Optical classification of MERIS radiances at global and regional scales: implications for algorithm development.
(1) European Commission - Joint Research Centre, Via E Fermi 1, 21020, Ispra, Italy
There is requirement to describe a considerable amount of variability, for empirical and semi-analytical inversion algorithms to be applicable at global scale yet remain quantitatively accurate in both the open ocean and coastal/shelf seas. It is accepted that this is unlikely to be achieved in the foreseeable future, with a single representation of algorithm parameters (i.e. a statistical fit coefficients or IOP subcomponent models).
This rationale is the background around which we conceived and developed the Universally Tailored Optical Parameter Inversion Algorithm (UTOPIA). The approach adopted uses fuzzy logic to define and identify in radiance space distinct bio-optical provinces that implicitly reduce the variance in the IOP subcomponent models.
A large, globally representative, dataset (NOMAD & UTOPIA5) of match-up AOP - IOPs has been used. From this dataset, using a fuzzy c-means clustering algorithm and objective validity functions, an optimum number of 8 optical classes were identified. These classes occupy multi-spectral radiance space associated with “traditional” Case I: oligotrophic, mesotrophic and eutropic waters as well as multiple classes for high absorption ad highly scattering waters.
The statistics retrieved from the clustering procedure were used to map the optical water classes with multiple years worth of MERIS data at the global scale. The global distributions obtained in the global products were compared with equivalent monthly product from the SeaWiFS and MODIS sensors.
Initial attempts to identify empirical model fit parameters and IOP sub-component models for each of the classes are presented, allowing variability in terms such as the spectral slope of CDOM (Sys), the power-law slope of backscattering and the specific absorption coefficient of phytoplankton.
These subcomponent model are being tested in the context of different inversion schemes. Finally, general considerations for the systematic processing of MERIS data with such methods are provided.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,