Satellites Measure Drought Stress in Plants with Aim of Increasing Crop Yields

By Fraunhofer Gesellschaft

With a satellite system that measures drought stress in plants, two researchers from the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI, have now founded the spin-off ConstellR. Their technology enables the agricultural sector to optimize the irrigation of areas under cultivation to increase crop yields. The first sensor system will be launched into space in early 2022 and be installed on board the International Space Station (ISS).

The global population is growing—and demand for food is growing along with it. Since arable land is limited, farmers will need to harvest more from the same area in the future, meaning that cultivation will have to be improved, too. One important lever is an ideal supply of water—because when plants respond to drought stress, they invest less energy into their fruits, thereby reducing the harvest. One major problem is the difficulty of measuring the condition of plants on the vast arable land that spans the world. Although satellite data has been used since the 1970s to provide a general overview, it remains relatively inaccurate. To date, scientists have primarily used visual and near-infrared sensors that detect the plant pigment chlorophyll which breaks down when plants are not watered enough. "But by then, it's already too late," says Max Gulde, a physicist at the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI, in Freiburg. "What we need is a technology that tells us within the space of a few hours whether plants have sufficient access to water."

Algorithms determine the temperature on the leaf's surface

Max Gulde and his colleague Marius Bierdel at Fraunhofer EMI have taken on the task of developing precisely this type of technology. Satellite technology is applied here too, with the research team using an advanced thermal imaging camera in the satellite. Special algorithms evaluate the data to determine the temperature on the surface of the plants' leaves, which enables researchers to draw conclusions on the water supply. When there is a water shortage, less water is evaporated through the leaves. This increases the temperature on the leaf's surface. "Within the space of two hours, the temperature can change by two to three degrees Celsius," explains Max Gulde. "Our method can measure temperature differences very precisely, to within a tenth of a degree." In technical terms, the sensor measures the amount of energy emitted by the plants in the form of photons.

One challenge that arose during the development stage was how to factor out interfering heat emitted by the atmosphere, the Earth's surface or from the satellite itself. This heat distorts the temperature data obtained from the leaf's surface. Thanks to their algorithms, the EMI researchers also succeeded in overcoming this challenge. And it was the European Space Agency (ESA), no less, that confirmed how well the system works: "We weren't sure about our approach until the ESA informed us that this was a real breakthrough. Before us, no one had been able to solve the problem of temperature measurement in such a compact system," emphasizes Max Gulde. The data is downloaded from the satellites to ground stations, processed in data centers, prepared for the user and finally transferred to the agricultural users' app.