Calibration and validation of a generic multisensor algorithm for mapping of turbidity in coastal waters

Turbidity, as defined in the standard ISO7027, is a parameter that is routinely measured in many national and regional water quality monitoring programmes. The definition of turbidity according to ISO and as related to satellite data products is discussed. While satellite data products are beginning to become available for the closely related parameter, Total Suspended Matter (TSM), the direct estimation of turbidity as a satellite data product has not yet been addressed. In situ measurements of TSM and of turbidity, obtained in the Southern North Sea (SNS), show high correlation (correlation coefficient of 98.6%). A generic multisensor algorithm for TSM as function of reflectance has been previously developed. The methodology is extended here to the estimation of turbidity from water-leaving reflectance. A set of 49 seaborne measurements of reflectance in the spectral range 600-850nm and turbidity in the SNS are used to calibrate the algorithm. The algorithm is also calibrated for the specific bands of MERIS. Validation of these models is carried out using an independent set of seaborne measurements of turbidity and reflectance and shows low relative errors in turbidity retrieval at 681nm (less than 35%). This wavelength is recommended, provided no significant fluorescence affects this range