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Satellites measure drought stress in plants
The global population is growing, and arable land is limited, so farmers will need to harvest more from the same area of land in the future. One important factor is an optimal water supply - because when plants respond to drought stress, they invest less energy in producing their fruits, resulting in decreasing harvests.
One major problem is the difficulty of measuring the condition of plants on the vast area of 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 don’t get sufficient water. “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/Germany. “What we need is a technology that tells us within few hours whether plants have sufficient access to water.”
Algorithms determine the temperature on the leaf’s surface
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 two hours, the temperature can change by two to three degrees Celsius,” explains 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 phase of the new technology was how to factor out interfering heat emitted by the atmosphere, the Earth’s surface or 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.
The European Space Agency (ESA) eventually confirmed that the new technology of temperature measurement in such a compact system would be a real breakthrough, researcher Gulde notes. The data is downloaded from the satellites to ground stations, processed in data centres, prepared for the user and finally transferred to the agricultural user’s app, he explains.
Optimal irrigation in close to real time
The technology’s key advantage is that data and information about the water supply to plants is available after just a few hours. As a result, farmers can adjust their irrigation levels practically in real time to specifically irrigate those fields or plants that are most affected. Moreover, pinpoint-precise irrigation systems help to save water and enable more accurate crop forecasts. This means that prices of agricultural products can be calculated accordingly at an early stage because farmers can predict how badly a drought could damage their crops many weeks in advance. “This provides agricultural producers with significantly increased planning security,” explains Gulde.
The new technology is scheduled to go into operation in space aboard the International Space Station in the beginning of 2022. “I am very pleased that Fraunhofer EMI’s first spin-off will use the technologies developed at the institute to help optimise the irrigation of fields and arable land as well as the yield of crops world-wide. This improves food security for people around the world and represents significant progress, especially in times of climate change,” enthuses Professor Frank Schäfer, Head of the Systems Solutions department at the institute.
The two young experts have founded the company ConstellR to further develop and commercialise the technology.
Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI