Hyperspectral cameras unveil unseen colours and double up as chemical detectors that can be used in countless applications.
This image of Lake Geneva, taken by a hyperspectral camera aboard an ultralight aircraft, reveals biological activity (in red), sediment carried in by the Rhône River (upper left), and areas of dirt (white), grass (green), as well as trees and certain crops (blue).
The image was taken in an initial phase of the Elemo project conducted by the École Polytechnique Fédérale de Lausanne (EPFL). The goal is to study Lake Geneva and its pollution from the air, the surface and underwater using submersibles.
“An algorithm automatically combines the 250 wavelengths captured by the camera and generates an image with maximum contrast,” explains EPFL scientist Dragos Constantin, an expert in spatial-data acquisition.
“This image doesn’t try to pinpoint the presence of specific details that stand out at specific wavelengths, but rather generates hypotheses that must then be further studied and verified,” he says. “The red is probably correlated with biological activity and the presence of chlorophyll because it’s particularly intense in the water on the left-hand side of the image. It indicates algal activity in waters near the lakeshore.”
The second image (inset) shows the mouth of the Venoge River, west of Lausanne. This time the algorithm maximised the contrast in the water. It clearly reveals the sediment carried by the river, as well as currents in the lake.
“Installing a hyperspectral camera on the ultralight aircraft was a huge job,” says Constantin. “We had to synchronise all the devices, notably the GPS and the inertial measurement unit, which estimates the vehicle’s orientation and speed very precisely. This is critical because the camera takes images line-by-line, 50 times a second. You have to know exactly where you are at every moment in order to reconstruct the composite image.”