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You are here: GES DISC Home Ozone Keep for Review Old TOMS Nimbus-7 TOMS Version 7^MReflectivity Data^M Nov 1978 - May 1993

Nimbus-7 TOMS Version 7^MReflectivity Data^M Nov 1978 - May 1993


INTRODUCTION

This 2 CD-ROM set contains the latest version (version 7) of reflectivity data from the TOMS (Total Ozone Mapping Spectrometer) instrument onboard the Nimbus 7 spacecraft.Data covering the entire Nimbus 7 TOMS lifetime, November 1, 1978 through May 6, 1993, are given as daily files of gridded data, as zonal means, and as monthly averages.


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 Windowsand 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 is recommended.Graphic support for at least 256 colors is recommended and an FPU (Floating Point Unit) is recommended.


OVERVIEW OF THIS CD-ROM

The first CD-ROM, designated OPT_005A, contains daily and monthly gridded data for the period November 1978 through 1987. The second CD-ROM, designated OPT_005B, contains similar data for 1988 through May 1993, along with daily and monthly zonal means, and daily GIF images.The second CD-ROM also contains a SOFTWARE subdirectory with PC and MAC subdirectories containing platform-specific software to image or view the data.The data are described in more detail in the DATA FILES section.Each CD-ROM contains a DOCUMENT subdirectory that has a full copy of the TOMS User's Guide in Adobe Acrobat format.


THE REFLECTIVITY MEASUREMENT

The reflectivity values on this CD are given as percent reflectivity. 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 sunglint.

Derivation of atmospheric ozone content from measurements of the backscattered radiances requires a treatment of the reflection from the Earth's surface and of the scattering by clouds and other aerosols.These processes are not isotropic; the amount of light scattered or reflected from a given scene to the satellite depends on both the solar zenith angle and view angle, the angle between the scene and the nadir as seen at the satellite. intensity by assuming that radiation is reflected from a particular pressure level called the "scene pressure" with a Lambert-equivalent "scene reflectivity" R.When this method was applied, at the non-ozone-absorbing wavelengths the resulting reflectivity exhibited a wavelength dependence correlated with partially clouded scenes.To remove this wavelength dependence, a new treatment has been developed, based on a simple physical model that assumes two separate reflecting surfaces, one representing the ground and the other representing clouds.The fractional contribution of each to the reflectivity is obtained by comparing the measured radiances with the values calculated for pure ground and pure cloud origin.


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 reflectivity value is a 3 digit integer (see sample).LECT is the local equator crossing time.

Both CDsexample: \y87\m8710\ga871008.n7t

sample data:
Day: 359 Dec 25, 1979 Production V70 NIMBUS-7/TOMS REFLECT. Asc LECT: 11:51 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)
  93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93
  93 93 93 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 89 89 89 89 93 93 93 93 92 92 92
  92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 94 94 94 94
  93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93
  93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 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 91 91 91 91 92 92 92 92 93 93 93 93 92 92 92 92 92
  92 92 92 88 88 88 88 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92
  92 92 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   lat =  -89.5
Gridded Monthly Average:Data in the same format as the gridded daily, but averaged for each month.For each grid cell at least 20 days of data must be good for the average to be computed.

Both CDsexample: \y79\gm7903.n7r

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.

2nd CD onlyexample: \images\iy79\im7903\nr790301.gif

Zonal Means:Daily and monthly averaged data in 5 &150; latitude zones. At least 75% of possible data must be present for the mean to be given.

2nd CD onlyexample: \zonalmen\zonalmon.n7r
                                            example: \zonalmen\daily\zonal_79.n7r


PROBLEMS WITH THE DATA

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

Missing Data: During 1978/1979 the TOMS instrument was turned off periodically to conserve power, including a 5 day period (6/14-6/18) in June 1979.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 reflectivity 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 reflectivity field.Since TOMS takes 24 hours to map the entire Earth, near the dateline the reflectivity measurements have been taken almost 24 hours apart.If the reflectivity is changing with time, this will produce the observed discontinuity.


SOFTWARE DESCRIPTION

LVIEW and JPEGVIEW

Lview 3.1 is a freeware imaging program for Windows which can easily view GIF and JPG images.It is located on the second CD-ROM only.

JpegView is a commonly used image viewer for the Macintosh.It can read JPG, GIF and other image formats.It is located on the second CD-ROM only.


DIRECTORY STRUCTURE

CDROM #1 - OPT_005A
 root
     \DOCUMENT           (TOMS User's guide)
     \SOFTWARE           (Source Code Templates)
       \MAC
         \ACROBAT        (MAC Acrobat reader)
       \PC
         \ACROBAT        (PC Acrobat reader)
     \Yxx                (Month average grid files)
       \Myymm            (Daily grid files)
CDROM #2 - OPT_005B
 root
     \DOCUMENT           (TOMS User's guide)
     \SOFTWARE           (Source Code Templates)
       \MAC
         \ACROBAT        (MAC Acrobat reader)
         \JPEGVIEW       (MAC GIF image viewer)
       \PC
         \ACROBAT        (PC Acrobat reader)
         \LVIEW          (PC GIF image viewer)
     \IMAGES
       \Iyyy
         \IMyymm         (Daily GIF images)
     \Yxx                (Month average grid files)
       \Myymm            (Daily grid files)
     \ZONALMEN           (Monthly average zonal means)
       \DAILY            (Daily average zonal means)

DOCUMENTATION

There are README files on the CD-ROM for all of the software under the appropriate directory.A complete copy of the TOMS User's Guide is on the CD-ROM in PDF Format.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 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/nimbus7


CONTACTS

Science:
Dr. Richard McPeters
NASA Goddard Space Flight Center, Code 916
Greenbelt, Maryland20771 USA
mcpeters@wrabbit.gsfc.nasa.gov
(301) 614-6038
(301) 614-5903 (fax)
General:
Russell Wooldridge
NASA Goddard Space Flight Center, Code 916
Greenbelt, Maryland20771 USA
wooldridge@qhearts.gsfc.nasa.gov
(301) 614-6048
(301) 614-5903 (fax)
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Last updated: Jun 15, 2012 10:36 AM ET
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