Release 97-165

NASA's primary ozone monitoring spacecraft will be moved from its current 300-mile orbit to a higher 450-mile orbit beginning Dec. 4 to help scientists monitor ozone globally and to extend the life of the current spacecraft until the launch of a replacement Total Ozone Mapping Spectrometer (TOMS) instrument in the year 2000.

A second TOMS instrument on the Japanese Advanced Environmental Orbiting Satellite (ADEOS) previously performed global ozone monitoring until that satellite failed earlier this year.

NASA’s Earth Probe satellite carries the TOMS instrument that maps the world's ozone levels. TOMS’ instruments measure not only ozone, but also sulfur dioxide and ash from large volcanic eruptions, smoke from forest fires and from forest clearing in the tropical rain forests, and the flux of ultraviolet radiation reaching the Earth's surface.

TOMS-EP was launched in 1996 and placed in the 300-mile orbit. The second TOMS instrument, on ADEOS, was put into a higher 500-mile orbit for global monitoring of ozone. The low altitude was chosen for Earth Probe to provide improved horizontal resolution for viewing small scale features like volcanoes, forest fires, and pollution sources. The higher orbit will lose a little bit of horizontal resolution, going from a 15 mile footprint to a 22 mile footprint, in order to see almost all the earth every day.

At the new 450 mile orbit, the orbit decay of the TOMS-EP spacecraft will be much slower and no further re-boosts will be needed until the year 2001. By that time, however, the TOMS-3 instrument is scheduled to already be in orbit. The TOMS series will continue with the launch of the third and final TOMS instrument aboard a Russian Meteor-3M spacecraft in the year 2000. An advanced version of TOMS is under consideration for inclusion in the National Polar Orbiting Environmental Satellite System (NPOESS), beginning in the year 2007.

The TOMS-EP spacecraft is currently dropping about half a mile per month, and the orbit can be expected to decay even more rapidly over the next few years as the maximum of the 11-year sunspot cycle approaches.

The original TOMS instrument on Nimbus-7 monitored ozone for almost 14 years, from 1978 until 1993. Data from this instrument was crucial for confirming the destruction of ozone at the South Pole each year, the "ozone hole" that is now an annual feature.

TOMS data are processed at the Goddard Space Flight Center in Greenbelt, Md. In most cases, ozone values are mapped and made available within hours, and full global maps are usually available within 24 hours. These data, including color images of the global ozone, are available over the internet on the TOMS home page at http://jwocky.gsfc.nasa.gov .

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