The Colour of Water is determined by substances in the water, and measuring the water colour allows a retrieval of the water quality. Eutrophic waters appear green, while sediment loaded waters get a brown colour. Highly sensitive multispectral cameras, deployed on satellites, allow a quantification of such water constituents from space, at global scale and with a spatial resolution of down to 10s of meters.
The retrieval of water constituents, or its optical properties, is achieved by inversion of the water leaving reflectance spectrum, measured at top of atmosphere and thus requiring a correction for atmospheric effects. This multi-variate problem is extremely challenging in so-called optically complex, or Case-2, waters. The Case–2 Regional processor, originally developed by DOERFFER and SCHILLER, uses a large database of radiative transfer simulations inverted by neural networks as basic technology.