BackForwardInstrument:  CSAR 

Instrument details
Acronym CSAR
Full name Cryogenic Solar Absolute Radiometer
Purpose To measure Total Solar Irradiance (TSI) and to provide an absolute reference for calibration
Short description The CSAR is cooled to cryogenic temperatures and makes use of an electrical rather than an optical standard as the basis of its calibration. it covers the spectral range 200 nm to > 30000 nm (for TSI) it is spectrally flat it is used as a calibration standard 320 to 2400 nm. TSI measurements are accurate to 0.02% (k=2) integrated over the full 200 to 30000 nm range. As a calibration reference for the HIS it is accurate to <0.1% (k=2) over the spectral range 320 to 2400 nm. TSI measurements over this range are accurate to 0.02%, and the absolute accuracy in the target range is 0.3%, achieved by cooling down to 60 K
Background New Development enabling high accuracy SI-Traceable measurements of TSI and serving as in-flight SI reference to enable reduction in uncertainty of other spacecraft sensors operating in the UV-SWIR.
Scanning Technique Sun pointing
Resolution N/A
Coverage / Cycle Daily TSI measurements.
Mass Power Data Rate


Providing Agency ESA
Instrument Maturity Demonstrated by simulations
Utilization Period: 2031 to 2041
Last update: 2022-11-28
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
  • Solar irradiance monitor
WIGOS Subcomponents
  • Subcomponent 1
  • Absolutely calibrated broadband radiometers, and TSI and SSI radiometers
  • TSI and SSI radiometers (for solar irradiance)
  • On-orbit measurement reference standards for VIS/NIR, IR, MW absolute calibration.
  • On-orbit measurement reference standards for VIS/NIR, IR, MW absolute calibration.
Mission objectives
Primary mission objectives
  • Downward short-wave irradiance 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
Downward short-wave irradiance at TOA*3 - highNo specific limitation.TSI over the range from UV to TIR