Optical remote sensing of waters and tidal flats in western Wadden Sea

In order to investigate the optical remote sensing applications over the turbid waters and the tidal flats of the Wadden Sea, color measurements were performed during periods of three months in summer 1981 and of one week in 1982, combined from a mounted-tower and from an airplane. Relationships between the optical properties and the seatruth were developed. A simple type of algorithm appears to be useful: reflectance ratio at two wavelengths in relation to the component concentration. It appears possible to retrieve the different components of the waters like total and mineral suspended matter, pigment and chlorophyll a, as long as they are correlated to each other (which is the case in 1981), by using a ratio of red/green reflectances, from the tower, and a ratio of red/blue reflectances, from the airplane. Also the fluorescent effect of chlorophyll is detectable from airplane, which provides another method to determine the pigment concentration of the waters. The pigment concentration of the microphytobenthos, which gives a browngreen color and which is an important parameter for global production in the Wadden Sea, can be retrieved from the ratio of airborne reflectances green/blue. These relationships are the first results of remote sensing experiments above the Wadden area. Further measurements are needed, especially using airborne instruments to cover larger inhomogeneous areas and to provide a better statistical sample which is needed to validate these first results. More adapted methods for sampling the seatruth (continuous for example) are also necessary to get a better precision on the estimation of the different components. In a first conclusion, the remote sensing of the different components of the waters appears positive, despite the great particulate matter concentration of the waters which mask the effect of the others substances on the optical properties