WO2023223101A1

WO2023223101A1 - Gnss-equipped auv for deploying positioning transponders

Info

Publication number: WO2023223101A1
Application number: PCT/IB2023/000291
Authority: WO
Inventors: Donald Clarke; Alexander Johnson
Original assignee: Cellula Robotics, Ltd.
Priority date: 2022-05-17
Filing date: 2023-05-17
Publication date: 2023-11-23

Abstract

An autonomous underwater vehicle (AUV) including a payload section for storing and deploying a transponder is provided. Processing circuitry determines an underwater location for deploying a transponder, causes the AUV to deploy the transponder, determines a surface position of the AUV, determines an underwater position of the transponder, and conducts an underwater survey using the position of the transponder as a reference.

Description

GNSS-EQUIPPED AUV FOR DEPLOYING POSITIONING TRANSPONDERS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of and priority, under 35 U.S.C. § 119(e), to U.S. Provisional Application Serial No. 63/342,978, filed on May 17, 2022, entitled “GNSS-EQUIPPED AUV FOR DEPLOYING POSITIONING TRANSPONDERS.” The entire disclosure of the application listed above is hereby incorporated by reference, in its entirety, for all that it teaches and for all purposes.

FIELD

[0002] Example embodiments relate to underwater vehicles capable of deploying positioning transponders and performing underwater surveys using the positioning transponders.

BACKGROUND

[0003] When performing underwater mapping surveys, it is desirable to accurately determine the position of the survey platform, which may be a vehicle. Global Navigation Satellite Systems (GNSS) are not available underwater, so submerged survey vehicles may rely on acoustic systems for positioning. The acoustic systems may utilize communication between the transponders or transceivers with established positions and transponder(s) or transceiver(s) on the vehicle. Through calculation of time of flight plus triangulation or wave front bearing, the position of the survey vehicle can be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The present disclosure is described in conjunction with the appended figures, which are not necessarily drawn to scale:

[0005] Fig. 1 shows a block diagram of a system in accordance with embodiments of the present disclosure.

[0006] Fig. 2 is a schematic view of a transponder deployment including elements from the system of Fig. 1.

[0007] Figs. 3 A and 3B are schematic views of example implementations of the system of Fig. 1.

[0008] Fig. 4 is a schematic view of an AUV conducting an underwater survey according to at least one example embodiment.

[0009] Fig. 5 illustrates a method for performing an underwater survey according to at least one embodiment. DETAILED DESCRIPTION

[0010] The ensuing description provides embodiments only, and is not intended to limit the scope, applicability, or configuration of the claims. Rather, the ensuing description will provide those skilled in the art with an enabling description for implementing the described embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the appended claims.

[0011] It will be appreciated from the following description, and for reasons of computational efficiency, that the components of the system can be arranged at any appropriate location within a distributed network of components without impacting the operation of the system.

[0012] Furthermore, it should be appreciated that the various links connecting the elements can be wired, traces, optical, or wireless links, or any appropriate combination thereof, or any other appropriate known or later developed element(s) that is capable of supplying and/or communicating data to and from the connected elements. Transmission media used as links, for example, can be any appropriate carrier for electrical signals, including coaxial cables, copper wire and fiber optics, electrical traces on a PCB, and/or the like.

[0013] Various aspects of the present disclosure will be described herein with reference to drawings that may be schematic illustrations of idealized configurations.

[0014] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this disclosure. [0015] Methods for underwater mapping surveys include using acoustic systems for determining the position of submerged vehicles. The acoustic systems include ultra short baseline (USBL), short baseline (SBL), long baseline (LBL) and sparse LBL systems. USBL positioning systems use a tight cluster of transceivers (e.g., transceivers spaced about 0.1 meters (m) apart) that compare the phase of incoming wavefronts to establish the direction to the source of the soundwave. These positioning systems can be mounted on a vessel that uses GNSS to establish the vessel’s position.

[0016] SBL and LBL systems may use three or more transmitters to establish the position that are spaced far apart relative to similar devices of USBL systems to allow triangulation. For example, the SBL systems may have transponders that are spaced more than 10 meters apart, while LBL systems may have transponders that are spaced more than 100 meters apart. The transmitters can be deployed on the water’s surface and tracked with GNSS, or may be placed just above the seafloor. In the latter case, the positions of the transmitters need to be established by another acoustic positioning system (e.g., a vesselbased short baseline acoustic positioning system) before the underwater survey is carried out.

[0017] Sparse LBL systems use as few as one transponder of established position on the seafloor that communicates with a transceiver coupled to an Inertial Navigation System (INS) on the AUV. A Kalman filter may use the ranges from the LBL transponder to minimize INS drift and smooths noise in the LBL range measurements using the INS, combining the measurements into a low error position estimate.

[0018] Related art underwater mapping surveys require a surface vessel (i.e., a ship) to deploy transponders and then perform a series of maneuvers to establish underwater positions of the transponders, which increases operating costs of the survey.

[0019] Inventive concepts propose systems, devices, and methods to overcome limitations and solve various problems associated with related art methods and devices for mapping surveys. In some examples, one or more positioning transponders are set up for deployment on the seafloor. The transponder may include a base or anchor which lands on the seafloor, a float surrounding the transponder, and a cable connecting the base to the transponder and/or the float. The transponder may be held stationary above the seafloor according to the specifications of the transponder.

[0020] In some examples, one or more AUVs are equipped with a module for storing and releasing the one or more positioning transponders at desired positions; a transceiver orientated to enable communication with the seafloor-deployed transponder(s) deployed below the AUV on the seafloor, with communication between the transceiver and the transponder(s) possible both when the AUV is surveying at depth and while the AUV is at the surface; and a GNSS receiver for establishing AUV position while the AUV is at the surface.

[0021] In some examples, a procedure for releasing transponders onto the seafloor comprises the AUV diving to the seafloor and releasing the transponders; additionally or alternatively, the transponders may be released by the AUV while the AUV is at the surface of the water. In this case, the transponders may be configured to descend through the water column and land in a desired orientation. [0022] In some examples, a procedure for surveying transponders in from the AUV comprises the AUV ascending to the surface; establishing the AUV position with, for example, GNSS; and then querying the seafloor-deployed transponders and establishing their positions from a series of positions on the surface using, for example, a USBL system on the AUV.

[0023] In some examples, the position-established transponders may be used as position references as the AUV carries out an underwater mapping survey. In some cases, after the AUV has completed the mapping survey, the transponders (e.g., LBL transponders) may be collected. In another example, the AUV may deploy a buoy equipped with a USBL system, a GNSS, and an INS which provides acoustic positioning for the AUV from the surface. Alternatively, one or more buoys may be deployed, each buoy including a GNSS and an LBL transponder. In some examples, the buoys are collected by the AUV after the completion of the survey. In some examples, the buoys may be repositionable by the AUV, such as in a case of a wayward buoy.

[0024] Inventive concepts will now be further described with reference to the figures. [0025] Fig. 1 illustrates a block diagram of a system 100 according to at least one example embodiment. The system 100 includes an Autonomous Underwater Vehicle (AUV) 104, a vessel 108, a post-mission processor 112, and external positioning system(s) 114. As indicated by the two-way arrows, these elements of the system 100 may be in wired and/or wireless communication with one another, although not necessarily at all times during the methods described herein. Stated another way, an element may lose the ability to communicate (or have the ability to communicate limited) with another element at certain points during an underwater survey process. For example, when the AUV 104 is at or above the surface of the water, the AUV 104 is able to communicate with the external positioning system 114 (e.g., embodied as a GPS satellite) but loses the ability to communicate with the external positioning system 114 when the AUV 104 is submerged below the water’s surface.

[0026] In general, the AUV 104 includes processing circuitry 116, sensor(s) 120, memory 124, power source 128, underwater positioning system(s) 132, surface positioning system(s) 136, propulsion device(s) 140, buoyancy system(s) 144, communication interface(s) 148, and payload compartment(s) (also called payload sections) that house transponder(s) 156, all of which are discussed in more detail below with reference to Fig.

1 and the remaining figures. In at least one example embodiment, the AUV 104 is a remotely operated vehicle (ROV) that is controllable (wired or wirelessly) remotely by an operator instead of or in addition to being autonomously controlled.

[0027] The vessel 108 may correspond to a surface vessel, such as a naval ship, commercial liner, or other marine vessel suited for above surface marine travel. In some examples, the vessel 108 corresponds to a subsurface marine vessel, such as a submarine or other vessel suitable for subsea travel. The vessel 108 may comprise the same or similar components as those illustrated for the AUV 104 and discussed in more detail below.

[0028] The post-mission processor 112 may comprise suitable hardware and/or software for processing sensor data from an AUV 104 for the sake of generating information related to an underwater survey conducted by the AUV 104 using one or more deployed transponders 156. The post-mission processor 112 may comprise processing circuitry having the same or similar structure as the processing circuitry 116 of the AUV 104 discussed below. In some examples, the post-mission processor 112 comprises a graphical user interface (GUI), such as a display, that enables user interaction to sift through sensor data and display of outputs relevant to the performed underwater survey. One non-limiting example of the post-mission processor 112 is a personal computer, such as a laptop, executing one or more software applications for underwater survey mapping based on data gathered by the AUV 104.

[0029] The external positioning system(s) 114 may comprise a satellite-based system, such as an GNSS, or other suitable system for determining positions of the AUV 104 and/or the vessel 108. As such, the external positioning system(s) 114 may be remotely located from the AUV 104 and the vessel 108.

[0030] Various components of the AUV 104 will now be discussed, beginning with the processing circuitry 116 and memory 124. The processing circuitry 116 includes suitable components for carrying out AUV component control, AUV navigation, and the various other computer-related or computer-controlled tasks described herein. Such processing circuitry 116 may comprise software, hardware, or a combination thereof. The processing circuitry 116 may be coupled to memory 124 that includes executable instructions. In this case, the processing circuitry 116 may comprise a processor (e.g., a microprocessor) that executes the instructions on the memory 124. The memory 124 may correspond to any suitable type of memory device or collection of memory devices configured to store instructions and/or other data (e.g., sensor data). Non-limiting examples of suitable memory devices that may be used include flash memory, Random Access Memory (RAM), Read Only Memory (ROM), variants thereof, combinations thereof, and/or the like. In some embodiments, the memory 124 and the processor may be integrated into a common device (e.g., a microprocessor may include integrated memory 124). Additionally or alternatively, the processing circuitry 116 may comprise hardware, such as an application specific integrated circuit (ASIC). Other non-limiting examples of the processing circuitry 116 include an Integrated Circuit (IC) chip, a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), a microprocessor, a Field Programmable Gate Array (FPGA), a collection of logic gates or transistors, resistors, capacitors, inductors, diodes, and/or the like. Some or all of the processing circuitry 116 may be provided on a Printed Circuit Board (PCB) or collection of PCBs. It should be appreciated that any appropriate type of electrical component or collection of electrical components may be suitable for inclusion in the processing circuitry 116.

[0031] The sensor(s) 120 may comprise one or more sensors suitable for sensing parameters that are relevant to underwater mapping surveys, such as a magnetometer, optical sensors, electric field sensors, conductivity sensors, oxygen sensors, depth sensors, sonar, cameras, and/or the like. The sensors 120 may further include sensors for general operation of the AUV 104 in an underwater environment. For example, the sensors 120 may comprise an accelerometer and/or a gyroscope for determining AUV 104 orientation, a temperature sensor, a water quality sensor, a light sensor, a power sensor, and/or the like. [0032] The power source 128 may comprise hardware and/or software for powering the other illustrated and non-illustrated components of the AUV 104. In at least one example, the power source 128 comprises a battery, such as a rechargeable battery. However, example embodiments are not limited thereto and the power source 128 may comprise a fuel cell (e.g., a hydrogen fuel cell) or other fueled power source.

[0033] The underwater positioning system 132 may comprise suitable hardware and/or software for determining an underwater position of the AUV 104, for example, relative to the vessel 108 and/or relative to other AUVs 104. Nonlimiting examples of the underwater positioning system 132 include a high precision Inertial Navigation System (INS), a Doppler Velocity Log (DVL), and/or an acoustic system such as an ultrashort baseline (USBL) acoustic system or a long baseline (LBL) acoustic system.

[0034] The surface positioning system(s) 136 may comprise suitable hardware and/or software for determining and/or tracking a surface position of the AUV 104 (e.g., a position of the AUV 104 when the AUV 104 is at or above the water’s surface). Nonlimiting examples of a surface positioning system 136 include a GNSS or other satellitebased system that provides positioning, navigation, and/or timing services for the AUV 104. In at least one embodiment, the surface positioning system 136 determines a surface position of the AUV 104 relative to a position of the vessel 108 and/or relative to a position of another AUV 104 (or relative to multiple AUVs 104). As described in more detail below with reference to Figs. 2 and beyond, the surface positioning system 136 and the underwater positioning system 132 may both be used to determine and help guide the AUV 104 to an appropriate underwater position for taking sensor measurements useful for performing an underwater survey using the transponders 156.

[0035] Still with reference Fig. 1, the propulsion device(s) 140 may include suitable hardware and/or software for causing underwater movements of the AUV 104. The propulsion device(s) 140 may include one or more motors (e.g., electric motors) with associated propeller(s) or thruster(s) or jets, as well as fixed and/or pivoting fins to control pitch, roll, and yaw of the AUV 104.

[0036] The buoyancy system(s) 144 may comprise suitable components for controlling the buoyancy of the AUV 104. For example, the AUV 104 may include a variable buoyancy system (VBS) that helps control AUV depth.

[0037] Communication interface(s) 148 may include suitable hardware and/or software for enabling wired and/or wireless communication between components of the AUV 104 and between the AUV 104 and the vessel 108, post-mission processor 112, and/or the external positioning system(s) 114. For example, the communication interface(s) 148 may include interfaces for acoustic serial communication (e.g., a peripheral component interconnect express (PCIe) bus), acoustic communication, blue light communication, Ethernet communication, Wi-Fi communication, cellular communication, BLUETOOTH communication, satellite communication, universal serial bus (USB) communication, and/or the like.

[0038] The payload compartment(s) 152 may include storage space for housing the one or more transponder(s) 156. In some cases, the payload compartment 152 may comprise a plurality of compartments, with each compartment housing a separate transponder 156. The payload compartment 152 may comprise an electromechanical release mechanism controlled by the processing circuitry 116 to deploy the transponders 156. For example, the payload compartment 152 may include a door controlled by the processing circuitry 116 to open to deploy the transponder 156. In this example, the processing circuitry 116 may cause the door to open when the AUV 104 is positioned at a desired location for deploying the transponder 156. [0039] The transponder 156 may be or comprise a device capable of receiving an acoustic signal and, in response, generate and emit a corresponding acoustic signal. For example, the transponder 156 may comprise one or more piezoelectric elements that convert acoustic energy into electrical energy and vice versa. In some examples and depending on the type of acoustic system used, the transponder 156 may be configured to be used in USBL systems, SBL systems, LBL systems, sparse LBL systems, combinations thereof, and/or the like. The transponder 156 includes one or more components that enable the transponder 156 to be positioned on the seafloor when the AUV 104 deploys the transponder 156. For example, the transponder 156 may comprise a base or anchor that anchors the transponder 156 to the seafloor. The transponder 156 may also comprise a float (e.g., a buoy) that partially or completely surrounds the body of the transponder 156. The float enables the body of the transponder 156 to float above the base of the transponder 156 when the transponder 156 is deployed at the seafloor.

[0040] A position of an element as described herein may refer to the position of the element in two dimensional and/or three dimensional space. For example, a two dimensional coordinate system may be used to refer to AUV surface positions and/or underwater positions (or locations) that are expressed in longitude and latitude. Additionally or alternatively, a three dimensional coordinate system established by the AUV 104 may be used to express surface positions and/or underwater positions (or locations) of the AUV 105 and/or transponders 156 in three dimensions. Similarly, determining a distance between two elements as described herein may occur in two dimensions and/or three dimensions. A distance between two elements may comprise a distance component indicative of a Euclidean distance between the two elements and a directional component that indicates how the two elements are positioned in the two or three dimensional space. The directional component may take the form of a bearing or other suitable directional indicator.

[0041] Fig. 2 is a schematic view of a transponder deployment 200 including elements from the system of Fig. 1. As may be appreciated, Fig. 2 illustrates one possible way for the transponder 156 to be deployed by the AUV 104. As depicted in Fig. 2, the transponder deployment 200 comprises the AUV 104 submerging below the waterline 204 to deploy the transponder 156. It is to be understood that while the AUV 104 is illustrated as deploying a single transponder 156, the AUV 104 may carry and deploy a plurality of transponders 156. [0042] While the AUV 104 is on the subsurface side 208 of the waterline 204, the AUV 104 may navigate along or near the seafloor 212. The processing circuitry 116 within the AUV 104 may track the position of the AUV 104 (e.g., based on signals from the sensors 120, based on the underwater positioning system 132, etc.) and may deploy the transponder 156 in accordance with an underwater survey plan, which may specify an estimated underwater location to deploy the transponder 156 for the purpose of conducting an underwater survey. When the AUV 104 arrives at the underwater location, the processing circuitry 116 may determine that the AUV 104 has reached the underwater location, and cause the transponder 156 to be deployed by actuating payload doors of the AUV 104. The processing circuitry 116 may repeat this process for each transponder 156 carried by the AUV 104 as the AUV 104 moves along the seafloor 212 with each transponder being dropped by the AUV 104 at a corresponding underwater location determined in accordance with the underwater survey plan.

[0043] The deployed transponder 156 may descend or sink from the AUV 104 onto the seafloor 212. In some embodiments, the base or anchor of the transponder 156 may provide sufficient weight to the transponder 156 to overcome buoyant forces, such that the transponder 156 lands on the seafloor 212. In some cases, the float of the transponder 156 may be attached to the base or anchor with a cable, with the float causing the acousticgenerating and/or acoustic-emitting portions of the transponder 156 to float above the base or anchor of the transponder 156. In some cases, once the AUV 104 has deployed the transponder(s) 156, the AUV 104 may resurface such that a portion of the AUV 104 is positioned on the surface side 206 of the waterline 204.

[0044] In some cases, the AUV 104 may deploy the transponder(s) 156 while remaining at the waterline 204. In other words, the AUV 104 may remain on the surface side 206 while navigating to the position in which the transponder 156 is to be deployed. In these cases, the transponder 156 may be configured to descend through a water column aligned with the AUV 104 when the AUV 104 deploys the transponder 156. The transponder 156 may include, in some examples, one or more stabilization components that minimize or mitigate transponder drift as the transponder 156 descends within the water column.

[0045] Fig. 3 A is a schematic view of an example implementation 300 of transponder surveying including elements from the system of Fig. 1. As may be appreciated, Fig. 3 A illustrates one possible way to survey transponders from the AUV 104. As depicted in Fig. 3A, the implementation 300 comprises the AUV 104 surfacing above the waterline 204 to survey the transponder 156. It is to be understood that, while a single transponder 156 is illustrated, the implementation 300 may comprise more than one transponder 156 being surveyed by the AUV 104. Surveying a transponder 156 may include determining an underwater position of the transponder 156 relative to the AUV 104 or some other reference point.

[0046] Once the AUV 104 ascends to the surface (e.g., such that one or more portions of the AUV 104 are positioned above the waterline 204), the external positioning system 114 (e.g., GNSS) may be used to establish various surface positions of the AUV 104 at various surface positions. For example, the external positioning system 114 may generate one or more signals 304 that are received by the AUV 104 (e.g., by a GNSS receiver) and processed by elements of the surface positioning system 136 in the AUV 104 to establish the position of the AUV 104. Based on the signals 304, the surface positioning system 136 may determine the position of the AUV 104. In one example, the external positioning system 114 may be used to determine a first surface position 316A of the AUV 104. The first surface position 316A may correspond to the position of the AUV 104 when the AUV 104 initially resurfaces after deploying the transponders 156. As discussed in more detail below, while at the first surface position 316A and at each surface position thereafter, the AUV 104 may determine its position relative to one or more of the transponders 156 using underwater positioning system 132. As a result, each surface position of the AUV 104 is associated to a set of relative distances of the AUV 104 to transponders 156. The AUV 104 may store and use the associations for navigational purposes when conducting an underwater survey to use the transponders 156 as position references.

[0047] The AUV 104 may, after surfacing, move along the surface of the waterline 204 to continue to establish a GPS position at each surface position and positional relationships with the transponders 156 at each surface position. For example, the AUV 104 may move from the first surface position 316A to a second surface position 316B at a second, later time. While at the second surface position 316B, the surface position of the AUV 104 may be tracked and/or established using the external positioning system 114 in a similar manner as to when the AUV 104 was positioned at the first surface position 316A. As noted above, the AUV 104 may also measure relative distances to each transponder 156 at each surface position. The AUV 104 may then move from the second surface position 316B to a third surface position at a third time later than the second time, and the AUV 104 may determine distances to transponders 156 at the third surface position. In some cases, the surface position of the AUV 104 may be continuously tracked using the external positioning system 114 and the surface positioning system 136 of the AUV 104, such that the surface position of the AUV 104 is continuously updated and known by the surface positioning system 136. Surface position information and associated transponder position information may be stored in the memory 124. The AUV 104 may continue to move to different surface positions and determine distances to transponders 156 until sufficient information has been collected to create a coordinate system in which the AUV 104 can navigate underwater accurately to conduct an underwater survey. In some cases, the AUV 104 may move to each surface position in a predetermined pattern as specified by the underwater survey plan (e.g., the surface positions are determined in advance as being useful for creating the coordinate system). For example, the underwater survey plan may specify an area to be surveyed and into which the transponders 156 have been deployed. The AUV 104 may, in this example, move along the surface of the waterline 204 over the area or a portion thereof to detect positions of the transponders 156 at different surface positions.

[0048] As described above, the AUV 104 may exchange acoustic signals 308 with one or more transponders 156 from two or more surface positions. In general, the acoustic signals 308 are generated by the AUV 104 and the transponder 156 in a manner that enables propagation of the signals through the water to be received by an AUV 104 or transponder 156. The acoustic signals 308 may be emitted from the transponders 156 at predetermined intervals or, alternatively, may be continuously emitted by the transponders 156. In some cases, the acoustic signals 308 may be emitted based on a query signal (e.g., an acoustic query signal) emitted by the AUV 104 and received by the transponders 156, with such query signal causing the transponders 156 to emit the acoustic signals 308. The AUV 104 may emit the query signal periodically, such as when the AUV 104 is at the first surface position 316A and at a later time when the AUV 104 is at the second surface position 316B. In some examples, the AUV 104 may output acoustic signals 308 that are received at the transponders 156, with the transponders 156 automatically providing a return acoustic signal that is received at the AUV 104. The AUV 104 and transponder 156 may generate acoustic signals with characteristics that are distinguishable from other underwater signals so as to reduce the possibility of interference. Distinguishable characteristics may include generating a certain number of acoustic signals with specific timing (e.g., three signals each one second apart), generating acoustic signals at a specific frequency, and/or the like.

[0049] As the AUV 104 moves along the surface of the waterline 204 to different surface positions, the AUV 104 and transponders 156 communicate acoustically which enables the processing circuitry 116 to collect information about the positions of the transponders 156 relative to the AUV 104 and/or relative to one another, which positions may be used to create an underwater coordinate system in which the AUV 104 operates during an underwater survey. The processing circuitry 116 may utilize one or more algorithms stored in the memory 124 (e.g., time of flight algorithms, triangulation algorithms, wave front bearing algorithms, combinations thereof, and/or the like) that use surface position information of the AUV 104 and the parameters of the acoustic signals 308 received and/or transmitted at each surface position to determine the underwater positions of the transponders 156. As an illustrative example, the AUV 104 receives acoustic signals 308 from the transponder 156 shown in Fig. 3 A at a first time while the AUV 104 is at the first surface position 316A and determines a position of the transponder 156 relative to the AUV 104 at the first surface position 316A. The AUV 104 then moves across the waterline 204 to the second surface position 316B at a second, later time. While in the second surface position 316B, the AUV 104 receives the acoustic signals 308 from the transponder 156 and determines a position of the transponder 156 relative to the AUV 104 at the second surface position 316B. The processing circuitry 116 uses the first surface position 316A and the second surface position 316B (and any other surface positions as determined by the surface positioning system 136) and parameters of the acoustic signals 308 (e.g., magnitude, direction, time of flight, etc.) sensed when the AUV 104 at each surface position to establish an underwater coordinate system that enables the AUV 104 to have accurate knowledge of its underwater position when performing an underwater survey. During the underwater survey, the AUV 104 may use the transponders 156 as position references.

[0050] In some examples, each of the transponders 156 may query one or more other transponders 156 to determine distances between one another. The distance information may be sent to the processing circuitry 116 on the AUV 104 (e.g., via an acoustic signal), with the processing circuitry 116 using such distance information to assist with determining the positions of the transponders 156. For example, the processing circuitry 116 may determine the underwater position of a first transponder 156, and then use the distance information between the first transponder 156 and a second transponder 156 to determine the underwater position of the second transponder 156.

[0051] In some embodiments, various operations of the AUV 104 described in Fig. 3 A may instead be performed by an additional entity. Fig. 3B illustrates a system 300A where one or more surface buoys 320 are deployed at the waterline 204 to provide surface position information to the AUV 104. For example, the AUV 104 (or other vessel) may deploy a buoy 320 equipped with of the same or similar underwater positioning system 132 (e.g., a USBL system and an INS) and the same or similar surface positioning system 136 (e.g., GNSS). In some examples, using buoys with a GNSS system obviates the need for the AUV 104 to use its GNSS system or even be equipped with a GNSS system. In general, the buoys 320 are capable of maintaining a relatively constant surface position via an anchor to the seafloor 212 (not shown) or by way of some other suitable mechanism (e.g., propeller(s)). In at least one example, a buoy 320 has autonomous navigation capabilities similar to or the same as the AUV 104.

[0052] In operation, the buoys 320 are deployed on the surface of the waterline 204, and may communicate with the external positioning system 114 in the same manner and for the same reasons as those described above (e.g., for the purpose of enabling the AUV 104 to establish its position relative to transponders 156 to track the AUV 104 during an underwater survey). Meanwhile, the buoys 320 communicate with the AUV 104 (e.g., via the USBL system) while the AUV 104 is submerged and/or with the transponders 156 in the same manner as described above to enable the AUV 104 to establish its position relative to transponders 156 to track the AUV 104 during an underwater survey. Alternatively, one or more buoys 320, each equipped with elements of the surface positioning system 136 (e.g., GNSS) and an LBL transponder may be deployed on the surface of the waterline 204. The LBL transponder may exchange acoustic signals with the AUV 104 and/or the transponders 156 while the AUV 104 is submerged, enabling the underwater position of the AUV 104 and/or the transponder 156 to be determined and tracked. Once the underwater survey has been completed, the buoy(s) may be collected by the AUV 104 or another vessel.

[0053] With reference to Fig. 4, an underwater survey 400 is shown in accordance with at least one example embodiment. As may be appreciated, Fig. 4 illustrates one possible way to conduct an underwater survey based on the underwater position of one or more transponders. As depicted in Fig. 4, the underwater survey 400 comprises the AUV 104 carrying out an underwater survey using the transponder 156 and a second transponder 156a as position references. It is to be understood that, while two transponders 156, 156a are illustrated in the underwater survey 400, the underwater survey 400 may comprise fewer or more transponders.

[0054] The underwater survey 400 may occur after the transponder surveying described with reference to Figs. 3 A and 3B, such that the AUV 104 can accurately navigate underwater to perform the underwater survey 400. As shown, the AUV 104 may submerge under the waterline 204 to conduct the underwater survey 400. For example, the AUV 104 may begin at a first underwater position 408A and move while remaining submerged to a second underwater position 408B and then to a third underwater position 408C. The AUV 104 may follow an underwater path as defined by the underwater survey plan. While travelling between underwater positions, the sensors 120 of the AUV 104 sense parameters that are relevant to the survey being conducted. For example, one or more magnetometers of the AUV 104 sense changes in magnetic field which may be used to characterize geological features of the seafloor 212, sonar of the AUV 104 may be used to map a contour of the seafloor 212, and/or the like. Data collected during the underwater survey 400 may be sent to the post-mission processor 112 for additional processing once the underwater survey 400 is complete.

[0055] The AUV 104 may conduct the underwater survey 400 while using the transponder 156 and the second transponder 156a as position references. The processing circuitry 116 may control the propulsion device 140 to cause the AUV 104 to perform the underwater survey 400. During the underwater survey 400, the AUV 104 may navigate from the first underwater position 408A to the second underwater position 408B by using the transponder 156 as a position reference. Similarly, the AUV 104 may navigate from the second underwater position 408B to the third underwater position 408C using the second transponder 156a as a position reference. In some cases, the AUV 104 may use both the transponder 156 and the second transponder 156a (and in some cases, additional transponders) as position references throughout the underwater survey 400. The AUV 104 may exchange acoustic signals with the transponder 156 and/or the second transponder 156a while conducting the underwater survey 400, which, in combination with the information obtained during the maneuvers from Figs. 3 A and/or 3B, enable the underwater positioning system 132 to determine the position of the AUV 104 while submerged.

[0056] In some cases, the underwater positioning system 132 may adjust or alter the navigation route of the AUV 104 when the determined position of the AUV 104 (e.g., based on the exchanged acoustic signals) does not comply with the underwater survey plan. For example, based on the position of the AUV 104 relative to the transponder 156 and/or the second transponder 156a, the underwater positioning system 132 may determine that the AUV 104 is off-course from the route specified in the underwater survey plan, and may adjust the path of the AUV 104 to correct course. In some embodiments, the underwater positioning system 132 may cause the AUV 104 to further exchange acoustic signals with the transponder 156 and/or the second transponder 156a to confirm that the AUV 104’s corrected course is in compliance with the underwater survey plan. In some embodiments, information about the exchanged signals between the AUV 104 and the transponder 156 and/or the second transponder 156a may be sent to the postmission processor 112. In some embodiments, the transponders (e.g., the transponder 156 and/or the second transponder 156a) may be collected at the end of the underwater survey 400.

[0057] Fig. 5 illustrates a method 500 for performing an underwater survey according to at least one example embodiment. The method 500 may be carried out by various elements described herein, including by the processing circuitry 116 controlling a corresponding AUV 104 to move and to collect sensor data with the sensors 120. Fig. 5 will be discussed with reference to a AUV 104, but the method 500 may be applied to additional AUVs. [0058] Operation 504 includes determining, based on an underwater survey plan, an underwater location for deploying a transponder. The underwater location for deploying the transponder 156 may be specified in the underwater survey plan, and may be predetermined before the underwater survey mapping is performed. The underwater location for deploying the transponder 156 may be determined based on a variety of factors, such as the underwater area being surveyed, the type of vessel 108 or AUV 104 used, the type of acoustic positioning system used, combinations thereof, and/or the like. The underwater location may be determined based on the surface position information and underwater position information collected and described with reference to Figs. 3 A and/or 3B. In some examples, the underwater location at which a transponder 156 is deployed from the AUV 104 is determined as a location that is directly above the intended position for the transponder 156 on the seafloor 212. In other examples, the underwater location at which the transponder 156 is deployed is determined to be some distance away from the intended position on the seafloor 212, in which case the course of the transponder 156 may be altered by underwater currents. In any event, the AUV 104 may be capable of moving the transponder 156 if needed. For example, the AUV 104 may be equipped with a hook or other suitable tool to “grab” and move the transponder 156 after deployment.

[0059] Operation 508 includes causing an AUV 104 to deploy, at the underwater location, the transponder 156. The processing circuitry 116 controls the propulsion device 140 to move the AUV 104 to the underwater location. The AUV 104 comprises the payload compartment 152 that carries the transponder 156 in the AUV 104 until the AUV 104 has reached the underwater location. In some embodiments, the underwater position of the AUV 104 may be tracked using, for example, the underwater positioning system 132. Upon reaching the underwater location, the AUV 104 may deploy the transponder 156. The AUV 104 may continue to deploy other transponders 156 at other underwater locations in the same or similar manner.

[0060] Operation 512 includes determining, after the AUV has deployed the transponder and based on satellite navigation information, a first surface position of the AUV at a first time. For example, the AUV 104 may deploy the transponder(s) 156 in operation 508 and then resurface at the first surface position 316A. Once the AUV 104 has resurfaced, the external positioning system 114 and the surface positioning system 136 may be used to determine that the AUV 104 is at the first surface position 316A.

[0061] Operation 516 includes receiving first signal information about first acoustic signals exchanged between the AUV 104 and the transponder 156 with the AUV at the first surface position. Operation 516 may occur at or near the first time mentioned in operation 512. While the AUV 104 is at the first surface position 316A, the first acoustic signals may be exchanged between the AUV 104 and the transponder 156. In some embodiments, the AUV 104 and the transponder 156 may exchange the first acoustic of signals while the surface positioning system 136 is being used to determine the surface position of the AUV 104. In some examples, the first of acoustic signals include one or more acoustic signals sent from the AUV 104 to the transponder 156 and one or more acoustic signals sent from the transponder 156 to the AUV 104 in response to receipt of a signal or signals from the AUV 104. Information about the first acoustic signals exchanged between the AUV 104 and the transponder 156 may be received by the processing circuitry 116 and saved in the memory 124.

[0062] Operation 520 includes receiving second signal information about second acoustic signals exchanged between the AUV 104 and the transponder 156 at a second time later than the first time. The AUV 104 may move from the first surface position 316A to the second surface position 316B, and the external positioning system 114 and the surface positioning system 136 may be used to determine that the AUV 104 is in the second surface position 316B. While the AUV 104 is in the second surface position 316B, the second acoustic signals is exchanged between the AUV 104 and the transponder 156 in the same or similar manner as the first acoustic signals. In some embodiments, the AUV 104 and the transponder 156 may exchange the second acoustic signals while the surface positioning system 136 is being used to determine the surface position of the AUV 104. Information about the second acoustic signals exchanged between the AUV 104 and the transponder 156 may be received by the processing circuitry 116 and saved in the memory 124.

[0063] Operation 524 includes determining, based on the first signal information and the second signal information, an underwater position of the transponder. The operation 524 may be performed by the processing circuitry 116 accessing one or more algorithms in the memory 124 to determine the underwater position of the transponder 156. For example, the processing circuitry 116 may implement a time of flight algorithm that determines a distance between the AUV 104 and the transponder 156 based on the amount of time taken for an acoustic signal to travel to from the AUV 104 to the transponder 156 and an amount of time taken for the AUV 104 to receive an acoustic signal from the transponder 156 that is generated by the transponder 156 in response to receiving the signal from the AUV 104. As another example, the processing circuitry 116 may use a triangulation algorithm that determines a direction associated with an acoustic signal and a direction associated with one or more additional acoustic signals to determine the distance between the AUV 104 and the transponder 156, and then uses the determined distance along with the surface position of the AUV 104 to determine the underwater position of the transponder 156.

[0064] In some cases, the operations 516, 520, and 524 may be repeated for each transponder when multiple transponders have been deployed. For example, when the AUV 104 is at the first surface position 316A, the AUV 104 may receive separate acoustic signals from each of the transponders 156 in response to each transponder 156 receiving acoustic signal(s) from the AUV 104. Similarly, when the AUV 104 is at the second surface position 316B the AUV 104 may again receive separate acoustic signals from each of the transponders 156. As a result, in the operation 524 the underwater position of each transponder 156 of the plurality of transponders may be determined.

[0065] Operation 528 includes causing the AUV 104 to conduct an underwater survey according to the underwater survey plan using the underwater position of the transponder as a reference. In some embodiments, the AUV 104 may perform the underwater survey 400 discussed above, and may use the transponder 156 and the second transponder 156a as positional references for conducting the underwater survey 400. The AUV 104 may exchange additional acoustic signals with the transponder 156 and/or the second transponder 156a as the AUV 104 conducts the underwater survey. Based on the exchanged signals, the underwater positioning system 132 may track the underwater position of the AUV 104 and apply that information to the map being constructed by the survey. In some embodiments, information generated by the AUV 104 may be sent to the post-mission processor 112.

[0066] As may be appreciated, the operations of the method 500 are performed autonomously and are carried out without corresponding human input (other than the human input to program the AUV to perform the autonomous operations). However, more or fewer operations of the method 500 may exist and/or more or fewer operations of the method may be performed autonomously.

[0067] It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It should also be understood that, depending on the example or embodiment, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, and/or may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the disclosed techniques according to different embodiments of the present disclosure). In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a computing device.

[0068] It should be appreciated that inventive concepts cover any embodiment in combination with any one or more other embodiments, any one or more of the features disclosed herein, any one or more of the features as substantially disclosed herein, any one or more of the features as substantially disclosed herein in combination with any one or more other features as substantially disclosed herein, any one of the aspects/features/embodiments in combination with any one or more other aspects/features/embodiments, use of any one or more of the embodiments or features as disclosed herein. It is to be appreciated that any feature described herein can be claimed in combination with any other feature(s) as described herein, regardless of whether the features come from the same described embodiment.

[0069] Specific details were given in the description to provide a thorough understanding of example embodiments. However, it will be understood by one of ordinary skill in the art that example embodiments may be practiced without these specific details. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. [0070] While illustrative embodiments of the disclosure have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.

[0071] It should be understood that the terms “first,” “second,” “third,” etc. are used for convenience of description and do not limit example embodiments. For example, a particular element may be referred to a “first” element in some cases, and a “second” element in other cases without limiting example embodiments.

[0072] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “include,” “including,” “includes,” “comprise,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The term “and/or” includes any and all combinations of one or more of the associated listed items.

[0073] The phrases “at least one,” “one or more,” “or,” and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “one or more of A, B, or C,” “A, B, and/or C,” and “A, B, or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together.

[0074] The term “a” or “an” entity refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more,” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising,” “including,” and “having” can be used interchangeably.

[0075] The term “automatic” and variations thereof, as used herein, refers to any process or operation, which is typically continuous or semi-continuous, done without material human input when the process or operation is performed. However, a process or operation can be automatic, even though performance of the process or operation uses material or immaterial human input, if the input is received before performance of the process or operation.

[0076] Aspects of the present disclosure may take the form of an embodiment that is entirely hardware, an embodiment that is entirely software (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module,” or “system.” Any combination of one or more computer-readable medium(s) may be utilized. The computer- readable medium may be a computer-readable signal medium or a computer-readable storage medium.

[0077] A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer-readable storage medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[0078] A computer-readable signal medium may include a propagated data signal with computer-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer- readable signal medium may be any computer-readable medium that is not a computer- readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer-readable medium may be transmitted using any appropriate medium, including, but not limited to, wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0079] The terms “determine,” “calculate,” “compute,” and variations thereof, as used herein, are used interchangeably and include any type of methodology, process, mathematical operation or technique.

[0080] Example embodiments may be configured as follows:

(1) A system, comprising: an Autonomous Underwater Vehicle (AUV) including a payload section for storing and deploying a transponder; a processor; and a memory coupled with the processor and storing instructions thereon that, when executed by the processor, enable the processor to: determine, based on an underwater survey plan, an underwater location for deploying the transponder; cause the AUV to deploy, at the underwater location, the transponder; determine, after the AUV has deployed the transponder and based on satellite navigation information, a first surface position of the AUV at a first time; determine, based on at least the first surface position and a set of acoustic signals exchanged between the AUV and the transponder, an underwater position of the transponder; and cause the AUV to conduct an underwater survey according to the underwater survey plan using the underwater position of the transponder as a reference.

(2) The system of claim 1, wherein the set of acoustic signals comprises first acoustic signals exchanged at the first time and second acoustic signals exchanged at a second time later than the first time.

(3) The system of one or more of (1) to (2), wherein the AUV is in a second surface position at the second time, and wherein the underwater position of the transponder is determined further based on the second surface position.

(4) The system of one or more of (1) to (3), wherein the processor determines the underwater position of the transponder relative to the AUV.

(5) The system of one or more of (1) to (4), wherein the processor determines the underwater position of the transponder based on time of flight information associated with set of acoustic signals.

(6) The system of one or more of (1) to (5), wherein the AUV deploys the transponder while the AUV is submerged.

(7) The system of one or more of (1) to (6), wherein the AUV comprises a Global Navigation Satellite System (GNSS) receiver.

(8) A method, comprising: determining, based on an underwater survey plan, an underwater location for deploying a transponder; causing an Autonomous Underwater Vehicle (AUV) to deploy, at the underwater location, the transponder; determining, after the AUV has deployed the transponder and based on satellite navigation information, a first surface position of the AUV at a first time; receiving first signal information about first acoustic signals exchanged between the AUV and the transponder at the first surface position; receiving second signal information about second acoustic signals exchanged between the AUV and the transponder at a second time later than the first time; determining, based on the first signal information and the second signal information, an underwater position of the transponder; and conducting an underwater survey with the AUV according to the underwater survey plan using the underwater position of the transponder as a reference.

(9) The method of (7), wherein the AUV is at a second surface position at the second time, and wherein the second surface position is included in the second signal information.

(10) The method of one or more of (7) to (9), wherein the underwater position of the transponder is determined relative to the AUV.

(11) The method of one or more of (7) to (10), wherein the underwater position of the transponder is determined based on time of flight information associated with the first and second acoustic signals.

(12) The method of one or more of (7) to (11), wherein the AUV deploys the transponder while the AUV is submerged.

(13) The method of one or more of (7) to (12), further comprising: receiving third signal information about third acoustic signals sent between the AUV and a second transponder with the AUV at the first surface position; receiving fourth signal information about fourth acoustic signals sent between the AUV and the second transponder with the AUV at a second surface position; and determining, based on the third signal information and the fourth signal information, an underwater position of the second transponder.

(14) The method of one or more of (7) to (13), wherein the AUV conducts the underwater survey using the second underwater position of the second transponder as a reference.

(15) An Autonomous Underwater Vehicle (AUV) system, comprising: a payload section for storing and deploying a transponder; a transceiver capable of communicating with the transponder; a Global Navigation Satellite System (GNSS) receiver; a processor; and a memory coupled with the processor and storing instructions thereon that, when executed by the processor, enable the processor to: determine, based on an underwater survey plan, an underwater location for deploying the transponder; cause the AUV to deploy, at the underwater location, the transponder; determine, after the AUV has deployed the transponder and based on a signal received at the GNSS receiver, a first surface position of the AUV at a first time; determine, based on the first surface position and a plurality of acoustic signals exchanged between the transceiver and the transponder, an underwater position of the transponder; and cause the AUV to conduct an underwater survey according to the underwater survey plan using the underwater position of the transponder as a reference.

(16) The AUV system of (15), wherein the plurality of acoustic signals comprises first acoustic signals exchanged at the first time and second acoustic signals exchanged at a second time later than the first time.

(17) The AUV system of one or more of (15) to (16), wherein the AUV is in a second surface position at the second time, and wherein the underwater position of the transponder is determined further based on the second surface position.

(18) The AUV system of one or more of (15) to (17), wherein the instructions, when executed by the processor, further enable the processor to: receive third signal information about third acoustic signals sent between the AUV and a second transponder with the AUV at the first surface position; receive fourth signal information about fourth acoustic signals sent between the AUV and the second transponder with the AUV at a second surface position; and determine, based on the third signal information and the fourth signal information, a second underwater position of the second transponder.

(19) The AUV system of one or more of (15) to (18), wherein the processor determines the underwater position of the transponder based on time of flight information associated with the plurality of acoustic signals.

(20) The AUV system of one or more of (15) to (19), wherein the AUV deploys the transponder from the payload section when the AUV is submerged in a body of water at a second time before the first time.

Claims

What Is Claimed Is:

1. A system, comprising: an Autonomous Underwater Vehicle (AUV) including a payload section for storing and deploying a transponder; a processor; and a memory coupled with the processor and storing instructions thereon that, when executed by the processor, enable the processor to: determine, based on an underwater survey plan, an underwater location for deploying the transponder; cause the AUV to deploy, at the underwater location, the transponder; determine, after the AUV has deployed the transponder and based on satellite navigation information, a first surface position of the AUV at a first time; determine, based on at least the first surface position and a set of acoustic signals exchanged between the AUV and the transponder, an underwater position of the transponder; and cause the AUV to conduct an underwater survey according to the underwater survey plan using the underwater position of the transponder as a reference.

2. The system of claim 1, wherein the set of acoustic signals comprises first acoustic signals exchanged at the first time and second acoustic signals exchanged at a second time later than the first time.

3. The system of claim 2, wherein the AUV is in a second surface position at the second time, and wherein the underwater position of the transponder is determined further based on the second surface position.

4. The system of claim 1, wherein the processor determines the underwater position of the transponder relative to the AUV.

5. The system of claim 1, wherein the processor determines the underwater position of the transponder based on time of flight information associated with set of acoustic signals.

6. The system of claim 1, wherein the AUV deploys the transponder while the AUV is submerged.

7. The system of claim 1, wherein the AUV comprises a Global Navigation Satellite System (GNSS) receiver.

8. A method, comprising: determining, based on an underwater survey plan, an underwater location for deploying a transponder; causing an Autonomous Underwater Vehicle (AUV) to deploy, at the underwater location, the transponder; determining, after the AUV has deployed the transponder and based on satellite navigation information, a first surface position of the AUV at a first time; receiving first signal information about first acoustic signals exchanged between the AUV and the transponder at the first surface position; receiving second signal information about second acoustic signals exchanged between the AUV and the transponder at a second time later than the first time; determining, based on the first signal information and the second signal information, an underwater position of the transponder; and conducting an underwater survey with the AUV according to the underwater survey plan using the underwater position of the transponder as a reference.

9. The method of claim 8, wherein the AUV is at a second surface position at the second time, and wherein the second surface position is included in the second signal information.

10. The method of claim 9, wherein the underwater position of the transponder is determined relative to the AUV.

11. The method of claim 8, wherein the underwater position of the transponder is determined based on time of flight information associated with the first and second acoustic signals.

12. The method of claim 8, wherein the AUV deploys the transponder while the AUV is submerged.

13. The method of claim 8, further comprising: receiving third signal information about third acoustic signals sent between the AUV and a second transponder with the AUV at the first surface position; receiving fourth signal information about fourth acoustic signals sent between the AUV and the second transponder with the AUV at a second surface position; and determining, based on the third signal information and the fourth signal information, an underwater position of the second transponder.

14. The method of claim 13, wherein the AUV conducts the underwater survey using the underwater position of the second transponder as a reference.

15. An Autonomous Underwater Vehicle (AUV) system, comprising: a payload section for storing and deploying a transponder; a transceiver capable of communicating with the transponder; a Global Navigation Satellite System (GNSS) receiver; a processor; and a memory coupled with the processor and storing instructions thereon that, when executed by the processor, enable the processor to: determine, based on an underwater survey plan, an underwater location for deploying the transponder; cause the AUV to deploy, at the underwater location, the transponder; determine, after the AUV has deployed the transponder and based on a signal received at the GNSS receiver, a first surface position of the AUV at a first time; determine, based on the first surface position and a plurality of acoustic signals exchanged between the transceiver and the transponder, an underwater position of the transponder; and cause the AUV to conduct an underwater survey according to the underwater survey plan using the underwater position of the transponder as a reference.

16. The AUV system of claim 15, wherein the plurality of acoustic signals comprises first acoustic signals exchanged at the first time and second acoustic signals exchanged at a second time later than the first time.

17. The AUV system of claim 16, wherein the AUV is in a second surface position at the second time, and wherein the underwater position of the transponder is determined further based on the second surface position.

18. The AUV system of claim 15, wherein the instructions, when executed by the processor, further enable the processor to: receive third signal information about third acoustic signals sent between the AUV and a second transponder with the AUV at the first surface position; receive fourth signal information about fourth acoustic signals sent between the AUV and the second transponder with the AUV at a second surface position; and determine, based on the third signal information and the fourth signal information, a second underwater position of the second transponder.

19. The AUV system of claim 15, wherein the processor determines the underwater position of the transponder based on time of flight information associated with the plurality of acoustic signals.

20. The AUV system of claim 15, wherein the AUV deploys the transponder from the payload section when the AUV is submerged in a body of water at a second time before the first time.