Pollen reveals huge gyre in Lake Geneva

There is a flip side to the annoying blankets of pollen found on cars, garden furniture and other surfaces: when it comes to satellite images, pollen on lakes reveals currents that are otherwise only visible in computer models. This makes the waterbody researchers and remote sensing experts very happy.
Visible from an altitude of almost 800 km: pollen on Lake Geneva. (Photo: Sentinel-2; 10 m resolution)
Warm and dry weather, in the first half of April especially, led to the deposition of large quantities of flower pollen. When this was followed by precipitation in some regions, the pollen was washed into the lakes and formed visible swathes sometimes stretching several kilometres – big enough to be clearly visible on satellite images taken from space.

This image of Lake Geneva was captured by the Sentinel-2A satellite on Friday, 24 April, and shows deposits of pollen that match the currents on the lake surface. For remote sensing expert Daniel Odermatt of the Eawag aquatic research institute, the image is not only aesthetically pleasing but also extremely interesting because the currents that are suddenly visible can be compared with models. Indeed, the pattern shows very good agreement with the calculation issued for the same day on www.meteolakes.ch.

The large, central gyre off the shore of Lausanne rotates approximately once every two days. “We have many individual point measurements taken from boats or from the floating platform LéXPLORE,” says Odermatt, “but the patterns in the satellite photos help us gain a better understanding of the lake’s behaviour across its entire surface.”