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Advances in Undersea Warfare
Dr. Frank Herr,
Head, Ocean Battlespace Sensing Department,
U.S. Office of Naval Research
This year marks the 70th anniversary of the U.S. Office of Naval Research (ONR), the U.S. Navy’s science and technology (S&T) directorate. Established right after World War II, the office began with a strong focus on undersea warfare (USW). Today, ONR’s program is broad and covers all facets of USW, including surveillance, search, localization, torpedo defense, environmental prediction and decision support.
During the Cold War, ONR was instrumental in the development of passive and active acoustic signal processing and sensors, including: technology to analyze narrow band lines produced by rotating machinery on submarines detected by the Sound Surveillance System (SOSUS) of fixed hydrophone arrays, circa the late 1960s; technology for flow noise reduction of towed hydrophone arrays enabling use at tactical speeds during the late 1970s to early 1980s; development of neutrally buoyant floats for oceanographic measurements, later incorporated into Directional Frequency Analysis and Recording (DIFAR) air-dropped sonobuoys, resulting in lowered noise and effective use of very low-frequency acoustic emissions of quiet submarines in the late 1980s; and the Long Range Acoustic Propagation Project (LRAPP) that collected data on acoustic propagation and underwater noise globally in the 1970s and 1980s.
Since the end of the Cold War, ONR has been developing signal processing and sensors effective in the shallow-water littoral environment and against ever more quiet submarines.
The Navy’s redesign of maritime patrol aircraft, the higher-flying P-8 Poseidon by Boeing, spurred ONR to develop hardware and software for the Multistatic Active Capability (MAC) family of air-dropped sonobuoys. Several technologies to support this change have been developed, including: flextensional transmitters by BAE Systems; multistatic processing by JHU/APL; remote ground stations by Signal Systems Corp.; and operational tactical decision aids (TDAs) by Metron.
As submarines become quieter, nonacoustic sensors become more important. The Automatic Radar Periscope Detection and Discrimination (ARPDD) signal-processing system was developed during the ‘90s by Raytheon, JHU/APL and the Naval Air Systems Command. Ultrasensitive He3 and He4 magnetometers were developed during the ‘90s and ‘00s for underwater and airborne applications by Polatomic, together with automatic magnetic noise cancelation and signal-processing algorithms by Dynamics Technology Inc. and Raytheon.
Now, primary opportunities involve advances in big data analytics and autonomy to enhance signal-processing and sensing capabilities, including sensing the marine environment. Deciphering signals from ocean clutter and noise has assumed new relevance and importance because of advances in machine learning.
While we are approaching full automation of signal processing, emphasis is increasingly moving to information processing. Advances in materials science, particularly with piezo crystals that exhibit high strains, and embedded computing have produced increasingly sensitive and compact acoustic and nonacoustic sensors. Future emphasis will be on how to deploy these sensors against increasing threats from underwater vehicles and advancing submarine stealth.
Much has been learned about the undersea environment relative to Cold War operations and more recently in the littoral regions. Still, much is left to learn as the dynamic marine environment changes and relatively unexplored regions gain importance as threats change. We also need to update knowledge, particularly in the North Atlantic, where a generation has passed since we engaged in intensive investigation of its acoustics.
Looking forward, signal processing and sensor development will continue, but emphasis will expand to include information processing and means of deploying effective automatic and autonomous anti-submarine warfare systems over wide areas and in difficult environments. TDAs will be developed to recommend patterns of asset deployment automatically for a wide array of missions, and mission planning for unmanned vehicles will expand the capacity of our assets.
Finally, environmental measurements will extend to the changing Arctic and the Indian Ocean, emerging as potentially important locations of future USW.