Case2X (ESA SEOM, 2015-2017)

Ocean Colour remote sensing has significantly improved over the last 15 years. Over many years the emphasis was on chlorophyll-a retrieval in Case 1 waters. In recent years progress has been made to derive water quality parameters in Case 2 waters, however, still remaining within a rather narrow range of concentrations and variability, and not yet fully satisfactory success. It is the objective of this project to study and advance the state of the art of retrieval of water reflectances, IOPs and concentrations from ocean colour data of extreme absorbing and extreme scattering Case 2 waters, demonstrating this with MERIS historical data and preparing algorithms and processors for the near future Sentinel 3 OLCI and SLSTR sensors. The approach of the study comprises a comprehensive state-of-the art review and experimental research, algorithm intercomparison of atmospheric correction (polymer, neural networ, SWIR based) and water constituent retrievals (spectrum inversion, empirical polynomials). The processors will be implemented in the open source ESA Sentinel SNAP toolbox.

The C2X project objectives are:


  • implement and validate existing atmospheric correction algorithms and water constituents retrieval methods in extreme Case-2 waters,

  • synergistic exploitation of the capabilities of the Envisat/MERIS and the future Sentinel-3/OLCI instrument, possibly in combination with the spectral bands of the SLSTR instrument

  • addressing specific challenges of extreme turbid (scattering) and extreme absorbing waters: low marine:atmosphere signal, aerosol retrieval under non-zero NIR reflectance, adjacency effect, absorbing aerosols, Rayleigh correction, sun-glint

  • validation of the identified and selected atmospheric correction and in-water retrieval algorithms, with in-situ data (knowing that there are only few available) and heuristic methods.

  • Engage the user community and link the development work to ongoing international activities, such as the ESA Ocean Colour Climate Change Initiative, the International Ocean Colour Coordination Group (IOCCG) and GEO.

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