Introduction

Due to the global change of the environment and the strong human impact on natural water resources it is crucial to improve regular aquatic monitoring methods. Remote sensing has the capability of “viewing” large water areas within seconds, and is therefore a very cost-effective method to monitor changes in aquatic ecosystems. Since water bodies often cross boundaries of different countries, remote sensing can add an international dimension to monitoring programs. This is especially important for the EC Water Framework Directive (WFD) which requires the assessment of the ecological status of European waters (C.E.C., 2000). Water quality parameters that must be determined in transitional and coastal waters include phytoplankton biomass, the amount of dissolved carbon, frequency and intensity of blooms and water transparency. All of these can be assessed by combining remote sensing with modelling and other monitoring methods, such as collection of optical in situ data (so-called “sea-truth” data or validation). Monitoring of harmful algal blooms is particularly important for marine aquaculture and fisheries, as well as for tourism. In northern latitudes the winter season introduces particular problems with ice formation and melting. Human activities are different than in ice free conditions and safe traveling on ice is a critical question.