Monitoring from space – Lake Constance is being systematically observed – News


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Lake Constance is monitored as part of various research projects. Blue-green algae are in focus.

For the past four years, the German federal state of Baden-Württemberg has had Lake Constance monitored in various research projects. The last project has been completed since the end of 2022. The public should soon benefit from the recordings from very high up.

A Sentinel-3 satellite flies over Lake Constance every day.

In the last 10 to 15 years, more and more satellites have been put into orbit with which small bodies of water such as Lake Constance can also be viewed. “Every day, a Sentinel-3 satellite flies over Lake Constance and collects data,” says Thomas Wolf. Satellites with an even better image resolution fly over the lake between Germany and Switzerland every five days or less.

In theory, the whole world has access to these images.

The data and images come from the European Space Agency ESA and the American NASA. They upload them to special platforms. “Theoretically, the whole world has access there,” says the physicist and project manager at the Baden-Württemberg State Institute for the Environment, Thomas Wolf.

Statements on temperature and algae

Thomas Wolf and his team have evaluated this large amount of data over the past few years and also compared it with the data that was measured in the lake itself. “For example, you can use the satellite images to determine the temperature on the lake surface,” says Wolf. You can say where there is algae and therefore nutrients in the lake, for example, and where there is a risk of blue-green algae.

Faster bathing ban

Thanks to the images from space, it should be possible to determine promptly where a swim in the lake could be dangerous for dogs or humans. “The satellites can determine whether potentially dangerous blue-green algae are also present,” says Thomas Wolf.

Going out by ship, taking water samples and evaluating them in the laboratory is quite time-consuming. The water samples are also limited to a few places in the lake. “The satellite images also allow us to see what’s happening throughout the lake,” says Thomas Wolf. For example, the distribution of algae in the vicinity of several kilometers can be precisely identified.

Be prepared for the unexpected

Lake Constance is used in many ways. It is of great importance as a tourist hotspot and it is a large drinking water reservoir for the region. “It is therefore important to monitor the lake as well as possible,” Wolf is convinced. In this way, it can be recognized quickly if an unexpected change should occur in the lake. That is, should the water change or new algae suddenly appear.

The water research institute of the ETH, Eawag, has been producing daily updated lake water quality data with Sentinel-3 data for all larger Swiss lakes since 2021.

The challenge, according to Dr. Daniel Odermatt from Eawag to prove the accuracy and reliability of this data. Of course, this is easier if you only have Lake Constance in view than if you look at several lakes, says Odermatt on request.

the Data can be presented and evaluated in combination with ground measurements and model calculations.

This experimental database was created in a research project for the Federal Office for the Environment. It is mainly used by researchers, but is also intended to increasingly support operational environmental monitoring by the Confederation and the cantons.

So far, the Baden-Württemberg Lake Constance monitoring has only been carried out internally at the Institute for Lake Research in Langenargen. The first space data from Lake Constance should be published next year at the earliest.

The goal is quick information.

During the research projects of the state of Baden-Württemberg, the data were only evaluated afterwards. “The goal is to have the information evaluated just a few hours after a satellite has crossed the lake,” says Thomas Wolf about the future.

In the medium to long term, the data from Germany should be available to the general public – also in Switzerland. This can then see what the current water quality is and where Lake Constance is and how warm.

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