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Stratospheric Aerosol Measurement II (SAM-II)

NSSDCA ID: 1978-098A-06

Mission Name: Nimbus 7
Principal Investigator:Dr. M. Patrick McCormick

Description

The objective of the Stratospheric Aerosol Measurement (SAM II) experiment was to provide vertical distribution of stratospheric aerosols in the polar regions of both hemispheres. When no clouds were present in the instantaneous field of view (IFOV), the tropospheric aerosols could also be mapped. The instrument, basically a sun photometer, measured the extinction of solar radiation at 1.0 micrometer wavelength during spacecraft sunrise and sunset. The SAM II instrument package consisted of optics and electronics subassemblies. The optical assembly consisted of gimbals, a flat entrance window (which filters out UV radiation), Cassegrain optics, a flat scanning mirror, Sun acquistion sensors, and a sun-photometer detector package. Solar radiation was reflected from the scan mirror into the Cassegrain telescope forming a solar image at the slit plate, which contained two solar edge sensors for monitoring solar limb crossings on either side of the detector aperature. Solar radiation passed through the aperature, was collected by a field lens, passed through an interference filter for wavelength discrimination, and finally measured by a silicon photodiode detector. The optics assembly was gimbaled in azimuth. After acquisition in azimuth, the mirror servo scanned in elevation until the Sun was aqcuired. The Sun was then scanned back and forth. The photometer viewed a portion of the solar disk with a 0.145 mrad IFOV and a sampling rate of 50 samples per second. As the spacecraft first viewed the sunrise, the photometer-pointing axis was depressed approximately 0.52 rad with respect to the spacecraft horizontal. The photometer continued looking at the sun until its depression angle was on the order of 0.44 rad (approximately 1.4 minutes observing time). Before sunset, the photometer head rotated 3.14 rad in azimuth and viewed the sun from a depression of approximately 0.44--0.52 rad as the spacecraft orbited to the dark side of the earth. The extinction measurements were inverted for the number density times the aerosol scattering cross section by using the Lambert-Beer Law and assuming the atmosphere to be composed of layers. To determine the stratospheric aerosol optical properties, ground-truth and in situ balloon-borne aerosol measurements were also made. For more detailed information, see Section 5 in ``The Nimbus 7 Users' Guide'' (NSSDC ID B30045-000A), available from NSSDC.

Alternate Names

  • Nimbus7/SAM-II
  • SAM-II

Facts in Brief

Mass: 17 kg
Power (avg): 0.8 W
Bit rate (avg): 4 kbps

Funding Agency

  • NASA-Office of Space Science (United States)

Discipline

  • Earth Science: Atmospheric Chemistry

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. M. Patrick McCormickTeam LeaderNASA Langley Research Center
Dr. Theodore J. PepinTeam MemberUniversity of Wyoming
Mr. Len R. McMasterTeam MemberNASA Langley Research Centerl.r.mcmaster@larc.nasa.gov
Dr. Gerald W. GramsTeam MemberGeorgia Institute of Technology
Dr. Philip B. RussellTeam MemberNASA Ames Research Centerprussell@mail.arc.nasa.gov
Prof. Benjamin M. HermanTeam MemberUniversity of Arizonaherman@air.atmo.arizona.edu

Selected References

  • McCormick, M. P., SAM 2 measurements of the polar stratospheric aerosol, NASA-LRC, RP-1081, Hampton, VA, Dec. 1981.
  • McCormick, M. P., and C. R. Trepte, SAM II measurements of Antarctic PSO's and aerosols, Geophys. Res. Lett., 13, No. 12, 1276-1279, doi:10.1029/GL013i012p01276, Nov. 1986.
  • Kent, G. S., et al., Validation of SAM 2 and SAGE satellite, NASA CR-178256, Apr. 1987.
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