Meteor-3 TOMS Version 8          August 21, 1996
          Gridded Ozone and Reflectivity Data
                     1991-1994


INTRODUCTION

This CD-ROM contains the latest version (version 8) of ozone
and reflectivity data from the TOMS (Total Ozone Mapping
Spectrometer) instrument onboard the Russian Meteor-3
spacecraft.  Data covering the entire Meteor-3 TOMS
lifetime, August 22, 1991 through December 27, 1994, are
given as daily files of gridded data, as zonal means, and as
overpass data.  Software is included to image the data.

     Note:  because Meteor 3 was in a precessing orbit,
     there are periods when the spacecraft was flying near
     the terminator.  The ozone data taken during these
     periods have been edited out because of their decreased
     accuracy.


HARDWARE REQUIREMENTS

For PC:  The data on this CD-ROM are ASCII format and can be
accessed by most systems. The image display software
requires Microsoft Windows and a VGA or better graphics card
that can support at least 256 colors.  For best performance,
a 486 or faster machine with a math co-processor is
recommended.

For Mac:  Because the software is designed for a
multi-platform environment, it has been written to the ISO
9660 Standard.  All filenames are given in the 8.3 format.
For best performance, a 68030 or faster machine with a
floating point unit (FPU) is recommended. Graphic support
for at least 256 colors is also recommended.

OVERVIEW OF THIS CD-ROM

This CD-ROM, designated OPT_006, contains daily gridded
ozone data for the period August 1991 through December 1994.
Daily zonal means and overpass data and daily GIF images are
included for the ozone product.  For the reflectivity data
only the daily grid files are included.  The data are
described in more detail in the DATA FILES section.  The
CD-ROM also contains a SOFTWARE subdirectory with PC and MAC
subdirectories containing platform-specific software to
image or view the data.


ORBIT CONSIDERATIONS

The Meteor 3 spacecraft was in a slowly precessing polar
orbit.  Ozone measurements were taken for the entire world
every 24 hours.  Unlike Nimbus 7, which was in a very stable
near-noon orbit, the Meteor 3 orbit precesses such that it
goes from near noon ascending (south to north) to near
terminator in about 53 days, to near noon descending (north
to south) in about 106 days.  A complete cycle is 212 days.
This orbit drift is seen as a variation of the local equator
crossing time (LECT in first line of each daily file).  Data
taken for an LECT outside the range 8:00 AM to 4:00 PM have
not been included on this CD-ROM because of the greatly
increased uncertainty in ozone measurements taken at very
high solar zenith angles.  Data for 1991 have been
restricted to the range 9:00 AM to 3:00 PM because high
levels of volcanic dust from the Pinatubo eruption increased
the solar zenith angle dependent errors.

Dates for which Meteor 3 TOMS data are available:
    Aug 22, 1991           Apr  1, 1993
    Sep  2, 1991           Jun 10, 1993

    Oct 26, 1991           Jul 17, 1993
    Dec 17, 1991           Sep 25, 1993

    Feb  9, 1992           Oct 31, 1993
    Apr  2, 1992           Jan  9, 1994

    May 26, 1992           Feb 14, 1994
    Jul 17, 1992           Apr 25, 1994

    Aug 31, 1992           Jun  1, 1994
    Nov  9, 1992           Aug 10, 1994

    Dec 16, 1992           Sep 15, 1994
    Feb 24, 1993           Nov 24, 1994


THE OZONE MEASUREMENT

TOMS directly measures the ultraviolet sunlight scattered by
the Earth's atmosphere.  Total column ozone is inferred from
the differential absorption of scattered sunlight in the
ultraviolet range.  Ozone is calculated by taking the ratio
of two wavelengths (312 nm and 331 nm, for example), where
one wavelength is strongly absorbed by ozone while the other
is absorbed only weakly.  The instrument has a 60 kilometer
square field of view at the sub-satellite point.  TOMS
collects 35 measurements every 8 seconds as it scans right
to left producing approximately 200,000 ozone measurements
daily.  These individual measurements vary typically between
100 and 650 Dobson Units (DU) and average about 300 DU.
This is equivalent to a 3 mm (about a 10th of an inch) thick
layer of pure ozone gas at NTP conditions.

In order to derive ozone, the scene reflectivity must first
be derived using channels not absorbed by ozone: 360 nm and
380 nm.  Note that this is "effective" reflectivity - the
reflectivity of a Lambertian reflective surface that would
explain the observed backscattered radiance.  It can be less
than 0% when volcanic aerosols are present and greater than
100% in areas of sun-glint.  The reflectivity values on this
CD are given as percent reflectivity.


THE DATA FILES

Gridded Daily:  The individual TOMS measurements have been
averaged into grid cells covering 1 degree of latitude by
1.25 degrees of longitude.  The 180x288 ASCII data array
contains data from 90S to 90N, from 180W to 180E.  Each
ozone value is a 3 digit integer (see sample).  LECT is the
local equator crossing time.
                             example:  \OZONE\Y94\GA941008.M3T
                             example:  \REFLECT\Y94\GA941008.M3R

sample ozone data:

 Day: 281 Oct  8, 1994 Production V70 METEOR-3/TOMS OZONE    Asc LECT:  1:22 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)
 136136136136136136136136136136136136136136136136136136136136136136136136129
 129129129129129129129129129129129129129129129129129129129129129129129129129
 129129129129129129129129129129129129129129129129129129129129129129129129129
 129129129129129129129129129129129129129129129129129129129129129129129129129
 125125125125125125125125125125125125125125125125125125125125125125125125125
 125125125125125125125125125125125125125125125125125125125125125125125131131
 131131131131131131131131131131131131131131131131131131131131131131131131131
 131131131131131131131131131131131131131131131131131131131131131131131131131
 131131131131131131131131131131131131129129129129129129129129129129129129129
 129129129129129129129129129129129129129129129129129129129129129129129129129
 129129129129129129130130130130130130130130130130130130130130130130130130130
 130130130130130130130130130129129129129   lat =  -89.5

sample reflectivity data:

 Day: 281 Oct  8, 1994 Production V70 METEOR-3/TOMS REFLECT. Asc LECT:  1:22 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)
  91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 92 92 92 92 92
  92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92
  92 92 92 92 92 92 92 92 92 92 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91
  91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91 91
  92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92
  92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92
  92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 90 90 90 90 90 90 90
  90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
  90 90 90 90 90 90 90 90 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89
  89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89
  89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89 89
  89 89 89 89 89 89 89 89 89 89 89 89 89   lat =  -89.5


GIF Image:  Each day of data has a corresponding GIF image.
Each image is 640x480 pixels (full screen in standard VGA)
at 256 colors.  North polar, south polar, and Aitoff
projections are shown.
   Ozone data only           example:  \images\iy94\mi941008.gif

Overpass Data:  These files contain "overpass" data, the
best match single TOMS observation each day, for 371 ground
locations worldwide.  (Dobson and other science sites, along
with major cities)  See README file in \overpass for list of
sites.
   Ozone and reflectivity    example:  \ozone\overpass\mtoms035.m3t

Zonal Means:  Daily averaged data in 5 degree latitude
zones.  At least 75% of possible data must be present in a
zone for the mean to be given.
   Ozone data only           example:  \ozone\zonalavg\zonal_94.m3t


PROBLEMS WITH THE DATA

Polar Night:   Because TOMS measures ozone using scattered
sunlight, it is not possible to measure ozone when there is
no sun (in the polar regions in winter).  Consequently, maps
of the Antarctic ozone hole for August and September, for
example, will always have areas of missing data due to polar
night.

Missing Data:   Because of increased uncertainty at high
solar zenith angles, data are not given for those periods
when Meteor 3 was flying near the terminator.  On many days,
data were lost due to missing orbits or other problems.

Edge Effects:   At the transition between good and flagged
or missing data, an "edge effect" will appear, consisting of
a few pixels of apparently low ozone values.  These are
artifacts generated when the original data were interpolated
to produce the stored image data.  A second type of edge
effect will be noticed in the polar plots consisting of
apparent discontinuities in the ozone field.  Since TOMS
takes 24 hours to map the entire Earth, near the dateline
the ozone measurements have been taken almost 24 hours
apart.  If the ozone is changing with time, this will
produce the observed discontinuity.

High Terrain:   The ozone reported is total column ozone to
the ground.  Over high mountains (the Himalayas, the Andes)
low ozone will be noticed relative to surrounding low
terrain.  This is not an error.

Volcanic Aerosols:   After the eruption of Mt. Pinatubo in
June of 1991, there were large amounts of sulfate aerosol
present in the lower stratosphere.  This introduces a scan
angle dependent error into TOMS ozone that is negative near
nadir but positive in the outer scan positions.  The average
error is small, and by 1992 the aerosol loading dropped
enough for these errors to be small.  (See "Properties of
Mt. Pinatubo aerosols as derived from Nimbus 7 total ozone
mapping spectrometer measurements," by Torres, Herman,
Bhartia, and Ahmad, J. Geophys. Res., 100, 14043-14055,
1995.)


SOFTWARE DESCRIPTION

1.  LVIEW and JPEGVIEW

Lview 3.1 is a freeware imaging program for Windows which
can easily view GIF and JPG images.

JpegView is a commonly used image viewer for the Macintosh.
It can read JPG, GIF and other image formats.

2.  THE VISUANALYZE LITE PROGRAM

VisuAnalyze Lite is designed to provide the user with a
means of viewing the daily ozone data.  Once loaded, the
program will display a window consisting of a pull down menu
and three boxes:  one each for the image, the data table and
the site information selected by the cursor.

The menu allows you to control the viewing process and has a
number of controls over the screen image.  North
Orthographic, South Orthographic, and Hammer-Aitoff
projections are supported.  An overlay provides grid and
continental maps for easy reference.  Palette permits the
user to select between different color patterns to aid in
image analysis.  There are minor differences between the MAC
and PC versions.  The included version limited to viewing TOMS
ozone data.  Contact:

      Bharat Thacker
      Research and Professional Services (RPS)
      5711 Sarvis Avenue, Suite 510
      Riverdale, Maryland  20737 USA
      (301) 699-7771 or (313) 278-7719


DIRECTORY STRUCTURE

 OPT_006

 root
  \DOCUMENT            (Meteor-3 TOMS User's Guide)
  \OZONE
     \IMAGES
       \IYyy           (Daily .GIF images)
     \Yyy              (Daily ozone grid files)
     \OVERPASS         (Daily values at specific locations)
     \ZONALAVG         (Daily zonal means)
  \REFLECT
     \Yyy              (Daily reflectivity data)
  \SOFTWARE            (Source Code Templates)
     \MAC
       \ACROBAT        (MAC Acrobat reader)
       \JPEGVIEW       (MAC .GIF viewer)
       \VISANLZE       (MAC imaging software)
     \PC
       \ACROBAT        (PC Acrobat reader)
       \LVIEW          (PC .GIF viewer)
       \VISANLZE       (PC imaging software)


DOCUMENTATION

There are README files on the CD-ROM for all of the software
under the appropriate directory.  A complete copy of the
Meteor-3 TOMS User's Guide is on the CD-ROM in PDF format in
the DOCUMENT directory:   USRGIDM3.PDF
Adobe Acrobat readers are included in the subdirectories:
   \SOFTWARE\PC\ACROBAT and  \SOFTWARE\MAC\ACROBAT.
Free Adobe Acrobat readers for other platforms can be found
on the Adobe homepage at:      http://www.adobe.com


INTERNET SERVICES

NASA/Goddard Space Flight Center's Laboratory for
Atmospheres has a Web Site devoted to Atmospheric Science.
This site contains ozone related information including
aircraft missions, spacecraft, tropospheric data,
atmospheric modeling, and more.  The URL address of this
site is:       http://hyperion.gsfc.nasa.gov


News about the TOMS data, the Earth Probe and ADEOS TOMS
missions, and any software updates will appear on the TOMS
homepage.  For Internet access to the TOMS Home Page use the
URL address:      http://jwocky.gsfc.nasa.gov

Direct data access is available via an anonymous FTP
account:
     ftp jwocky.gsfc.nasa.gov.
     logon: anonymous
     password: your e-mail address
     cd pub/meteor3



CONTACTS

Dr. Jay Herman                     (science)
NASA Goddard Space Flight Center, Code 916
Greenbelt, Maryland  20771 USA
herman@tparty.gsfc.nasa.gov
(301) 286-7821   (301) 286-1754 (fax)