The TOMS aerosol optical depth record covers the periods from January 1979 to April 1993 (Nimbus7-TOMS observations), and from July 1996 to December 2000 (Earth Probe TOMS measurements).

The retrieval algorithm [Torres et al, 1998,2002], was applied to observations at 340 and 380 nm by the Nimbus7-TOMS sensor, and to 331 and 360 nm measurements by the Earth Probe instrument. For the sake of continuity, however, the optical depth record is reported at 380 nm for both instruments.

Data products

Files of monthly average optical depth on a 1 degree X 1 degree resolution over the oceans and the continents were produced. In addition, files containing the number of days per month used in the calculation of the monthly mean value at each grid point were also created.

Format

The data is written in a 360X180 ASCII array, going from 90 to -90 in latitude, and from -180 to 180 in longitude. Effectively, however, no data is available beyond 70 degrees latitude in both hemispheres. Optical depth values have been multiplied by 1000. When no data is available, a fill value of zero (0) is reported.

Filenames

The monthly optical depth data files are:
nimbus7/data/aot/yYYYY/globe_tau_MMMYY.asc (1979 through 1993) eptoms/data/aot/yYYYY/globe_tau_MMMYY.asc (1996 through 2000)

where YYYY is four-digit year
MMM first three letters of month'name (e.g., jan)
YY two digit year.

The files containing number of days per grid are:
nimbus7/data/aot/yYYYY/globe_ndy_MMMYY.asc (1979 through 1993) eptoms/data/aot/yYYYY/globe_ndy_MMMYY.asc (1996 through 2000)

References

Torres, O., P.K. Bhartia ,J.R. Herman, A. Sinyuk and B. Holben, A long term record of aerosol optical thickness from TOMS observations and comparison to AERONET measurements, J. Atm. Sci.,59,398-413, 2002

Torres O., P.K. Bhartia, J.R. Herman and Z. Ahmad, Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation. Theoretical Basis, J. Geophys. Res., 103, 17099-17110, 1998
-------------------------------------------------------------------------------- If these data are downloaded and used in publications, please give proper credit to the NASA/GSFC TOMS group.
For more information about the TOMS aerosol optical depth product, contact

Dr Omar Torres
Joint Center for Earth Systems Technology
University of Maryland, Baltimore County


Mailing address:
Code 613.3
NASA Goddard Space Flight Center
Greenbelt, MD, 20771
torres@tparty.gsfc.nasa.gov