Pulse news magazine

Volume 23, September 2018

Innovating for Undersea warfare

Electronic Systems has applied its expertise in ocean systems to the challenge of designing and building technologies that project and receive acoustic signals clearly
As the U.S. Navy Submarine Force conducts operations in the dark depths of the oceans, they need to find a way to communicate, navigate, detect objects of interest, and generally maintain situational awareness.

Radio waves do not penetrate the ocean surface and light does not travel far in the ocean. So, without access to light and radio, submariners rely on acoustics. However, the underwater environment introduces a set of challenges that degrade acoustic signals – including a multitude of manmade and natural sounds, and complicated environmental conditions introduced by temperature, salinity, and surface motion that affect sound wave stability and the reliability of travel paths. For more than 40 years, Electronic Systems has applied its expertise in ocean systems to the challenge of designing and building technologies that project and receive acoustic signals clearly.

In the late 1990’s, ES’ research and development business helped the U.S. Navy gain significant advantage in antisubmarine warfare by creating the most-powerful transducer array in the world, which the T-AGOS Ocean Surveillance Ships tows to detect enemy submarines.

“The system is critical to national defense. It provides the Navy with the capability of detecting quiet submarines at long ranges” said Mike Houle, director of Maritime Sensors of ES’ C4ISR Systems business. “The need for active sonar capabilities is increasing as our near-peer competitors continue to get quieter in the undersea domain.” However these powerful transducer arrays are large and heavy.

As the Navy begins to embrace unmanned undersea vehicles (UUVs) for existing and future missions, ES’ FAST Labs research and development business is tackling the challenge of maximizing signal power in smaller devices.

“Our transducers have significantly higher power density than other transducers on the market. That is, they take up less space on a small vehicle, and put out more powerful signals,” said Geoff Edelson, technical director of the Maritime Systems & Technology R&D directorate. “Depending on our customers’ mission needs, we create the right balance of size and power.”

To meet the Navy’s growing need for undetected undersea communications, the R&D team is also creating enabling technology that permits reliable communication while minimizing the probability of being detected by adversaries. This requires exceptionally effective waveforms and associated signal processing that are able to process signals that are, themselves, well below the ambient noise.

“Above the surface of the ocean or on land, there are fewer things in the environment that complicate or redirect a signal’s propagation. However, in the ocean soundwaves interact with the ocean surface and bottom, and with the ocean volume that send the waves along different pathways that change over time. For example, they reflect off of hard ocean floors, are scattered by sandy bottoms, and are absorbed by muddy sediments,” Edelson said.

“The processing is complex in that you have to plan for and track both the direction and the timing of individual signal arrivals at the receiver. These signal features create very interesting, difficult problems to solve.”

With recent advances in signal processing, transducers, and UUVs, customers are now seeking more than just individual acoustic equipment components in the R&D space. They need systems to enable capabilities like acoustically-aided navigation and coordinated communications to or between multiple undersea vehicles.

Modern adversary submarine quieting technology challenges passive anti-submarine warfare sonar detection range and performance. BAE Systems researchers are designing breakthrough capabilities for extended range submarine detection and precision target tracking through collaborative operations using unmanned vehicles and active sonar techniques.

Also, given that RF signals of the Global Positioning System (GPS) do not penetrate water to any useful depth, effectively denying undersea GPS, the FAST Labs team is participating in the development of an undersea system that provides omnipresent, robust positioning from ocean basins. When successful, an undersea platform would be able to obtain continuous, accurate positioning without surfacing for a GPS fix by ranging to a small number of long-range acoustic sources.

“For these, and other customer system needs, there are also opportunities for technologies that BAE Systems has produced for ground and air operations, such as advanced sensors, cyber resilience, and autonomy, to be adapted to undersea applications,” Edelson said. “As mission needs grow and evolve, ES can draw on a diverse technology product portfolio to help craft integrated solutions.”

Barb Driscoll, Communications, Merrimack, New Hampshire

THE TECHNOLOGY  - Transducers and arrays

A sonar (Sound Navigation and Ranging) transducer is an electromechanical device that puts sound in the water much like a speaker puts sound in the air – pushing the water to create sound pressure waves that propagate through the ocean. The receiving transducer senses the wave and converts it to the appropriate electronic signal.

To detect other objects in the water such as enemy submarines, the sonar transducer produces sound pressure waves that, when reflected off other vehicles, reveals their locations.

Arrays are groups of these transducers arranged in a pattern for collecting and processing soundwave signals.