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Visible Infrared Spin-Scan Radiometer Atmospheric Sounder (VAS)

NSSDCA ID: 1980-074A-01

Mission Name: GOES 4
Principal Investigator:


The Visible-Infrared Spin-Scan Radiometer Atmospheric Sounder (VAS) operated in three distinct modes to provide parameter measurement flexibility, spectral band selection, geographic location, and variable sensitivity. The VISSR mode was the same as the VISSR system on board GOES 1, 2, 3. Both the IR channel (10.5 to 12.5 micrometers) and visible channel (0.55 to 0.75 micrometer) used common optics. Incoming radiation was collected by a Ritchey-Chretien optical system. The spinning motion of the spacecraft (100 rpm) provided a west-to-east (W-to-E) scan motion. Scan mirror tilt after each spin provided a north-to-south (N-to-S) scan motion. A full picture took 18.2 min to complete and 2 min to reset for the next image. Eight visible-spectrum detectors (0.9-km horizontal resolution) and one mercury-cadmium-telluride IR detector (6.9-km horizontal resolution) swept the earth during each scan. In the dwell-sounding mode, up to 12 spectral filters in a wheel covering the range 678.7 per cm (14.74 micrometers) through 2535 per cm (3.94 micrometers) were positioned into the optical train while the scanner was dwelling on a single N-to-S scan line. The filter wheel could be programmed so that each spectral band filter could dwell on a single scan line for from 0 to 255 spacecraft spins. Either the 6.9-km or 13.8-km resolution detectors could be selected for the seven filter positions operating in the spectral region 701.6 per cm (14.25 micrometers) through 1487 per cm (6.725 micrometers). For the remaining five spectral bands the 13.8-km resolution detectors were used. Selectable frame size, position and scan direction were also programmable via ground command. For the VAS demonstration, 10-bit reduced resolution (3.5-km) visible data were provided for imaging. In some of the spectral regions, multiple-line data were required to enhance the signal-to-noise ratio. Typically, 20-50 satellite spins at the same N-to-S scan line position were required to obtain the desired sounding data. This number of spins per line should be adequate to obtain soundings having a 30- x 30-km resolution and require approximately 1.9 minutes on the average. The multispectral imaging (MSI) mode could provide normal VISSR IR imaging plus data in any two selected spectral bands having a spatial resolution of 13.8 km. This mode of operation took advantage of the small mercury-cadmium-telluride detector offset in the N-to-S plane. Using the data from these detectors simultaneously produced a complete infrared map when the detectors were operated every other scan line. This allowed using the larger detectors during half of the imaging/scanning sequence period to obtain additional spectral information. Unlimited N-to-S frame size and position selection, within the maximum N-to-S FOV scan direction, could be selected. The VISSR output was digitized and transmitted to the NOAA Command and Data Acquistion Station, Wallops Island, Va. There the signal was fed into a "line stretcher," where it was stored and time-stretched for transmission back to the satellite at reduced bandwidth for rebroadcast to APT user stations. Data from the VAS MSI mode and the dwell sounding mode were not "stretched". The VISSR data were handled by NOAA and eventually sent to the National Climatic Center, Satellite Data Services Division, NOAA, Washington, D.C., for archiving.

Alternate Names

  • VAS

Funding Agency

  • NOAA National Environmental Satellite Service (United States)


  • Earth Science: Atmospheric Dynamics

Additional Information

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



NameRoleOriginal AffiliationE-mail
Mr. William E. ShenkOther InvestigatorNASA Goddard Space Flight Center
Principal InvestigatorNOAA National Environmental Satellite, Data and Information Service
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