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The data files for all TOMS products offered on this DVD are in ASCII file format. The format is the same as that used for all TOMS CD-ROMs and the products offered on our website. Software written to read those files may be used to read all TOMS data files by changing filename and date entries. The file rdgrid.for (linked here and in this DVD's CDDOCS folder) contains a sample FORTRAN routine to read the data files.
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 (using an Earth Probe ozone data file), the first few lines of a data file may look like the following:
Day: 355 Dec 21, 1997 EP/TOMS NRT OZONE GEN:97.357 Asc LECT: 11:20 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) 250250250250250250250250250250250250250250250250250250250250250250250250250 250250250250250250250250250250250250250250250250250250250250250250250250250 250250250250250250250250250250250250250250250250250250250250250250250250250 250250250250250250250250250250250250250250250250250250250250250250250250250 250250250250255255255255256256256256256256256256257257257257257257257257256 256256256256256256256256256256256256256256256256256256256256256256256257257 257257257257257257257257257257257257257257257257257257254254254254254254254 254254254254254254254254254254254254254254254254254253253253253253253253253 253253253253253253253253253253253253253253253253248248248248248248248248248 248248248248248248248248248248248247247247247247247247247247247247247247247 247247247247247247247247247247247247247247247247247247247247247247247247247 247247247247247247247247247247247247247 lat = -89.5 260260260260259259259259259259259259259259259259260260260260260260260260264 264264264265265265265265265265265265265265265200000000000065265265265200066 200000062262262262262262262262262262262262256256256256256256256256253253253 253252252252252252252252252250250250250252252252252253253253253254254254254 254254254254255255255255255255255255256256256256257257257257257257257257257 257257257257257257257259259259259262262262262262262262262262262262262263263 263263265265265265263263263263263263263263263263263263262262262262264264264 264262262262262262262262262262262262262262262262262257257257257255255255255 254254254254254254254254254254254254250250250250250250250250251251251251251 251251251250250250250250250250250249249249249243243243243243243243243245245 245245245245245245244244244244245245245245245245245245246246246246246246246 246246246246246245245245245250250250250 lat = -88.5 259259259259261261261261264264264264200000000000000000000000069269269269270 270270270268268268268268268268268200000000000069269269269269269269269270270 270270271271271271273273273273270270270270271271271271261261261261261261261
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 feature of study (ozone or aerosols), the generation date of the file, and the local equator crossing time of the satellite.
Data values at 288 longitudes for each latitude centered at -89.5 degrees are given. The next 288 values are given for the latitude centered at -88.5 degrees and so on. The zeros denote missing or flagged data, i.e. data that could not be collected due to lack of sunlight or other problems for ozone. In the case of aerosols, "999" is used for missing or flagged data. All ozone 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.
The aerosol monthly average data sets were computed using only positive values (i.e. absorbing aerosol indices) of the aerosol index for each month. Values of zero are used in the averaging anytime the aerosol index is negative. The final monthly average data sets contain aerosol index values greater than or equal to 0.7.
The general README file provides additional format information for all TOMS data products.