BackForwardInstrument:  VAS 

Instrument details
Acronym VAS
Full name VISSR Atmospheric Sounder
Purpose Cloud imagery and atmospheric temperature and humidity sounding
Short description

Filter radiometer alternatively used for cloud imagery (2 channels: 0.55-0.75 μm and 10.5-12.6 μm) or atmospheric sounding (12 channels centred on 3.94, 4.44, 4.51, 6.7, 7.2, 11.2, 12.7, 13.3, 14.0, 14.2, 14.5 and 14.7 μm). The required SNR is achieved by selecting appropriate spatial resolution and number of repeated scan lines for the different channels
Background

Implemented by adding absorbing channels to VISSR flown on SMS 1/2 and GOES 1/2/3
Scanning Technique

W-E continuous scanning (100 rps) by the spinning satellite rotation, N-S by mechanical stepping. For sounding channels, for each step the line can be repeated a number of times as required by SNR considerations
Resolution VIS channel: 0.9 km at s.s.p.; 10.5-12.6 μm channel: 6.9 km at s.s.p.; all other channels: either 6.9 or 13.8 km
Coverage / Cycle Imaging mode: full disk each 30 min; sounding mode: 400x400 km2 in 20 min; several combinations possible
Mass 74.8 kg Power Data Rate

 

Providing Agency NOAA
Instrument Maturity Flown on operational programme
Utilization Period: 1980 to 1996
Last update: 2026-06-08
Detailed characteristics
Satellites this instrument is flying on

Note: a red tag indicates satellites no longer operational, a green tag indicates operational satellites, a blue tag indicates future satellites

Instrument classification
  • Earth observation instrument
  • Passive optical radiometer or spectrometer
  • Cross-nadir infrared sounder, possibly including VIS channels
WIGOS Subcomponents No WIGOS subcomponents have been defined.
Mission objectives
Primary mission objectives
  • Atmospheric temperature
  • Integrated Water Vapour (IWV)
  • Specific humidity
Evaluation of Measurements

The following list indicates which measurements can typically be retrieved from this category of instrument. To see a full Gap Analysis by Variable, click on the respective variable.

Note: table can be sorted by clicking on the column headers
Note: * Primary mission objective.
VariableRelevance for measuring this variableOperational limitationsExplanation
Atmospheric temperature*3 - highCloud sensitive.. Coarse vertical resolution.Several MWIR and TIR channels in the 4.3 and 15 micrometer bands. Frequent sampling (GEO) enables monitoring instability onset
Cloud cover4 - fairDiscontinuous coverage.MWIR and TIR channels
Cloud top height2 - very highDiscontinuous coverage.TIR channels in window and water vapour band (for emissivity) for temperature; and in CO2 band for atmospheric column above cloud top
Cloud top temperature2 - very highDiscontinuous coverage.TIR channels in window and water vapour band (for emissivity)
Cloud type4 - fairDiscontinuous coverage.MWIR and TIR channels
Downward long-wave irradiance at Earth surface3 - highCloud sensitive.. Highly indirect.MWIR and TIR channels including water vapour and CO2 bands
Land surface temperature3 - highCloud sensitive.. Coarse spatial resolution.MWIR and TIR window channels (high sensitivity to high temperature, cloud impact reduction, water vapour correction)
Sea surface temperature2 - very highCloud sensitive.MWIR and TIR window channels (cloud impact reduction, water vapour correction)
Specific humidity*3 - highCloud sensitive.. Very coarse vertical resolution.. Middle troposphere only.TIR channels in the water vapour band around 6.3 micrometers
Integrated Water Vapour (IWV)*3 - highCloud sensitive.. Inaccurate in high troposphere.TIR channels around 6.3 micrometers and in the 11 micrometers split window
Upward long-wave irradiance at TOA4 - fairSpectral interpolation needed.MWIR and TIR channels in windows around 3.7 and 11 micrometers, and in water vapour and CO2 bands around 4,3, 6.3 and 15 micrometers
Upward long-wave irradiance at Earth surface3 - highCloud sensitive.. Highly indirect.MWIR and TIR channels in windows around 3.7 and 11 micrometers, and in water vapour and CO2 bands around 4,3, 6.3 and 15 micrometers