Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRHigh-Resolution Radar Images of the Moon
The antenna of the TIRA tracking radar is 34 meters in size – yet still too small to resolve the surface of the Moon. Researchers at Fraunhofer FHR therefore utilized the movement of the Earth and the Moon to create a virtual antenna several hundred kilometers in size. The result: a high-resolution radar image of the Moon’s surface and – even more importantly – proof that the new radar system operates with great stability.
The Moon’s surface in high resolution: This is what new images from the Fraunhofer FHR’s TIRA tracking radar show. As beautiful as these images are, the focus wasn’t on the Moon itself – after all, there are already high-resolution images of its surface, and the tracking radar isn’t designed for imaging purposes. "The goal of the images was rather to test the stability of the radar system," explains Dr. Florian Behner, a scientist at Fraunhofer FHR. TIRA is set to receive both a new receiver and a new transmitter, with only the existing power amplifier, which generates the high output power, remaining in place. The installation of these key components is planned for 2025. For an initial test measurement, all components were connected and tested in prototype mode. The test object: the Moon’s surface.
Test object: the Moon
In general, the larger the antenna, the narrower its beam. The 34-meter TIRA antenna has a very precise beam, as TIRA is designed to detect small objects at great distances. In the L-band at 1.33 gigahertz, its radar beam is about the apparent diameter of the Moon, meaning it would normally only detect a single point. However, the researchers took advantage of the movements of both the Moon and the Earth. “Since the Earth is in a different position relative to the Moon with each measurement, we recorded the signals over an extended period. By using the movement of the Earth, we virtually placed our TIRA antenna side by side multiple times and thus created an antenna several hundred or even a thousand kilometers wide. This is known as a synthetic aperture,” explains Behner. “This only works if TIRA's antenna remains coherent and stable over the entire half-hour measurement period.” The sharp image of the Moon’s surface is not only visually impressive but also demonstrates that the system was stable. This stability is crucial for the future operation of the new TIRA radar. Only with a stable system can the signal energy from multiple pulses be coherently integrated, which significantly enhances precision.