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Joint Education Initiative
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Joint Education Initiative.iso
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programs
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dos
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toms
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readme.doc
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Text File
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1991-04-15
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18KB
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220 lines
GENERAL INFORMATION:
All files under the TOMS sub-directory are ASCII files, except for
...\TOMS\SOFTWARE\TOMS.EXE and ...\TOMS\SOFTWARE\LIB\TOMSLIB.LIB. Each line
in an ASCII file contains 80 characters where the 79th character is a
carriage return and the 80th character is a line feed.
The program was written specifically for an IBM PC compatible with an 8086
processor or better. However, the source code (written in the language C)
is included in the ...\TOMS\SOFTWARE and ...\TOMS\SOFTWARE\LIB
sub-directories and can be compiled using other computers with minor
modifications. Documentation files are also included in sub-directory
...\TOMS\SOFTWARE.
In order to run the program, the CD-ROM drive must be the default drive and
the sub-directory ...\TOMS\SOFTWARE must either be the default directory or
be included in the path. The program can be executed by typing TOMS. Below
is an example of the commands that will set the default drive and directory
accordingly (let us assume that d is the CD-ROM drive) and run the program
on an IBM PC compatible:
d:
cd \programs\dos\toms\software
toms
A) SOFTWARE DESCRIPTION
The program which reads and displays the ozone data is in file:
...\TOMS\SOFTWARE\TOMS.EXE. The program can display the gridded ozone
values themselves, ozone for a specific location and time, or statistical
information for latitude zones. The program was designed to be largely
self explanatory with help files available at each step. For a more
detailed description, refer to file ...\TOMS\SOFTWARE\TOMS.DOC.
B) DATA DESCRIPTION
The sub-directories under ...\TOMS contain daily gridded ozone data and
statistical data for the first ten years of operation of the TOMS (Total
Ozone Mapping Spectrometer) instrument on the Nimbus 7 spacecraft.
1. The Ozone Measurement
Nimbus 7 is in a south-north sun synchronous polar orbit such that it is
always close to local noon/midnight beneath the satellite. Thus, ozone
over the entire world is measured every 24 hours. TOMS measures ozone by
measuring the ultraviolet sunlight scattered from the Earth's atmosphere.
Total column ozone is inferred from the differential absorption of
scattered sunlight in the ultraviolet. Ozone is calculated from the ratio
of two wavelengths, 312 nm and 331 nm for instance, where one wavelength is
strongly absorbed by ozone while the other is only weakly absorbed. Ozone
is measured in a 40 km square field of view of the instrument. TOMS
collects 35 measurements every 8 seconds as it scans from right to left,
giving about 200,000 ozone measurements every day. These individual
measurements have been averaged into grid cells 1 degree in latitude by
1.25 degrees in longitude. These gridded data for individual days are
contained in the data files.
2. The Data Files
There are four sub-directories under the TOMS sub-directory on this CD-ROM.
The SOFTWARE sub-directory contains information files and software for
accessing the data. The DECADE sub-directory contains daily gridded data
for October 5 from 1979 to 1988. These data will show how much the ozone
has depleted in the last ten years. The OZONHOLE sub-directory contains
daily gridded data from September 1, 1987 through October 31, 1987 (the
ozone hole in the Southern Hemisphere usually forms in August and dissolves
in December, and is the largest and deepest in the first week of October).
The daily gridded data files contain ozone data for the entire world for a
single day. The naming convention for theses files is D for day, a two
digit year (79 for 1979), the month number (01 for January), and the day
(01 for January 1). The STATS sub-directory contains pre-computed
statistical data for 10 degree latitude zones averaged either daily or
monthly. The names of the statistical files in this sub-directory are
DSTATSyy.DAT (daily data) and MSTATSyy.DAT (monthly data), where yy denotes
the year. The tree structure is as follows:
...\TOMS
| README.DOC
|
|---SOFTWARE
| TOMS.EXE
| TOMS.DOC
| SOFTWARE.DOC
| Source code files
| |
| |---LIB
| Library files
|
|---DECADE
| D791005.DAT
| D801005.DAT
| D811005.DAT
| D821005.DAT
| D831005.DAT
| D841005.DAT
| D851005.DAT
| D861005.DAT
| D871005.DAT
| D881005.DAT
|
|---OZONHOLE
| D870901.DAT
| :
| D870930.DAT
| D871001.DAT
| :
| D871031.DAT
|
|---STATS (pre-computed statistics)
DSTATS78.DAT (daily)
:
DSTATS88.DAT
MSTATS78.DAT (monthly)
:
MSTATS88.DAT
3. Data Format
Statistical Data:
There are two statistical data files for each year, one for the daily data
and one for the monthly data. In the daily data file, each record in the
file (5 lines) consists of: the year, the day of the year (julian day), the
global minimum value and the index for its latitude, the global maximum
value and the index for its latitude, and 18 area weighted zonal means, 18
standard deviations, 18 minimum values and 18 maximum values. These four
sets of 18 values correspond to the statistics calculated for each of the
10 degree latitude zones (-90 to -80, -80 to -70, ..., 80 to 90). The
monthly data file is just like the daily data file, except that the second
number is the month number (1 -- 12) instead of the day of the year. Below
is the first record of the daily data file for 1978:
1978 305 229 162 526 25 350.8 382.3 416.6 397.4 359.9 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 325.1 321.3 0.0 0.0 27.3 58.9 43.0 34.9
28.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 35.3 39.2 0.0
0.0 296 285 314 332 275 268 264 262 249 250 247 245 244 249 254 238 229 0
422 508 526 500 459 420 379 314 303 303 301 331 361 391 408 406 381 0
When the daily zonal means and standard deviations were computed, if there
were less than 85 percent of valid data points present in the zone (more
than 15 percent were flagged), the zonal means and standard deviations were
set to 0.0. When calculating the monthly zonal means and standard
deviations, if there were less than 20 days in the month with valid
(non-zero) zonal means and standard deviations, these values were set to
0.0.
An example of a FORTRAN program that can be used to read the statistical
data is included if file ...\TOMS\SOFTWARE\READSTAT.FOR.
Gridded Data:
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 D781101.DAT looks as follows:
Day: 305 November 1, 1978 Creation Date: 11-OCT-90 Version: 6.0
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 0366366366366352352352352 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0362362362362 0 0 0 0368368368368 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0362362362362 0 0 0
0359359359359361361361361 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0352352352352357357357357348348348348 0
0 0 0 0 0 0 0348348348348350350350350 0 0 0 0345345345345 0 0
0 0 0 0 0 0348348348348 0 0 0 0 0 0 0 0 0 0 0 0348348348
348 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0345345345345 0 0 0 0
0 0 0 0342342342342 0 0 0 0345345345345 0 0 0 0 0 0 0 0343
343343343342342342342346346346346 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0338338338338 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0346346346346 LAT = -89.5
The first three lines are header information specifying the data format.
Then, the 288 longitude values for one latitude zone, centered at -89.5,
are given. The zeros denote flagged data, i.e. data that could not be
collected due to lack of sunlight or other problems. Each actual ozone
value is an integer with 3 significant figures, so longitude zones 1
through 4 have no data, then zones 5 through 8 all have 366 Dobson units of
ozone. A Dobson unit is defined as a milli-atmosphere-centimeter of ozone.
If all the ozone in the atmosphere in these zones were compressed into a
layer, that layer would be only 2.92 mm thick (about a tenth of an inch).
An example of a FORTRAN program that can be used to read the gridded data
is included if file ...\TOMS\SOFTWARE\READGRID.FOR.
C) CONTACTS:
Patricia T. Guimaraes
Affiliation: ST Systems Corporation
Code 916
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
(301) 286-7806
Dr. Richard McPeters
Affiliation: NASA/GSFC
Code 916
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
(301) 286-3832
Dr. Arlin Krueger
Affiliation: NASA/GSFC
Code 916
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
(301) 286-6358