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REVAMP Résumé de rapport

Project ID: EVG1-CT-2001-00049
Financé au titre de: FP5-EESD
Pays: Norway

REVAMP chlorophyll-a algorithm

The main tangible scientific achievement of the algorithm work was the emergence of a new CHL retrieval algorithm with associated quality estimation algorithm. The REVAMP algorithm is a new water quality algorithm to retrieve concentrations from reflectance spectra in turbid coastal waters. Because of the optical complexity of such waters, frequently used simplified equations were abandoned in favour of the more sophisticated Hydrolight radiative transfer code.

This code can predict the observed remote sensing reflectance under any angle as a function of absorption and scattering within the water, taking into account the angular distribution of the downwelling radiance and the transmission through the air-water interface for a given wind speed.

The inversion of this model is accomplished by a non-linear optimization scheme (Levenberg-Marquardt). The concentrations are found by fitting the modelled remote sensing reflectance spectrum to an observed reflectance spectrum, by altering the concentrations of chlorophyll-a, total suspended matter and absorption by coloured dissolved organic matter.

Approximating the Hydrolight output with high degree polynomial functions substantially reduced the execution time of the algorithm. Because Hydrolight (and the derived sets of polynomial coefficients) are based on total absorption and scattering, and not directly on concentrations, the calibration with different specific inherent optical properties is easy and completely transparent. Apart from the concentrations, the algorithm also calculates a statistical measure of the so-called goodness-of-fit and standard errors in the retrieved concentrations.

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