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Anti-submarine warfare (ASW) has always been a game of hide and seek, with adversarial states looking to adopt and deploy emerging technologies in submarine stealth or detection to give them the strategic edge. The advantage has shifted back and forth, but, on the whole, it has proved easier to hide a submarine than find one: the oceans are wide, deep, dark, noisy, irregular and cluttered. Sonar detection is one of the most important techniques for the detection of overwater and underwater vessels. But with the development of noise reduction and stealth material, the overall noise of some advanced warships is close to ocean background noise level, resulting in traditional sonar detection ability of this kind of “quiet” type ship have been on the verge of the limit.
The U.S. Navy is in process of developing a new, more rapidly deployable, fixed, persistent, deep water active anti-submarine surveillance system. This system would consist of large sonar arrays attached to buoys that ships could emplace in a particular spot in the ocean straight from inside a standard shipping container. This is just one part of a multi-tier effort that comes as senior naval officers continue to warn publicly about increasing worrisome submarine activity from potential adversaries, especially with regards to Russian subs operating more regularly off the coast of the Eastern United States.
On Feb. 19, 2020, the Office of Naval Research (ONR) issued a notice on beta.SAM.gov, the U.S. government’s central contracting website, asking for white papers detailing possible options to meet the demands for what it is calling the Affordable Mobile Anti-Submarine Warfare Surveillance System, or AMASS. ONR’s goal is to eventually develop a “persistent, deep water, active ASW [anti-submarine warfare] system that can detect new emerging threat submarines at extended ranges.”
DARPA under TUNA program developed a network of “radio relay mounted on sea buoy”, deployed from ships or planes, that are tethered together by fiber optic cables to create data network. These very-small-diameter fiber-optic cables will be able to last 30 days in the rough ocean environment, which is long enough to provide essential connectivity until primary methods of communications are restored.
Integrated Undersea Surveillance System (IUSS)
Tracking submarines across large areas of ocean remains a key challenge for ASW. Manned platforms have limited ranges, and while the US Navy’s passive sonar system, SOSUS, is still in operation in parts, it is geographically bounded and requires substantial modernization to detect today’s quiet submarines. This gap has been partially filled by modern acoustic sensor arrays like the fixed reliable acoustic path, but in relative terms these cover very small areas of ocean.
The Integrated Undersea Surveillance System (IUSS) is comprised of fixed, mobile, and deployable acoustic arrays that provide vital tactical cueing to ASW forces. IUSS provides the Navy with its primary means of submarine detection both nuclear and diesel. With the advent of submarine warfare and it’s impact on Allied forces and supply lines in WWII, the need for timely detection of undersea threats was made a high priority in Anti-Submarine Warfare (ASW). As technology of the time progressed, it was recognized that shore-based monitoring stations were the answer to the problem since they could be made basically impervious to destruction, foul weather, and ambient self-generated noise.
Since the early 1950s the Atlantic and Pacific oceans have been under the vigilence of the Sound Surveillance System (SOSUS), with long acoustic sensors (hydrophones) installed across the ocean bottom at key locations.With the development of quieter submarines and counter-tactics to evade SOSUS, newer technologies have been implemented over the years to “keep up with the threat”. Faster processors, higher capacity storage devices, and “cleaner code” has enabled the advancement of the art of locating undersea threats.
The Navy says that AMASS is intended as a supplement, not a replacement for “established Fixed Surveillance Systems (FSS) and Mobile Surveillance Systems (MSS).” The FSS refers to fixed deepwater passive sensor networks, the best known of which is the Sound Surveillance System (SOSUS). SOSUS, the first versions of which entered service in 1959, had already seen its military function diminished by the end of the Cold War and had become used increasingly for scientific research, a role that it continues to perform to this day.
Currently, the Integrated Undersea Surveillance System (IUSS) uses all of these advancements in the Fixed Surveillance System (FSS), Fixed Distributed System (FDS), and the Advanced Deployable System (ADS).The program has undergone a major transition from emphasis on maintaining a large dispersed surveillance force keyed to detection and tracking of Soviet submarines to a much smaller force that is effective against modern diesel and nuclear submarines in regional/littoral or broad ocean areas of interest. Work stations, enhanced signal processing, and modern communication technologies enable remote array monitoring, which reduces manpower costs and improves efficiency.
The MSS component refers to ship-towed passive and active sonar arrays, also known as the Surveillance Towed Array Sensor System (SURTASS). “SURTASS provides … long range detection [of submarines] and cueing for tactical weapons platforms or other vessels of interest,” according to the Navy. At present, the only ships equipped to employ the latest iteration of the SURTASS towed array, also known as the TB-29A Twin-Line Array, are the USNS Impeccable and the four ships in the Victorious class. Japan also operates three Hibiki class ocean surveillance ships, which are also catamaran types, equipped with SURTASS.
The FSS and MSS together, along with associated communications networks and other infrastructure, form the Navy’s Integrated Underwater Surveillance System (IUSS). AMASS is also only one part of a larger plan for a new family of Deployable Surveillance Systems (DSS). AMASS would fill the role of the DSS-Deep Water Active (DSS-DWA) component.
Active sonar systems, such as the kinds ONR is seeking for AMASS program, detect threats by sending out pulsed soundwaves and then listening for the echoes as they bounce off objects in the distance. Passive sonars, as well as other passive sensor systems, such as hydrophones, simply allow operators to listen for telltale sounds belonging to submarines below the water or ships sailing above. Some sonar systems have both active and passive modes.
The issue with active sonars is that, by emitting the sound pulses, they alert opponents to their presence, giving them the opportunity to attempt to evade or avoid detection. It also makes them easy to detect and therefore vulnerable to hostile action. It’s not clear how a persistent active sonar system might work in practice, but it could only activate when passive sensors detect an object of interest.
The Navy’s plans for the complete DSS family does also include a DSS Deep Water Passive (DSS-DWP) component, as well as a system that is “mobile” and can operate in both active and passive modes. In 2017, the Navy began work on a program known as the Expeditionary Surveillance Towed Array Sensor System, or SURTASS-E, which “provides a SURTASS passive capability packaged into ISO-Vans [standardized shipping containers] for mobilization on Vessels of Opportunity (VOOs),” according to official budget documents, which also cover various other work on sustaining and modernizing the IUSS, as a whole. As such, SURTASS-E offers greater flexibility in that it could be installed readily on various ships, but also does not feature the active sonar capability found on ships equipped with the standard SURTASS system.
Buoys
A buoy is a floating device and is used in the middle of the seas as locators or as warning points for the ships. It can be anchored (stationary) or allowed to drift with ocean currents. Mooring buoys are a type of buoy, to which, ships can be moored in the deep oceanic areas. A mooring buoy weighs more than the general type of buoys. Buoys are generally bright (fluorescent) in colour. The cable that connects the surface buoy to its anchor contains copper and fiber-optic wires for power and data communications from the surface to the seafloor. An array of solar panels and a wind generator on the surface buoy are used to generate power .
The mooring buoy is designed in a manner that there is a heavier weight located right in the bottom of the sea. This weight is like an anchor holding the buoy afloat in the water. A mooring buoy has loops or chains attached to its top that floats on the water. These chains are provided so that ships or boats can be effectively moored to them. The entire application of a mooring buoy works in such a way that the buoy is floating while the ships are moored to a very firm support without using the anchor system of halting a ship.
Navy also uses many kinds of buoys: Marker buoys – used in naval warfare, particularly anti-submarine warfare, is a light-emitting or smoke-emitting, or both, marker using some kind of pyrotechnic to provide the flare and smoke. It is commonly a 3-inch (76 mm) diameter device about 20 inches (500 mm) long that is set off by contact with seawater and floats on the surface. Some markers extinguish after a set period and others are made to sink.
Target buoy – used to simulate target (like small boat) in live fire exercise by naval and coastal forces, usually targeted by weapons (medium size) like HMG’s, rapid fire cannons (20 or so mm), autocannons (bigger ones up to 40 and 57mm) and also anti-tank rockets. Sonobuoy – used by anti-submarine warfare aircraft to detect submarines by SONAR
Buoy can have many applications like application-specific communications hardware, the buoy can also serve as a platform for more traditional sensing and navigational instrumentation. Temperature, current, and salinity sensors as well as a GPS unit may all be accommodated. In addition to the extensive network of navigational buoys which are used and maintained for the commercial fishing industry and its associated regulatory agencies, there is also a fleet of data collection buoys which serves an equally important role in aiding this industry. As the NDBC so aptly states at their web-site, “moored buoys are the weather sentinels of the sea”. Their systems provide the nation with information about barometric pressure, wind direction and speed, air and sea temperatures, and directional wave energy spectra.
Navy searches for enabling technologies for new-generation sonobuoy to detect quiet enemy submarines
U.S. Navy researchers are asking industry for enabling technologies for a new advanced air-deployed passive sonobuoy able to detect, identify, and track new generations of extremely quiet enemy submarines. Goals are to deploy the prototype from an A-size package; automatic precise localization of hydrophone elements on the hydrophone array; and in-buoy signal processing for beam-forming and communicating data to a receiving system.
Included will be upper float, communications and GPS receiver, and surface suspension for motion isolation of the upper assembly from the array. A lower electronics section will have power for the sonar hydrophone array, telemetry, beamforming, and signal processing hardware with sufficient processing power to run software developed and provided by the Navy.
A contractor proposed system for array element location will be required to enable accurate beamforming at the frequencies of interest. The contractor will be responsible for integrating components into an A-size sonobuoy and demonstrating ability to achieve air launch certification, water entry and array deployment.
Cost of manufacturing the sonobuoy in small numbers is a key objective. The size constraints of an A-size sonobuoy impose severe restriction on the size of hydrophones and the schedule of the project imposes the necessity that proposed hydrophones be non-developmental with low self-noise ( < 58 dB ref μPa/√Hz at 100 Hz and < 16 dB ref μPa/√Hz at 15kHz), capable of being calibrated with +/- 0.3 dB in amplitude, and capable of being calibrated in relative phase within +/- 2 degrees when assembled in groups of up to 150 .
Seatrec, Northrop Grumman Receive DARPA Award for Developing Deep Sea Robots
Seatrec, a renewable energy company that harvests energy from temperature differences in the environment, announced today that it has been awarded a Phase II Small Business Innovation Research (SBIR) grant from the Defense Advanced Research Projects Agency (DARPA). As part of the grant, Seatrec has assembled a multi-disciplinary team of scientists and engineers and subcontracted Northrop Grumman to support the development of a float that can dive to 1000 meters at a speed of 1 meter per second, a factor of 10 faster than the current state-of-the-art. Dr. Yi Chao, Founder and CEO of Seatrec, is the Principal Investigator on the grant and built the company’s technology he started at NASA’s Jet Propulsion Laboratory.
“Today’s buoyancy engines are too small to support such a fast profiling speed. If we increase the size of the buoyancy engine and add a propeller, the required 1 m/s speed can be achieved, however, a significantly larger battery would be necessary in order to maintain long endurance. We’re excited to partner with Professor Doug Hart from MIT to explore the use of aluminum fuel, when mixed with water, to create the extra buoyancy required to achieve a 10x increase of the profiling speed,” said Chao.
“Aluminum, long used as a solid rocket propellant, is among the most energy-dense materials known but has found little use in other applications due to difficulties in harnessing its power. My group at MIT has developed a method to safely create a liquid slurry that can be reacted with water on contact releasing hydrogen gas and heat. In this project, the hydrogen gas will be used to generate positive buoyancy to achieve an order of magnitude increase in profiling speed,” said Hart.
“Ocean data needs a sea change to help navigate the warming world,” stated in a recent article in Nature, “The ocean covers about 70 percent of Earth’s surface, regulates the climate and it’s home to countless species of fish, a major source of protein for more than one billion people. It is now under threat from climate change, overfishing and pollution.” This technological advancement will certainly accelerate the evolution of ocean observation and monitoring. “There are simply no other energy harvesting solutions available like Seatrec. The synergy of these innovative technologies and our experience in developing military-grade solutions will result in a very promising offering to better observe our oceans,” said Brian Theobald, Chief Engineer for Northrop Grumman Undersea Systems.
US Navy awards fibre optic mooring technology contract to OPT
The US Navy has awarded a contract to Ocean Power Technologies (OPT) to develop a fibre optic mooring system to enable the transmission of subsea sensor data to airplanes, ships, and satellites. The Phase I contract is valued at $125,000 and includes three options worth an aggregate value of $100,000. Designed to address the Navy’s need for reliable and low-cost ‘optical-mechanical mooring cables’, the contract work will be delivered under OPT’s Innovation & Support Services line.
The company noted that the fibre optic-based buoy mooring concepts being developed under the US Navy contract is likely to be incorporated into its PowerBuoy and Subsea Battery Module product lines. Ocean Power Technologies CEO George Kirby said: “We’re very excited for this Phase I award by the US Navy to develop a fibre optic mooring line which may be used for both defence and commercial applications.
“We believe that this new contract award further validates our technical expertise and experience with ocean energy systems and could also lead to additional future contract awards where we might utilise OPT technologies which are already in advanced stages of development.”
OPT expects to bid on a Phase II contract. As part of a prior contract with the Office of Naval Research, OPT advanced its anchorless PowerBuoy design. The company is currently in the process of prototyping the design for both defence and commercial applications. Kirby added: “The anchorless PowerBuoy design is very encouraging to our customers due to its innovative and patented approach to power generation and also the need for a quick-deploy solution throughout markets such as defence and offshore oil and gas.”
Technology Development of Fiber Optic Moorings for Surface Communication Buoys
Navy SBIR topic seeks to support the transmission of Navy sensor data to and from subsea nodes to airplanes, Navy ships, and satellites. The status quo is to use a geometric compliant mooring cable with clamp-on floats, which is not suitable for specific Navy programs that require unique deployment and winching operations.
The cables would be used to moor buoys in ocean waves and ocean currents such that the moorings will include optical fibers. The cable must be able to withstand motions of buoy tugging on the cable in ocean waves, ocean currents and wind loading.
An example would be an underwater winch that pays out cable to a buoy and then winds the cable back into a garage. The target cable to be designed and tested under this SBIR topic will be for small-size buoys with displacement ranges of 100-500 pounds. The focus will be axial stiffness and fatigue life of the compliant cable.
For proposal purposes, assume the compliant cable section will need to have a low stiffness (axial) to stretch in the range of 10 feet in the range of 50-100 pounds, and operate reliably for a duration of 60 days at sea in Sea State 3-4 conditions.
The compliant stretchable cable section will need to be
(a) light weight in seawater (for instance, it is desired to be neutral buoyant to not have a large dead weight pulling down on the buoy reserve buoyancy) and
(b) as small diameter is feasible to reduce fluid drag loading which would adversely impact the surface buoy performance and
(c) have a diameter of 3 inches or less if feasible (the diameter is the structural member, the flexible member, the fiber optic cable included).
In addition, if this compliant cable is to be flange connected to interface to the surface buoy and interface to the remaining fiber optic mooring cable, it is desired to have the flanges as compact as possible to reduce handling and dead weight and for fluid drag loading on the buoy mooring as a whole.
The phase III goal is to produce compliant fiber optic cables per specifications required by each Navy project that needs these moored transceiver buoys. Assist the Navy in transitioning the technology to the fleet. Other dual use applications are the technology can be spun off to the ocean science measurement community at large that needs high bandwidth data from small buoys. While the technology is targeted for small buoys, in theory, it may be scalable for larger, longer-duration buoys typically used in the science community (e.g., Scripps Institute of Oceanography, Woods Hole Oceanographic Institution, Monterey Bay Aquarium Research Institute).
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