More Effective Anti-Submarine Warfare with Unmanned Craft
(Source: Swedish Defence Matériel Agency, FMV; issued March 14, 2013)
(Issued in Swedish only; unofficial translation by defense-aerospace.com)
Underwater vehicle AUV62 can be launched from ships, submarine and from land. It has found both mines matching known mechanical resonances and drowned people who hadn't been located by divers.
It is currently being tested in the submarine hunting exercises by the armed forces, but there may be even more uses for FMV’s unmanned submersible AUV62.
“Flying drones playing an increasingly important role in conflicts around the world. But unmanned craft could be at least as important under the surface,” says Carl-Johan Andersson, a development engineer at FMV.
The craft developed by FMV, FOI and Saab has the form of a heavy torpedo and can therefore be used from a submarine. The system is modular, and today there are modules for minehunting and submarine-hunting operations.
For minehunting, AUV62 is equipped with a so-called synthetic aperture sonar. The technology is based on the system accurately keeps track of how the craft moving in the water in all planes, and then takes account of it when the image of sonar echo is calculated. In this way, the AUV can give a resolution of 5 inches at distances up to 200 metres.
"There is no other technology that can map the ocean floor in the same resolution as fast as synthetic aperture sonar,” says Carl-Johan Andersson.
Another advantage of minehunting is that the system is unattended and takes care of itself. Minehunting ships can work as usual with clearing while the AUV independently finishes mapping a different area on the side. When it is finished it will return to the mother ship and report on what it found on the bottom.
“In this way, Minehunting operations become more efficient while also becoming safer for staff, since their ships do not have to come close to the mines,” says Carl-Johan Andersson.
During submarine hunting exercise, AUVs could behave like a submarine, both by its sonar echo and its noise. When used as a target during anti-submarine warfare exercises, it transforms the ping the chasing sonars transmit so that they sound like when detecting a submarine. In addition, it can make noises like a submarine. In this way, the cost of training is reduced because crew training no longer requires a real submarine.
“Unmanned underwater vehicles are a new world for the armed forces. Now, we have tested minehunting and submarine hunting exercises, but for other potential uses is to allow yourself to look for submarines or monitor surface modes,” says Carl-Johan Andersson.
Because AUVs has the same format as a heavy torpedo, they can be both launched and recovered via a submarine’s torpedo tube. It may also be possible to use AUV62 for electronic surveillance capabilities.
“One can take significantly higher risks when you don't involve personnel.”
Today AUV62 can run 20 hours at a speed of 4 knots. One possible vision for the future is to replace batteries with fuel cells and get significantly longer endurance. Then the craft could leave harbour in underwater mode along with the mother ship.
Defense and offshore industry
Contractor Saab has recently completed a first contract for AUV62 and more deals are pending. Customers include both various countries' militaries and the offshore industry, in which the main use is the inspection of pipelines and of other fixed ground installations.
“The trend is to go to unmanned systems, both in the air and underwater. Partly because it is cost-effective, but also to reduce the risk to personnel,” says Bo Rydell, responsible for business development and strategy at Saab's underwater activity.
“The Swedish Government and the armed forces have driven the development of technology and created this capability in Sweden. At the moment, we are testing and trying to work out how to exploit the system operationally, beyond the initial point of view,” says Bo Rydell.
FACTS: AUV demonstrator
-- Length: approx. 6, 5 m.
-- Diameter: 53 cm.
-- Weight: approx. 1250 kg depending on configuration.
-- Speed: max 5 m/s.
-- Propulsion: electric motor coupled to a pumpjet propulsor.
-- Batteries: Lithium Polymer
-- Action time: depending on the mission profile, maximum of ca. 20 h.
-- Navigation errors: 1–3/ooo of distance under water, as well as GPS accuracy (18 feet 4 inches).
-- Communication: Selectable between LAN, WLAN, UHF radio, Satellite, Hydroacoustics.
FACT: Explosive waste in the Baltic Sea
At the bottom of the Baltic Sea lie about 150,000 landmines from World War I and World War II. In addition, there are thousands of tonnes of dumped munitions and other waste. Most of it is in bad condition. New infrastructure construction such as gas pipelines can also be interesting to inspect.
FACTS: Minehunter with synthetic aperture sonar
Synthetic aperture sonar uses your vessel's speed and powerful computers to simulate a 30-metre antenna. When the vessel is moving at 4 knots 20-25 metres above the surface gives the system a 400-meter wide image, where each pixel is equivalent to 5 centimetres on the bottom. The high resolution enables the AUV to detect mines even in areas that are considered as unattainable.
FACTS: Anti-submarine Warfare Exercise
During anti-submarine warfare practice a corvette sends out a sonar ping. The AUV receives and sends back another ping, just as if it was a submarine. In addition, it can make a noise like a submarine if units want to practice to just listen.