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Instrument: ERB : Earth Radiation Budget
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The objective of the Nimbus 7 Earth Radiation Budget (ERB) experiment,
a follow-on to the Nimbus 6 ERB, was to determine the Earth radiation
budget on both synoptic and planetary scales by simultaneous
measurements of incoming solar radiation and outgoing earth-reflected
(shortwave) and emitted (longwave) radiation. Both (1) fixed
wide-angle sampling of terrestrial fluxes at the satellite altitude
and (2) scanned narrow-angle sampling of the angular radiance
components, were used to determine outgoing radiation (reflected and
emitted). The ERB subsystem consisted of a 22-channel radiometer
containing separate subassemblies to perform the required solar,
earth-flux (wide angle), and scanned earth radiance (narrow angle)
measurements. The systems used optical filters for spectral
discriminations, and for uncooled thermal detectors, thermopile
detectors in the solar and fixed-earth-flux channels, and pyroelectric
detectors in the scanning channels. The 10 solar channels observed the
sun in front of the observatory in the X-Y plane. The solar channels
obtained usable solar data only during a period of about 3 min in each
orbit when the spacecraft was over the Antarctic region. Their full
response field of view (FOV) was 0.18 rad. The solar channel
subassembly was pivoted plus or minus 0.35 rad in the X-Y plane to
compensate for sun-angle deviation when required. The channel 10c
solar channel was a model H-F self-calibrating cavity thermopile used
for monitoring the total solar irradiance (0.2 to 50 micrometers). The
four fixed earth-flux channels (numbered 11-14) were mounted so that
they could continuously view the total earth disk, and record data at
0.25-s intervals. The eight narrow FOV scanning channels were mounted
in the scanning head. The NFOV channels consisted of four shortwave
(0.2 to 4.8 micrometers) and four longwave (4.5 to 50+ micrometers)
channels. The scanning head was gimbal-mounted in the radiometer unit
main frame. The FOVs of the telescopes were asymmetric (4.4 by 89.4
mrad) and those of the shortwave and longwave channels were
coincident. The 89.4 mrad FOVs of the four pairs of channels were not
contiguous, but covered only alternate 89.4 mrad angular intervals
along the horizon.

Contact Information:

NASA Langley Research Center
Mail Stop 157D
2 South Wright Street
Hampton, Virginia 23681-2199
Telephone: (757) 864-8656
FAX: (757) 864-8807

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