Instead of relying on expensive satellites and aircraft, researchers from Ulm, Erlangen and Nuremberg are turning to drones for Earth observation and remote sensing. For this purpose, the Research Training Group 2680 “Cooperative Aperture Synthesis for Radar Tomography (KoRaTo)” is developing a special sensor technology that makes it possible to network a large number of radar sensors. The system has already been tested for the first time in the Alps: it records how glaciers, snow and ice surfaces are changing due to climate change – and does so with unusually high spatial resolution. The joint Research Training Group run by Ulm University and Friedrich-Alexander University Erlangen-Nuremberg (FAU) has been extended by the German Research Foundation (DFG).
Against the backdrop of snow- and ice-covered Alpine peaks, a group of young men and women launch several drones equipped with radar sensors. They are using them to study glaciers and slope vegetation. The early-career researchers come from six different countries and are pursuing their doctorates in GRK 2680 “Cooperative Aperture Synthesis for Radar Tomography (KoRaTo)”. In the joint Research Training Group, they are developing a cooperative radar system that makes it possible to generate tomographic images of the surrounding area whilst flying over the Earth’s surface, and to do so with unprecedented accuracy.
With the help of radar sensors, the young researchers from the engineering sciences are collecting geophysical data on the biosphere and cryosphere – that is, the living environment and the snow- and ice-covered Earth’s surface. “In the second funding phase of our Research Training Group, we aim to put the fundamental technical systems and sensor functions we developed in the first phase into practice. Specifically, this concerns the field of radar remote sensing, or Earth observation,” explains Professor Christian Waldschmidt. The engineer heads the Institute of Microwave Technology at Ulm University and is the spokesperson for the Research Training Group.
To determine the composition and structure of the Earth’s surface, it is scanned using electromagnetic waves. The radar sensors detect the reflected microwave radiation and, based on the measurement data, generate a layer-by-layer three-dimensional image of the surroundings. The advantage: unlike in photography, neither night nor fog, rain nor snow interfere with the image, and the images not only cover the surface but also form a three-dimensional model of the interior of an entire glacier or the vegetation.
A novel radar system for sensor networks
Normally, satellites and aircraft are used for remote sensing, but this is complex and expensive. With the help of drones, sensor networks can be set up that can also be used for Earth observation. Thanks to special technical ‘tricks’ – which involve complex algorithms – such networked radar systems can even achieve much higher resolution.
The trick lies in artificially enlarging the so-called ‘aperture’ of the entire measurement system, i.e. the radius of the area over which the reflected microwave radiation is collected. To do this, drones are equipped with small radar sensors and fly over the observation area in a swarm. As they detect different radar echoes at the same time due to their varying positions, the antenna positions must be taken into account and time-of-flight differences must be calculated out. A radar signal processor calculates the intensity and phase of the respective received radar echoes to produce a coherent signal, enabling spatial resolutions in the centimetre range.
Over the next four years, other young scientists will now work on further optimising the technology for the acquisition of specific geophysical data. As a Mercator Fellow, Professor Irena Hajnsek from ETH Zurich, an internationally renowned expert in the field of radar remote sensing, will support the Research Training Group. “We offer our PhD students an excellent research environment. Our two universities already possess strong expertise in the field of high-frequency and communications engineering, and with our new research findings we will make an important contribution to radar-based remote sensing and the geosciences,” says Professor Martin Vossiek with confidence. The Head of the Institute of Microwave and Photonics at FAU is co-spokesperson for the DFG-funded Research Training Group.
Further information:
Prof. Dr.-Ing. Christian Waldschmidt, Head of the Institute of Microwave Engineering at Ulm University, email: christian.waldschmidt(at)uni-ulm.de
Text and media contact: Andrea Weber-Tuckermann