Washed up whales on beaches are a stark reminder of how damaging sonar is to their systems. Whale stranding happen due to whales being confused by sonar from ships and submarines which in turn meddles with their own sonar leading them to beach themselves on the shore.
Whale unfriendly Sonar may soon have a competitor. A BBC report quotes Lori Adornato, a project manager at US military research agency Darpa, saying that we could detect submarines by paying more attention to natural sound than blasting out pulses of sonar.
“At the moment we treat all this natural sound as background noise, or interference, which we try to remove,” said Adornato to BBC. “Why don’t we take advantage of these sounds, see if we can find a signal?”
Persistent Aquatic Living Sensors (PALS), a project developed by her, snoops on marine life as a way of figuring out threats underwater. On the other hand, air-dropped sonar buoys which detect military threats underwater, have a limited lifespan due to battery life and only work for a few hours.
In comparison, the PALS system can cover a wide region for months on end. It could be a consistent way of monitoring and scouting underwater channels and coastlines. Adornato is of the opinion that reef-dwelling species that tend to stay in one place are most likely to be the best sentries.
“You want to make sure your organism always is going to be there,” Adornato told BBC. Pals is sponsoring a gamut of teams researching multiple approaches using differing reef species.
Laurent Cherubin is the lead researcher of the Grouper Guard team at Florida Atlantic University, working with goliath groupers. These fish, which can weigh up to 300kg (660lb), are common in US waters and produce loud calls to deter intruders. “It’s a loud, low-frequency boom,” Cherubin told BBC. “They are territorial and will boom at any intruder on their territory.”
The team focusses on alert calls from marine life akin to a guard dog barking. Categorising and distinguishing these calls are by no means an easy task, hence the team uses machine-learning algorithms.
Once perfected, these algorithms can be programmed into software which will run on tiny but powerful processor which can be mounted on underwater microphones or hydrophones.
Tapping fish conversations may seem crazy. By contrast the work of Ratheon’s Pals team looks much more like traditional anti-submarine sonar. It does, however, have a twist.
“We are trying to detect the echoes that are created when shrimp snaps reflect off of the vehicles,” said Raytheon scientist Alison Laferriere to BBC. “In much the same way that a traditional sonar system detects echoes from the sound that its source generates.”
“The signal created by a pistol shrimp is very short in duration and incredibly broadband,” says Laferriere. “A single shrimp snap is much quieter than a traditional sonar source, but there can be thousands of snaps happening per minute.”
According to BBC, Pals has completed the first phase, which was a feasibility study for the two different approaches of listening in on how reef species react to intruders, and snapping shrimp sonar. Adornato hopes to carry out field testing in 2023. After that, if successful, the technology would be transferred to users (initially the US Navy) for development into a production system.
