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TOMS Data File Format

All data files contained on this web site are ASCII files.

Ozone data for each day are gridded into 1 degree latitude zones by 1.25 degree longitude zones. Latitudes go from -90 degrees (the south pole) to 0 degrees (the equator) to +90 degrees (the north pole) in 1 degree steps, so there are 180 latitude zones. The first zone extends from -90 to -89, so the grid cell is considered to be centered on -89.5. Similarly, longitudes go from -180 (west longitude) to 0 (Greenwich, England) to +180 (east longitude) in 1.25 degree steps, so there are 288 longitude zones (360/1.25). The first longitude zone extends from -180 to -178.75, so the grid cell is considered to be centered on -179.375.

As an example, the first few lines of a data file may look like the following: 

 Day:  22 Jan 22, 1997    EP/TOMS    NRT OZONE    GEN:97.091 Asc LECT: 11:17 AM
 Longitudes:  288 bins centered on 179.375 W to 179.375 E  (1.25 degree steps)
 Latitudes :  180 bins centered on  89.5   S to  89.5   N  (1.00 degree steps)
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
   0  0  0  0  0  0  0  0  0  0  0  0  0   lat =  -89.5
 290290290290290290290290290290290290290290290290291291291291291291291291290
 290290290290290290290289289289289289289289289290290290290290290290290286286
 286286286286286286286286286286289289289289290290290290290290290290290290290

The first three lines are header information which includes the date the data were taken, the instrument, the type of processing (eg production, near real time, etc), the generation date of the file, and the local equator crossing time of the satellite.

Then, the 288 longitude values for one latitude zone, centered at -89.5, are given. The next 288 longitude values are given for the latitude zone zone centered at -88.5, and so on. The zeros denote flagged data, i.e. data that could not be collected due to lack of sunlight or other problems. All measurements are given in Dobson units and are integers with 3 significant figures. A Dobson Unit represents the physical thickness of the ozone layer if it were brought to the Earth's surface. A value of 300 Dobson units equals three millimeters or 1/10th of an inch.

This format is the same as the format used for the Nimbus-7 and Meteor-3 TOMS CD-ROM's. Code written to read those files may therefore, with a few minor alterations, be used to read these files. The file rdgrid.for contains a sample FORTRAN routine to read the data files.

Go !! Original Original : NASA/GSFC