Mission Performance

Mission Performance - Altimetry

Sentinel-3 Surface Topography Mission

The series of Sentinel satellites mark a major step forward in the collection of Earth Observation data with the commitment to a series of spacecraft and sensors to construct long time series of data suitable for both climate applications and widespread operational use. Each Sentinel mission is based on a constellation of two satellites to fulfil revisit and coverage requirements, providing robust datasets for Copernicus Services.

Sentinel-3A and Sentinel-3B are multi-instrument missions to measure sea-surface topography, sea- and land-surface temperature, ocean colour and land colour with high-end accuracy and reliability. The missions will support ocean forecasting systems, as well as environmental and climate monitoring.

Sentinel-3A was launched on 16 February 2016 and the SRAL and MWR sensors were switched-on 1 March and 29 February 2016 respectively. After 5 months of commissioning, the Routine operations started in July 2016.

After 6 first weeks of acquisition in LRM mode, Sentinel-3A was switched to SAR mode on 12 April 2016 and since then it has operated in SAR mode continuously and over all surfaces, being the first altimetry mission to use this mode at global scale.

Sentinel-3B was launched on 25 April 2018. Sentinel-3A and -3B flight during five months in tandem formation, separated by only 30 seconds. During this tandem phase, different acquisition modes have been tested out on Sentinel-3B: LRM, SARM Open Loop and SARM Close Loop. Sentinel-3B has reached its final orbit (interleaved) on 23 November 2018. Since then, Sentinel-3B operates in SAR, following the same Open loop / Close loop mask as Sentinel-3A.

Calibration and Validation

There are three main objectives for calibration and validation (cal/val) activities.

  • To provide a comprehensive initial assessment of product validity and quality at the end of commissioning activities.
  • To monitor the stability and the quality of the products throughout the operational phase of the mission.
  • To continuously improve the quality of the products throughout the operational phase of the mission following the evolving user requirements.

The cal/val plan defines the scope of activities that calibrate the on-board instruments and validate the data products generated operationally and disseminated by the PDGS centres.

All SENTINEL-3 cal/val activities are linked to mission requirements. A product error source analysis is performed to identify the main sources for each product. There are five generic sources that can contribute to total product error.

  • Instrument errors refer to those errors associated with instrument hardware and their calibration parameters.
  • Satellite-instrument coupling errors refer to errors associated with interactions between the platform and the instrument.
  • Satellite errors refer to errors associated with satellite operations.
  • Processing errors refer to errors associated with data processing.
  • Validation errors refer to errors arising within the validation process.

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