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Satellite Infrared Spectrometer (SIRS)

NSSDCA ID: 1969-037A-04

Mission Name: Nimbus 3
Principal Investigator:Dr. David Q. Wark


The Nimbus 3 Satellite Infrared Spectrometer (SIRS) experiment was designed to indirectly determine the vertical temperature profiles of the atmosphere by measuring the infrared radiation emitted from the earth and its atmosphere in seven spectral intervals in the carbon dioxide band (11 to 15 micrometers) and one interval in the atmospheric window centered at 11.1 micrometers. The main components of the Fastie-Ebert fixed-grating spectrometer consisted of (1) a plane, light-collecting mirror to provide a single earth-viewing beam fixed in the vertical, (2) a rotating chopper mirror, (3) a spherical mirror, (4) a 12.7-cm diffraction grating with 1250 lines per inch, (5) a set of eight exit slits with a single interference filter, (6) eight wedge-immersed thermistor bolometers, (7) a blackbody radiation source for calibration, and (8) eight preamplifiers and eight operational amplifiers. The incoming radiation was chopped, spectrally dispersed by the diffraction grating, focused on the exit slits as a spectrum by the spherical mirror, and converted to electrical signals. The signals were then amplified and stored on magnetic tape for subsequent playback to a ground acquisition station. The instrument field of view was 11.5 by 11.5 deg centered on nadir. This provided data over an area roughly 220 km on a side at a satellite height of 1100 km. Data from the 11.1-micrometer channel yielded surface and/or cloudtop temperatures. Data from the carbon dioxide band could be used to generate temperature-pressure profiles by a mathematical inversion technique. The resulting temperatures had rms errors slightly less than 1 deg C. For a more detailed description, see Section 6 of "The Nimbus III User's Guide" (TRF B03409). The SIRS experiment was successful and good data were obtained. On June 21, 1970, the experiment was turned off and all data acquisition effort was transferred to the SIRS experiment on Nimbus 4.

Alternate Names

  • Nimbus3/SIRS
  • SIRS

Facts in Brief

Mass: 41 kg
Power (avg): 24 W
Bit rate (avg): 0.1 kbps

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Earth Science: Atmospheric Dynamics
  • Earth Science: Land Surface Processes

Additional Information

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



NameRoleOriginal AffiliationE-mail
Mr. D. T. HillearyOther InvestigatorNOAA National Environmental Satellite, Data and Information Service
Dr. David Q. WarkPrincipal InvestigatorNOAA National Environmental Satellite, Data and Information Service
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