Ocean colour remote sensing relevant water constituents and optical properties of the Baltic Sea

Inherent and apparent optical properties have been investigated in coastal regions and in the open Baltic Sea for more than 20 years. The area of investigation included the open parts of the central and western Baltic Sea and the Pomeranian Bight, with the largest fresh water inflow into the western Baltic via the Oder river. The main focus of the research was the seasonal and regional variation in the concentration and composition of optically active water constituents and their inherent optical properties and the influence on the apparent optical properties like spectral reflectance and the vertical attenuation coefficient. This publication combines results of earlier studies and new investigations on the absorption of yellow substances and the volume-scattering function. A volume-scattering phase function, an important variable in modelling of radiative transfer in the water, was derived for the Baltic Sea. The best correlation was found in a two-term Henyey-Greenstein function, in contrast to the Petzold phase function. The optical measurements were already used to modify reflectance models, to validate Coastal Zone Color Scanner (CZCS), MOS (Modular Optical Scanner) and Sea-viewing Wide Field of view Sensor (SeaWiFS) data, and to derive ground data algorithms. They will be important for the future validation and adaptation of Medium Resolution Imaging Spectrometer (MERIS) data evaluation procedures on the conditions of the Baltic Sea.