Secchi depth (SDT)

This dataset is not yet available in the current version of Tarkka.

Secchi depth describes the transparency of the water and is an indicator for eutrophication. It is interpreted from observations of satellite instruments, especially from the sea areas and lakes around Finland in cloudless times. The water areas where the Secchi depth is large are depicted on the map in blue whereas in the areas where water transparency is low the colors in the map change from yellow to red. The accuracy of the interpretation is good compared to the Secchi depth measurements made at the monitoring stations. Background map material is visible from areas with land, clouds, ice, or no observation. The interpretation uses Sentinel-2 series MSI instruments and NASA’s Landsat-8 satellite OLI instrument observations. An interpretation made with an accuracy of 60 m. The Secchi depth material is under development and there are mainly example material available. Satellite-based Secchi depth are not observed daily from the entire coastal areas.

Secchi depth material from the Archipelago Sea area on 9 May 2016.

Correspondence of satellite data compared to station observations

When comparing visual depth observations at the water body level, the EO visual depth observations correspond well to the observations made at the stations (r2 = 0.65, RMSE = 1.09 m (51.27%), MAE = 0.82 m, N = 1592). For the time being, however, the data in the map is from time to time granular and gross errors occur, so the method will be further developed in the next few years.

Figure 1: As an example, two areas from the coastal waters, from the Bothnian Sea (left) and Kvarken (right) inland water bodies, correspondence between the station (x-axis) and satellite (y-axis) observations at the station site during the same day.