BackForwardInstrument:  FWS 

Instrument details
Acronym FWS
Full name Filter Wedge Spectrometer
Purpose Temperature and humidity sounding in bands SWIR and MWIR
Short description Spectral scanning by alternating filters placed on the border of a wheel. Two bands, 3.2-6.4 μm and 1.2-2.4 μm; spectral resolution 0.6-1.2 %
Background Prototype of filter radiometers still in use, for instance the current HIRS of POES and MetOp.
Scanning Technique Non-scanning. Nadir viewing only
Resolution 70 km s.s.p.
Coverage / Cycle Global in 20 days for the MWIR band, 40 days for the SWIR band
Mass Power Data Rate


Providing Agency NASA
Instrument Maturity Flown on an R&D satellite
Utilization Period: 1970 to 1980
Last update: 2017-03-29
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
  • 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*2 - very highCloud sensitive.. Inaccurate in high troposphere.. Night time only.. Along-track only.MWIR spectrometry in the CO2 band around 4.3 micrometers
Specific humidity*3 - highCloud sensitive.. Very coarse vertical resolution.. Middle troposphere only.. Along-track only.TIR channels in the water vapour band around 6.3 micrometers