Forward Looking Sonar Can Improve Collision Avoidance

Marine Electronics and Communications

A new style of 3D sensor hopes to do for sonar technology what radar and GPS has done for surface navigation

Many different types of marine sonar are in use today. Some use one narrow, downward-looking beam, such as depth sounders and fish finders. Others only see a narrow slice of water. Examples of such 2D systems include sidescan sonar and small craft navigational sonars. Effective obstacle detection and avoidance, however, requires continuously updated range, bearing, and depth information on all of the underwater hazards in front of a ship.

Unlike 1D and 2D sonar systems, FarSounder's innovative 90 degree forward-looking sonar displays a 3D underwater map updated every two seconds, and provides mariners with a major advance in obstacle avoidance and navigation technology.

The simple 1D echo-sounder, also known as a depth sounder, only tells the user how deep the water is directly below the sounder. Basically, it draws a picture of where the user has traveled, but does nothing to warn of obstacles that may lie ahead.

Moving beyond 1D, there are forward-looking 2D sonars, which provide the user with two of the components needed: range and bearing. They do not provide depth, and in shallow water, they do not provide navigationally useful information. By definition, shallow water means that there is a bottom that a mariner needs to know about.

With these systems, the user is told that there is bottom everywhere. They may let him know that there is something ahead, but not necessarily that he will hit it. Some manufacturers have tried to overcome this limitation by rotating the system 90 degrees; however, this creates a single, narrow vertical slice, giving range and depth but not bearing.

By contrast, FarSounder combines all three navigationally significant components - range, bearing and depth - in a real-time view of the whole volume of water ahead of the ship, with easy to interpret colour mapping revealing uncharted obstacles such as rocks, and possibly the occasional basking whale. Also, by creating 3D images of flotsam and jetsam floating in or under the water, it can help reduce collisions with hundreds of partially submerged containers that fall off cargo ships each year.

Such a product might have come in handy for Empress of the North, a cruise ship that ran aground off Alaska last year. It might also have warned Queen Elizabeth 2 about the uncharted shoal off New England that damaged its keel in 1992. It may also have saved Explorer from sinking in November last year after that ship struck ice off Antarctica. Therefore, it is unsurprising that cruise operators have shown a keen interest. In fact, to-date, four cruise ships have been retrofitted with the system, including vessels that regularly navigate icy waters.

Besides creating a 3D image with a single ping, FarSounder's technology distinguishes itself as a shallow water sonar system with its impressive water depth performance and its ability to detect objects in shallow water even beyond its water depth limit. To best understand how FarSounder's technology is able to operate so well in shallow water, it is necessary first to understand the metrics used in shallow water sonars.

There are two important metrics used when discussing the range of a forward-looking sonar: maximum range, which is the farthest distance at which the system can detect targets under ideal conditions, and water
depth performance, which is how far ahead bottom depths can be mapped as a multiple of the depth of water below the transducer. As an example, if a double water depth sonar system is operating in 15m (50ft) of water, that system can generate bottom maps out to 30m (100ft).

FarSounder's technology operates up to eight water depths. Beyond that, the sonar may not be able to determine the actual depth of the target, but can still alert the user to potential risk objects. These attributes make the system attractive to specialized vessels operating in poorly charted areas, carrying out salvage operations or even on search and rescue missions; it can also be useful for standard vessels approaching ports or carrying out other slow maneuvers. Product sales manager, Ian Bowles, says that it could also be of interest to maritime authorities as a tool for security applications, perhaps to detect intruders such as terrorist divers.

Yet, despite its performance, the system's range is currently limited to 0.25-0.5 nautical miles. However, Captain Bowles is confident that this will change, since the company has recently been awarded a US$2 million government grant to develop a 2 nautical mile range version that can work at considerably higher speeds, even up to 35 knots. He hopes eventually that FarSounder will do for sonar technology what radar and GPS have done for surface navigation.