Minimize Calibration and Validation
SENTINEL-3 calibration and validation (cal/val) activities are essential to the quality of the mission. Data quality will be assessed through determination of the radiometric, spatial, spectral and geometric fidelity of the satellite sensor and the accuracy of geophysical products. Three phases of cal/val are foreseen for SENTINEL-3:
  • Pre-launch phase instrument characterisation and on-ground calibration.
  • A commissioning phase (E1) lasting approximately 5 months will be performed for SENTINEL-3A where all instrument operation aspects will be verified and in-orbit calibration and validation activities will be initiated. Instrument data should be available from approximately 1 month after launch for initial tests and engineering commissioning verification, calibration and validation activities. Once complete, a final validation review authorises data dissemination to end-users.
  • An exploitation phase (E2) will then commence extending for the duration of the mission in which calibration and validation activities will continue for geophysical data products.

Dedicated SENTINEL-3 calibration tasks include:
  • full pre-launch characterisation and calibration of all instruments
  • full in-flight calibration and (re)characterisation of all instruments
  • comprehensive verification of Level-1 data processors (tuning of all relevant processing parameters, regeneration of all Level-1 auxiliary products)
  • preparing and advising on necessary Level-1 processor updates
  • routine calibration monitoring and assessment after the end of the commissioning phase.

Dedicated SENTINEL-3 validation tasks include:
  • commissioning phase Level-2 algorithm verification for all Level-2 'baseline' products
  • Level-2 algorithm validation starting during the commissioning phase and continued throughout phase E2
  • quantification of Level-1 and Level-2 product error estimates
  • long term monitoring for consistency and constant quality of geophysical products
  • advice on re-processing campaigns.

In addition, the cal/val component of the SENTINEL-3 mission includes maintenance and evolution of prototype ground processors, generation of all pre-launch auxiliary data sets needed for Level-1 and Level-2 processing and the definition and planning of in situ campaigns to be conducted during the commissioning phase. SENTINEL-3 cal/val plans will be reviewed and updated on a regular basis as required by the mission. In particular, a PDGS re-processing capability will support calibration and validation activities as well as potential tuning of algorithms and product evolution.

The responsibilities for the 3 SENTINEL-3 cal/val specific phases will be split as follows:
  • the cal/val preparation activities to take place before launch will be conducted and organised by the relevant parties
  • the space segment commissioning phase, including all its cal/val activities, will be led by the SENTINEL-3 ESA satellite project with the support of other ESA and EUMETSAT teams for the validation activities
  • the routine operations phase, including all its cal/val activities, will be the responsibility of SENTINEL-3 mission management.

SLSTR Calibration and Validation Overview

For the majority of channels, SLSTR is a self-calibrating instrument (based on the approach successfully implemented in the (A)ATSR series of instruments). Notably, the F1 and F2 Fire channels are not self-calibrating as the upper dynamic range of these channels exceeds that of the on-board black bodies. F1 and F2 will require vicarious adjustments using reference radiance sources on ground. The on-board calibration system involves the use of two highly stable Black Body (BB) reference targets (for the thermal channels) maintained at different temperatures above and below the range of earth targets (but optimised for SST retrievals), and a diffusely reflecting target (VISCAL) that is illuminated once per orbit (for the VIS-SWIR channels). Traceability to international standards is maintained through the on-ground characterisation, on-board calibration sources and pre-launch calibration. The validation process for geolocation is similar to OLCI with the use of SPS and GPP. Due to the scanning mechanism, pre-launch characterisation of scanner and mirror performance is essential. For Level-2 SST and LST products, the main purpose is to validate the products using a variety of reference data.