Synthetic Aperture Sonar on Unmanned underwater vehicle (UUVs) and AUVs is transforming Mine Countermeasures and Undersea Warfare

SOund Navigation And Ranging or SONAR is a technique of distance measuring between detector and an object base on sound reflection. The distance can be calculated from propagation time and speed of sound in specific mediums. For military, Sonars are the eyes and ears of ships or submarines in water used to detect, locate and identify objects in water. They are used for underwater navigation, especially by submarines and surveillance.  Sonar systems can also be used to realign inertial navigation systems by identifying known ocean floor features.

 

One of the evolutions of modern sonar is synthetic aperture sonar (SAS), which allows for much higher resolution images than traditional sonar by combining different acoustic pings. Active synthetic aperture sonar (SAS) is a powerful imaging technique that coherently combines echoes from multiple pings along the trajectory of a survey path to construct a long virtual array of hydrophones, which are microphones designed to be used underwater for recording or listening to underwater sound.

 

SAS technology  has potential in  many underwater imaging applications including offshore energy, seabed surveying, marine archaeology, debris mapping and search and salvage operations. Synthetic aperture sonar mounted on an autonomous underwater vehicle can be efficient  tool for  deep ocean mapping  of seafloor massive sulfide deposits generated by hydrothermal systemssuch deposits.  The fine resolution and
large areal coverage possible with SAS enables highly efficient mapping of the seabed with a resolution sufficient to determine the location of active and extinct hydrothermal systems.

 

Mine hunting in particular is an area where SAS promises to solve the inherent problem of covering a large area in a short time – with ­sufficiently high resolution to allow detection and classification of small, low-signature bottom mines. We have capable adversaries with equally capable mines, which can be planted very deep or in such a way that they’re camouflaged. Raytheon is really focused on, in particular, advancing the synthetic aperture sonars that we produce in order to be able to find these very difficult targets.

 

For some time, SAS was not practical because of the limitations associated with enabling technologies, such as underwater platforms, suitable motion measurement instrumentation, accurate motion estimation techniques, and the storage and processing components needed to meet the computational requirements associated with SAS beamforming. This has changed over recent years and SAS systems are now being fielded in a wide range of military and commercial applications such as geological mapping, telegraph and pipeline surveys, environmental remediation, marine salvage and archeology and mine countermeasures. Synthetic aperture sonar technology is currently commercially available from multiple vendors including Kongsberg Maritime, Kraken Sonar Systems and Raytheon.

 

Northrop Grumman demonstrated its  seabed warfare capabilities at U.S. Navy’s Advanced Naval Technology Exercise (ANTX) in August 2018  in Newport, Rhode Island. A central part of this demonstration was Northrop Grumman’s µSAS and real-time automated target recognition technologies. The µSAS is a low size, weight and power, high-performance payload that can operate off a man-portable autonomous underwater vehicle for real-time classification of mine-like objects. The demonstration showed how we can operate that level of μSAS from a man-portable AUV, company officials said. This data was then relayed to a ground control station comprising five displays, EO cameras, situation awareness tools, and advanced human-machine control software to manipulate the various unmanned systems.

 

“This technology is an example of leveraging digital transformation to rapidly provide software defined, hardware enabled capabilities to the fleet,” said Alan Lytle, vice president, undersea systems, Northrop Grumman. “Integration of unmanned and autonomous capabilities into the battle space reduces staffing required to conduct operations and risk to personnel, while supporting our nation’s continued undersea superiority.”