New era dawns in ASW as manned and unmanned submarines team for bistatic sonar

NEWPORT, R.I. — U.S. military researchers are asking two U.S. defense contractors to develop bistatic sonar for anti-submarine warfare (ASW) that teams manned and unmanned submarines and capitalizes on the benefits of active sonar without compromising the stealth of U.S. attack submarines.

Military researchers are developing bistatic sonar with manned and unmanned submarines to enhance sub-hunting capabilities.

Officials of the U.S. Naval Undersea Warfare Center (NUWC) in Newport, R.I., have announced a $4.6 million contract to the BAE Systems Electronic Systems segment in Merrimack, N.H.; and a $4.7 million contract to Applied Physical Sciences Corp. in Groton, Conn., for the Mobile Offboard Command and Control and Approach (MOCCA) program.

NUWC awarded the contracts in February on behalf of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va. MOCCA seeks to enable manned Navy submarines to use active sonar pings from nearby unmanned underwater vehicles (UUVs) to detect and track enemy submarines at long ranges without giving away their presence to potentially hostile vessels.

The project seeks to use UUVs as pingers and manned fast attack submarines as listeners to conceal the presence of the manned attack sub. Using this technology, the manned submarine could detect and target enemy submarines based on sonar returns from the UUV active sonar pingers.

Traditional active sonar bounces sound waves off submarines, surface warships, and other objects for detection and tracking. The problem with active sonar, however, is it’s like shining a flashlight in a darkened room: It can find objects effectively, but gives away its presence and forfeits any pretense of stealth.

Passive sonar, on the other hand, simply listens for sounds from enemy submarines or surface ships. It’s not as effective or as efficient as active sonar, but it preserves stealth and can keep the submarine’s presence secret from the enemy.

Bistatic sonar using sonar transmitters aboard a UUV and sonar receivers aboard nearby attack submarines, however, has the potential to gain the best of both worlds.

As long as attack submarine crews have precise knowledge of the position of the pinging UUV, they can detect the presence of enemy submarines based on sonar sound returns, and track their movements with accuracy. Moreover, attack submarines can keep their locations secret — if the enemy submarines don’t inadvertently receive acoustic signal returns from the attack submarines.

The DARPA MOCCA program seeks to develop active sonar solutions that will mitigate the limits of passive submarine sonar sensors, researchers say. The objective is to achieve significant standoff detection and tracking range by using an active sonar projector deployed offboard a submarine and onboard a UUV.

The submarine will need the ability to coordinate the operational functions of the supporting UUV. Thus, the program must demonstrate reliable clandestine communications between the host submarine and supporting UUV without sacrificing stealth.

The program is asking BAE Systems and Applied Physical Sciences to develop compact active sonar sources, signal processing, and secure undersea communications technology for an offboard UUV in support of ASW.

The first phase will last for 15 months and will involve preliminary designs for innovative sonar and communications concepts, as well as subsystem prototype demonstrations to validate design approaches.

The MOCCA program has two key technical challenges: an active sonar pinger small enough for UUVs, as well as signal processing, and a secure communications link to enable the host submarine to control the UUV at significant distances.

DARPA researchers are asking the two companies to build an active sonar with an active sonar projector small enough for UUV operations, and bistatic active sonar processing. This will involve developing high-output transducer materials, and a sonar projector that is as energy-efficient as possible.

Researchers want the ability to focus the projected acoustic signal in a direction of interest. The goal is to produce practical and flexible designs for the projector that can scale for several different UUVs and deployment options.

In addition to a small, power-efficient sonar projector, or pinger, researchers are asking the two companies to develop bistatic sonar processing advancements in reverberation and clutter rejection as well as precision localization capability. The host UUV is expected to be no larger than 21 inches in diameter.

The goal is to operate the system in bottom-limited acoustic environments, so projected sound will scatter and produce reverberation and signal loss. Scattered sound inadvertently may illuminate the host submarine and possibly compromise stealth, so researchers want detailed and accurate predictions of the acoustic environment to manage the sonar and potential exposures.

Researchers also need a secure and reliable communications link to provide positive control of a UUV and its sonar payload operating at a significant distance from its host submarine. The communications link also must be able to communicate information generated on the UUV back to the host platform.

An ideal link would have a low probability of intercept and of exploitation and provide high link reliability. The MOCCA communications link cannot degrade submarine stealth.

For more information visit BAE Systems Electronic systems online at www.baesystems.com, Applied Physical Sciences at www.aphysci.com, and DARPA at www.darpa.mil.