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Instrument: TOMS : Total Ozone Mapping Spectrometer
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The TOMS instrument is a second-generation backscatter ultraviolet ozone sounder. TOMS can measure "total column ozone"--the total amount of ozone in a "column" of air from the Earth's surface to the top of the atmosphere--under all daytime observing and geophysical conditions. TOMS observations cover the near ultraviolet region of the electromagnetic spectrum, where sunlight is absorbed only partially by ozone.

TOMS/EP measures total ozone by observing both incoming solar energy and backscattered ultraviolet (UV) radiation at six wavelengths. "Backscattered" radiation is solar radiation that has penetrated to the Earth's lower atmosphere and is then scattered by air molecules and clouds back through the stratosphere to the satellite sensors. Along that path, a fraction of the UV is absorbed by ozone. By comparing the amount of backscattered radiation to observations of incoming solar energy at identical wavelengths, scientists can calculate the Earth's albedo, the ratio of light reflected by Earth compared to that it receives. Changes in albedo at the selected wavelengths can be used to derive the amount of ozone above the surface.

The Total Ozone Mapping Spectrometer (TOMS) data represent the primary long-term, continuous record of satellite-based observations available for use in monitoring global and regional trends in total ozone over the past 25 years. TOMS also provides measurements of tropospheric aerosols, volcanic SO2, ultraviolet irradiance, erythemal UV exposure, and effective reflectivity from the Earth's surface and clouds. The data are produced by the Laboratory for Atmospheres at NASA's Goddard Space Flight Center.

Four TOMS instruments have been successfully flown in orbit ? aboard the Nimbus-7 (Nov. 1978 - May 1993), Meteor-3 (Aug. 1991 - Dec. 1994), Earth Probe (July 1996 - current), and ADEOS (Sep. 1996 - June 1997) satellites. Version 8 TOMS data products are available from the Goddard Earth Sciences Distributed Information and Services Center (GES DISC). These include level 3 gridded data (1.0 x 1.25) as well as level 2 instrument resolution data (between 50x50 km and 26x26 km pixel at nadir). At this time, the data are from the Nimbus-7 and Earth Probe TOMS instruments.

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