Underwater acoustic positioning system

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An underwater acoustic positioning system [1] [2] is a system for the tracking and navigation of underwater vehicles or divers by means of acoustic distance and/or direction measurements, and subsequent position triangulation. Underwater acoustic positioning systems are commonly used in a wide variety of underwater work, including oil and gas exploration, ocean sciences, salvage operations, marine archaeology, law enforcement and military activities.

Contents

Method of operation

Figure 1 describes the general method of operation of an acoustic positioning system, [3] this is an example of a long baseline (LBL) positioning system for ROV

Figure 1: Method of the operation of a Long Baseline (LBL) acoustic positioning system for ROV LBL Acoustic Positioning Aquamap ROV.jpg
Figure 1: Method of the operation of a Long Baseline (LBL) acoustic positioning system for ROV
Baseline station deployment and survey

Acoustic positioning systems measure positions relative to a framework of baseline stations, which must be deployed prior to operations. In the case of a long-baseline (LBL) system, a set of three or more baseline transponders are deployed on the sea floor. The location of the baseline transponders either relative to each other or in global coordinates must then be measured precisely. Some systems assist this task with an automated acoustic self-survey, and in other cases GPS is used to establish the position of each baseline transponder as it is deployed or after deployment.

Tracking or navigation operations

Following the baseline deployment and survey, the acoustic positioning system is ready for operations. In the long baseline example (see figure 1), an interrogator (A) is mounted on the ROV that is to be tracked. The interrogator transmits an acoustic signal that is received by the baseline transponders (B, C, D, E). The reply of the baseline transponders is received again at the ROV. The signal time-of-flight or the corresponding distances A-B, A-C, A-D and A-E are transmitted via the ROV umbilical (F) to the surface, where the ROV position is computed and displayed on a tracking screen. The acoustic distance measurements may be augmented by depth sensor data to obtain better positioning accuracy in the three-dimensional underwater space.

Acoustic positioning systems can yield an accuracy of a few centimeters to tens of meters and can be used over operating distance from tens of meters to tens of kilometers. Performance depends strongly on the type and model of the positioning system, its configuration for a particular job, and the characteristics of the underwater acoustic environment at the work site.

Classes

Underwater acoustic positioning systems are generally categorized into three broad types or classes [4] [5] [6]

Long-baseline (LBL) systems, as in figure 1 above, use a sea-floor baseline transponder network. The transponders are typically mounted in the corners of the operations site. LBL systems yield very high accuracy of generally better than 1 m and sometimes as good as 0.01m along with very robust positions [7] [8] This is due to the fact that the transponders are installed in the reference frame of the work site itself (i.e. on the sea floor), the wide transponder spacing results in an ideal geometry for position computations, and the LBL system operates without an acoustic path to the (potentially distant) sea surface.

Ultra-short-baseline (USBL) systems and the related super-short-baseline (SSBL) systems rely on a small (ex. 230 mm across), tightly integrated transducer array that is typically mounted on the bottom end of a strong, rigid transducer pole which is installed either on the side or in some cases on the bottom of a surface vessel. [9] [10] Unlike LBL and SBL systems, which determine position by measuring multiple distances, the USBL transducer array is used to measure the target distance from the transducer pole by using signal run time, and the target direction by measuring the phase shift of the reply signal as seen by the individual elements of the transducer array. The combination of distance and direction fixes the position of the tracked target relative to the surface vessel. Additional sensors including GPS, a gyro or electronic compass and a vertical reference unit are then used to compensate for the changing position and orientation (pitch, roll, bearing) of the surface vessel and its transducer pole. USBL systems offer the advantage of not requiring a sea floor transponder array. The disadvantage is that positioning accuracy and robustness is not as good as for LBL systems. The reason is that the fixed angle resolved by a USBL system translates to a larger position error at greater distance. Also, the multiple sensors needed for the USBL transducer pole position and orientation compensation each introduce additional errors. Finally, the non-uniformity of the underwater acoustic environment cause signal refractions and reflections that have a greater impact on USBL positioning than is the case for the LBL geometry.

Short-baseline (SBL) systems use a baseline consisting of three or more individual sonar transducers that are connected by wire to a central control box. Accuracy depends on transducer spacing and mounting method. When a wider spacing is employed as when working from a large working barge or when operating from a dock or other fixed platform, the performance can be similar to LBL systems. When operating from a small boat where transducer spacing is tight, accuracy is reduced. Like USBL systems, SBL systems are frequently mounted on boats and ships, but specialized modes of deployment are common too. For example, the Woods Hole Oceanographic Institution uses a SBL system to position the Jason deep-ocean ROV relative to its associated MEDEA depressor weight with a reported accuracy of 9 cm [11]

GPS intelligent buoys (GIB) systems are inverted LBL devices where the transducers are replaced by floating buoys, self-positioned by GPS. The tracked position is calculated in realtime at the surface from the Time-Of-Arrival (TOAs) of the acoustic signals sent by the underwater device, and acquired by the buoys. Such configuration allow fast, calibration-free deployment with an accuracy similar to LBL systems. At the opposite of LBL, SBL or USBL systems, GIB systems use one-way acoustic signals from the emitter to the buoys, making it less sensitive to surface or wall reflections. GIB systems are used to track AUVs, torpedoes, or divers, may be used to localize airplanes black-boxes, and may be used to determine the impact coordinates of inert or live weapons for weapon testing and training purposes [12] [13] [14] references: Sharm-El-Sheih, 2004; Sotchi, 2006; Kayers, 2005; Kayser, 2006; Cardoza, 2006 and others...).[ clarification needed ]

History and examples of use

Figure 2a: An acoustic short baseline (SBL) positioning system was installed on the USNS Mizar during the search dives to the wreckage of the submarine USS Thresher USNS Mizar.jpg
Figure 2a: An acoustic short baseline (SBL) positioning system was installed on the USNS Mizar during the search dives to the wreckage of the submarine USS Thresher
Figure 2b: The bathyscaphe Trieste was guided by its acoustic positioning system to the Thresher Bathyscaphe Trieste.jpg
Figure 2b: The bathyscaphe Trieste was guided by its acoustic positioning system to the Thresher

An early use of underwater acoustic positioning systems, credited with initiating the modern day development of these systems, [15] involved the loss of the American nuclear submarine USS Thresher on 10 April 1963 in a water depth of 2560m. [16] An acoustic short baseline (SBL) positioning system was installed on the oceanographic vessel USNS Mizar. This system was used to guide the bathyscaphe Trieste 1 to the wreck site. Yet, the state of the technology was still so poor that out of ten search dives by Trieste 1, visual contact was only made once with the wreckage. [17] Acoustic positioning was again used in 1966, to aid in the search and subsequent recovery of a nuclear bomb lost during the crash of a B-52 bomber at sea off the coast of Spain.

In the 1970s, oil and gas exploration in deeper waters required improved underwater positioning accuracy to place drill strings into the exact position referenced earlier thorough seismic instrumentation [18] and to perform other underwater construction tasks.

Figure 3: The Russian deep sea submersibles MIR-1 and MIR-2 searched the wreck site of the Japanese submarine I-52 in 1998. A LBL positioning system was used to guide and document the progressing search over multiple dives Mir front.jpg
Figure 3: The Russian deep sea submersibles MIR-1 and MIR-2 searched the wreck site of the Japanese submarine I-52 in 1998. A LBL positioning system was used to guide and document the progressing search over multiple dives

But, the technology also started to be used in other applications. In 1998, salvager Paul Tidwell and his company Cape Verde Explorations led an expedition to the wreck site of the World War 2 Japanese cargo submarine I-52 in the mid-Atlantic. [19] Resting at a depth of 5240 meters, it had been located and then identified using side scan sonar and an underwater tow sled in 1995. War-time records indicated the I-52 was bound for Germany, with a cargo including 146 gold bars in 49 metal boxes. This time, Mr. Tidwell's company had hired the Russian oceanographic vessel, the Akademik Mstislav Keldysh with its two manned deep-ocean submersibles MIR-1 and MIR-2 (figure 3). In order to facilitate precise navigation across the debris field and assure a thorough search, MIR-1 deployed a long baseline transponder network on the first dive. Over a series of seven dives by each submersible, the debris field was progressively searched. The LBL positioning record indicated the broadening search coverage after each dive, allowing the team to concentrate on yet unsearched areas during the following dive. No gold was found, but the positioning system had documented the extent of the search.

In recent years, several trends in underwater acoustic positioning have emerged. One is the introduction of compound systems such the combination of LBL and USBL in a so-called LUSBL [20] configuration to enhance performance. These systems are generally used in the offshore oil & gas sector and other high-end applications. Another trend is the introduction of compact, task optimized systems for a variety of specialized purposes. For example, the California Department of Fish and Game commissioned a system (figure 4), which continually measures the opening area and geometry of a fish sampling net during a trawl. That information helps the department improve the accuracy of their fish stock assessments in the Sacramento River Delta.

Figure 4: NetTrack is an example of a special-purpose underwater acoustic positioning system of the SBL type, designed to measure the opening geometry and area of a trawl net for accurate fish stock assessment purposes. Left: Four small responders (A, B, C, D) are mounted in the corners of the trawl net opening and wired via junction bottle (E) and umbilical (F) to a surface station computer. Center: The net is deployed. Right: The surface station computer sends instructions to one responder (ex. A) to transmit, while instructing the other responders (ex. B, C, D) to receive. By this method all six distances (A-B, A-C, A-D, B-C, B-D, C-D) are measured. The four sides of the opening and one diagonal are used to triangulate the trawl net opening geometry and area. The second diagonal is available to compute a measurement error metric for data quality verification. NetTrack Operation.jpg
Figure 4: NetTrack is an example of a special-purpose underwater acoustic positioning system of the SBL type, designed to measure the opening geometry and area of a trawl net for accurate fish stock assessment purposes. Left: Four small responders (A, B, C, D) are mounted in the corners of the trawl net opening and wired via junction bottle (E) and umbilical (F) to a surface station computer. Center: The net is deployed. Right: The surface station computer sends instructions to one responder (ex. A) to transmit, while instructing the other responders (ex. B, C, D) to receive. By this method all six distances (A-B, A-C, A-D, B-C, B-D, C-D) are measured. The four sides of the opening and one diagonal are used to triangulate the trawl net opening geometry and area. The second diagonal is available to compute a measurement error metric for data quality verification.

Water-proof smart devices like Apple Watch Ultra and Garmin Descent have been introduced to function as dive computers. These devices have a depth gauge sensor, provide a dive profile, and safety alerts for fast ascents and mandatory safety stops using the depth data. In 2023, University of Washington researchers demonstrated a fourth class of 3D underwater positioning for these smart devices that does not require infrastructure support like buoys. [21] Instead they use distributed localization techniques [22] by computing the pairwise distances between a network of diver devices to determine the shape of the resulting network topology. Combining this with depth sensor data from these devices, the lead diver can then compute the relative 3D positions of all the other diver devices.

Related Research Articles

<span class="mw-page-title-main">Sonar</span> Acoustic sensing method

Sonar is a technique that uses sound propagation to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels.

<span class="mw-page-title-main">Echo sounding</span> Measuring the depth of water by transmitting sound waves into water and timing the return

Echo sounding or depth sounding is the use of sonar for ranging, normally to determine the depth of water (bathymetry). It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; the resulting time of flight, along with knowledge of the speed of sound in water, allows determining the distance between sonar and target. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes.

<span class="mw-page-title-main">Dynamic positioning</span> Automatic ship station- and heading-holding systems

Dynamic positioning (DP) is a computer-controlled system to automatically maintain a vessel's position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors and gyrocompasses, provide information to the computer pertaining to the vessel's position and the magnitude and direction of environmental forces affecting its position. Examples of vessel types that employ DP include ships and semi-submersible mobile offshore drilling units (MODU), oceanographic research vessels, cable layer ships and cruise ships.

<span class="mw-page-title-main">Remotely operated underwater vehicle</span> A tethered underwater mobile device operated by a remote crew

A remotely operated underwater vehicle (ROUV) or remotely operated vehicle (ROV) is a free-swimming submersible craft used to perform underwater observation, inspection andphysicl tasks such as valve operations, hydraulic functions and other general tasks within the subsea oil and gas industry, military, scientific and other applications. ROVs can also carry tooling packages for undertaking specific tasks such as pull-in and connection of flexible flowlines and umbilicals, and component replacement.

<span class="mw-page-title-main">Surface marker buoy</span> Buoy towed by a scuba diver to indicate the divers position

A surface marker buoy, SMB, dive float or simply a blob is a buoy used by scuba divers, at the end of a line from the diver, intended to indicate the diver's position to people at the surface while the diver is underwater. Two kinds are used; one (SMB) is towed for the whole dive, and indicates the position of the dive group throughout the dive, and the other, a delayed surface marker buoy, DSMB or decompression buoy, is deployed towards the end of the dive as a signal to the surface that the divers have started to ascend, and where they are going to surface. Both types can also function as a depth reference for controlling speed of ascent and accurately maintaining depth at decompression stops. Surface marker buoys are also used by freedivers in open water, to indicate the approximate position of the diver when submerged. They may also be used to support a catch bag or fish stringer by underwater hunters and collectors. A DSMB is considered by recreational scuba divers and service providers to be a highly important item of safety equipment, yet its use is not part of the entry level recreational diver training for all training agencies, and there are significant hazards associated with incompetent use.

(Acoustic homing) is the process in which a system uses the sound or acoustic signals of a target or destination to guide a moving object. There are two types of acoustic homing: passive acoustic homing and active acoustic homing. Objects using passive acoustic homing rely on detecting acoustic emissions produced by the target. Conversely, objects using active acoustic homing make use of sonar to emit a signal and detect its reflection off the target. The signal detected is then processed by the system to determine the proper response for the object. Acoustic homing is useful for applications where other forms of navigation and tracking can be ineffective. It is commonly used in environments where radio or GPS signals can not be detected, such as underwater.

<span class="mw-page-title-main">Sonobuoy</span> Expendable sonar system dropped/ejected from aircraft or ships

A sonobuoy is a relatively small buoy – typically 13 cm (5 in) diameter and 91 cm (3 ft) long – expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic research.

<span class="mw-page-title-main">Autonomous underwater vehicle</span> Unmanned underwater vehicle with autonomous guidance system

An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring continuous 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.

An acoustic doppler current profiler (ADCP) is a hydroacoustic current meter similar to a sonar, used to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column. The term ADCP is a generic term for all acoustic current profilers, although the abbreviation originates from an instrument series introduced by RD Instruments in the 1980s. The working frequencies range of ADCPs range from 38 kHz to several megahertz.

USBL is a method of underwater acoustic positioning. A USBL system consists of a transceiver, which is mounted on a pole under a ship, and a transponder or responder on the seafloor, on a towfish, or on an ROV. A computer, or "topside unit", is used to calculate a position from the ranges and bearings measured by the transceiver.

An acoustic release is an oceanographic device for the deployment and subsequent recovery of instrumentation from the sea floor, in which the recovery is triggered remotely by an acoustic command signal.

<span class="mw-page-title-main">Short baseline acoustic positioning system</span> Class of underwater acoustic positioning systems used to track underwater vehicles and divers

A short baseline (SBL) acoustic positioning system is one of three broad classes of underwater acoustic positioning systems that are used to track underwater vehicles and divers. The other two classes are ultra short baseline systems (USBL) and long baseline systems (LBL). Like USBL systems, SBL systems do not require any seafloor mounted transponders or equipment and are thus suitable for tracking underwater targets from boats or ships that are either anchored or under way. However, unlike USBL systems, which offer a fixed accuracy, SBL positioning accuracy improves with transducer spacing. Thus, where space permits, such as when operating from larger vessels or a dock, the SBL system can achieve a precision and position robustness that is similar to that of sea floor mounted LBL systems, making the system suitable for high-accuracy survey work. When operating from a smaller vessel where transducer spacing is limited, the SBL system will exhibit reduced precision.

<span class="mw-page-title-main">Long baseline acoustic positioning system</span> Class of underwater acoustic positioning systems used to track underwater vehicles and divers

A long baseline (LBL) acoustic positioning system is one of three broad classes of underwater acoustic positioning systems that are used to track underwater vehicles and divers. The other two classes are ultra short baseline systems (USBL) and short baseline systems (SBL). LBL systems are unique in that they use networks of sea-floor mounted baseline transponders as reference points for navigation. These are generally deployed around the perimeter of a work site. The LBL technique results in very high positioning accuracy and position stability that is independent of water depth. It is generally better than 1-meter and can reach a few centimeters accuracy. LBL systems are generally employed for precision underwater survey work where the accuracy or position stability of ship-based positioning systems does not suffice.

GPS sonobuoy or GPS intelligent buoy (GIB) are a type of inverted long-baseline (LBL) acoustic positioning devices where the transducers are installed on GPS-equipped sonobuoys that are either drifting or moored. GIBs may be used in conjunction with an active underwater device, or with a passive acoustic sound source. Typically the sound source or impact event is tracked or localized using a time of arrival (TOA) technique. Typically several GIBs are deployed over a given area of operation; with the total number determined by the size of the test area and the accuracy of the results desired. Different methods of GPS positioning may be used for positioning the array of GIBs, with accuracies of cm to meter level in realtime possible.

Underwater searches are procedures to find a known or suspected target object or objects in a specified search area under water. They may be carried out underwater by divers, manned submersibles, remotely operated underwater vehicles, or autonomous underwater vehicles, or from the surface by other agents, including surface vessels, aircraft and cadaver dogs.

<span class="mw-page-title-main">Radio acoustic ranging</span> Method of accurately determining a ships position

Radio acoustic ranging, occasionally written as "radio-acoustic ranging" and sometimes abbreviated RAR, was a method for determining a ship's precise location at sea by detonating an explosive charge underwater near the ship, detecting the arrival of the underwater sound waves at remote locations, and radioing the time of arrival of the sound waves at the remote stations to the ship, allowing the ship's crew to use true range multilateration to determine the ship's position. Developed by the United States Coast and Geodetic Survey in 1923 and 1924 for use in accurately fixing the position of survey ships during hydrographic survey operations, it was the first navigation technique in human history other than dead reckoning that did not require visual observation of a landmark, marker, light, or celestial body, and the first non-visual means to provide precise positions. First employed operationally in 1924, radio acoustic ranging remained in use until 1944, when new radio navigation techniques developed during World War II rendered it obsolete.

<span class="mw-page-title-main">Theseus (AUV)</span> Large autonomous underwater vehicle for laying fibre-optic cable

Theseus is a large autonomous underwater vehicle (AUV) designed for laying fibre-optic cable on the seafloor.

Diving support equipment is the equipment used to facilitate a diving operation. It is either not taken into the water during the dive, such as the gas panel and compressor, or is not integral to the actual diving, being there to make the dive easier or safer, such as a surface decompression chamber. Some equipment, like a diving stage, is not easily categorised as diving or support equipment, and may be considered as either.

<span class="mw-page-title-main">Underwater survey</span> Inspection or measurement in or of an underwater environment

An underwater survey is a survey performed in an underwater environment or conducted remotely on an underwater object or region. Survey can have several meanings. The word originates in Medieval Latin with meanings of looking over and detailed study of a subject. One meaning is the accurate measurement of a geographical region, usually with the intention of plotting the positions of features as a scale map of the region. This meaning is often used in scientific contexts, and also in civil engineering and mineral extraction. Another meaning, often used in a civil, structural, or marine engineering context, is the inspection of a structure or vessel to compare actual condition with the specified nominal condition, usually with the purpose of reporting on the actual condition and compliance with, or deviations from, the nominal condition, for quality control, damage assessment, valuation, insurance, maintenance, and similar purposes. In other contexts it can mean inspection of a region to establish presence and distribution of specified content, such as living organisms, either to establish a baseline, or to compare with a baseline.

<span class="mw-page-title-main">Underwater exploration</span> Investigating or traveling around underwater for the purpose of discovery

Underwater exploration is the exploration of any underwater environment, either by direct observation by the explorer, or by remote observation and measurement under the direction of the investigators. Systematic, targeted exploration is the most effective method to increase understanding of the ocean and other underwater regions, so they can be effectively managed, conserved, regulated, and their resources discovered, accessed, and used. Less than 10% of the ocean has been mapped in any detail, less has been visually observed, and the total diversity of life and distribution of populations is similarly obscure.

References

  1. ↑ University of Rhode Island: Discovery of Sound in the Sea
  2. ↑ Underwater Acoustic Positioning Systems, P.H. Milne 1983, ISBN   0-87201-012-0
  3. ↑ The ROV Manual, Robert D. Christ and Robert L. Wernli Sr 2007, pages 96-103, ISBN   978-0-7506-8148-3
  4. ↑ "A Smooth Operator's Guide to Underwater Sonars and Acoustic Devices". Blue Robotics. Retrieved 2024-01-18.
  5. ↑ Milne, chapters 3-5
  6. ↑ Christ and Wernli, sections 4.2.6-4.2.7
  7. ↑ MIT Deepwater Archaeology Research Group
  8. ↑ B.P. Foley and D.A. Mindell, "Precision Survey and Archaeological Methodology in Deep Water," ENALIA The Journal of the Hellenic Institute of Marine Archaeology, Vol. VI, 49-56, 2002
  9. ↑ Milne, chapter 4
  10. ↑ Christ and Wernli, section 4.2.6.3
  11. ↑ Integrating Precision Relative Positioning Into JASON/MEDEA ROV Operations, Bingham et al., MTS Journal Spring 2006 (Volume 40, Number 1)
  12. ↑ Kayser, J.R., Cardoza, M.A., et al., "Weapon Scoring Results from a GPS Acoustic Weapons Test and Training System", Institute of Navigation National Technical Meeting, San Diego, CA, 24-26 January 2005
  13. ↑ Cardoza, M.A., Kayser, J.R., & Wade, B. "Offshore Scoring of Precision Guided Munitions", Inside GNSS April 2006, pages 32-39
  14. ↑ Cardoza, Miguel A.; Kayser, Jack R.; Wade, William F.; Bennett, Richard L.; Merts, John H.; Casey, David R. (10 March 2005). Offshore Weapon Scoring Using Rapidly Deployed Realtime Acoustic Sensors (PDF). 21st Annual National Test & Evaluation Conference. Charlotte, North Carolina.
  15. ↑ Milne, Chapter 2
  16. ↑ Christ and Wernle, page 96
  17. ↑ Milne, Chapter 3
  18. ↑ Christ and Wernli, section 4.2.1
  19. ↑ The Last Dive, National Geographic Magazine October 1999
  20. ↑ Flexible Acoustic Positioning System Architecture, Davis, MTS Dynamic Positioning Conference 2002
  21. ↑ Chen, Tuochao; Chan, Justin; Gollakota, Shyamnath (2023-09-10). "Underwater 3D positioning on smart devices". Proceedings of the ACM SIGCOMM 2023 Conference. ACM. pp. 33–48. arXiv: 2307.11263 . doi:10.1145/3603269.3604851. ISBN   979-8-4007-0236-5. S2CID   260091258.
  22. ↑ Alrajeh, Nabil Ali; Bashir, Maryam; Shams, Bilal (2013-06-01). "Localization Techniques in Wireless Sensor Networks". International Journal of Distributed Sensor Networks. 9 (6): 304628. doi: 10.1155/2013/304628 . ISSN   1550-1477.
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