Radar imaging could be key to monitoring climate change

InSAR has created digital elevation maps of the Earth’s surface with unparalleled precision and precision. The models now serve as the standard for many geoscientific, remote sensing, topographical and commercial applications. Moreira’s technology also helps track the effects of climate change.

For his “leadership and innovative concepts in the design, deployment, and use of airborne and space-based radar systems,” Moreira this year received the IEEE Dennis J. Picard Medal for Radar Technologies and Applications. Sponsored by Raytheon Technologies.

Moreira says he is honored to receive “the most prestigious award in the field of radar technologies and applications.”

“It’s an acknowledgment of the 20 years of hard work my team and I have put into our research,” he says. “What makes the honor even more special is that the award is presented by IEEE.”

Using radar to map the Earth’s surface

Moreira and his team say that before they developed their InSAR system in 2010, synthetic aperture radar systems were the state of the art. Unlike optical imaging systems, systems using SAR can penetrate clouds and rain to capture high-resolution images of the Earth from space. It can also work at night.

An antenna on an orbiting satellite sends pulsed microwave signals to the Earth’s surface as they pass over the terrain being mapped. The signals are then reflected back to the antenna, allowing the system to measure the distance between the antenna and the point on the Earth’s surface where the signal is reflected. Using data processing algorithms, the reflected signals are combined in such a way that the computationally generated artificial antenna acts as if it were a much larger antenna, providing better accuracy. That’s why it’s called the approach Artificial opening radar.

“The system documents changes occurring on the ground and facilitates early detection of irreparable damage.”

While leading a research team at the German Aerospace Center in the early 1990s, Moreira saw the potential to use information gathered from these radar satellites to help address societal issues such as sustainable development and the climate crisis. But he wanted to take the technology a step further and use a synthetic aperture radar for interferometry, called InSAR, which he realized would be more powerful.

SAR satellites provide 2D images, but InSAR allows 3D imaging of the Earth’s surface, which means you can map the terrain, not just the radar reflection.

It took Moreira and his team nearly 10 years to develop their InSAR system, the first to use two satellites, each with its own antenna.

Their approach allows the creation of height maps. The two satellites, called TerraSAR-X and TanDEM-X, revolve around the Earth in semi-circular orbits, and the distance between the two satellites ranges from 150 to 500 meters at any time. To avoid collisions, Moreira and his team developed a double helical orbit; The satellites move along an ellipse and wrap around each other.

The satellites communicate with each other and with ground stations, sending altitude and position data so that their separation can be fine-tuned to help avoid collisions.

Each satellite emits microwave pulses and each satellite receives scattered signals. Although the scattered signals received by each satellite are almost identical, they differ slightly due to the different viewing geometry. These differences in received signals depend on the elevation of the terrain, allowing the surface elevation to be determined. By combining measurements of the same area obtained at different times to form interferograms, scientists can determine whether there have been subtle changes in elevation in the area, such as sea level rise or deforestation, during the intervening time period.

The InSAR system was used on the German Aerospace Center’s 2010 TanDEM-X mission. Its goal was to create a topographic map of the Earth with a horizontal distance between pixels of 12 meters. After its launch, the system scanned the Earth’s surface several times over five years and collected more than 3,000 terabytes of data.

In September 2016, the first global digital elevation map with a height resolution of 2 meters was produced. Moreira says it was 30 times more accurate than any previous effort.

Satellites are currently used to monitor environmental impacts, specifically deforestation and melting glaciers. The hope, Moreira says, is that early detection of irreversible damage can help scientists determine where intervention is needed.

He and his team are developing a system that uses more satellites flying in close formation to improve the data available from radar imaging.

“By collecting more detailed information, we can better understand, for example, how forests change internally by imaging each layer,” he says, referring to the emergent layer, the canopy, the understorey, and the forest floor.

He is also working on developing a space-based radar system that uses digital beamforming to produce images of the Earth’s surface with higher spatial resolution in less time. Moreira says currently radar systems take about 12 days to produce a global map with a 20-meter resolution, but the new system will be able to do it in six days with a 5-meter resolution.

Digital beamforming represents a paradigm shift for space search and rescue systems. It consists of an antenna divided into several parts, each of which has its own receiving channel and an analog-to-digital converter. The channels are combined in such a way that different antenna beams can be back-calculated to increase the imaged area and synthetic aperture length, allowing for higher spatial resolution, says Moreira. He says he expects to launch three such systems within the next five years.

A lifelong career in DLR

Moreira earned bachelor’s and master’s degrees in electrical engineering from the Aeronautical Technological Institute in São José dos Campos, Brazil, in 1984 and 1986. He decided to pursue his doctorate abroad after his master’s thesis advisor told him there were more research opportunities. in another place.

Moreira received his Ph.D. in Engineering at the Technical University of Munich. As a doctoral student, he conducted research at the German Aerospace Center (DLR) on real-time radar processing. In his thesis, he created algorithms that generate high-resolution images from one of the airborne radar systems located at the German Aerospace Center.

“Having students and engineers working together on large-scale projects is a dream come true.”

After graduating in 1993, he planned to return to Brazil, but instead accepted an offer to become the leader of the DLR group. Moreira led a 10-person research team working on airborne and satellite systems design and data processing. In 1996, he was promoted to chief scientist and engineer in the organization’s SAR Technology Division. He remained in this position until 2001, when he became Director of the Microwave and Radar Institute.

“I chose the right career,” he says. “I couldn’t imagine doing anything other than research and electronics.”

He is also a professor of microwave remote sensing at the Karlsruhe Institute of Technology in Germany, and has been a doctoral advisor to more than 50 students working on research at the facilities of the German Aerospace Center.

One of his favorite parts of his job as a director and professor is working with his students. “I spend about 20 percent of my time with them,” he says. “Having students and engineers working together on large-scale projects is a dream come true.” When I started my career at the German Center “For the first time in Aerospace Affairs (DLR), I did not know that this cooperation would be so strong.”

The importance of establishing the IEEE network

During his time as a doctoral student, Moreira learned about IEEE. He presented his first paper in 1989 at the International Geosciences and Remote Sensing Symposium, in Vancouver. He says that while attending his second conference, he realized that by not being a member he was “missing out on a lot of important things” like networking opportunities, so he joined.

He says IEEE has played an important role throughout his career. He presented all of his research at IEEE conferences, and also published research in the organization’s journals. He is a member of the IEEE Space and Electronic Systems, IEEE Antennas and Propagation, IEEE Geosciences and Remote Sensing (GRSS), IEEE Information Technology, IEEE Microwave Theory and Techniques, and the IEEE Signal Processing Societies.

“I recommend that everyone join not only the IEEE, but also at least one of its societies,” he says, calling it “the home of your research.”

He founded the IEEE GRSS German Section in 2003 and served as President of the Society in 2010. An active volunteer, he was a member of the IEEE GRSS Managing Committee and served as Associate Editor from 2003 to 2007 of the IEEE GRSS Journal. IEEE Earth Sciences and Remote Sensing Letters. Since 2005 he has been associate editor of the magazine IEEE Transactions on Geosciences and Remote Sensing.

He says that through his volunteer work and participation in IEEE events, he has connected with other members in various fields including aerospace technology, geosciences and remote sensing and collaborated with them on projects.

He was awarded the IEEE Dennis J. Picard Medal for Radar Technologies and Applications on May 5 during the IEEE Vision, Innovation, Challenges and Recognition Summit held in Atlanta. The event is available on IEEE.tv.