COLOGNE, Germany — The German Air Force has begun testing so-called passive radar as a complementary surveillance technique for ground-based air defense formations, aimed at helping covert operations surprise adversaries.

Service officials want to find out whether the technology, which measures disturbances in the soup of commercial television and radio broadcast signals permeating crowded airspaces, can provide an “early cue” about approaching threats, German Air Force chief Lt. Gen. Ingo Gerhartz said in an interview with Defense News.

Passive radar works covertly because it measures aerial objects’ echos from existing radio waves and doesn’t itself pulse the airspace for threats. The use of passive radar still requires defenders to turn on their active radar, which exposes them to detection, but only for brief periods.

“Then you only have to go active for the shot itself,” Gerhartz said, referring to active radar guiding an interceptor missile to a target.

The system in question is called Twinvis, made by sensor specialist Hensoldt. Defense News reported in June 2022 that the company was expecting to sell a small number of these systems to the air service, with money from a €100 billion (U.S. $105 billion) special military fund created by the German government after Russia launched a full-scale invasion of Ukraine in February 2022.

A company spokesman confirmed that a system is now under contract.

Passive radar technology has existed for decades, but only recent advances in sensing and signals processing have made it usable in real-world operations, Hensoldt has said.

Experts liken it to a hunter observing an animal move through dense reeds. While the exact type of prey may remain unknown, the position information is crucial for the hunter closing in.

The German Air Force’s expectations around passive radar come in the context of observations from the battlefields of Ukraine, where neither Russia nor Ukraine have been able to establish air superiority because ground-based defenses are so effective.

The term air superiority refers to the ability to deploy aircraft uncontested, which analysts consider a prerequisite for victory.

Germany has delivered several of the latest-generation IRIS-T SLM air defense weapons to Ukraine to help protect population centers from Russian drones and missiles. The system, made by Diehl Defence, is optionally available with Twinvis passive radar.

Sebastian Sprenger is associate editor for Europe at Defense News, reporting on the state of the defense market in the region, and on U.S.-Europe cooperation and multi-national investments in defense and global security. Previously he served as managing editor for Defense News. He is based in Cologne, Germany.

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