Method of determining the position of an autonomous underwater vehicle, autonomous underwater vehicle, transmitter station, system

Abstract

A method of determining the position of an autonomous underwater vehicle The method comprises: transmitting a plurality of acoustic signals from one or more transmitters, receiving the plurality of transmitted acoustic signals at an autonomous underwater vehicle; and determining, from the received acoustic signals, the position of the autonomous underwater vehicle; wherein the plurality of acoustic signals are offset from one another in frequency.

Description

METHOD, AUTONOMOUS UNDERWATER VEHICLE, TRANSMITTER STATION, SYSTEM

[0001] This application claims priority from GB2418472.3 filed 17 December 2024 and from, the contents and elements of which are herein incorporated by reference for all purposes.TECHNICAL FIELD

[0002] The present disclosure relates to a method, an autonomous underwater vehicle, a transmitter station, and a system.BACKGROUND

[0003] Whilst techniques for navigating the ocean surface are well-established and varied (for example, celestial navigation, global positioning systems, dead reckoning etc.), the techniques for underwater navigation are more nascent. Previously, landmark navigation, dead reckoning, or periodic surfacing have been used to track or confirm the location of an underwater vehicle. However, these techniques can be less practicable when it is an autonomous vehicle to be tracked.

[0004] One-way travel time (OWTT) acoustic positioning is a technique which can be used for the underwater navigation of autonomous underwater vehicles (AUVs). The technique can be useful for determining the location of one or more AUVs used to carry out marine seismic surveys, such as that described in GB 2541189.

[0005] Broadly, it works in a similar manner to global navigation satellite systems (GNSS, e.g., GPS) whereby a transmitter with a known location (e.g., stored in an almanack on the receiver) transmits a signal which includes at least an identifier of the transmitter. A receiver receives this signal and, together with other data, is able to derive a location of itself relative to the transmitter.

[0006] However, where there is a desire to deploy relatively large numbers of AUVs, and where useful bandwidth is limited (by corresponding increases in traffic, environmental factors, or a mixture thereof), OWTT can be cumbersome to implement or limited by available bandwidth.

[0007] The present disclosure was arrived at in light of the above considerations.SUMMARY

[0008] Accordingly, in a first aspect, embodiments of the invention provide a method of determining the position of an autonomous underwater vehicle, the method comprising: transmitting a plurality of acoustic signals from one or more transmitters, receiving the plurality of transmitted acoustic signals at an autonomous underwater vehicle; anddetermining, from the received acoustic signals, the position of the autonomous underwater vehicle; wherein the plurality of acoustic signals are offset from one another in frequency.

[0009] Such a method provides a significantly improved position update rate of the autonomous underwater vehicle. This can be achieved due to the ability to reduce the separation in arrival times at the receiving entity (e.g., autonomous underwater vehicle). It can further provide additional time windows available to interleave acoustic communication / other data transfer.

[0010] Herein, the term autonomous underwater vehicle is intended to be synonymous with and equivalent to the term uncrewed underwater vehicle. The autonomous underwater vehicle includes at least some degree of autonomous functionality, which may include significant levels of autonomous functionality. However it may also be remotely controlled, either directly or indirectly, by an operator (for example located in a surface vessel).

[0011] The acoustic signals may include, as encoded information, the time at which the signal was transmitted. That is, one or more of the acoustic signals may be or may include as a component of the message a timestamp indicative of the time at which that respective acoustic signal was transmitted by its transmitter. The acoustic signals may include, as encoded information, an identifier of the transmitter transmitting the respective acoustic signal. The acoustic signals may include, as encoded information, the location of the transmitter transmitting the respective acoustic signal. The acoustic signals may be encoded according to any encoded method known per se in the art,

[0012] The autonomous underwater vehicle may utilise a depth value in the step of determining, from the received acoustic signals, the position of the autonomous underwater vehicle. The depth value may derive from an on-board pressure sensor, altimeter measurement, or combination of the two.

[0013] The acoustic signals may include any one or any combination of the previously mentioned data (transmission time, transmitter ID, and transmitter location). The entity determining the position of the autonomous underwater vehicle from the received acoustic signals may have access to an almanac or other database of information relating to the transmitters such as a transmission schedule. As such, the determiner may know, for example, that transmitter A transmitters from location X at time interval Y. It can be seen then how the transmitted signal need not include all of the above, as where certain information is known to the determiner it can (clock synchronization permitting) infer other values needed for determining the position.

[0014] For example, where the determiner receives only the transmission time, it may be able to look up the corresponding position (e.g., because only transmitter X transmits within an applicabletime window). As a further example, where the determiner receives only an identification of transmitter X, it may be able to look up the corresponding position and transmission time (e.g., because transmitter X has a known position, is the only transmitter to transmit within an applicable time window, and is scheduled to transmit at a certain time). A further example, where the determiner receives only the location of the transmitter, it may be able to look up the corresponding transmission time (e.g., because transmitter X is known to be at or is scheduled to be at that location and is scheduled to transmit at a certain time).

[0015] The frequencies of the acoustic signals may be within the Hz to kHz ranges. For example, greater than 500 Hz and no more than 100 kHz. The frequencies may be equally spaced (i.e., with a constant difference value between adjacent utilised frequencies) or non-equally spaced (i.e., with a varying difference value between adjacent utilised frequencies). The frequencies may be fixed, or may vary based on a schedule. The frequencies may be chosen so that they are respectively out-of-band of one another (i.e., there is no significant or meaningful overlap or cross-talk).

[0016] The method may include a step of transmitting, by the autonomous underwater vehicle to a determiner of the position of the autonomous underwater vehicle, values indicating the time of receipt of the plurality of transmitted acoustic signals at the autonomous underwater vehicle. The determiner may be a transmitter station, another autonomous underwater vehicle, or another installation / surface vessel. Alternatively, the autonomous underwater vehicle may determine it’s own position using the received acoustic signals.

[0017] The transmitters may be located in one or more transmitter stations of the type discussed below. Alternatively, or additionally, the transmitters may be located (or at least one transmitter may be located) in a further autonomous underwater vehicle. The autonomous underwater vehicle(s) may include a global navigation satellite system (GNSS) and when surfaced may use this to function as a transmitter station of the type discussed below.

[0018] The determination of the position of the autonomous underwater vehicle may utilise a speed of sound in water. The method may include a step of modifying one or more properties of the received signals on the basis of environmental data stored on the autonomous underwater vehicle. The environmental data may comprise speed of sound (or sound speed) data for one or more points between the surface of the water and the depth of the autonomous underwater vehicle). This sound speed measurement may be estimated for a set of or for each received signal based on measurements of the water conductivity, temperature, and depth (so called CTD). The determination of the position of the autonomous underwater vehicle may utilise a previously determined position of the autonomous underwater vehicle (for example, by dead reckoning utilising an on-board odometer, which is verified against the position as determinedvia the acoustic signals).

[0019] The position of the transmitters (which may be transceivers), whether they transmit the measurement signal or receive the measurement signal, is known. For example, via GPS or another GNSS. In some examples, the AUV may transmit the initial signal(s), the surface transceivers may receive these signal(s), and may either determine the position of the AUV themselves (and transmit this back to the AUV) or may return to the AUV the information necessary for the AUV to make that determination (the one-way travel time, and / or the position of the surface transceiver if not known by the AUV from an almanac). In other examples, the surface transceiver(s) may transmit the signal(s) themselves. This could be responsive to a query from the AUV, or according to a transmission schedule. The AUV may receive the signal(s) from the surface transceiver(s), and use the travel time as before to determine its location. Again, the location of the surface transceivers may be encoded in the transmitted signal, or an identifier of the respective surface transceivers may be encoded, the AUV having an almanac of known positions for each of the surface transceivers.

[0020] Preferably, the latter is performed, whereupon the surface transceivers transmit (e.g., periodically) the signals to the AUV. This is because where a very large number of AUVs are deployed, the number of signals travelling backwards and forwards would grow significantly, and this may degrade the overall signal quality. Additionally, where a very large number of AUVs are deployed, it may be very difficult and potentially impossible to assign each AUV a unique frequency bandwidth with which to identify the UAV.

[0021] A plurality of transmitted acoustic signals are used, which are transmitted in sync from multiple sources (e.g., a plurality of surface transceivers). These signals can be spread across multiple out of band frequencies. That is, the method includes synchronously transmitting broadcast messages using n different, sufficiently separated, carrier frequencies (where n >1 , e.g., 4).

[0022] Each broadcast message can be triggered by PPS (pulse per second) at a specific second past the minute. The receiving units (e.g., in the AUVs) can have knowledge of the transmit configuration. Both of these may be dynamically customisable. A maximum time may be defined based on the transmit range so as to account for overlap / missed transmissions. Each broadcast message may contain the encoded positional information of the transmitter / transceiver. The AUVs may be taking direct measurements of the speed of sound velocity (e.g., via the CTD (conductivity, temperature, depth measurements) onboard the AUVs), which can allow accurate sound speed corrections to be applied. Four or more in range broadcast units may be used to allow for optimisation and estimation of the sound speed from the received broadcast packets.

[0023] There may be at least 2, at least 3, or at least 4 acoustic signals offset from one another in frequency. The plurality of acoustic signals may be transmitted simultaneously or substantially simultaneously. The plurality of acoustic signals may be transmitted within a time window of no more than 1 second, 10 seconds, 1 minute, or 10 minutes. For example, Broadcast 1 may be transmitted on band A, Broadcast 2 may be transmitted on band B, Broadcast 3 may be transmitted on band C, and Broadcast 4 may be transmitted on band D. n receiving agents (e.g., AUVs) receive and decode the signals. The ranges are computed from all sources, and the 3D position multilaterated. This determining of the position can be aided in the z (height) direction by use of an on-board pressure sensor, altimeter measurement, or combination of the two.

[0024] Determining the position may include identifying a time of flight from the transmitter(s) to the receiver (the autonomous underwater vehicle), and discounting those acoustic signals which have a time of flight in excess of a threshold value. The threshold value may be fixed or dynamic (e.g., updated based on environmental conditions, received instructions to modify the threshold value, and the like). As an example, the threshold value may be 30 seconds, 60 seconds, 120 seconds, 180 seconds, or 360 seconds.

[0025] In a second aspect, embodiments of the invention provide an autonomous underwater vehicle, including a process or controller configured to: receive a plurality of transmitted acoustic signals, and determine from the received acoustic signals, the position of the autonomous underwater vehicle; wherein the plurality of received acoustic signals are offset from one another in frequency.

[0026] The autonomous underwater vehicle may include one receiver configured to simultaneously receive acoustic signals at a plurality of frequencies or a plurality of receivers each configured to receive acoustic signals at a particular frequency (or a combination thereof).

[0027] The autonomous underwater vehicle may include one or more transmitters, and the processor or controller may be configured to utilise the transmitters to communicate with one or more transmitter stations. The transmitter(s) and receiver(s) may be a single unit: a transceiver.

[0028] In a third aspect, embodiments of the invention provide a transmitter station for use in determining the position of an autonomous underwear vehicle, the transmitter station comprising: one or more transmitters, configured to transmit a plurality of acoustic signals to the autonomous underwater vehicle for use in determining the position of the autonomous underwater vehicle;wherein the plurality of acoustic signals are offset from one another in frequency.

[0029] The transmitter station may be a surface vessel, or other surface entity (e.g., buoy) and may be configured to utilise a global navigation satellite system, GNSS, to determine it’s own location (e.g., when it’s acoustic signal transmissions encode the location of the transmitter station). The transmitter station may be a fixed surface installation (such as a floating platform, but whose position is fixed). The transmitter station may be a fixed subsurface installation, such as being attached to the seabed or other subsurface features, and may have a known, fixed, location. The transmitter station may be a further autonomous underwater vehicle whose location is known (e.g., due to being surfaced and using GPS, or having recently determined its own location through other means).

[0030] In a fourth aspect, embodiments of the invention provide a system for determining the location of one or more autonomous underwater vehicles, comprising: one or more autonomous underwater vehicles as set out with reference to the second aspect; and one or more transmitter stations as set out with reference to the third aspect.

[0031] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0032] Further aspects of the present invention provide: a computer program comprising code which, when run on one or more computers, causes them to perform the method of the first aspect; a computer readable medium storing a computer program comprising code which, when run on one or more computers, causes them to perform the method of the first aspect; and a computer system programmed to perform the method of the first aspect.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Fig. 1 shows a system;

[0034] Fig. 2 shows a variant system;

[0035] Fig. 3 shows a partial view of an autonomous underwater vehicle;

[0036] Fig. 4 shows a transmitter station; and

[0037] Fig. 5 shows a method.DETAILED DESCRIPTION

[0038] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

[0039] Fig. 1 shows a system. In this example, the system includes three transmitter stations 102a - 102c which float on the surface of a body of water 101 (e.g., the sea). An autonomous underwater vehicle 100 is located below the surface, above the seabed 103. In use, the transmitter stations 102a-102c transmit acoustic signals with respectively different frequencies (vi to V3) to the autonomous underwater vehicle 100. In this example, the frequencies are all within the high Hz to medium kHz ranges (e.g., greater than 500 Hz and up to around 100 kHz). The frequencies are equally spaced (i.e., with a constant difference value between adjacent frequencies) and the frequencies are fixed. An opposite transmission path is also possible (the ADV transmitting n acoustic signals to the transmitter stations 102a- 102c with respectively different frequencies).

[0040] When received by the ADV, the ADV compares the time of receipt to a value retrieved from each of the received acoustic signals. In this example, the retrieved values include: the time of transmission from the respective transmitter 102a - 102c, and the location of the respective transmitter. This allows the ADV to determine its position using multilateration in a manner known per se in the art (determination of the intersection point on three spheres having radii derived from the one-way travel time).

[0041] Fig. 2 shows a variant system. Here a single transmitter station 202 transmits the three signals vi - V3, and an optional further transmitter station 204 fixed to the seabed 103 transmits a further signal V4. The variant system can operate in the same manner discussed previously.

[0042] Fig. 3 shows a partial view of an autonomous underwater vehicle 100. It includes a transceiver 102, which is connected to a process or controller 104. The controller also connects to a database 106, which may contain an almanac or other transmission schedule information as discussed previously. The controller also connects to a local time source 108 (although shown separately, the local time source may form a part of the controller, e.g., as a local oscillator). The controller 104 is also connected to a sensor array 110, the sensor array being able to measure: current depth; water temperature; and water conductivity. These values can be provided to the controller for use in determining the location of the autonomous underwater vehicle.

[0043] Fig. 4 shows a transmitter station 400 which may be a transmitter station 102a - 102c or 204 as discussed previously. It includes a controller or processor 402, which is connected to a transceiver or transceiver array 404 (where the transmitter station should transmit a pluralityof simultaneous but frequency separated acoustic signals). The controller 402 is also connected to a database 406, containing an almanac or other transmission schedule information as discussed previously. The controller 402 also connects to a local time source 108 (although shown separately, the local time source may form a part of the controller, for example as a local oscillator). The local time source 108 may be, or may form part of, a global navigation satellite system. In this sense, the local time source may derive a time value from the GNSS satellites.

[0044] Fig. 5 shows a method of determining the location of an AUV. In a first step, S502, a plurality of acoustic signals are transmitted from one or more transmitters. Each of the plurality of acoustic signals are offset from one another in frequency, such as to be out of band. The transmitters in this example are each in a respective transmitter station, but as discussed previously could be in a single transmitter station. Next, in step S504, the plurality of transmitted acoustic signals is received at an autonomous underwater vehicle. Finally, in step S506, the received acoustic signals are used to determine the position of the autonomous underwater vehicle.

[0045] The systems and methods of the above embodiments may be implemented in a computer system (in particular in computer hardware or in computer software) in addition to the structural components and user interactions described.

[0046] The term “computer system” includes the hardware, software and data storage devices for embodying a system or carrying out a method according to the above described embodiments. For example, a computer system may comprise a central processing unit (CPU), input means, output means and data storage. The computer system may have a monitor to provide a visual output display. The data storage may comprise RAM, disk drives or other computer readable media. The computer system may include a plurality of computing devices connected by a network and able to communicate with each other over that network.

[0047] The methods of the above embodiments may be provided as computer programs or as computer program products or computer readable media carrying a computer program which is arranged, when run on a computer, to perform the method(s) described above.

[0048] The term “computer readable media” includes, without limitation, any non-transitory medium or media which can be read and accessed directly by a computer or computer system. The media can include, but are not limited to, magnetic storage media such as floppy discs, hard disc storage media and magnetic tape; optical storage media such as optical discs or CD-ROMs; electrical storage media such as memory, including RAM, ROM and flash memory; and hybrids and combinations of the above such as magnetic / optical storage media.

[0049] While the disclosure has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the disclosure set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the disclosure.

[0050] In particular, although the methods of the above embodiments have been described as being implemented on the systems of the embodiments described, the methods and systems of the present disclosure need not be implemented in conjunction with each other, but can be implemented on alternative systems or using alternative methods respectively.

[0051] The features disclosed in the description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the disclosure in diverse forms thereof.

[0052] While the disclosure has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the disclosure set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the disclosure.

[0053] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0054] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0055] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0056] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

CLAIMS1 . A method of determining the position of an autonomous underwater vehicle, the method comprising: transmitting a plurality of acoustic signals from one or more transmitters, receiving the plurality of transmitted acoustic signals at an autonomous underwater vehicle; and determining, from the received acoustic signals, the position of the autonomous underwater vehicle; wherein the plurality of acoustic signals are offset from one another in frequency.

2. The method of claim 1 , wherein the acoustic signals include, as encoded information, the time at which the signal was transmitted.

3. The method of claim 1 or 2, wherein the acoustic signals include, as encoded information, an identifier of the transmitter transmitting the respective acoustic signal.

4. The method of any preceding claim, wherein the acoustic signals include, as encoded information, the location of the transmitter transmitting the respective acoustic signal.

5. The method of any preceding claim, further comprising a step of modifying one or more properties of the received signals on the basis of environmental data stored on the autonomous underwater vehicle.

6. The method of claim 5, wherein the environmental data comprises speed of sound data for one or more points between the surface of the water and the depth of the autonomous underwater vehicle.

7. The method of any preceding claim, wherein there are at least 2, at least 3, or at least 4 acoustic signals offset from one another in frequency.

8. The method of any preceding claim, wherein the plurality of acoustic signals are transmitted simultaneously or substantially simultaneously.

9. The method of any preceding claim, wherein the plurality of acoustic signals are transmitted within a time window of no more than 1 second, 10 seconds, 1 minute, or 10 minutes.

10. An autonomous underwater vehicle, including a process or controller configured to: receive a plurality of transmitted acoustic signals, and determine from the received acoustic signals, the position of the autonomous underwater vehicle; wherein the plurality of received acoustic signals are offset from one another in frequency.

11. A transmitter station for use in determining the position of an autonomous underwater vehicle, the transmitter station comprising: one or more transmitters, configured to transmit a plurality of acoustic signals to the autonomous underwater vehicle for use in determining the position of the autonomous underwatervehicle; wherein the plurality of acoustic signals are offset from one another in frequency.

12. A system for determining the location of one or more autonomous underwater vehicles, comprising: one or more autonomous underwater vehicles as set out in claim 10; and one or more transmitter stations as set out in claim 11 .

Images