Autonomous underwater vehicle (AUV) technologies for surveillance, and anti-submarine warfare missions

Rajesh Uppal September 26, 2021 Navy, Technology, Unmanned Comments Off on Autonomous underwater vehicle (AUV) technologies for surveillance, and anti-submarine warfare missions 1,564 Views

An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles (ROVs) – controlled and powered from the surface by an operator/pilot via an umbilical or using remote control. In military applications an AUV is more often referred to as an unmanned undersea vehicle (UUV). Underwater gliders are a subclass of AUVs.

Modern autonomous underwater vehicle (AUV) is an intelligent unmanned platform to perform a variety of military and civilian missions in complex marine environment, which can better meet the needs, such as scientific research, military operations and commercial applications. The truly autonomous systems are typically deployed from a research vessel, they are not tethered to the vessel and do not require direct human control while collecting data.

AUV’s are designed to travel underwater and can be equipped with different kinds of payloads such as cameras, sonar, bottom profilers, multibeam echo sounders and more. The versatility of the configuration of AUV’s combined with the underwater vehicles ability to carry out an independent movement makes AUVs a powerful instrument in any underwater surveying or inspection job.

They have various applications in pipeline inspection, sub-sea inspection, sub-sea survey, cable inspection, sampling, oceanographic, environmental monitoring, iceberg profiling, under-ice surveys, countermeasures, underwater photography, and mine detection. Their ability to operate autonomously of a host vessel makes them well suited to exploration of extreme environments, from the world’s deepest hydrothermal vents to beneath polar ice sheets. They have revolutionised our ability to image the seafloor, providing higher resolution seafloor mapping data than can be achieved from surface vessels, particularly in deep water.

Vehicle designs

There are a large variety of autonomous underwater vehicles, those ranging from a weight of tens of kilograms to vehicles that weigh thousands of kilograms. Vehicles range in size from man portable lightweight AUVs to large diameter vehicles of over 10 metres length. Large vehicles have advantages in terms of endurance and sensor payload capacity; smaller vehicles benefit significantly from lower logistics (for example: support vessel footprint; launch and recovery systems). For instance, Britain’s Autosub Long Range, nicknamed Boaty McBoatface, is claimed to have a 6,000km range with endurance of up to six months.

The market is effectively split into three areas: scientific (including universities and research agencies), commercial offshore (oil and gas, etc.) and military application (mine countermeasures, battle space preparation). The majority of these roles utilize a similar design and operate in a cruise (torpedo-type) mode. They collect data while following a preplanned route at speeds between 1 and 4 knots.

Commercially available AUVs include various designs, such as the small REMUS 100 AUV originally developed by Woods Hole Oceanographic Institution in the US and now produced commercially by Hydroid, Inc. (a wholly owned subsidiary of Kongsberg Maritime); the larger HUGIN 1000 and 3000 AUVs developed by Kongsberg Maritime and Norwegian Defence Research Establishment; the Bluefin Robotics 12-and-21-inch-diameter (300 and 530 mm) vehicles and the International Submarine Engineering Ltd.

Most AUVs follow the traditional torpedo shape as this is seen as the best compromise between size, usable volume, hydrodynamic efficiency and ease of handling. There are some vehicles that make use of a modular design, enabling components to be changed easily by the operators.

The market is evolving and designs are now following commercial requirements rather than being purely developmental. Upcoming designs include hover-capable AUVs for inspection and light-intervention (primarily for the offshore energy applications), and hybrid AUV/ROV designs that switch between roles as part of their mission profile. Again, the market will be driven by financial requirements and the aim to save money and expensive ship time.

For military, their autonomy allows AUVs to be used for missions where a surface vehicle or manned submersible would be at risk, such as mine countermeasure (MCM), under-ice operations or underwater survey missions such as detecting and mapping submerged wrecks, rocks, and obstructions. The AUVs are applied mainly in the military aspects such as the underwater search, surveillance, anti-submarine warfare, reconnaissance, and navigation.

Canada has recently taken delivery of two AUVs (ISE Explorers) to survey the sea floor underneath the Arctic ice in support of their claim under Article 76 of the United Nations Convention of the Law of the Sea. Also, ultra-low-power, long-range variants such as underwater gliders are becoming capable of operating unattended for weeks or months in littoral and open ocean areas, periodically relaying data by satellite to shore, before returning to be picked up.

Extra-large diameter AUV systems can be deployed and recovered from shore, so launch and recovery is simpler and they can operate in a much wider set of sea states. They do, however, need a large battery pack and very accurate navigation. The promise of this technology is that it can deliver science at a fraction of the cost of a vessel and crew.

Therefore countries are developing larger Autonomous Underwater Vehicles (AUVs) because of the increased capabilities they bring. The thought leaders in this space have been the U.S. Navy who first laid out a UUV Master Plan in 2004. This included a category of ‘large’ Unmanned Underwater Vehicles (UUVs) of over 20,000 lb. Today these are termed Large Displacement Unmanned Underwater Vehicles (LDUUV) following U.S. Navy terminology. The U.S. Navy and industry has learned a lot from the successive trials of the LDUUV-INP and other large UUVs. The operational U.S. Navy Orca AUVs will be even larger though, reaching ~25.5 meters (84 ft) in length. These will likely be the largest UUVs in service for some time but could be challenged by future Japanese and British projects.

Russia will launch its first nuclear-powered submarine capable of carrying the nuclear-capable underwater drone ‘Poseidon,’ alternatively referred to as an unmanned underwater vehicle (UUV), autonomous underwater vehicle (AUV), or simply an intercontinental-range, nuclear autonomous torpedo, according to Russian President Vladimir Putin. Sea trials of the Posedon UUV were reportedly successfully completed.

AUV Technology

AUVs carry sensors to navigate autonomously and map features of the ocean. Typical sensors include compasses, depth sensors, sidescan and other sonars, magnetometers, thermistors and conductivity probes. Some AUVs are outfitted with biological sensors including fluorometers (also known as chlorophyll sensors), turbidity sensors, and sensors to measure pH, and amounts of dissolved oxygen.

Navigation

Radio waves cannot penetrate water very far, so as soon as an AUV dives it loses its GPS signal. Therefore, a standard way for AUVs to navigate underwater is through dead reckoning. Navigation can however be improved by using an underwater acoustic positioning system. When operating within a net of sea floor deployed baseline transponders this is known as LBL navigation. When a surface reference such as a support ship is available, ultra-short baseline (USBL) or short-baseline (SBL) positioning is used to calculate where the sub-sea vehicle is relative to the known (GPS) position of the surface craft by means of acoustic range and bearing measurements.

To improve estimation of its position, and reduce errors in dead reckoning (which grow over time), the AUV can also surface and take its own GPS fix. Between position fixes and for precise maneuvering, an Inertial Navigation System on board the AUV calculates through dead reckoning the AUV position, acceleration, and velocity. Estimates can be made using data from an Inertial Measurement Unit, and can be improved by adding a Doppler Velocity Log (DVL), which measures the rate of travel over the sea/lake floor. Typically, a pressure sensor measures the vertical position (vehicle depth), although depth and altitude can also be obtained from DVL measurements. These observations are filtered to determine a final navigation solution.

Propulsion

There are a couple of propulsion techniques for AUVs. Some of them use a brushed or brush-less electric motor, gearbox, Lip seal, and a propeller which may be surrounded by a nozzle or not. All of these parts embedded in the AUV construction are involved in propulsion. Other vehicles use a thruster unit to maintain the modularity. Depending on the need, the thruster may be equipped with a nozzle for propeller collision protection or to reduce noise submission, or it may be equipped with a direct drive thruster to keep the efficiency at the highest level and the noises at the lowest level. Advanced AUV thrusters have a redundant shaft sealing system to guarantee a proper seal of the robot even if one of the seals fails during the mission.

Underwater gliders do not directly propel themselves. By changing their buoyancy and trim, they repeatedly sink and ascend; airfoil “wings” convert this up-and-down motion to forward motion. The change of buoyancy is typically done through the use of a pump that can take in or push out water. The vehicle’s pitch can be controlled by changing the center of mass of the vehicle. For Slocum gliders this is done internally by moving the batteries, which are mounted on a screw. Because of their low speed and low-power electronics, the energy required to cycle trim states is far less than for regular AUVs, and gliders can have endurances of months and transoceanic ranges.

Communications

Since radio waves do not propagate well under water, many AUV’s incorporate Acoustic Modems to enable remote command and control. These modems typically utilize proprietary communications techniques and modulation schemes. In 2017 NATO ratified the ANEP-87 JANUS standard for subsea communications. This standard allows for 80 BPS communications links with flexible and extensible message formatting.

Power

Most AUVs in use today are powered by rechargeable batteries (lithium ion, lithium polymer, nickel metal hydride etc.), and are implemented with some form of Battery Management System. Some vehicles use primary batteries which provide perhaps twice the endurance—at a substantial extra cost per mission. A few of the larger vehicles are powered by aluminum based semi-fuel cells, but these require substantial maintenance, require expensive refills and produce waste product that must be handled safely. An emerging trend is to combine different battery and power systems with supercapacitors

Technology trends

New AUV models have been launched and these can gather more data, over longer periods and more accurately. Many of these AUV systems are more compact than their predecessors despite their increased capacity.

Better endurance, improved communications, more accurate navigation, enhanced imaging, artificial intelligence and big data are all contributors. Recent advances in energy density, spearheaded by the mobile phone industry, have helped improve AUV endurance. In parallel, communications, navigation and payload instruments are becoming more effective.

The latest advances in signal design are being used to make acoustic communications travel further and carry more data, using less power. Other techniques like free space optical modems are also enabling large amounts of data to be transferred through-water to AUV systems, using the visible light spectrum at distances of up to 150m. More than ten thousand times more data can be transferred this way than is possible with acoustics. In parallel, navigation performance is improving thanks to new inertial navigation systems that can dead-reckon with as much as twice the certainty of what was possible even two years ago. This is possible by combining latest generation gyros and acoustic aiding from Doppler velocity logs as part of a single instrument.

There are now many more options for AUV payloads. When thinking about a mission, operators can choose from lasers, sonars and even stereoscopic high-definition video. Electronically scanned sonar systems are now manufactured in all sizes – even as small as a GoPro camera – for every application. Some produce stunning imagery at 5m range using high frequencies. Others, working at lower frequencies, can spot obstacles at ranges of over 1000m. For inspection missions, video and laser are combining to provide stunning pictures of the subsea environment as it has never been seen before; at centimetric resolution and in full colour.

When it comes to survey, operators are not just limited to side-scan sonar imagery and multibeam bathymetry. There is now a new generation of multi aperture sonar systems capable of extending range and producing three-dimensional bathymetry. Synthetic aperture sonar has also proved popular for large AUV systems. This is an industry generating more data than ever before. Fortunately, it is at a time when storage solutions have become more prevalent, and machine learning and big data techniques are becoming wide-spread.

AUV Swarms

Another development is the proliferation of low cost, small AUV units, which collaborate and work together for one common goal. This is typically referred to as a swarm of AUV systems. The biggest commercial driver for this technology is thought to be for marine seismic applications. However, the military and oceanographic bodies are also keen to develop tools that enable them to cover larger swaths of the oceans. Crucial technical hurdles still need to be met: How does the swarm communicate? What payload sensors can it carry and afford while remaining commercially viable? How do we launch, operate and recover each and every AUV?

Autonomous Underwater Vehicle Market

According to Verified Market Research, The Global Autonomous Underwater Vehicle Market was valued at USD 354.90 Million in 2018 and is projected to reach USD 580.30 Million by 2026, growing at a CAGR of 6.49% from 2019 to 2026. Autonomous Underwater Vehicles have several advantages such as their stability and agility, their highly improved data quality as well as reliability, the reduction in operational errors and costs that result from the operation of a human operator. It also has low deployment costs as well as does not require any complex support systems. These advantages are driving the market for Global Autonomous Underwater Vehicle Market. Factors such as the lack of quality assurance in comparison to human exploration as well as their large size are restraining the growth of the market.

AUV’s are employed for applications such as obtaining high-resolution maps of the deep seafloor or establishing a pervasive ocean presence. The frequent utilization of AUV technology has picked up over the recent years, leading to increased investment in AUV technology as well as the establishment of more commercial suppliers of AUVs and their services. The increasing number of applications for autonomous underwater vehicles combined with the evolution of AUV technology is leading to the increased penetration of AUV in various end-use sectors.

There are mainly three types under which the several AUVs presently used in the market are categorized. The shallow AUVs are the ones which can go up to water depths of 100 meters. They are majorly used in application areas of studying the marine habitat in the shallow waters. The medium-sized AUVs can go up to the water depths of 1000 meters. Although these types of AUVs do have several application areas, such as in a various hydrographic survey, mine warfare and more. The large systems are equipped with a wide range of sensors and navigation & positioning systems and are robust owing to which several companies are investing in the R&D of large AUVs.

Some of the major players involved in the Global Autonomous Underwater Vehicle Market are International Submarine Engineering Ltd. (ISE), Teledyne Technologies Incorporated., CA Group, Saab AB, Lockheed Martin Corporation, Fugro, Atlas Elektronik GMBH, General Dynamics (Bluefin Robotics), GRAAL Tech. Other companies that sell AUVs on the international market, including Kongsberg Maritime, Hydroid (now a wholly owned subsidiary of Kongsberg Maritime), Bluefin Robotics , International Submarine Engineering (ISE) Ltd, and OceanScan.