How we do it: Use of Earth Observation for monitoring of aquatic environment

The Sentinel satellites of the European Union’s Copernicus programme have brought the monitoring of aquatic environment to a new era. These satellites offer frequent overpasses, long term availability of images and good data quality, which enables building powerful new monitoring tools.

Earth Observation (EO) satellites capture optical or microwave images of the Earth. The optical images are composed of sunlight reflected by the target in different wavelengths. Some properties of the target (e.g. surface color, concentrations of certain substances) affect how the sunlight is reflected, and thus by analyzing the spectra captured by the satellite instrument the physical and biogeochemical characteristics of the target can be determined.

Although there are mathematical methods in use to analyze satellite observations, the simplest analysis is to look at the images with one’s own eyes, and see the complex variations in water. The high spatial resolution images of Sentinel-2 are excellent for this purpose. Below are examples where various targets can be seen in so called true color images, which show the colors as close as possible to the human vision. These are available through SYKE’s TARKKA map application (link TARKKA is a publicly available service designed for visualization of not only EO images and products, but also in situ data and various geographical information layers related to water bodies.

The first example shows a springtime image from the Bay of Bothnia. Sea ice is visible and the reddish hue in some coastal areas indicates that rivers bring suspended and dissolved material from land to water during the melting period. By clicking the link below the image you can access TARKKA, and pan and zoom the map in your browser.

True color visualization of Sentinel-2 image taken on 14.5.2018.

Link to the image in the TARKKA-service:

The second example shows the area north of Hailuoto in the northern coast of Finland. The features of the coastal areas (especially sandy beaches) are clearly visible.

True color visualization of Sentinel-2 image taken on 20.6.2018.

Link to the image in the TARKKA-service:

Estimation of water quality parameters such as turbidity and the concentration of Chlorophyll a is possible by utilizing more complex methods. These methods often utilize neural network solutions to model the interactions between the measured spectra and the water quality parameters. Water quality cannot be determined in shallow waters, through clouds or areas covered by the shadows of the clouds. Therefore, these are removed from the image before it is delivered via interfaces. Examples of these products are also available in TARKKA.

Aggregate of all summerly turbidity observations (Sentinel-2) in 2018. The areas in light gray color are land. The areas in dark gray color are shallow areas that are masked from the image.

Link to the image in the TARKKA-service:

We are constantly adding more products, parameters and other data to TARKKA so stay tuned for more updates. If you have questions or comments you can contact our team in SYKE by sending an email to

Sampsa Koponen and Jenni Attila making reference reflectance measurements with hand-held spectrometers in the Archipelago Sea. These measurements are important for the validation of the satellite products. (Photo Eeva Bruun).

Written by Sampsa Koponen, Kari Kallio, Jenni Attila, Hanna Alasalmi, Mikko Kervinen, Vesa Keto, Eeva Bruun, Finnish Environment Institute (SYKE)

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