Use of MERIS data in the Wadden Sea

With its 500 km length the Wadden Sea is the largest mudflat area in the world. Discharges from various rivers mix here with water from the North Sea. Due to surfacing mudflats, the variation in source water, resuspension and extremely high concentrations of optically active substances, large temporal and spatial differences in watercolour can be seen.

To predict concentrations of suspended particulate matter, chlorophyll-a, and coloured dissolved organic matter from in-situ reflectance measurements and later from MERIS images, two approaches were followed. The first approach was an inverse bio-optical model called Hydropt, in which the absorption and scattering properties of the water constituents (Specific Inherent Optical Properties) can be changed. The second was an end-member method based on spectral shapes. This is often applied in land remote sensing but not often used in remote sensing of water. We compared the predicted concentrations with in-situ data and with knowledge on (tidal) distributions of water masses in the Wadden Sea.

Preliminary results show that both methods are able detect patterns of water with certain optical properties and spectral shapes in the area (“water types”). Until now the precise calculation of concentrations remains difficult.