Algae blooms in large quantities make the water toxic and can be directly dangerous, both for humans and for pets. Therefore, it is important that the public receives information about where in Sweden it can pose a health risk to swim or drink the water.

Manually taking water samples at sea is no longer the only way to predict the progress of algal blooms. Data from space satellites can tell you what kind of particles are in the water and how high the concentrations are in an area.

– With the help of the satellite images, SMHI can, among other things, produce current maps that show the areas where it is currently not safe to swim, says Tobias Edman, who works with innovation and societal benefits at the Swedish Space Agency.

Exact snapshots

The satellites, which are part of the EU’s environmental monitoring and safety program Copernicus, have sensitive sensors that read different colors in the water, where each color gives a certain measurement value. The color is determined by which particles and algae are present in the water.

– It is mainly the Sentinel 3 satellites supplemented with Sentinel 2 that monitor the algal blooms. Sentinel 3 sends images on a daily basis that are a little rougher in resolution. The images from Sentinel 2 have a better resolution, but we in Sweden get access to them every other to every third day, says Tobias Edman.

Thanks to the satellites, you can see very precisely where the algae are in the sea and with the help of models for currents, you can also see how they will move. Satellite monitoring of algae in the Baltic Sea started experimentally as early as the 1990s, and since then the technology has been refined.

– It started with manual interpretations and not so frequent. For a few years now, SMHI has been using automatic analyzes and interpretations. It provides very good and updated snapshots, which means that you can quickly come out with information, says Tobias Edman.

Combination of sources

Research based on satellite data is growing rapidly and the Copernicus program is one of the most important research areas supported by the Swedish Space Agency. The satellites are also used to collect data over a longer period. Then the purpose of the monitoring is to be able to make a more general quality assessment of the water.

If the water turns out to be of poorer quality, it may be because the catchment area needs to be remedied with the construction of wetlands and protection zones or because more work is needed with the treatment from individual sewers or treatment plants.

– Satellite monitoring is a very valuable resource, but in the long-term monitoring it is just as much about getting access to information from other measuring tools. It is ultimately the combination of different information sources that indicates what efforts are required to improve water quality, says Edman.