Transparency of the Baltic Sea during the growth season 2008 according to MERIS Satellite data

 

	Seppo Kaitala, FIMR, Antoine Mangin, Philippe Garnesson and Odile Fanton d’Andon, ACRI-ST

Assessment

Decreased water transparency was observed during the spring bloom in May and July  in the Bothnian Sea, the Baltic Proper, the Archipelago Sea, the Gulf of Finland and in the Gulf of Riga.

In the early summer (June), the water transparency increased slightly after the spring bloom especially in the Bothnian Sea.  The water transparency decreased again in July almost everywhere in the Baltic area except in the Bay of Bothnia.

The water transparency increased in all areas toward the late summer (August and September).

 

April	May
June	July
August	September

Fig. 1. Monthly averages of water transparency (m) according to MERIS satellite observations. The white area in the Bothnian Bay is covered by ice. Click images to enlarge.

 

Technical information

 

1.       Data source: The data is provided by Marine & Coastal Environmental Information Services (MarCoast), a three year Global Monitoring for Environment and Security (GMES) Service Element started in 2005. Funding is from the European Space Agency (ESA) focusing in marine and coastal information services. The pan-European water quality assessment service is provided by ACRI-ST. The validation activities undertaken in Baltic are performed in close partnership with FIMR. The service is targeted to end-users in charge of providing information to support decisions regarding measures to take to protect lives, properties and loss of natural values in protected areas. In the case of the Baltic Sea, the purpose of the service is to provide transparency data interpreted as monthly Secchi depths for the Baltic Sea monitoring.

2.       Description of data: Water transparency information obtained by MERIS satellites and validated against in situ Secchi measurements. The validation shows from 2 to 3 meters distortion showing lower values measured by satellite than by the Secchi white-disc (Fig. 2).

3.       Geographical coverage: All regions of the Baltic Sea.

4.       Temporal coverage: April 2008 to September 2008.

5.       Methodology and frequency of data collection:  Secchi depths have been evaluated daily from Meris satellite data. 

6.       Methodology of data manipulation:  Monthly averages have been counted from the daily cloud free data.

7.       Strength and weakness of data: Satellite mapping provides frequent data with high spatial resolution, enabling coverage of the entire Baltic Sea. Data cannot be collected from cloud-covered areas, and this may cause bias in the monthly averages during time-periods with frequent cloudiness.

8.       Reliability, accuracy, robustness, uncertainty (at data level):  The Secchi depths are underestimated about 2 – 3 meters evaluated from satellite data. The regression of satellite data against in situ Secchi depth data explains 42 % of the variation.

9.       Further work required (for data level and indicator level):  Underestimation and distortion are considerable and satellite data analysis algorithm needs further development.

 

Return to main report:   Water transparency in the Baltic Sea between 1903 and 2007

 

For reference purposes, please cite this indicator fact sheet as follows:

[Author’s name(s)], [Year]. [Indicator Fact Sheet title]. HELCOM Indicator Fact Sheets 2008. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.

 

Last updated: 14 October 2008