MERIS; however, is especially adapted to the low reflectance from water, and due to its 15 narrow bands (10 nm

wide) also has an improved spectral resolution. MERIS 1.2 km resolution is too low to investigate Himmerfjärden, and one can only derive a limited number of water pixels within Himmerfjärden [17]. The 300 m resolution MERIS image shows that one can derive a reasonable amount of water pixels within the bay. One can also apply an adjacency correction that corrects for the high reflectance from land [17] and [26]. The optical properties of a given coastal water body are determined by the optical properties of water itself, phytoplankton, Colored Dissolved Organic Matter (CDOM, also termed humic substances), and Suspended Particulate Matter (SPM, also termed total suspended matter, TSM). Together, these substances determine the color of the sea, and also jointly Sotrastaurin contribute to the attenuation of light in the water body [25]. The light attenuation decreases exponentially with water depth and is a measure of the gradual loss in light intensity, measured as the diffuse attenuation coefficient; Kd(490). The main processes involved in the attenuation of light are absorption and scattering by all optical components in the water.

CDOM, for example mostly absorbs light, especially in the blue part of the visible spectrum. Inorganic suspended matter scatters light more, which increases the water-leaving radiance, and thus is recorded on a satellite image. Phytoplankton absorbs light in the blue and in the

red part of the spectrum, and also scatters light. mTOR inhibitor It is these specific absorption and scattering properties that can be used to derive the concentrations of optical components in the water quantitatively. The ocean color bands in MERIS were carefully chosen in order to be able to derive the light attenuation, chlorophyll a and SPM concentration, as well as Progesterone CDOM [27]. In order to interpret satellite images in the coastal zone correctly, one needs to have a good understanding of the optical properties in the coastal zone. Kratzer and Tett [16] developed an attenuation model for the coastal zone that can act as an ecosystem synthesis of a given coastal area (Fig. 3). The attenuation follows a surface water gradient from the UWWTP at the head of Himmerfjärden bay to Landsort Deep (station BY31), the deepest part of the Baltic Sea (Fig. 2). Hence, the model is 2-dimensional and describes how the attenuation of the three main optical in-water components changes when moving from coastal (source) into open sea waters (sink). The model results highlight the typical optical features of a given coastal area in the Baltic Sea. The optical properties of the open Baltic Sea are clearly dominated by colored dissolved organic matter.