BackForwardInstrument:  FSI 

Instrument details
Acronym FSI
Full name FORUM Sounding Instrument
Purpose To provide new insight into the planet’s radiation budget and how it is controlled. To measure the scattering of ice cloud at 20 um and the emissivity of snow/ice over the poles.
Short description Four-port double pendulum Fourier-Transform interferometer, to cover the range 100-1600 cm-1 (6.25-100 μm) with a spectral resolution of 0.5 cm-1 (unapodised). An embedded TIR imager centred at 10.5 μm with a bandwidth of 1.5 μm looking at the same scene as the interferometer acquires co-located images during the dwell time for detection of scene inhomogeneities. NedT of sounder 0.1K above 300 cm-1 and 0.2K for 200-300 cm-1.
Background New development
Scanning Technique Non-scanning. Step-and-stare acquisition along-track. FOV's of about 36 km x 36 km sampled at 100 km intervals. Inside the FOV there are a single 15-km IFOV of the interferometer and 60x60 0.75-km IFOV's of the embedded imager. The embedded imager collects at least 5 images over the FOV during a dwell time of 14 s.
Resolution Interferometer: 15 km; embedded imager; 0.75 km.
Coverage / Cycle The repeat cycle of the FORUM orbit is 29 days. Note only measurements at nadir are made.
Mass Power Data Rate

 

Providing Agency ESA
Instrument Maturity Flown on an R&D satellite
Utilization Period: 2027 to 2033
Last update: 2023-11-30
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
  • Subcomponent 1
  • IR hyperspectral sounders [in SSO]
  • IR hyperspectral sounder [in SSO]
Mission objectives
Primary mission objectives
  • Atmospheric temperature
  • Cloud ice
  • Cloud ice Total Column
  • Cloud ice effective radius
  • Height of the tropopause
  • Integrated Water Vapour (IWV)
  • Sea surface temperature
  • Specific humidity
  • Temperature of the tropopause
  • Upward long-wave irradiance at TOA
  • Upward spectral radiance at TOA
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 low troposphere.. Along-track only.TIR spectrometry in the 15 micrometer band
C2H23 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. C2H2 lines around 7.5 and 13.7 micrometers
C2H63 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. C2H6 lines around 12 micrometers
CFC-113 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. CFC-11 lines around 9.2 and 11.7 micrometers
CFC-123 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. CFC-12 lines around 8.8 and 10.8 micrometers
CH43 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. CH4 lines around 7.7 micrometers
ClONO22 - very highCloud sensitive.. Coarse vertical resolution.. Along-track only.MWIR and TIR spectrometry. ClONO2 lines around 5.7, 7.7 and 12.5 micrometers
Cloud cover5 - marginalDiscontinuous coverage.. Along-track only.TIR spectrometry
Cloud ice*2 - very highAlong-track only.Cirrus clouds observed in the UT/LS by FIR spectrometry
Cloud ice Total Column*3 - highAlong-track only.Cirrus clouds observed in the UT/LS by FIR spectrometry
Cloud ice effective radius*2 - very highAlong-track only.Cirrus clouds observed in the UT/LS by FIR spectrometry
Cloud top height2 - very highDiscontinuous coverage.. Along-track only.MWIR and TIR spectrometry in window and water vapour band (for emissivity) to estimate cloud top height from its temperature
Cloud top temperature1 - primaryDiscontinuous coverage.. Along-track only.TIR spectrometry in window and water vapour band (for emissivity)
CO23 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. CO2 lines around 15 micrometers
COS3 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. COS lines around 11.6 micrometers
Downward long-wave irradiance at Earth surface2 - very highCloud sensitive.. Highly indirect.. Along-track only.MWIR and TIR spectrometry including water vapour and CO2 bands
H2O1 - primaryCloud sensitive.. Along-track only.Spectrometry in MWIR/TIR in a range centred on 6.3 micrometers; and FIR in a range centred on 18 micrometers
Height of the top of PBL5 - marginalCloud sensitive.. Along-track only.TIR spectrometry. Height of PBL top from temperature profile
Height of the tropopause*5 - marginalCloud sensitive.. Along-track only.TIR spectrometry. Height of tropopause from temperature profile
HNO33 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.MWIR and TIR spectrometry. HNO3 lines around 5.9, 7.6 and 11.3 micrometers
Land surface temperature4 - fairCloud sensitive.. Coarse spatial resolution.. Along-track only.TIR spectrometry (inclusive of several narrow-bandwidth windows and absorption bands for atmospheric corrections)
Long-wave Earth surface emissivity2 - very highCloud sensitive.. Long time series needed.. Along-track only.MWIR and TIR spectrometry measuring land temperature in many windows. Emissivity inferred by statistical analysis
N2O3 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. N2O lines around 7.7 micrometers
N2O53 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.MWIR and TIR spectrometry. N2O5 lines around 5.8 and 8 micrometers
NO3 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.MWIR spectrometry. NO lines around 5.3 micrometers
NO23 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. NO2 lines around 6.1 micrometers
NO2 Total Column4 - fairCloud sensitive.. Along-track only.TIR spectrometry. NO2 lines around 6.1 micrometers
O33 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. Ozone band around 9.7 micrometers
O3 Total Column3 - highCloud sensitive.. Along-track only.TIR channel(s). Ozone lines in band around 9.7 micrometers
PAN3 - highCloud sensitive.. Coarse spatial resolution.. Along-track only.MWIR and TIR spectrometry. PAN lines around 5.7, 8.6 and 12.5 micrometers
PSC occurrence2 - very highCoarse vertical resolution.. Along-track only.MWIR and TIR spectroscopy
Sea surface temperature*3 - highCloud sensitive.. Along-track only.TIR spectrometry (inclusive of several narrow-bandwidth windows and absorption bands for atmospheric corrections)
SF63 - highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. SF6 lines around 10.5 micrometers
SO22 - very highCloud sensitive.. Coarse vertical resolution.. Along-track only.TIR spectrometry. SO2 lines around 7.3 and 8.6 micrometers
SO2 Total Column2 - very highCloud sensitive.. Along-track only.TIR spectrometry. SO2 lines around 7.3 and 8.6 micrometers
Specific humidity*1 - primaryCloud sensitive.. Along-track only.TIR and FIR spectrometry in bands around 6.3 and 18 micrometers
Integrated Water Vapour (IWV)*1 - primaryCloud sensitive.. Along-track only.TIR and FIR spectrometry in bands around 6.3 and 18 micrometers
Temperature of the tropopause*4 - fairCloud sensitive.. Along-track only.TIR spectrometry. Tropopause temperature from temperature profile
Upward spectral radiance at TOA*1 - primaryMissing all Short-waves and MWIR.. Along-track only.TIR and FIR spectrometry resolving water vapour lines in the bands around 6.3 micrometers and 18 micrometers
Upward long-wave irradiance at TOA*3 - highSpectral interpolation needed.. Along-track only.TIR and FIR spectrometry in the 11 micrometers window region, and in water vapour and CO2 bands around 6.3, 15 and 18 micrometers
Upward long-wave irradiance at Earth surface2 - very highCloud sensitive.. Highly indirect.. Along-track only.TIR spectrometry covering the 11 micrometers window region and the water vapour and CO2 bands around 6.3 and 15 micrometers