Use of MERIS for WFD Lake Monitoring in Finland
Koponen, Sampsa; Kallio, Kari; Attila, Jenni; Kervinen, Mikko; Alasalmi, Hanna; Mitikka, Sari; Pyhälahti, Timo
Finnish Environment Institute, FINLAND

Finland has over 56 000 lakes (size > 1 ha). The number of lake water bodies defined by the Water Framework Directive (WFD) is about 4300 in Finland. It is not practical to monitor them by using only conventional methods. For example, chlorophyll a, which is a measure algal biomass and indicates lake's trophic status, is annually measured only in about 1400 lakes. Due to this lack of monitoring data about 60% of WFD lakes were not ecologically classified in the last WFD reporting. Thus, with the conventional methods and the limited (and diminishing) resources the monitoring goals of the WFD cannot be reached and additional approaches, such as Earth Observation (EO), are needed.

In this paper we show how MERIS full resolution (300 m) data can be used to monitor chl a concentrations, one of the main parameters of the WFD, of Lake Säkylän Pyhäjärvi in Southern Finland. The MERIS estimates are compared with in situ data measured at a raft with continuously operating measurement equipment and water samples analysed in a laboratory. The method is then used to estimate chl a in large and applicable medium size lakes in Southern Finland presenting the potential of MERIS type instruments in a lake rich region.

The results show the types of products that can be generated to cover the needs of the directive reporting and the areas where improvements are still necessary. E.g., in Finland many lakes have a high CDOM concentration which can affect the retrieval of chl a from satellites.

The objectives are to use EO products as a back ground material in the WFD reporting taking place in spring 2013 and to prepare for the next reporting period (data collection during: 2013-2018) by taking into account the possibilities brought by the Sentinel satellites.