Launch Date - October 24, 1978
Operational through 1994, TOMS instrument failed in May 7, 1993
Launch Vehicle - Two-stage Delta 2910
Launch Site - Vandenberg Air Force Base, CA
Orbit - Sun-synchronous, near polar
Nominal Altitude (km) - 955
Inclination (deg) - 99.1
Orbit Period (min.) - 104
Equator Crossing Time - 12:00 noon (ascending)
Purpose: physical characterization of the global atmosphere, the oceans, the ocean-atmosphere interface, and the Earth's heat balance.
Description: The spacecraft was designed and configured the same as all previous NIMBUS satellites. The total weight of the spacecraft was the largest ever for a meteorological satellite - 2,176 pounds!
NIMBUS-7 carried eight sensors which were all improved versions of sensors previously flown. The craft was powered by 10,500 solar cells and two SNAP-19 nuclear powered generators (NIMBUS was one of the first to use these).
Ozone depletion over Antarctica, first noted by British scientists, was confirmed by measurements from the Nimbus-7 Total Ozone Mapping Spectrometer (TOMS), launched in 1978. TOMS has made polar ozone maps of an ozone hole as large as the United States. Satellite data were invaluable in supporting the first international environmental agreement, the Montreal Protocol.
Sun-synchronous orbit with transmission of data
from all of the experiments successful meant that for the first time NASA and
ESA (European Space Agency) were able to receive data concerning the global
atmosphere in real time.
The TOMS instrument is a single stage fixed-grating Ebert-Fastie monochromater which resolves the incoming light into 6 wavelengths with one nanometer bands.
312.3 nm 317.4 nm 331.1 nm
339.7 nm 360.0 nm 380.0 nm
TOMS scans in the cross-track direction in 3 degree steps from 51 degrees on one side of nadir to 51 degrees on the other, for a total of 35 samples. The instantaneous field-of-view (IFOV) of 3 degrees x 3 degrees results in a footprint varying from a 50 km x 50 km square at nadir to a 125 km by 280 km diamond at the scan extremes.
The total swath width is 3000 km, implying that consequtive orbits overlap to create a contiguous mapping of ozone data, approximately 200,000 measurements are made on a daily basis.
The ratios of backscattered ultraviolet radiation to incident radiation at the four shortest wavelengths are used to infer total ozone, while the corresponding ratios at the two longer wavelengths (which are not sensitive to ozone absorption) are used for estimating the effective reflectivity due to the combined influence of the earth's surface, clouds and aerosols.
The Coastal Zone Color Scanner (CZCS) instrument was flown on NIMBUS 7 and collected ocean color data from November 1978 to June 1986.