitation Radar and TRMM VIRS. |
| squall_info |
shape (2) |
This shapefile contains points of interest related to this severe weather event. Display the name or description of these points to see what was occurring at each location. |
| squall_lightning |
shape (2) |
This shapefile contains the locations of lightning flashes detected by the TRMM Lightning Imaging System (LIS). |
(1) "image" refers to "png" and "tif" files plus their associated world files with the "pngw" and "tifw" file extensions.
(2) "shape" refers to ESRI shape "files". For a single data set, there are three files that make up a singlefile. Those files have extensions of "shp", "shx", and "dbf". Generally, it is best to open the "shp" file in a GIS because opening one of the other components of the shapefile can produce unexpected results.
|
On March 8 and 9 of 1998, a squall line traveled east across the southeastern United States.
According to NOAA's
Storm Event Database,
the squall line and the related storms caused over $300 million of damage. Several counties in the Florida panhandle were declared federal disaster areas. The TRMM satellite gives us a snapshot of the squall line's structure as it passed over southern Florida on March 9, 1998, at 0827 UT.
The
Squall zip file
enables you to explore this storm.
|
Squall line over Florida
09 March 1998
|
|
The African savanna south of the Saharan Desert is a semi-arid region, but each year, it is home to some of the most intense storms on Earth. Some of these storms are triggered by the passing of tropical waves, which are the precursors of some Atlantic hurricanes. A field campaign in the summer of 2006 studied these waves as they passed over Africa and over the Atlantic. (See the
AMMA
and
NAMMA
web sites.) Intense storms have strong updrafts that lift raindrops to such a high altitude that they freeze. A mixture of ice and liquid water near the freezing level is associated with lightning generation. You can examine these storms by downloading the
Africa zip file
containing the storm observed at 0129 UT on September 10, 2005.
|
Isolated convection over Africa
10 September 2005
|
|
On August 25 of 2005, Hurricane Katrina struck the east coast of Florida as a category 1 hurricane according to the National Hurricane Center
(NHC).
On August 29, Katrina struck New Orleans as a category 3 hurricane. Between those days, Katrina became a category 5 hurricane in the Gulf of Mexico. During the time that Katrina was at category 5, the TRMM satellite
flew over it at 0325 UTC on August 28, 2005. You can download the zip file for this satellite overflight by clicking here:
Katrina zip file.
This TRMM overflight was featured in the
NASA
Earth Observatory
and the NASA
TRMM homepage.
|
Hurricane Katrina in Gulf of Mexico
28 August 2005
|
How to use ESRI ArcExplorer
The Earth Science Research Institute
(ESRI)
manufactures several widely used GIS applications including ArcView, ArcInfo, and ArcGIS. In Addition, ESRI manufacters the free GIS
called ArcExplorer. To download ArcExplorer, visit the following URL:
http://www.esri.com/software/arcexplorer/.
As of January 2007, the default version of ArcExplorer is version 9, which is written in Java. It can be run on a Microsoft Windows system or a UNIX system. On a Windows machine, you can install ArcExplorer by first extracting the contents of the zip file that you downloaded. Then go into the directory that the extraction operation created and double click on the setup program. After the installation, launch the ArcExplorer program and you should see a window that looks like the one shown below.
ArcExplorer Graphical User Interface
To open a file in ArcExplorer, click on the red plus sign in the row of buttons along the top of the window or choose the "Add Layer" item in the Layer menu. After you do this the Catalog window will open. In the left column of the Catalog window, click through the list until you reach the directory that contains the file that you want to open. To do so, double click on a directory name to open the directory. Once you reach that directory, the Catalog window will show either the shapefiles in that directory or the image files, depending on what the File Type pulldown menu is displaying. To open a file in this directory, you can either double click on the filename or click once on the filename and then click on the red plus button on the top of the Catalog window (not the red plus button at the top of the ArcExplorer main window). When the file is opened, its name will appear in the list on the left column of the main ArcExplorer window. Next to the filename will be an open box. Click on the open box, and a check mark will appear, and the file will be displayed in the window. Once the file is displayed, you may wish to right click on the filename and select the Layer Properties item in the menu that pops up. In the Layer Properties menu, you can adjust some aspects of how the file is displayed. Another way to reach the File Properties window is to click on the filename in the ArcExplorer main window and then select the Layer Properties item from the Layer menu. You can also reach the File Properties window by double clicking on the filename on the left side of the ArcExplorer main window. If you wish to change the order that the images are displayed, you can drag the filenames in the left hand column or right click on a filename and select the Move Layer item of the menu that pops up.
After you have downloaded an uncompressed a zip file containing TRMM data in geotiff files and shapefiles, here is a suggestion for a sequence of geotiff files to open in ArcExplorer. First, open the *_land.png image to see an image of the land and ocean over the whole
Tropics. Then open the *_rain48hr.png image to see the regions of the Tropics where rain has fallen in the past 48 hrs. This provides background information about where in the world rain has been falling recently. The advantage of opening the PNG file instead of the TIF file is that the PNG file is transparent where there is no rain, so that the continents can been seen underneath it. Next, open the *_rainTMI.png image, which contains high resolution rainfall information about the specific rain event that you have downloaded. In order to zoom into the high resolution area, right click on the *_rainTMI.png filename in the left column of the window and select Zoom to Active Layer. If you already know where the event took place, you can use the manual zoom tool. To turn on the manual zoom tool, click on the magnifying glass with a plus sign in it in the row of buttons along the top of the Arc Explorer window. Then click on the window, where you want to zoom in, or click and drag to select a rectangular region that you would like to see. Similarly, you can select the magnifying class with the minus sign in it to zoom out. Select the hand tool if you wish to re-center the image by clicking and dragging with your mouse.
Next, open the following shapefiles. Open the *_edge.shp file to display the edge of the TRMM satellite swath that is included in the high resolution rainfall data. The inner lines are the edges of the field of view of the TRMM Precipitation Radar (PR), and the outer lines are the edges of the field of view of the TRMM Visible and Infrared Scanner (VIRS) which has a similar swath width to that of the TRMM Microwave Imager (TMI). Open the *_lightning.shp file to display a dot at each location where the TRMM Lightning Imaging System (LIS) detected a lightning flash. For some events there is a *_info.shp file, that contains a dot at several locations where a specific effect of the storm was felt. To display a very short description of the effect, right click on the *_info.shp filename and select Layer Properties. In the Layer Properties window, select the Labels tab. In the Labels tab, pull down the menu next to the "Label features using" field and select the "NAME" field. To be able to see the text more easily, you may wish to increase the font size to 20 and to change the font color to white.
So far, the only files that have been mentioned are files that contain browse images or vector data of ancillary data. If you wish to process this TRMM data using GIS software, you may wish to open different files. To open gridded data in a format that is easier to analyze numerically, open the *_rain48hr_float.tif file which contains floating point rainfall accumulation for the past 48 hours. Also, you can open the *_rainPR and *rainTMI shapefiles, which contain floating point rainfall rates at the time the TRMM satellite flew over the storm.
If you have questions or suggestions about these Google Earth files, please contact the PPS/TSDIS Helpdesk at the e-mail address given at the bottom of this page.
How to use Global Mapper
The geotiff images and shapefiles can be displayed using the free trial version of the Global Mapper GIS application, which can be downloaded from
http://globalmapper.com/.
After you have installed Global Mapper, launch the program. Then open a file by clicking on "Open your own data". Alternatively, you can open a file by clicking on the open folder icon in the row of buttons along the top of the Global Mapper window. A third option for opening a file is to select the File -> Open File menu item.
First, open the *land* image to see an image of the land and ocean over the whole
Tropics. Then open the *_rain48hr* image to see the regions of the Tropics where rain has fallen in the past 48 hrs. You can open either the geotiff or the PNG version of these images. To make the locations with zero rain transparent so that you can see the continents underneath the rain field, open the control panel. To open the control panel, you could click on the image of a computer screen in the row of icons along the top of the Global Mapper window or you could select the Tool -> Control Panel menu item. In the Control Panel window that will appear, click on the *rain48hr* filename to highlight it. Then click on the options button. In the Raster Options window that appears, click on the box next to the Transparent field to turn on transparency, then click the Apply button followed by the OK button. The Control Panel can also be used to temporarily hide a file by clicking on the Hide Overlay button. You can also change the order that images are display in by right clicking on the name of the file and selecting one of the "Move Overlay" buttons in the menu that pops up.
Next, open the *_rainTMI.png image, which contains high resolution rainfall information about the specific rain event that you have downloaded. In order to zoom into the high resolution area, turn on the manual zoom tool.
To turn on the manual zoom too, click on the magnifying glass with a plus sign in it in the row of buttons along the top of the Global Mapper window. Then, click on the window, where you want to zoom in, or click and drag to select a rectangular region that you would like to see. Similarly, you can select the magnifying class with the minus sign in it to zoom out. Select the hand tool if you wish to re-center the image by clicking and dragging with your mouse.
Next, open the following shapefiles. Open the *_edge.shp file to display the edge of the TRMM satellite swath that is included in the high resolution rainfall data. The inner lines are the edges of the field of view of the TRMM Precipitation Radar (PR), and the outer lines are the edges of the field of view of the TRMM Visible and Infrared Scanner (VIRS). Open the *_lightning.shp file to display a dot at each location where the TRMM Lightning Imaging System (LIS) detected a lightning flash. For some events there is a *_info.shp file, that contains a dot at several locations where a specific effect of the storm was felt.
If you have questions or suggestions about these Google Earth files, please contact the PPS/TSDIS Helpdesk at the e-mail address given at the bottom of this page.
