Countering the underwater drone threat

In this edition of The Watch, we talked with Simon Goldsworthy, Global Business Development Manager at our technology partner Wavefront Systems, about the latest advances in intruder detection technology.

The current conflict in Ukraine has highlighted the disruptive effect of drones. It’s shown that a rogue squadron of uncrewed systems can pose an asymmetric challenge to any harbour or ship. In the right hands, the damage can be significant. To date, airborne drones and uncrewed surface vessels have shown their ability to penetrate conventional defences. Though difficult to counter, they are anything but covert. Sinking below the water’s surface, the autonomous or unmanned underwater vehicle, takes advantage of the waters cloaking to pose a much more significant threat. Programmed from afar, these systems can follow a predetermined course and remain underwater for long periods, making them invisible to radars and optical systems. Though more complex to manufacture, their proliferation and availability over the last decade makes them a viable threat accessible to many near-peer adversaries. As of today, it is relatively simple to program a flight path and equip the drones with multiple payloads, each presenting a different threat.

Needle in a haystack

When detecting targets underwater, the technology of choice is sonar: sound waves are transmitted through the water and the reflections from targets can be used to detect and track them. Underwater drones, also known as autonomous underwater vehicle (AUV) systems or uncrewed underwater vehicle (UUV) systems, are challenging for sonar operators as they present a relatively small target. In a confined environment where the sound reflects from the seafloor, the sea surface or harbour walls and travels at different speeds through changing water column temperatures, the ability to detect these vehicles is no simple feat.

Our technology partners, Wavefront Systems, know how difficult this challenge is, they manufacture the world’s most deployed intruder detection sonar, Sentinel. This system was developed to detect and alarm when divers approach. Although divers are a challenging target, their speed, pattern of movement and equipment works against them. This weakness is exploited by Sentinel to keep customers safe across a myriad of environments whilst deployed from ships, on the side of a dam wall, on a seabed mounting or by expeditionary teams from RHIBs.

However, when Wavefront first looked at an AUV signature they realised a new challenge had emerged. AUV’s and UUV’s have much smaller noise signatures, can present a smaller target and travel at greater speed. Sentinel has always excelled at finding the needle in the haystack but with underwater drones, it was difficult to detect and then keep track of them at the ranges which we had become accustomed to when tracking divers.

Feel the noise

“Our R&D team are never happier than when they have a new challenge to defeat”, Goldsworthy recalls, “At the speed which AUV technology was being developed, we knew they were clearly going to become a threat to our customer base. Fortunately for us, AUV’s and UUV’s are machines with mechanical parts which is unfortunate for them, as we can listen out for their telltale systemic noise. We filed for a patent to enable us to combine Simultaneous In-band Active and Passive Sonar to track underwater targets, a technology we refer to as SInAPS®. That’s the story behind Sentinel 2. The results have been better than we ever hoped for.”

Merging active data returns, with the passive track provides a substantial performance improvement, especially so when active returns are weak and infrequent. We conducted early trials against one-person portable UUV’s which demonstrated the capability. Since that time, several trials have been conducted against different UUV’s of varying sizes and mechanical construction. Sentinel 2 can find more drones with small to medium vehicles commonly detected at distances of over 500 m. This means more time in which to plan your response.

Simple to operate

“Say you’d like to protect a vessel alongside, the Sentinel sonar head can be deployed on a tripod from the vessel itself, from a RIB or other small boat. The sonar system is lightweight and portable, weighing less than 35 kg. It can be connected to a topside portable computer system to run the user interface. In addition, sonar performance indicator (SPI) software allows the operator to take a local environment probe of the seawater to assess the expected perimeter of protection of the Sentinel wherever it is being operated.” Goldsworthy also said, “The Sentinel sonar system can also be deployed by cable, without a tripod. We provide a weighted plate that can be fitted to the bottom of the sonar to maximise its stability in the water. No calibration is needed. It can be turned on and used instantly, giving the operator an immediate view of their surroundings.”

Reporting to your chain of command

“Sentinel offers a user-friendly interface designed for non-sonar operators to use. It can be set up to show all detections within the sonar range or to show only the critical threats. The information is colour coded and an audible alarm is triggered for the end client. The system is automated and can output to leading command-and-control systems through simple application programming interface.” Goldsworthy adds,” Consider this: the sonar system generates thousands of signals from the sea floor, rocks, other vessels, pier legs and anything else in the underwater environment. Sentinel then uses active and passive detection algorithms to filter out the signals that are not from divers, subsea vehicles, or AUV’s. The remaining signals are then classified as critical or non-critical for the end user. With now fifteen years of experience delivering the world’s most deployed intruder detection sonar, we understand how important it is to report the correct data.”

Every ship can be equipped with the means to counter underwater drones today

“We have trained hundreds of users and are able to accommodate different levels of ability. From maintenance to operations, we can cater for multiple trainees and all we want from your team is a handful of days. We can even train your trainers if required.”

Please contact Forcys to find out more.