Water quality monitoring in the Gulf of Bothnia and the Bothnian Bay
During a couple of years, the possibility to use satellite data for monitoring of water quality has been investigated, and since May 2010, a service (www.vattenkvalitet.se) based on satellite data for regular water quality monitoring in the Great Lakes and Northern Baltic Sea, has been available by Brockmann Geomatics Sweden AB. The purpose of this project was to investigate the possibility to expand the monitored area to also cover the Bothnian Sea and the Bothnian Bay.
SwAM, The Swedish Water Authorities, the River Basin District Authorities, the county administrative boards, the societies for water conservation, water companies and other organisations have the task to monitor, restore and preserve the natural conditions of the lakes and sea, and to provide the community with high quality drinking water. Their work consists of, for example, sampling, analysis and evaluation of the results from their field based programs. With the demands from European directives etc., a growing demand of a remote tool for status classification on a general level is foreseen and remote sensing could be the right tool to accomplish that.
The general objective of this project was to evaluate if remote sensing based water quality monitoring is possible in the Bothnian Sea and the Bothnian Bay. Good results have been achieved over the lakes and the northern Baltic Sea, but the sun angles are lower and the water is darker (more dissolved organic matter) in these areas. If good results could be achieved, the goal was also to further develop the operational service and user oriented products to also include this area.
The satellite based chlorophyll and Secchi depth estimates were in good agreement with the field based estimates and there are good opportunities to substantially increase the amount of monitoring data for chlorophyll a also in the Gulf of Bothnia using this technique. The satellite based TSM estimates were lower than the field based estimates and the variability appears to be large. It should be noted however that most of the field based concentrations are < 2 mg/l, which made this parameter difficult to properly validate. The satellite based CDOM estimates were also lower than the field based estimates but positive trends have been seen in the validation. It should be noted however that most of the field based concentrations are < 1.5m-1, which made this parameter difficult to properly validate. The investigations will continue for TSM and CDOM using other processors.
Chlorophyll a (Chl a) and Secchi depth (SD) are two of the parameters that are defined as quality factors for status assessment of Swedish water bodies. With respect to the promising results of this and earlier projects regarding these parameters, the complete MERIS fr archive between 2009-2011, covering the coastal zone, as well as the Swedish lakes Mälaren, Vänern, Vättern and Hjälmaren, will
be reprocessed by Brockmann Geomatics Sweden AB and Brockmann Consult Germany GmbH in the beginning of 2013. Based on this homogeneously processed data set, water quality products corresponding to annual means of Chl a and SD for each water body will be produced and translated to “Ecological Quality Ratios” and status class, and used as a basis for the revision of the status classification within the Water Framework Directive in 2013. Latest reprocessing, calibrations and corrections will be applied as well as recently developed and defined masking and filtering techniques. Due to the loss of MERIS in April 2013, there will be no operational service during 2013, but instead a focus on refinement and development of products based on existing data in the MERIS archive (2002-2012). The service can be resumed again with the launch of Sentinel-3 in 2014.