The Use of MERIS and MODIS Data for Monitoring Coastal WFD Water Bodies
Attila, Jenni1; Kauppila, Pirkko1; Kallio, Kari1; Kaitala, Seppo1; Mitikka, Sari1; Alasalmi, Hanna1; Kervinen, Mikko1; Lindfors, Antti2; Junttila, Sofia1; Bruun, Eeva1
1Finnish Environment Institute, FINLAND; 2Luode Consulting oy, FINLAND
The reporting activities required by the EU water framework directive (WFD) and the marine strategy framework directive (MSFD) necessitate comprehensive collection of monitoring information from all water bodies of Finland and the adjacent water areas, including definitions of the status of these water bodies. These requirements cannot be fulfilled using traditional monitoring station measurements alone. The increased monitoring demand calls for the development and implementation of new monitoring methods and approaches. Currently available data consists of Earth observations (EO), ferrybox, traditional monitoring stations and mooring buoys. The inclusion of EO methods with other efficient techniques to measure the status of the Baltic Sea can assist in providing required monitoring actions, particularly in areas out of the reach of the traditional methods.
The northern Baltic Sea is characterized by a fragmented coastline and multitude of islands of various sizes. Among the satellite instruments available now and in the forthcoming years, MERIS (MEdium Resolution Imaging Spectrometer) and its follow-up instrument OLCI (Ocean Land Colour Instrument onboard Sentinel-3) can provide the best functionality for the estimation of parameters related to chlorophyll a (chl-a) and turbidity. This is related to both the spatial resolution of 300m as well as the band combination of MERIS and OLCI.
The Alg@line ferrybox system provides in real-time information on the water quality with high-frequency automated sampling onboard eight merchant ships on the Baltic Sea. Alg@line devices measure salinity, chl-a, temperature, turbidity, and in summertime also the amount of cyanobacteria (phycocyanin fluorescence). The depth of the inlet is ca. 5 m below the surface with a spatial resolution of 200 m. The system includes a sequence water sampler storing 24 water samples along the route.
The comparison of the results of various types of monitoring methods is carried out using five different approaches: EO, traditional monitoring station data, ferrybox, and a coastal flow-through transect system on a moving boat and mooring buoys. Firstly, coastal monitoring station data using extensive historical dataset of in situ and EO data match-ups the data of years 2006-2011. The second type of validation dataset consists of five coastal field campaigns which have produced continuous transect measurements with ac-9 and water samples analyzed in laboratory. The comparison is made in the coastal waters of Finland by showing time series and histograms calculated using EO, Alg@line, mooring buoys and traditional monitoring station data within the water bodies, used for ecological classification. Part of the validation is made using MERIS and MODIS (The Moderate Resolution Imaging Spectroradiometer) satellite instrument data.
An example on the time series with monitoring station measurements and EO is shown in Figure 1 for one WFD water body on the coastal waters of Finland.