It's now possible to monitor health of Estonian lakes from space
Next time you're standing by Lake Peipus or Võrtsjärv and notice the water has turned murky or suspiciously green, know that satellites can help reveal why. New technology allows scientists to distinguish whether the change is caused by an algal bloom, stronger river inflow or toxic cyanobacteria.
A study published in the journal Applied Sciences confirms that a new generation of satellites can assess the water quality of Estonia's largest lakes with far greater accuracy than before, offering much better tools for monitoring their condition.
The research was conducted by scientists from the University of Tartu's Tartu Observatory in collaboration with colleagues from Italy and France. They used data from two new European satellites, PRISMA and EnMAP, analyzing a total of 12 satellite images of Lake Peipus and Võrtsjärv. To ensure accuracy, the satellite data was compared with measurements taken directly on the lakes.
What sets these satellites apart is their so-called hypersensitive vision. While older satellites would register only broad swaths of green or brown, the new technology can detect extremely fine variations in color. This matters because different substances and organisms in the water have distinct reflective signatures.
For example, the satellites detected the presence of phycocyanin, a pigment characteristic of cyanobacteria, in Lake Peipus — something older Sentinel satellites missed. Lab analyses confirmed that a species of cyanobacteria was indeed dominant in the lake at that time. This capability allows for early and widespread assessments of potential algal blooms.
Beyond identifying algae, the scientists could also use satellite images to closely observe how rivers affect lake ecosystems. The inflow of the nutrient-rich, browner water from the Emajõgi River into Lake Peipus appeared clearly in the form of a fan-like shape, showing how the river water gradually mixed with the lake water. Images taken after heavy rainfall and strong winds revealed how the river carried significantly more sediment into the lake.
The accuracy achieved is thanks to hyperspectral technology. Instead of capturing light in a few broad bands, these satellites divide it into hundreds of narrow spectral bands. This allows them to detect the subtle chemical "fingerprints" of substances and organisms in the water — something previously possible only in laboratories.
The study also showed that satellites can map the spread of aquatic vegetation. In Võrtsjärv, for instance, the technology made it possible to distinguish between underwater plants and those floating on the surface.
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Editor: Airika Harrik, Jaan-Juhan Oidermaa
