Swimmer Detection

Written by Tom Marlowe

The terrorist attack on the city of Mumbai, India, at the end of November 2008 demonstrated a need to protect waterways and ports from threats approaching from above or under the water. Suspected terrorists entered the city from an inflatable RIB boat, but they also could have approached individually by swimming underwater.

The U.S. military has long been aware of the challenge of dealing with the threat posed by individual divers hostile to U.S. assets, but it hasn’t been until recent years and advances in computing power that units small enough to detect such divers have become practical. The U.S. Naval Undersea Warfare Center (NUWC) Division, based in Newport, R.I., has been focused over the last year on fielding an integrated solution to detect and deter divers from attacking sensitive assets.

Last September, NUWC demonstrated its Integrated Swimmer Defense (ISD) System, designed to provide harbor security and vessel protection. The complete system uses a combination of sonar, radar and optics along with infrared sensors to detect the approach of hostile swimmers on or under the water.

“Once we’ve detected these threats, we have to do something to engage them because their mission is to destroy the high-value asset,” said James Pollock, director of Homeland Defense Programs at NUWC Newport in a statement. “The underwater sensors are typically active sonar devices that put acoustic energy out into the water. That energy is reflected back off of all the surfaces that are out there. We then process the information and take action.”

A NEW APPROACH

The Navy’s ISD system utilizes the Sentinel sonar system developed by Sonardyne Inc., which has a global headquarters in Yateley, England. Sonardyne successfully detected swimmers and divers at a long range, providing the Navy with information to deter hostile individuals arriving via the water.

Nearly three years ago, Sonardyne assembled a team of professionals from other companies involved in detecting swimmers via sonar to examine the problem from the ground up, Eric Levitt, Sonardyne’s business development manager for maritime security, told Special Operations Technology. Sonardyne, long involved in underwater acoustics for positioning operations on the ocean floor, saw the need to go outside existing sensors and hardware to tackle the threat of underwater swimmers.

The result was the Sentinel system, Levitt said. It’s a small, portable, easy-todeploy system that requires only one man to carry it. Operators can lower it over the side of a boat or put it on a tripod on the seafloor in a port and let it go to work. “It has ranges equal to or better than any of our competitors and a very significant target tracking capability,” Levitt declared.

Competing systems might cost from $700,000 to $900,000, Levitt estimated, but Sentinel is only about $270,000, providing a much more economic means of addressing the swimmer threat. While other sensors systems weigh 300 to 800 pounds, the Sentinel sensor weighs a mere 70 pounds.

Sentinel works much like any other sonar device; it pings then listens for a result. The small system then performs analytics that would have been impossible for a system of its compact size 10 years ago, Levitt described.

“Underwater environments are very complex,” Levitt commented. “There is so much else going on with sonar that you have to compensate for likely daily changes in water temperature and tidal changes. All of that affects the performance of the sonar. We take all of those factors into account. Using our patented technology, we have employed that level of processing with Sentinel to get the results that we get.”

Sentinel is pretty much ready to work out of the box, he added, but operators must determine how to best position the system to get the results they seek. They may place it at the end of a pier, hang it off a ship, or place it on a sea floor. It can sit in a fixed location or ride on a trolley. The Sentinel system comes ready for any of these applications.

Operators also could network Sentinel systems together to expand their range and to feed the information into a central command and control station. Sonardyne had demonstrated a network of 10 units. They communicate with one another and ping simultaneously. Using several units in conjunction is ideal for protecting an asset like an aircraft carrier in dock or at anchor, Levitt noted.

Sentinel alone provides only swimmer detection. Sailors, once they detect hostile swimmers, could then turn them back with powerful air guns or with an underwater announcement. Sonardyne has just unveiled a sound system that connects to Sentinel for making underwater announcements to approaching divers.

“That confirms a threat’s intent,” Levitt remarked. “If you announce underwater that it is a restricted area and the swimmer keeps coming, then you know this is really a hostile threat and not someone out snorkeling or scuba diving.

“So we have incorporated an underwater hailer as an attachment to the Sentinel head. It is a speaker that plugs directly into the sound head and we can now broadcast that message from the sound head. So if the sound head is 300 meters offshore on a tripod, we can attach the speaker to the tripod, and now we have dual capability for alerting a target. Now it’s all in one system as opposed to having another system with different cabling and telemetry into a loudspeaker,” he added.

The company also plans to add blue force tracking capabilities so operators can distinguish friendly divers from hostile divers. The Navy plans to use the system, and private clients can order it as well, Levitt revealed.

“Say you have a mega-yacht that is anchored out in a bay and your boss is out there swimming around and you see another target,” he said. “If you have blue force tracking on, you know who is good and who is not. Then you can redirect your people. We can send a text message under water now as well to say you have a threat 200 meters behind you that we are picking up. That is all technology that is coming on line early this year.”

TIERED SECURITY

The Office of Naval Research (ONR) is working with other technology providers as well to explore alternative technologies. For example, ONR has funded QinetiQ, based in Farnborough, England, to produce a smaller, lighter and less expensive version of its Cerberus diver detection sonar.

Cerberus currently is a device slightly larger than an oil drum in size. It can detect underwater intruders at a distance of about 700 meters on a 360-degree axis, Chris Brook, QinetiQ’s maritime sonar business lead, told SOTECH. Cerberus also has the flexibility to be placed off a boat or on a seabed. The idea is to place it in shallow water in a chokepoint or a sensitive area to maximize its effectiveness, Brook noted.

QinetiQ began developing Cerberus in 2003 in the wake of the 9/11 terrorist attacks on the United States, Brook recalled. Several nations and companies began asking QinetiQ if it could start helping them with protecting their ports and vessels. Although the 9/11 attacks occurred through an air attack, military and private officials recognized that another successful attack could occur via water as well.

In such situations, QinetiQ recognized the need to react quickly, so it developed a simplified display for Cerberus that is very simple by default. Military officials or technically savvy individuals can change the display for a more complicated readout, but the goal of the system is to provide easily understood information for rapid response. About half of QinetiQ’s customers use it in the simplified display, designed for easy reading and comprehension by security guards on patrol.

Once Cerberus detects divers approaching, it then tracks them. Operators can use a tracking mode to follow the direction and speed of swimmers as they approach their targets. Given this information, the operators can react with confidence and deal with hostile swimmers in an appropriate manner, Brook said.

Hostile swimmers of course may approach their targets above or below the water, so Cerberus is typically deployed in combination with a small surface radar. It is often more useful to detect the small boat that is dropping divers off at a distance before detecting and tracking the individual divers, Brook acknowledged.

“A lot of security involves tiered effect,” Brook explained. “It’s no good having one layer of physical security to protect something. You need to have multiple layers of security acting standoff so that you can track insurgency from land, sea or air, above and below, at varying degrees. It’s no good necessarily knowing that you have somebody at the 700-meter mark if your surface radar didn’t pick up the launch vessel at 10 kilometers out. You tie the two together.”

Special operators can carry Cerberus with them from location to location, Brook noted, because its small size allows it to be portable. Cerberus also has networking capabilities available through an Ethernet connection. Operators can connect the unit to a central command center to track sensor feeds from several different sources.

Cerberus is in use worldwide on several different continents, but Brook could not reveal exactly where due to the sensitive nature of operations connected to its use. It is completely operational and providing vital information to the nations that have deployed it, he observed. Cerberus is extremely durable, enabling it to provide continual information for long periods. One customer has deployed it on a seabed for about eight months or so as of press time, and it continues to provide information upon demand.

COMPREHENSIVE SOLUTIONS

Some systems offer integrated options so that military forces need not deploy companion systems for swimmer detection. In the case of the technologies discussed so far, operators may resort to separate radar systems to detect swimmers and other threats approaching on or above water.

Not so with the Vessel Image Processing System (VIPS) available from Stratech Systems Limited, headquartered in Singapore.

VIPS was developed to provide an all-in-one solution that overcomes the weakness of other options, Dr. David K.M. Chew, Stratech Systems’ executive chairman, told SOTECH. VIPS can detect both vessels and swimmers, above and below water.

“Stratech recognizes that there is an emerging demand for next-generation coastal/waterway surveillance system for vessel traffic management as well as enforcement of safety and security regulations and standards,” Chew explained.

“The prevalent solutions in the market are non-vision based; for example, the radar-based systems and Automatic Information System, where there are limitations to be overcome to further improve safety and security at coastal waterways. For example, existing radar-based surveillance systems have limitations such as blind spots, limited resolutions, and a lack of an accurate and factual visual image of potential threats.”

For vessel tracking, VIPS acts as a comprehensive and accurate waterway surveillance system, which provides a cost-effective alternative to radar and AIS systems for small vessel containment areas like fisheries, ports, harbors and marinas, Chew asserted. Working alone, VIPS can provide surveillance from 5 to 10 km.

VIPS can also cooperate with radar and AIS systems for surveillance at ranges greater than 10 km. The system employs “intelligent vision” technology and integration with radar and AIS to automatically detect, identify, track and predict vessels’ path in real time. It has intelligent algorithms to provide static information such as length, height, name, shape, vessel classification, as well as dynamic information like latitude, longitude, velocity, heading and time, Chew explained.

For swimmer detection, VIPS incorporates advanced underwater sonar to detect underwater threats. The sonar offers excellent underwater threat detection capabilities even in shallow waters. It has an extended range of up to 2,000 meters.

VIPS was developed and tested, in collaboration with Maritime and Port Authority of Singapore (MPA), in 2001. The version developed for MPA includes features like using vision-based technology to perform real-time detection and tracking of vessels, measuring position, speed and course of vessels. Stratech is marketing VIPS to potential clients globally—targeting offshore nuclear plants and refineries, hydroelectric dams, sea border stations, and military installations. “We believe that there is tremendous demand for VIPS due to the rapid buildup and expansion of port facilities in the world, as well as global emphasis on security,” Chew concluded. “VIPS has the ability to set the trend for next-generation coastal and waterway surveillance, which overcomes the challenges faced by prevalent technologies.” ♦