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Space-Based Measurements of Ozone and Air Quality in the Ultraviolet and Visible


The TOMS program began with the launch of TOMS Flight Model #1 on the Nimbus-7 spacecraft on October 24, 1978. Valid measurements started in November of that same year and the instrument continued to return data long after all other on-board experiments had failed. The TOMS instrument fell silent in May 1993. The software to derive useful information from the data returned by Nimbus 7 TOMS is the basis for the algorithm used to analyze all TOMS data and has gone through a lengthly evolutionary process bring it to the current version.

Current TOMS and OMI data were processed with the Version 8 algorithm that has been developed by NASA Goddard's Ozone Processing Team to address errors associated with extreme viewing conditions. The basic algorithm used just 2 wavelengths (317.5 and 331.2 nm under most conditions, and 331.2 and 360 nm for high ozone and high solar zenith angle conditions). The longer of the two wavelengths is used to derive the surface reflectivity (or cloud fraction). Once the surface reflectivity has been established, the shorter wavelength, which is heavily absorbed by ozone, may be used to derive total ozone. The algorithm also calculates the "aerosol index" (AI) from the difference in surface reflectivity derived from the 331.2 and 360 nm measurements. The AI primarily provides a measure of absorption of UV radiation by smoke and desert dust. This algorithm is described in detail in the TOMS algorithm theoretical basis document (ATBD). Interested viewers may also wish to read about the Version 8 algorithm.

Algorithmic Improvements include:

    • use of wavelength "triplets" that correct for errors linear in wavelength
    • improved ISCCP cloud height climatology, higher resolution terrain height maps
    • use of improved profile shape selection to improve total ozone at very large solar zenith angles
    • use of a more accurate model for partially-clouded scenes
    • improved radiative transfer calculations for table generation

More Nimbus-7 TOMS information

Check out Nimbus-7 TOMS data and images.

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