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Satellite - macrovegetation

Beside conventional ground-based survey techniques there is a growing interest in using satellite-based remote sensing. This technique has for a long time been used for extraction of geological and biological data from terrestrial ecosystems, but the applications in aquatic environments are still in a relatively early stage and technically far from consensus (McKenzie et al., 2001, Phinn et al., 2005).

In the Baltic Sea environment there is little information of about optical properties of benthic macrophytes, and distinguishing bottom vegetation types from each other is difficult and there is a need to develop the technique if this would be convincingly performed (e.g. Siegel, 1992; Kutser et al., 2006, Vahtmäe et al. 2006). The Baltic Sea is relatively turbid, which is a major challenge to the remote sensing field of science.

Submerged seagrass meadows have been spatially mapped and monitored in numerous studies using aerial photography (e.g. Kelly, 1980; Ferguson et al., 1993; Ferguson and Korfmacher, 1997; Lehmann et al., 1997; Robbins, 1997; Kendrick et al., 1999; Kendrick et al., 2000; Kendrick et al., 2002), whereas the use of satellite remote sensing, despite the potential to frequently repeated mapping, is still somewhat restricted in the field of applications and often critically discussed (Kirkman, 1996; McKenzie et al., 2001).

The use of satellite imagery for mapping of seagrass meadows has been successful in clear waters of temperate systems (e.g. Ackleson and Klemas, 1987; Ward et al., 1997; Lundén and Gullström, 2003) as well as within tropical regions (e.g. Dahdouh-Guebas et al., 1999; Turner and Klaus, 2002). It has been shown along the Swedish west coast that there is a potential to map and monitor eelgrass coverage using satellite remote technique (Lundén and Gullström, 2003), while using satellite data for mapping is generally not applicable in the Baltic Sea due to limited Secchi depth. The technique has been tested in a number of studies on different types of aquatic vegetation (see useful links below); mainly with unconstructive results except in very shallow areas (cf. intertidal sand flats).

With high-resolution alternative, such as IKONOS, it might be possible to use satellite imagery in some shallow areas of the Baltic (primarily in the Kattegat environment), but the cost for such images is fairly high although it is not as high now as it was some years ago.

In some studies from the Swedish west coast it is indicated that satellite remote sensing has a good potential for mapping and monitoring of eelgrass in the west, while so far it .

Limitations in using satellite technique for mapping macrovegetation
However, there are still some issues that have to be taken into consideration and where more research should be carried out before the technique can be fully operational:

1. What is the limiting depth for the satellite remote sensing technique?
Eelgrass normally grows where the water depths are between about one and six meters, with the main distribution from one to four meters at the Swedish west coast and two to six meters at the Swedish east coast. At the west coast it has been shown that satellite image mapping of eelgrass is possible down to around five meters using visual interpretation of images.

2. How sensitive is the technique to wind conditions?
The interpretation of satellite data can be limited when related to stronger winds.

3. What are the spectral characteristics for other shallow-bottom vegetation?
To avoid severe misclassifications, the appearance in satellite images of other vegetation types in the same environment should be studied.


Useful links:

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