Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRHowling winds and heaving seas with towering waves – when a person goes overboard in a storm like this, the crew quickly loses sight. And conventional navigation radar does not help much either. A novel radar system, however, is capable of reliably locating shipwrecked persons, as such providing valuable help for rescue missions. A first field test was extremely promising, but a lot of development work is still required until the system can be used routinely. When someone goes overboard on the high seas, it is difficult for the crew to find the person among the towering waves and the ship's radar only helps to a limited degree. That is because the waves reflect the emitted radar signals similar to how a person does – so waves and people give off almost the same echo. This physical challenge has so far greatly limited the performance of conventional systems.
Locating Shipwrecked Persons from up to Six Kilometers Away
This is not the case with the new SEERAD system: It makes it possible to detect people and small rescue boats from large distances. It was developed by the Institute for Microwaves and Plasma Technology of FH Aachen University of Applied Sciences, Fraunhofer FHR, and the company Raytheon Anschütz GmbH. The solution addresses the weaknesses of existing radar technologies in a targeted manner and significantly broadens their range of applications.
To do this, SEERAD uses the following trick: The radar signals are usually reflected by the water and the person in such a way that the signal's frequency remains the same. But by attaching a transponder to the life jacket that returns the signal with a different frequency, the echoes of waves and the person can be distinguished. This requires two antennas on the ship: One for the ordinary navigation radar and a second one for the echo of the transponder. When a transponder signal reaches the ship, the rescue crew will know: Someone is in distress here.
All antennas were developed at Fraunhofer FHR – the two antennas on the ship together are no larger than a ship's conventional radar antenna. In addition, the ones in the transponder are seaworthy and resist the heavy strains placed on it by the waves. This ensures that integration into existing platforms remains economically and technically feasible.
Tested under real-world conditions: the system in field trials
A test run on the Baltic Sea demonstrated that the system is highly promising. When the dummy that “went overboard” carried a passive transponder – without a battery – on its life jacket, it could be located at distances of up to 600 metres. With an active, battery-powered transponder, the “person in the water” could even be detected at a distance of six kilometres with a transmit power of only 100 watts. For comparison: previous harmonic radar systems covered a range of around one kilometre, but required a transmit power of 1000 watts. This points to a substantial efficiency and performance potential of the new technology.
Extensive research still required, with clear application potential
Extensive research is still necessary before the system can be used routinely in maritime search and rescue: the system must be integrated into ship navigation systems, interference must be minimised, and it must be ensured that the system operates reliably over the long term under harsh sea conditions. Nevertheless, the results obtained so far clearly demonstrate that SEERAD has the potential to sustainably enhance maritime safety and significantly support rescue operations.