Minimize Calibration and Validation Activities
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 continuing throughout phase E2
  • quantification of Level-1 and Level-2 product error estimates
  • long term monitoring for consistency and constant quality of geophysical products
  • advising 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:
  • 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.

OLCI Calibration and Validation Overview

The OLCI imaging spectrometer is calibrated in-flight using three diffuser panels and a shutter plate placed on a calibration wheel and respectively inserted in the instrument field of view to perform radiometric calibration, to trace degradation of the diffusers themselves, and to perform spectral calibration, all supported by contemporary dark calibrations. Traceability to international standards is ensured through pre-launch characterisation of the diffuser plates.
Post-launch, essential activities are planned to systematically monitor and model OLCI absolute response and degradation of its radiometry and characterisation in order to assure long-term stability. The OLCI radiometric model needs to be independently validated by vicarious means, including sensor inter-comparisons.
In Level-1B processing, spectral and geometric models are taken into account. Those models are initiated from pre-launch characterisation (e.g. FPA stability, line of sight), and need to be updated during the first months of satellite life and throughout routine operations using measurements from spectral calibrations and campaigns or over Ground Control Points (GCP).
For Level-2 ocean colour, the final performance is met by the system, and not only by the instrument itself. Mission requirements surpass instrument specifications.