Ukrainian acoustic sensor network: The innovative approach against Russian drones

General James Hecker is the leader of NATO's Allied Air Force Command, and also the commander of the American air forces in Europe and Africa (United States Air Forces in Europe - Air Forces Africa). At the recent AFA Warfare Symposium, this American military officer showcased a singular solution to the problem of drones utilized during the war by Ukrainians.

According to The War Zone quoted by Gen. Hecker, a vast network of acoustic sensors, constructed from several thousand stations and making use of smartphones and directional microphones, serves to aid Ukrainian "drone hunters".

With the help of thousands of dispersed sensors, it becomes feasible to detect and monitor numerous objects, even those flying at very low altitudes, to evade radar detection.

An effective response to such a threat is a dense network of stations, equipped with acoustic sensors that can detect - even in the dark - low-flying Russian drones. This is possible because even small drones with less powerful engines, such as the Shahid-136, generate significant noise.

This permits effective detection of passing objects, plotting their routes, and dispatching alerts to drone hunters' smartphones. Gen. James Hecker does not detail the exact methods the Ukrainians utilize.

However, he mentions that a popular means of communication for issuing alerts and coordinating anti-drone operations is the Telegram platform, widely used amongst Ukrainian volunteer drone trackers.

While the media typically focuses on visually striking weaponry, such as the Flakpanzer Gepard or Skynex, as Gen. Hecker highlights, the backbone of the Ukrainian anti-drone defence system comprises mobile, makeshift clusters of "drone hunters".

Their arsenal includes a variety of lightweight vehicles, and they engage drones primarily with adaptively fitted firearms of diverse sorts, like machine guns or - more infrequently - small-calibre automatic cannons.

A prime example is the usage of obsolete Maxim machine guns to counter drones, which, due to their intense firepower, prove to be an efficient weapon.

Equipment also includes night vision and thermal imaging scopes, laser indicators, and searchlights, enabling the detection and elimination of targets in the dark.

Ukrainian experiences emphasize discovering the most economically viable solutions, enabling kamikaze drones to be efficiently counteracted using appropriate methods without the need for sophisticated, complex, uncommon, and costly weapon systems.

All these experiences provide invaluable knowledge. As Gen. Hecker points out, detailed information about constructing a dispersed network of acoustic sensors has already been presented to decision-makers, including those from the U.S. Missile Defense Agency. The analyses aim to establish whether and how NATO may use the information gathered in Ukraine.

It's noteworthy that detecting flying trespassers with microphones, or - more broadly - diverse types of acoustic sensors, is an example of history repeating itself. Before the advent of radar, early warning systems functioned exactly in this manner.

In the early days of aviation development, when it was a challenge to locate aircraft flying, for instance, above a layer of clouds, sound detection devices turned out to be the solution. These came in multiple forms - from portable devices worn on human heads to gather sounds to larger devices fitted onto vehicles and even to substantial, several-yard concrete structures.

Perhaps the most spectacular example of such a solution is the "sound mirrors", erected in the 1920s and 30s in the UK.

The inventor of this solution, William Sansome Tucker, was a British physicist who, during World War I, was assigned to the Experimental Sound Measurement Station.

This institution researched sound propagation, aiming to develop early counter-battery systems. These were based on recording artillery shots via a network of stations: the discrepancy in the time each station recorded the shot enabled the location of enemy artillery positions.

This system was also adjusted to detect incoming aircraft. In addition to various types of mobile listening posts, permanent infrastructure was constructed. Some facilities - like the RAF Denge station - have survived to the present day, forming large concrete structures that reflect and amplify sound waves.

Work on enhancing sound mirrors ceased in the 1930s, and radars gradually replaced them.