TOMS Version 8 Level 3 Data File Format
Ozone, Aerosol, and Reflectivity
The data files for OMI standard L3 products (ozone, reflectivity, aerosol, 1.25 degree longitude x 1.00 degree latitude gridding) are in ASCII file format. The format is the same as that used for all previous TOMS CD-ROMs and the products offered on the TOMS website. Software written to read those files may be used to read all OMI standard L3 data files by changing filename and date entries. The file rdgrid.for contains a sample FORTRAN routine to read the data files. This same format is used for the OMI High resolution L3 products whose gridding is .25 degree longitude x .25 degree latitude.
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 should look like the following:
Day: 355 Dec 21, 1997 EP/TOMS NRT OZONE GEN:04.073 V8 ALECT: 12:00 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) 228228228228228228228228228228228228228228228228228228228228228228228228228 228228228228228228228228228228228228228228228228228228228228228228228228228 228228228228228228228228228228228228228228228228228228228228228228228228228 228228228228228228228228228228228228228228228228228228228228228228228228228 228228228228232232232232232232232232232232232232232232232232232232232232233 233233233232232232232232232232232232232232232232232232232232232232232235235 235235235235235235235235235235235235235235235235235235234234234234233233233 233233233233233233233233233233233233233230230230230231231231231231231231231 231231231231231231231231231231231231230230230230226226226226226226226226226 226226226226226226226226226226226225225225225225225225225225225225225225225 225225225225225225225225225225225225225225225225225225225225225225225225225 225225225225225225225225225225225225225 lat = -89.5 236236236236237237237237244244244244238238238238238238238238238238238238241 241241241242242242242242242242242242242242242243243243243242242242242243243 243243240240240240240240240240240240240240234234234234234234234234230230230 230229229229229229229229229228228228228228228228228230230230230231231231231 231231231231232232232232232232232232234234234234236236236236236236236236236 236236236237237237237238238238238241241241241241241241241241241241241241241 241241243243243243242242242242242242242242242242242242241241241241242242242 242240240240240240240240240240240240240240240240240235235235235234234234234 233233233233233233233233232232232232230230230230230230230230230230230230229 229229229228228228228229229229229228228228228223223223223223223223223224224 224224223223223223223223223223224224224224224224224224225225225225225225225 225225225225225226226226226228228228228 lat = -88.5 238238238238240240240240243243243243245245245245246246246246248248248248249 249249249247247247247246246246246244244244244247247247247248248248248248248
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.
Data values at 288 longitudes for the latitude zone centered at -89.5 degrees are given. (Note: negative latitudes are South, negative longitudes are West). 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 or reflectivity, "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.