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
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.
Background New development
Scanning Technique Non-scanning. Step-and-stare acquisition along-track. FOV's of about 40 km x 40 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.
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: ≥2026-02 to ≥2030
Last update: 2021-11-03
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
  • Cloud ice
  • Cloud ice Total Column
  • Cloud ice effective radius
  • Height of the tropopause
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Tentative 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
VariableRelevance for measuring this variableOperational limitationsExplanation
Atmospheric temperature2 - 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
CH4 mole fraction3 - 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 ice2 - very highAlong-track only.Cirrus clouds observed in the UT/LS by FIR spectrometry
Cloud ice Total Column3 - highAlong-track only.Cirrus clouds observed in the UT/LS by FIR spectrometry
Cloud ice effective radius2 - 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)
CO2 mole fraction3 - 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 tropopause5 - 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
N2O mole fraction3 - 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
NO2 mole fraction3 - 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 temperature3 - 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 humidity1 - 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 tropopause4 - fairCloud sensitive.. Along-track only.TIR spectrometry. Tropopause temperature from temperature profile
Upward spectral radiance at TOA1 - 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 TOA3 - 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