Patent Description:
This invention relates to marine seismology and more particularly relates to the deployment of ocean bot o seismic autonomous underwater vehicles (AUVs).

Marine seismic data acquisition and processing generates a profile (image) of a geophysical structure under the seafloor. Reflection seismology is a method of geophysical exploration to determine the properties of the Earth's subsurface, which is especially helpful in determining an accurate location of oil and gas reservoirs or any targeted features. Marine reflection seismology is based on using a controlled source of energy (typically acoustic energy) that sends the energy though a body of water and subsurface geologic formations. The transmitted acoustic energy propagates downwardly through the subsurface as acoustic waves, also referred to as seismic waves or signals. By measuring the time it takes for the reflections or refractions to come back to seismic receivers (also known as seismic data recorders or nodes), it is possible to evaluate the depth of features causing such reflections. These features may be associated with subterranean hydrocarbon deposits or other geological structures of interest.

There are many methods to record the reflections from a seismic wave off the geological structures present in the surface beneath the seafloor. In one method, a marine vessel tows an array of seismic data recorders provided in streamers. In another method, seismic data recorders are placed directly on the ocean bottom by a variety of mechanisms, including by the use of one or more of Autonomous Underwater Vehicles (AUVs), Remotely Operated Vehicles (ROVs), by dropping or diving from a surface or subsurface vessel, or by attaching autonomous seismic nodes to a cable that is deployed behind a marine vessel. The data recorders may be discrete, autonomous units, with no direct connection to other nodes or to the marine vessel, where data is stored and recorded.

Emerging technologies in marine seismic surveys need a fast and cost-effective system for deploying and recovering seismic receivers that are configured to operate underwater, and in particular ocean bottom seismic nodes. Newer technologies use AUVs that have a propulsion system and are programmed to move to desired positions and record seismic data. In general, the basic structure and operation of a seismic AUV is well known to those of ordinary skill. For example, Applicant's <CIT>, discloses one type of autonomous underwater vehicle for marine seismic surveys. Applicant's <CIT>, discloses another type of seismic AUV. Further, it is also generally known how to guide AUVs to the bottom of the ocean to land at predetermined positions, such as that disclosed in Applicant's <CIT> and <CIT>. <CIT> discloses an autonomous underwater vehicle (AUV) for recording seismic signals during a marine seismic survey. The AUV includes a body having a flush shape; a buoyancy system located inside the body and configured to control a buoyancy of the AUV while traveling underwater; a processor connected to the buoyancy system and configured to select one of plural phases for the buoyancy system at different times of the seismic survey.

<CIT> discloses an oceanographic sampling system including two or more underwater vehicles disposed in an array and an array controller for controlling the array of underwater vehicles as data is acquired. Each underwater vehicle includes a propulsion system for moving the underwater vehicle independently of the other underwater vehicles, a sensor for sensing an ocean parameter and providing sensor data representative of the ocean parameter as the underwater vehicle moves, a navigation subsystem for determining position data representative of the position of the underwater vehicle as the sensor data is acquired and a synchronizing subsystem for time synchronizing the sensor data and the position data acquired by the underwater vehicle with sensor data and position data acquired by other underwater vehicles. The array of underwater vehicles may function as a large aperture phased array, and phased array analysis techniques may be applied to the time-synchronized sensor data and position data. <CIT> discloses apparatuses, systems, and methods for guiding and/or positioning a plurality of seismic nodes on or near the seabed by an autonomous underwater vehicle (AUV) or a remotely operated vehicle (ROV). <CIT> describes a method for measuring the location of an underwater body. Buoys <NUM> and <NUM> floating on the water surface transmit acoustic signals including information on its own absolute location as a beacon wave. An underwater body measures the relative location between the buoys and oneself according to the coming direction of the beacon wave transmitting from the buoys. Further, the body extracts the information on the buoy's absolute location including in the beacon wave. The body computes its own absolute location based on both the information on buoy's absolute location and the information on the relative location between the buoy and oneself.

Because a seismic survey may require hundreds if not thousands of AUVs for a particular survey, an AUV is needed that is easy to operate and relatively straightforward and cost-effective to manufacture. However, existing technologies for deploying a seismic AUV to the ocean bottom are not cost effective and present many operational problems. A need exists for an improved seismic AUV deployment method that is more cost effective and less complex, more reliable, and able to deploy thousands of seismic AUVs in an efficient manner.

The invention provides a method for performing a marine seismic survey in a body of water and a system configured to perform a marine seismic survey on the seabed as set out in the independent claims.

Some optional features are set out in the dependent claims. Systems and methods are disclosed for deploying seismic autonomous underwater vehicles (AUVs) to the seabed by using a variety of guidance systems and/or positioning/communication protocols based on a particular AUV's location. A combination of a USBL system and a phased array system may be used to deploy different groups of AUVs on one or more deployment lines of a seismic survey area. The deployment lines may be generally perpendicular or parallel to a deployment vessel' s direction of travel. Once a certain number of AUVs have landed on the seabed, the landed AUVs may be used to guide flying AUVs to their intended seabed destination by using acoustic pingers and phased array techniques. Time intervals for acoustic signals emitted from landed AUVs may be generated using a predetermined Time of Emission pattern and received by a phased array receiver on flying AUVs.

The method may further comprise emitting acoustic pulses at a first frequency from a first plurality of landed seismic AUVs on a first deployment line and emitting acoustic pulses at a second frequency from a second plurality of landed seismic AUVs on a second deployment line. The method may further comprise guiding a flying AUV across one or more deployment lines and upon crossing an intended destination deployment line guiding the flying AUV substantially in-line with the intended destination deployment line until reaching a target seabed position on the intended destination deployment line.

The system may comprise a first deployment line on the seabed comprising a first plurality of seismic AUVs and a second plurality of seismic AUVs. The first plurality of AUVs may be configured to be guided to the seabed using USBL.

The AUVs of each deployment line may be configured to emit acoustic pulses at a particular frequency after landing. A time interval of the emitted pulses may be determined by a Time of Emission (TOE) pattern, wherein each AUV after landing is configured to emit an acoustic pulse at a different time slot. The TOE pattern may repeat itself a plurality of times across a plurality of different AUV groups for each of the first and second deployment lines. The TOE pattern may create at least a predetermined minimum separation between the emitted pulses received by an approaching seismic AUV.

The system may further comprise a second deployment line on the seabed comprising a third plurality of seismic AUVs and a fourth plurality of seismic AUVs, wherein each AUV of the third plurality of seismic AUVs is configured to be guided to the seabed using USBL, wherein each AUV of the fourth plurality of seismic AUVs is configured to be guided to the seabed using phased array, wherein each of the AUVs of the first deployment line is configured to emit acoustic pulses at a first frequency after landing and each of the AUVs of the second deployment line is configured to emit acoustic pulses at a second frequency after landing.

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

Various features and advantageous details are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. The scope of the invention should be determined with reference to the appended claims.

An autonomous underwater vehicle (AUV) may be used to record seismic signals on or near the seabed. A seismic AUV in the following description is considered to encompass an autonomous self-propelled underwater node that has one or more sensors capable of detecting seismic waves in a marine environment. In general, the structure and operation of a seismic AUV is well known to those of ordinary skill. For example, Applicant's <CIT>, discloses one type of autonomous underwater vehicle for marine seismic surveys.

<FIG> is reproduced from <FIG> of Applicant's <CIT>. The disclosed embodiment may use one or more systems, components, and/or features from the AUV described in <FIG> illustrates AUV <NUM> having a body <NUM> in which a propulsion system may be located. The propulsion system may include one or more propellers <NUM> and a motor <NUM> for activating the propeller <NUM>. Other propulsion systems may be used, such as jets, thrusters, pumps, etc. Further, the propellers (or other propulsion systems) may be located at various parts of the AUV, such as front, sides, or the top or bottom of the AUV, such as that disclosed in <CIT>. Alternatively, the propulsion system may include adjustable wings <NUM> for controlling a trajectory of the AUV. Motor <NUM> may be controlled by a processor/controller <NUM>. Processor <NUM> may also be connected to one or more seismic sensors <NUM>. Seismic sensor <NUM> may have a shape such that when the AUV lands on the seabed, the seismic sensor achieves a good coupling with the seabed sediment. The seismic sensor may include one or more of a hydrophone, geophone, accelerometer, etc. For example, if a 4C (four component) survey is desired, the seismic sensors may include three accelerometers and a hydrophone, i.e., a total of four sensors. Alternatively, the seismic sensor may include three geophones and a hydrophone. Of course, other sensor combinations are possible, and may include one or more of a hydrophone, geophone, accelerometer, electromagnetic sensor, depth sensor, MEMs, or a combination thereof. Seismic sensor <NUM> may be located completely or partially inside body <NUM>. A memory unit <NUM> may be connected to processor <NUM> and/or seismic sensor <NUM> for storing seismic data recorded by seismic sensor <NUM>. Power system <NUM> (such as one or more batteries) may be used to power all these components. Battery <NUM> may be allowed to shift its position along a track <NUM> to change the AUV's center of gravity. This shift may be controlled by processor <NUM>. The AUV may also include a clock and digital data recorder (not shown).

In one embodiment, the AUV may also include an inertial navigation system (INS) <NUM> configured to guide the AUV within a body of water and to a desired location. An inertial navigation system may include a module containing accelerometers, gyroscopes, magnetometers, or other motion-sensing devices. The INS may initially be provided with the current position and velocity of the AUV from another source, for example, a human operator, a GPS satellite receiver, a deployed subsea station, a deployed ROV, another AUV, from one or more surface vessels, etc., and thereafter, the INS computes its own updated position and velocity by integrating (and optionally filtrating) information received from its motion sensors. One advantage of an INS is that it requires no external references in order to determine its position, orientation or velocity once it has been initialized. However, the E S may still require regular or periodic updates from an external reference to update the AUV's position to decrease the positioning error of the AUV, particularly after long periods of time subsea. As noted above, alternative systems may be used, as, for example, acoustic positioning. An optional acoustic Doppler Velocity Log (DVL) (not shown) can also be employed as part of the AUV, which provides bottom-tracking capabilities for the AUV. Sound waves bouncing off the seabed can be used to determine the velocity vector of the AUV, and combined with a position fix, compass heading, and data from various sensors on the AUV, the position of the AUV can be determined. This assists in the navigation of the AUV, provides confirmation of its position relative to the seabed, and increases the accuracy of the AUV position in the body of water. In other embodiments, and to reduce the complexity of the AUV, an INS may not be utilized.

Besides or instead of INS <NUM>, the AUV may include compass <NUM> and other sensors <NUM> as, for example, an altimeter for measuring its altitude, a pressure gauge, an interrogator module, etc. The AUV <NUM> may optionally include an obstacle avoidance system <NUM> and a communication device <NUM> (e.g. , Wi-Fi or other wireless interface, such as a device that uses an acoustic link) or other data transfer device capable of wirelessly transferring seismic data and/or control status data. One or more of these elements may be linked to processor <NUM>. The AUV further includes antenna <NUM> (which may be flush with or protrude from the AUV s body) and corresponding acoustic system <NUM> for subsea communications, such as communicating with a deployed ROV (or other underwater station), another AUV, or a surface vessel or station. For surface communications (e.g. , while the AUV is on a ship), one or more of antenna <NUM> and communication device <NUM> may be used to transfer data to and from the AUV. Stabilizing fins and/or wings <NUM> for guiding the AUV to the desired position may be used with propulsion system for steering the AUV. However, in one embodiment, the AUV has no fins or wings. The AUV may include buoyancy system <NUM> for controlling the AUV's depth and keeping the AUV steady after landing.

Acoustic system <NUM> may be an Ultra-Short Baseline (USBL) system, also sometimes known as Super Short Base Line (SSBL). This system uses a method of underwater acoustic positioning. A complete USBL system may include a transceiver or acoustic positioning system mounted on a pole under a vessel or ROV (such as Hi-PAP or µPAP, commercially available by Kongsberg) and a transponder on the AUV. In general, a hydro-acoustic positioning system consists of both a transmitter and a receiver, and any Hi-PAP or µPAP or transponder system acts as both a transmitter and a receiver. An acoustic positioning system uses any combination of communications principles for measurements and calculations, such as SSBL. In one embodiment, the acoustic positioning system transceiver comprises a spherical transducer with hundreds of individual transducer elements. A signal (pulse) is sent from the transducer (such as a Hi-PAP or µPAP head on the surface vessel), and is aimed towards the seabed transponder located on the AUV. This pulse activates the transponder on the AUV, which responds to the vessel transducer after a short time delay. The transducer detects this return pulse and, with corresponding electronics, calculates an accurate position of the transponder (AUV) relative to the vessel based on the ranges and bearing measured by the transceiver. In one embodiment, to calculate a subsea position, the USBL system measures the horizontal and vertical angles together with the range to the transponder (located in the AUV) to calculate a 3D position projection of the AUV relative to a separate station, basket, ROV, or vessel. An error in the angle measurement causes the position error to be a function of the range to the transponder, so an USBL system has an accuracy error increasing with the range. Alternatively, a Short Base Line (SBL) system, an inverted short baseline (iSBL) system, or an inverted USBL (iUSBL) system may be used, the technology of which is known in the art. For example, in an iUSBL system, the transceiver is mounted on or inside the AUV while the transponder/responder is mounted on a separate vessel/station and the AUV has knowledge of its individual position rather than relying on such position from a surface vessel (as is the case in a typical USBL system). In another embodiment, a long baseline (LBL) acoustic positioning system may be used. In a LBL system, reference beacons or transponders are mounted on the seabed around a perimeter of a work site as reference points for navigation. The LBL system may use an USBL system to obtain precise locations of these seabed reference points. Thus, in one embodiment, the reference beacon may comprise both an USBL transponder and a LBL transceiver. The LBL system results in very high positioning accuracy and position stability that is independent of water depth, and each AUV can have its position further determined by the LBL system. The acoustic positioning system may also use an acoustic protocol that utilizes wideband Direct Sequence Spread Spectrum (DSSS) signals. The AUV may be equipped with a plurality of communication devices, such as an USBL beacon capable of receiving and transmitting acoustic signals, and a phased array receiver (or system) that is able to determine the direction of an incoming acoustic signal by analysis of the signal phase. The AUV may also be equipped with an acoustic modem.

With regard to the AUV's internal configuration, the AUV includes a CPU that may be connected to an inertial navigation system (INS) (or compass or altitude sensor and acoustic transmitter for receiving acoustic guidance from the mother vessel), a wireless interface, a pressure gauge, and an acoustic transponder. The INS is advantageous when the AUV's trajectory has been changed, for example, because of an encounter with an unexpected object (e.g., fish, debris, etc.), because the INS is capable of taking the AUV to the desired final position as it encounters currents, wave motion, etc. Also, the INS may have high precision. For example, an INS may be accurate up to <NUM>. <NUM>% of the travelled distance, and a USBL system may be accurate up to <NUM>% of the slant range. Thus, it is expected that for a target having a depth of <NUM>, the INS and/or the acoustic guidance is capable of steering the AUV within +/- <NUM> of the desired target location. The INS may be also configured to receive data from a surface vessel and/or a deployed ROV to increase its accuracy. The AUV may include multiple CPUs. For example, a second CPU may be configured to control one or more attitude actuators and a propulsion system. One or more batteries may be located in the AUV. A seismic payload is located inside the AUV for recording the seismic signals. As another embodiment, an obstacle avoidance system may be included in the AUV, which is generally configured to detect an object in the path of the AUV and divert the AUV from its original route to avoid contact with the object. In one example, the obstacle avoidance system includes a forward looking sonar. The AUV includes any necessary control circuitry and software for associated components. In one embodiment, the AUV may have various operational modes, such as wakeup, sleep, maintenance, and travel modes.

Those skilled in the art would appreciate that more or less modules may be added to or removed from the AUV. For example, the AUV may include variable buoyancy functionality, such as the ability to release a degradable weight on the bottom of the ocean after seismic recording to assist in the rise or surfacing of the AUV to a recovery spot (such as on or near the ocean surface). In other embodiments, the AUV may include one or more buoyancy or ballast tanks that may be flooded with air or water to assist in the vertical navigation of the AUV, such as described in more detail in Applicant's <CIT>. In another embodiment, the AUV may include a suction skirt that allows water to be pumped out of a compartment under the AUV after it has landed to create a suction effect towards the seabed. In still other embodiments, the AUV may include one or more seabed coupling mechanisms or self-burying functionality, such as the ability to rock or twist into the ocean by specific movements of the AUV or the use of a plurality of water outlets on the bottom of the AUV to fluidize the seabed sediment, as described in more detail in Applicant's <CIT> and <CIT>.

In one embodiment, minimal acoustic devices may be required on the AUV, which decreases the overall cost of the AUV and guidance/deployment protocols during deployment and retrieval of the AUVs to and from the seabed. For example, for acoustic communications each AUV may only comprise a USBL beacon and a phased array system, such as but not limited to a Sonardyne beacon and an Arkeocean phase array system. In one embodiment, the phase array system may comprise a Combined Acoustic Phased Array (CAPA) and a Triton processing board. The phased array is configured to intercept and/or receive the acoustic signals emitted by other seismic AUVs (such as previously landed seismic AUVs) and to guide the AUV to the seabed based on those received acoustic signals.

The disclosed AUV deployment and guidance system provides numerous benefits over previously disclosed deployment systems and methods for out bound guidance of seismic AUVs from a deployment vessel to the seabed, including having AUVs that are less complex and more reliable, deploying a high number of AUVs within a relatively short time period, and more precise coordination for better seabed positioning of the AUVs. The disclosed system may be utilized whether the AUVs are deployed directly from a surface vessel or from a subsea station (such as a lowered basket). Further, one or more surface vessels may be utilized to deploy the AUVs and to communicate with the AUVs. Still further, the particular retrieval method of the AUVs is not limited, and a wide variety of retrieval options and inbound guidance protocols may be used to recover some or all of the AUVs.

The disclosed system and method may use a variety of guidance systems and/or communication protocols based on the particular AUVs location and deployment time, both relative to the surface vessel and the other AUVs. In embodiments, the system uses a combination of a USBL system and an acoustic pinger system detected by a phase array system of each AUV. The disclosed guidance system uses a first positioning/communications system (such as USBL) to deploy a first plurality of AUVs to the seabed, and then uses a second positioning/communications system comprising phased array detectors at each AUV detecting acoustic signals emitted by the first plurality of AUVs, (e.g. from acoustic pingers) to deploy a second plurality of AUVs to the seabed. Each of these positioning/communications systems, by themselves, is known in the art. However, the particular use of these different systems as described herein is novel and offers a much more efficient and effective AUV deployment model than currently available. The disclosed outbound guidance system is not particularly dependent on the particular seismic AUV utilized, as long as the AUV is able to communicate with the different types of USBL and acoustic pingers and comprises the phased array receiver utilized in the disclosed guidance system.

In embodiments, a USBL system is used to actively guide a first plurality of AUVs to the seabed, such as AUVs deployed to the seabed before any other AUVs are deployed to the seabed. The USBL system may be configured to measure the position of the AUV in flight to monitor each of the AUV trajectories. Some or all of the deployed AUVs are configured to act as sea bottom acoustic pingers, e.g., they are configured to emit an acoustic pulse at a given frequency and at a given time. Once a certain number of AUVs of a given deployment line have landed, their coordinates are measured by the USBL system and potentially given to a second plurality of AUVs, and the coordinates of the first plurality of AUVs may then be used to guide the second plurality of AUVs to their intended seabed destination. A final guidance phase is performed using a phased array system located on each AUV. Once a certain number of AUVs of a given deployment line has landed, each AUV may begin emitting pulses at its assigned frequency in its assigned time slot to therefore act as an additional pinger for guiding additional AUVs on the given deployment line. The pinger may be part of the phased array system. A LBL system may not be used, and a first plurality of AUVs are deployed to the seabed using a USBL system and a second plurality of AUVs are deployed to the seabed using a phased array system based on acoustic signals received from the previously landed AUVs.

<FIG> illustrates an AUV deployment system <NUM> from a side view through a body of water. Deployment system <NUM> uses a plurality of surface vessels located on surface <NUM>, such as first surface vessel <NUM> configured to store and deploy a plurality of AUVs into a body of water (e.g. , a deployment vessel) and second surface vessel <NUM> configured to communicate with some or all of the deployed AUVs, which may be an unmanned surface vessel ("USV") or a floating buoy with a communications system. Each AUV is configured to land on seabed <NUM>. Each of the first and second surface vessels may comprise an acoustic positioning system <NUM>, <NUM>, respectively, which may be a USBL system. One of the surface vessels (such as USV <NUM>) is equipped with a USBL system. Because second surface vessel <NUM> may be positioned closer to the deployed AUVs than the deployment vessel <NUM>, the second surface vessel may provide faster and better (e.g. , more accurate) positioning/communications with the AUVs. For example, towards the end of deploying the AUVs from the deployment vessel for a particular deployment line, the deployment vessel may be too far ahead along from the deployment line to accurately measure each position of the AUVs. Thus, one or more surface vessels, towed buoys, etc. configured with a USBL system may trail behind the deployment vessel so that it crosses a particular deployment line after all of the AUVs have landed and is able to better determine each AUV position on the seabed. The trailing surface vessel may travel in different patterns behind the deployment vessel to improve the accuracy of the USBL system for the landed AUV positions. The trailing vessel can travel much faster than the deployment vessel (and is thus able to travel via different patterns to be closer to the deployed AUVs) because the deployment vessel's speed is limited by the speed at which the AUVs can be deployed or ejected from the surface vessel as well as the AUV speed in water.

Only a single surface vessel may be utilized. Likewise, additional USVs or buoys may be used on the surface to better communicate with the plurality of deployed AUVs. Rather than using a second surface vessel, a second non-surface vessel may be positioned beneath the water surface, such as a remotely operated vehicle (ROV), basket, or similar subsea structure positioned subsea for deep water deployment, and equipped with a USBL system or similar acoustic system for positioning/communications with each of the deployed AUVs.

For a given seismic survey, the area to be surveyed is generally divided into a grid such that a seismic sensor node (such as a seismic AUV) may be located at a predetermined position on the seabed. In general, a deployment line is a line of predetermined seabed positions within the seismic survey area on which a plurality of seismic nodes (such as seismic AUVs) are positioned on the seabed. A wide variety of deployment line shapes and sizes are known in the art. For the present disclosure, the deployment lines may be substantially perpendicular to the direction of travel of the deployment vessel {see, e.g. , <FIG>) or may generally be in line and/or parallel with the direction of the deployment vessel (see, e.g. , <FIG>). Each deployment line may stretch up to <NUM> or more on each side of the deployment vessel and may contain tens or hundreds of AUVs. The seismic survey may contain approximately <NUM> AUVs, up to <NUM> AUVs, or even up to <NUM>,<NUM> AUVs, and all <NUM>,<NUM> AUVs may be deployed within a relatively short period of time, such as twenty-four hours. The spacing between the deployment lines and between each AUV of the deployment line depends on the particular seismic survey and is designed prior to deployment of the AUVs.

As shown in <FIG>, multiple groups or pluralities of AUVs (such as AUV group <NUM>, AUV group <NUM>, and AUV group <NUM>) may be deployed in the water at the same time and be guided to seabed destinations based on different acoustic positioning/communications and/or guidance protocols. For example, AUV group <NUM> has already landed on seabed <NUM> and may be the first AUVs of a given deployment line. For this disclosure, the first plurality of AUVs on any given deployment line may be considered as "pivots" or "pivot AUVs," because they provide all of the positioning for subsequently deployed AUVs on a given deployment line. Pivot AUVs <NUM> are actively guided to their seabed destination by a USBL system, such as USBL <NUM>. Once pivot AUVs <NUM> have landed, their coordinates are known by the surface vessel (such as through an USBL system). The coordinates of pivot AUVs <NUM> are then used as "fixed" position coordinates from which a sea bottom acoustic pinger system will emit signals intercepted and/or received by additionally deployed AUVs (such as a second plurality of AUVs <NUM>, <NUM>) as they are deployed from the surface vessel. The pinger system may be part of the phased array system. Pivot AUVs <NUM> may emit a pulse on a given frequency (such as one frequency per deployment line to avoid interferences) after seabed landing and according to a given time sequence. Any additionally deployed AUVs may detect the pulses emitted by pivot AUVs <NUM> (as well as by previously landed AUVs <NUM>, <NUM> once they land) and then by knowing their seabed geometry and the emission time and sequence of the pulses determine the AUVs own position and guide themselves to their pre-programmed seabed landing position.

The disclosed guidance system uses a first guidance system protocol (such as USBL) to guide a first plurality of AUVs (such as pivot AUVs <NUM>) on a first deployment line, and a second guidance system protocol (such as sea bottom acoustic pingers and phased array) to guide all of the remaining AUVs of the seismic survey and/or deployment line (such as AUVs <NUM>, <NUM>). For the deployment of the second plurality of seismic AUVs (which uses a one way acoustic protocol), the disclosed system is far more cost efficient, effective, and faster than traditional AUV deployment methods, such as USBL that will always suffer with the complexity of a three-way acoustic positioning/communication protocol. Further, based on the disclosed guidance system, each AUV does not require an expensive inertial navigation system (INS) or similar system, and is able to utilize relatively straightforward and known communications systems and components.

A phased array system is used for guiding some of the AUVs. Each AUV is equipped with a phased array receiver that can detect acoustic pingers or beacons. In one embodiment, the phased array system includes a pinger that enables each of the AUVs (or at least some of the AUVs) after landing to emit pulses at an assigned frequency in an assigned time slot. By using a phase array receiver on each AUV, the AUV is able measure the angles of the incoming beacon signals from the previously landed AUVs in the same deployment line. By knowing the seabed geometry of the landed AUVs, and the sequence according to which they are emitting their signals, the travelling AUVs are able to align themselves precisely with the already landed AUVs. The USBL system may be used to take control of any AUV if it is not following its pre-programmed flight path (or the phased array system is not working) and the USBL system may be used to measure each position of the AUV once it has landed on the seabed at a particular position for seismic recording.

In operation, AUVs may be deployed ahead of deployment vessel <NUM> so that the deployment vessel passes directly "overhead" of the AUVs after they have landed, which allows for a more precise measurement of the AUV position through the USBL system. The pivot AUVs on a predetermined number of deployment lines are all deployed first, and then the remaining AUVs of each of the deployment lines are then deployed. The pivot AUVs on each deployment line is first deployed followed by other AUVs on that deployment line prior to deploying any additional AUVs on subsequent deployment lines. The timing of the deployment of the AUVs is not as important as when (and how) the AUVs calculate their position and the guidance to their seabed destination.

As is known in the art, the AUVs may be physically deployed from the deployment vessel by any number of mechanisms, and once the AUVs have performed the seismic recording on the seabed, they may be recovered to a recovery vessel from the seabed by a variety of mechanisms. In general, the particular physical deployment and recovery method and system of the AUVs is not limited by this invention. For example, as is known in the art, the AUVs may be deployed and/or retrieved directly from a surface vessel or from a subsea station, such as an ROV or subsea basket, as described more fully in Applicant's <CIT>. In other words, the disclosed guidance method, system, and protocols can be utilized whether the AUVs are deployed directly from the surface vessel or from a subsea station in a body of water or from a subsea station (such as a basket) lowered from a surface vessel. Likewise, the AUVs may be recovered back to the same surface vessel that deployed the AUV, or to a dedicated recovery vessel that may be located on the surface or at a subsea position (such as an ROV or subsea basket). Further, the disclosed invention is not limited by the actual mechanism utilized by the AUVs for subsea movement. For example, during subsea movement of the AUV, one or more of the thrusters of the AUV propulsion system may be specifically operated to steer the AUV to the intended destination. In general, the use of horizontal and/or vertical thrusters for the seismic AUV during subsea travel, seabed landing, and seabed take-off are described in detail in Applicant's <CIT>. Again, the versatility of the disclosed seismic AUV allows it to be utilized in a wide variety of subsea deployment and retrieval operations, and the particular deployment and recovery method of the AUVs is not limited by this invention.

<FIG> illustrates an outbound guidance system that utilizes USBL, sea bottom acoustic pingers, and phased array techniques. As shown in <FIG>, deployment system <NUM> includes a plurality of deployment lines, such as first deployment line <NUM>, second deployment line <NUM>, third deployment line <NUM>, fourth deployment line <NUM>, fifth deployment line <NUM>, and sixth deployment line <NUM>. In operation, the number of deployment lines may be substantially greater. Each deployment line may be substantially parallel to each other and substantially perpendicular to a direction <NUM> of deployment vessel <NUM>. A second surface vessel, such as USV <NUM>, may travel a certain distance behind deployment vessel <NUM>, and at times may travel at various patterns or positions away from direction <NUM> to be closer to a particular group of deployed/landed AUVs.

Each deployment line may have or be assigned a large number of AUVs. In <FIG>, the first AUVs on any given deployment line may be considered as "pivots" or "pivot AUVs. " "Wingers" may be known as additional AUVs on a given deployment line separate from the pivot AUVs. Referring to <FIG>, first deployment line <NUM> may have pivot AUVs <NUM>, <NUM> and winger AUVs <NUM>, <NUM>. Similarly, second deployment line <NUM> may have pivot AUVs <NUM>, <NUM> and winger AUVs <NUM>, <NUM>, and so forth. The pivots and wingers may be deployed on either side of the vessel. For example, pivot AUVs <NUM> may land on one seabed side of the deployment vessel and pivot AUVs <NUM> may land on the other seabed side of the deployment vessel. Similarly, winger AUVs <NUM> may land on one side of the surface vessel and winger AUVs <NUM> may land on the other side of the vessel. The number of deployment lines, as well as the number of wingers and pivots per deployment line, may vary between seismic surveys.

The pivot AUVs may be landed first in a row on a deployment line and, once their position finalized, the subsequent AUVs on a given deployment line then land at their seabed destinations based on coordinates of the first pivots. In other words, the coordinate positions of the pivot AUVs establish the coordinate positions of the winger AUVs on each deployment line. The pivot AUVs from the first deployment line (pivot AUVs <NUM>, <NUM>) provide guidance and/or establish the coordinate positions of the pivot AUVs (such as pivot AUVs <NUM>, <NUM>, etc.) in the subsequent deployment lines.

Referring to <FIG>, the pivot AUVs of the first deployment line (e.g. , pivot AUVs <NUM>, <NUM>) are deployed from surface vessel <NUM> and actively guided by a USBL system (such as one located on surface vessel <NUM> or <NUM>) to a predetermined seabed position. Once landed, the positions of pivot AUVs <NUM>, <NUM> are then measured by a USBL system and used by the plurality of AUVs that they will guide, such as wingers <NUM>, <NUM> on the first deployment line, pivot AUVs <NUM>, <NUM> on the second deployment line, and subsequent pivots <NUM>, <NUM>, <NUM>, and optionally wingers from subsequent deployment lines, such as wingers <NUM> , <NUM>. As described above, based on the known coordinates of the first pivot AUVs and emitted signals, each guided AUV is able to determine is position and find its predetermined landing position by using the first pivot AUVs as effectively acoustic pingers. Thus, once the first pivot AUVs <NUM>, <NUM> are guided by a first guidance system and/or protocol (such as a USBL system), all of the remaining AUVs are guided by an acoustic pinger system with phased array system.

At or near the same time of deploying the first pivot AUVs <NUM>, <NUM>, wingers <NUM> and <NUM> may be deployed. Alternatively, wingers <NUM> and <NUM> may not be deployed until after all of the pivot AUVs of first deployment line <NUM>, second deployment line <NUM>, and third deployment line <NUM> (or more) have been deployed and landed. As shown in <FIG>, AUVs <NUM> and <NUM> have recently been launched from deployment vessel <NUM> and are travelling and/or "flying" through the water to their intended seabed destination and may be wingers on any one of the previously established deployment lines or pivots for new deployment line <NUM>. The pivots and wingers on each deployment line are deployed at substantially the same time from the surface vessel. The pivots on each deployment line may be deployed at substantially the same time from the surface vessel following by subsequent deployment of the wingers, which may be done at substantially the same time or line by line. AUVs may be deployed on a particular deployment line on both sides of the vessel at substantially the same time. Winger AUVs of earlier deployment lines may provide guidance and/or establish the coordinate positions of additional winger AUVs on subsequent deployment lines. Thus, the pivots of a given deployment line (such as the second or third deployment line) may also act as beacons in the deployment system to guide additionally deployed pivots in subsequent deployment lines (such as the fourth or fifth deployment line). Only the pivots of a given deployment line may be used to guide the wingers of that particular deployment line.

A first guidance system protocol (such as USBL) is used to guide a first plurality of AUVs (such as pivot AUVs <NUM>, <NUM>) on a first deployment line, and a second guidance system protocol provided by an acoustic pinger system and phased array system is used to guide a second plurality of AUVs of the seismic survey, including any wingers of the first deployment line (e.g. , AUVs <NUM>, <NUM>), and potentially any pivots on subsequent deployment lines (e.g., AUVs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), and potentially any wingers on the subsequent deployment lines (e.g. , AUVs <NUM>, <NUM>).

Deployment system <NUM> may also use a phased array guidance approach for some or all of the wingers (or even pivots) in each deployment line. In some instances, the flying AUVs may use a phased array guidance system (discussed above and below in greater detail) to detect and process the received signals from the landed AUVs (via acoustic pingers) to calculate their position. Some of the wingers of a deployment line may also act as acoustic pingers for the later deployed wingers on that deployment line. Similarly, some of the wingers from an earlier deployed deployment line (such as deployment line <NUM>) may act as an acoustic pinger for wingers in a later deployed deployment line (such as deployment lines <NUM>, <NUM>).

<FIG> illustrates a guidance system that utilizes USBL and phased array techniques, according to some embodiments of the present invention. While similar to <FIG>, in contrast to <FIG>, the deployment lines are generally in line and/or parallel to the direction of travel of the deployment surface vessel. This approach simplifies the guidance and deployment system as compared to that described in relation to <FIG>, and provides greater accuracy based on potential issues with triangulation using acoustic pingers.

As shown in <FIG>, deployment system <NUM> uses a deployment method that deploys seismic AUVs in one or more deployment lines on either side of the surface vessel that are in parallel and/or in-line with the surface vessel direction. For example, <FIG> shows two deployment lines on either side of the surface vessel, which include first deployment line <NUM>, second deployment line <NUM>, third deployment line <NUM>, and fourth deployment line <NUM>. Three or more deployment lines of seismic AUVs may be deployed at substantially the same time on either side of the surface vessel.

Each deployment line of deployment system <NUM> includes a first plurality of AUVs (such as AUV group <NUM>) that provides the initial markers or boundaries for subsequently deployed AUVs (such as AUV group <NUM>). First AUV group <NUM> may be guided to the predetermined seabed positions by a first guidance protocol provided by an USBL system and second AUV group <NUM> may be guided to the predetermined seabed positions by a second guidance protocol which in embodiments is a phased array system. Second AUV group <NUM> is guided to the seabed positions based on signals provided by first AUV group <NUM> as well as some of the earlier landed AUVs within second AUV group <NUM>.

The size of the seismic survey may require multiple passes of the AUV deployment vessel by using a serpentine deployment method. For example, <FIG> illustrates a seismic survey with eight deployment lines, including fifth deployment line <NUM>, sixth deployment line <NUM>, seventh deployment line <NUM>, and eighth deployment line <NUM>. The surface vessel makes two substantially parallel but opposite paths through the seismic survey. First, surface vessel <NUM> travels in direction or path <NUM> and deploys seismic AUVs on two deployment lines on either side of the vessel (deployment lines <NUM>-<NUM>). After finishing deploying the particular number of seismic nodes needed for the length of the deployment line and grid in the seismic survey, the surface vessel turns around and travels in direction/path <NUM> that is substantially parallel and opposite to direction/path <NUM>. Similar to the first path, the surface vessel deploys seismic AUVs on two deployment lines on either side of the vessel (deployment lines <NUM>-<NUM>). From a top aerial perspective (see <FIG>), the last deployed AUVs for deployment lines <NUM>-<NUM> substantially align with the first deployed AUVs of deployment lines <NUM>-<NUM>. Similar to deployment lines <NUM>-<NUM>, each deployment line <NUM>-<NUM> includes a first plurality of AUVs (such as AUV group <NUM>) that provides the initial markers or boundaries for subsequently deployed AUVs (such as AUV group <NUM>) of that deployment line. Like the first deployment lines illustrated in <FIG>, first AUV group <NUM> may be guided to the predetermined seabed positions by a first guidance protocol (such as an USBL system) and second AUV group <NUM> is guided to the predetermined seabed positions by a second guidance protocol, provided by a phased array system.

This serpentine method of the surface vessel and the laying of the deployment lines may be continued until the desired number of deployment lines have been laid for the seismic survey area until the overall desired width of the seismic survey has been reached. As illustrated in <FIG> and <FIG>, the surface vessel makes additional passes <NUM> and <NUM> and deploys additional deployment lines (not numbered) according to the procedure detailed above. In particular, the first AUVs of each deployment line act as marker or boundary AUVs and travel to the seabed destination by a first guidance protocol (such as using positioning/communications with a USBL system), while the subsequently deployed AUVs for each deployment line use a second guidance protocol using pings with a phased array system. Depending on the size of the seismic survey, more or less deployment lines are possible (as well as the number of seismic nodes within each deployment line) and in operation, the number of deployment lines may be substantially greater. A second surface vessel (such as a USV) or a subsea vehicle may travel a certain distance behind deployment vessel <NUM>, and at times may travel at various patterns or positions away from the deployment vessel path to be closer to a particular group of deployed/landed AUVs.

As is known in the art, the size of the seismic survey, the number of deployment lines, and the size (e.g., length) of the deployment lines may vary between different surveys. The seismic survey may comprise four to eight deployment lines (two to four deployment lines on either side of the deployment vessel) each separated by approximately <NUM> to <NUM> meters, and each deployment line may comprise approximately seismic nodes each separated by a physical distance on the seabed by <NUM>-<NUM> meters. Of course, these parameters may vary significantly between different seismic surveys. The width of the seismic survey (i.e., the total distance between the deployment lines) is approximately <NUM> or less to take into account the acoustic range of the phased array system. Thus, if a seismic survey is greater than <NUM> in width, the vessel must take multiple passes through the survey area in a generally serpentine method (as illustrated in <FIG>). However, as phased array systems become more complex in the future, increased ranges (and number) of the deployment lines may be possible.

As mentioned above, each deployment line may be assigned AUVs that are guided to predetermined seabed positions on the deployment line based on two different guidance protocols. Referring back to <FIG>, AUV group <NUM> comprises a first plurality of AUVs that are deployed by USBL and AUV group <NUM> comprises a second plurality of AUVs that are deployed by phased array. Although not marked, each subsequent deployment line of deployment system <NUM> likewise comprises AUVs that are deployed by either USBL or phased array. As mentioned above, the general techniques of USBL and phased array are well known. The first AUV group <NUM> may comprise three AUVs, which generally provides greater accuracy (and redundancy) than just one or two AUVs. The AUVs within second AUV group <NUM> of deployment line <NUM> may be deployed at substantially the same time as the first AUV group 411or after first AUV group <NUM> has landed.

Once the AUVs of first AUV group <NUM> have landed on the seabed, they start emitting acoustic emissions using pingers. Such acoustic emissions can be emitted at particular times and/or in particular patterns, as discussed in more detail below. Contrary to multiway acoustic positioning/communication devices (which are more costly and complex), pingers are typically one-way transmission devices only and are used to determine distance and bearing from the emitted location. The AUVs within second group of AUVs <NUM> sense the acoustic emissions from the already landed AUVs (whether from group <NUM> or earlier landed AUVs from group <NUM>) and based on those emissions, the travelling AUV is configured to use a phased array system to determine the AUVs position and to correctly land at the predetermined seabed location. There is no limit on the number of AUVs that may be deployed in second AUV group <NUM> along the length of each deployment line, but such a number depends on the overall size and density of the survey area.

Each of the travelling AUVs within AUV group <NUM> may detect the acoustic emissions from one or more of the previously landed AUVs. For example, a travelling node N within AUV group <NUM> may receive the emissions of previously landed nodes N-<NUM>, N-<NUM>, N-<NUM>, N-<NUM>, etc. of that deployment line. If one of the prior nodes has not landed (for example seismic node N-<NUM>), travelling node N may still take its place at its planned position based on the emissions of the remaining nodes (such as seismic nodes N-<NUM>, N-<NUM>, N-<NUM>). Once travelling node N lands, it will start to emit an acoustic signal that can be used to help guide subsequent seismic AUVs, such as N+l, N+<NUM>, N+<NUM>, etc. In other words, for a given deployment line, each of the AUVs within group <NUM> that are guided by the phased array system may use some or all of the emissions from the previously landed AUVs to guide the position of the travelling AUV to its seabed destination. Optionally, only the previously landed AUVs of a particular deployment line provide guidance to subsequently deployed AUVs for that same deployment line. Alternatively, AUVs from a plurality of deployment lines may provide guidance to subsequently deployed AUVs across multiple deployment lines.

<FIG> illustrate a top schematic view of various operational aspects of deployment system <NUM> from <FIG>. Similar to deployment system <NUM>, the illustrated guidance system of <FIG> utilizes two deployment lines on either side of deployment vessel <NUM> as it travels a particular direction. However, only two deployment lines <NUM> and <NUM> on a single side of the vessel are shown for clarity. In the operational position illustrated in <FIG>, first deployment line <NUM> and second deployment line <NUM> each have a plurality of landed seismic AUVs. For example, first deployment line <NUM> comprises first AUV group <NUM> and second AUV group <NUM>, and second deployment line <NUM> comprises first AUV group <NUM> and second AUV group <NUM>. Similar to deployment system <NUM>, each of the AUVs within first AUV groups <NUM>, <NUM> is deployed using USBL, and each of the AUVs within second AUV groups <NUM>, <NUM> is deployed using phased array. <FIG> track the approach of travelling / flying AUV <NUM> from surface vessel <NUM> to seabed target position <NUM>. In practice, a plurality of AUVs are travelling from the surface vessel to each of their intended seabed target positions at the same time. These figures also illustrate a "dog leg" navigational approach of the AUVs where the AUVs cross various deployment lines in route to the intended destination of the AUV. For the present disclosure, a "dog leg" approach is illustrated in AUV travel path <NUM> (<FIG>), which takes a first general travel direction across one or more deployment lines (e.g., <NUM>) prior to travelling generally in-line with the intended destination deployment line (e.g. , <NUM>).

Referring to <FIG>, travelling AUV <NUM> has just been deployed from surface vessel <NUM> and its target position is target <NUM> on a predetermined point within deployment line <NUM>. One exemplary travel path 581for AUV 561travels across second deployment line <NUM> and then moves in-line with first deployment line <NUM> until AUV <NUM> reaches its target position <NUM>. <FIG> illustrates a position where surface vessel <NUM> continues travel in its intended direction (e.g., substantially in-line with the deployment lines) and AUV <NUM> is in route to target position <NUM> by path <NUM>. Path <NUM> takes the AUV across second deployment line <NUM>, but the AUV has not yet crossed the second deployment line. At this point in time each of the previously landed AUVs (such as AUVs within AUV groups <NUM>, <NUM>, <NUM>, and <NUM>) are emitting acoustic signals (e.g. , pingers) that are being continually detected by travelling AUV <NUM>. Based on a phased array guidance system and the reception of the emitted pings, AUV <NUM> knows the general direction to travel towards target position <NUM>.

<FIG> illustrates a position where AUV <NUM> is at a first "way" point when it crosses second deployment line <NUM> via AUV travel path <NUM>. According to how a phased array guidance system works (which provides both a time of arrival and bearing for each received signal), AUV <NUM> knows that it is crossing second deployment line <NUM> when all of the emitted signals align from landed AUVs <NUM> and <NUM> on second deployment line <NUM>. For example, when the bearings from each of the emitted signals from AUVs on second deployment line <NUM> are substantially identical, AUV <NUM> is substantially in-line with the other AUVs on second deployment line <NUM>. Also shown in <FIG> is surface vessel <NUM> after it has moved a further distance away from AUV <NUM>. For simplicity, <FIG> do not show the surface vessel.

<FIG> illustrates a position where AUV 56is at a second "way" point when it crosses first deployment line <NUM> via AUV travel path <NUM>. Again, AUV <NUM> knows that it is crossing first deployment line <NUM> when all of the emitted signals from landed AUVs <NUM> and <NUM> on first deployment line <NUM> align (e.g. , the bearings from the emitted signals are substantially identical). At this time, the travel path of AUV <NUM> substantially changes from generally travelling across one or more deployment lines to travelling in-line with a particular deployment line. For example, as illustrated in <FIG>, because target position <NUM> is on first deployment line <NUM>, once AUV <NUM> travels across and/or hits deployment line <NUM> the AUV changes to travel path <NUM>, which is in-line with and/or along a path of deployment line <NUM> towards seabed target position <NUM>. The final guidance approach is illustrated by path <NUM> and involves AUV <NUM> listening to emitted signals from AUVs within deployment line <NUM> (and potentially ignoring signals from other deployment lines). <FIG> illustrates the position where AUV <NUM> has arrived and/or landed at the predetermined target position <NUM>, which is substantially in-line with the other landed AUVs of first deployment line <NUM> (e.g. previously landed AUVs within AUV group <NUM> and AUV group <NUM>). As shown, the AUV's final travel path <NUM> is substantially in-line with deployment line <NUM> as the AUV travels from its prior position as illustrated in <FIG>. The landing approach of AUV <NUM> may be performed according to the different signals emitted from the AUVs based a predetermined Time of Emission ("TOE") pattern, discussed in greater detail later. After landing at position <NUM>, AUV <NUM> begins to emit an acoustic signal according to a particular protocol and/or at a particular predetermined scheduled time. At this point, additional AUVs can be guided to predetermined positions on first deployment line <NUM> based (in part) on the acoustic signals emitted from AUV <NUM> (in addition to prior landed AUVs). One of skill in the art will realize that the intended travel path of the AUV may change in the final approach based on the received acoustic signals, and a travel path of the approaching AUV may move off of the deployment line from time to time based on general movements of the AUV and readjusted trajectories. Once the AUVs have landed and/or during landing, one or more of the AUVs may readjust their seabed positions based on the received acoustic signals from adjacent AUVs along the deployment line that landed before a particular N seismic node (N- <NUM>, N-<NUM>, etc.) as well as those that may have landed after a particular N seismic node (N+l, N+<NUM>, N+<NUM>).

<FIG> illustrates a top schematic view of various operational aspects of a guidance system disclosed herein that uses a phased array system. Each of the AUVs assigned to a given deployment line may be configured to emit an acoustic signal at a particular frequency. For example, first deployment line <NUM> may operate at a first frequency Fl, second deployment line <NUM> may operate at a second frequency F2, third deployment line <NUM> may operate at third frequency F3, and fourth deployment line <NUM> may operate at a fourth frequency F4. The frequencies may vary between <NUM> and <NUM>, with each deployment line separated by at least an interval of <NUM>. For example, AUVs assigned to first deployment line <NUM> may operate at a frequency Fl of <NUM>, and the remaining deployment line frequencies may be <NUM> for F2, <NUM> for F3, and <NUM> for F4. Other frequencies and combinations thereof are possible as is known in the art.

<FIG> illustrates a guidance system for a plurality of landed and traveling AUVs for a plurality of deployment lines. Deployment vessel <NUM> travels along path <NUM> and deploys a plurality of seismic AUVs, as described above, in two deployment lines on either side of surface vessel <NUM>. As described previously, the first plurality of AUVs (such as AUV group <NUM> or AUV group <NUM>) for each deployment line (such as two or three AUVs for each deployment line) are guided to their intended seabed destinations using USBL. Phased array may or may not be additionally used for the first group of AUVs on each deployment line. After the first group of AUVs have landed, they begin emitting acoustic signals that are used to guide all of the additional AUVs for a given deployment line. AUV group <NUM> illustrates a group of AUVs that have already landed at their seabed destination by being guided by the phased array system. AUV group <NUM> illustrates a group of AUVs that have been deployed by surface vessel <NUM> but are still travelling / flying towards their intended seabed destination on deployment line <NUM> and being guided by the phased array system based on the signals emitted from some of the AUVs within groups <NUM> and <NUM>. A similar arrangement is illustrated for deployment lines <NUM>, <NUM>, and <NUM>. For example, deployment line <NUM> has a first group of AUVs <NUM> that have already landed by USBL, a second group of AUVs <NUM> that have already landed by phased array, and a third group of AUVs <NUM> that are travelling to their intended destination based on phased array. As noted above, the AUVs on each deployment line are configured to emit acoustic signals at a given frequency after landing on the seabed. For example, the AUVs within AUV groups <NUM>, <NUM>, and <NUM> operate at frequency Fl and the AUVs within AUV groups <NUM>, <NUM>, and <NUM> operate at frequency F4.

Traveling AUVs <NUM> may be deployed from surface vessel <NUM> and travel in a "dog leg" approach (similar to the approach illustrated in <FIG>), whereby they travel across deployment line <NUM> and then after reaching deployment line <NUM> travel substantially in-line with the deployment line towards the target seabed destination. The traveling AUVs may or may not take a "dog leg" approach to the seabed destination. Further, the traveling AUVs may or may not cross over adjacent deployment lines. For example, travelling AUVs <NUM> have to cross over deployment line <NUM> prior to travelling to intended destination deployment line <NUM> , but travelling AUVs <NUM> do not have to cross over any adjacent deployment lines other than destination deployment line <NUM>. The traveling AUVs only listen to AUVs that have previously landed on the intended destination deployment line (e.g. , only AUVs at a single frequency). Alternatively, the traveling AUVs listen to AUVs that have previously landed on a plurality of different lines (e.g. , AUVs at a plurality of frequencies). Alternatively, the AUV may be instructed to listen to AUVs emitting signals from the same or different deployment lines as the travelling AUV based on the particular alignment and/or approach being performed by the traveling AUV.

<FIG> illustrate a Time of Emission (TOE) system. As is known in the art, each of the seismic AUVs being deployed for the seismic survey have an accurate clock for seismic recording purposes and is synchronized to a master clock. Because each of the seismic nodes landing on a particular deployment line emit signals on the same frequency, there needs to be a way to differentiate the signals. For some or all of the AUVs, a TDMA (Time Division Multiple Access) approach may be used for any acoustic signal transmissions, in which each AUV is assigned a given frequency and a given time slot at a point to emit or transmit a signal so that the collectively transmitted signals do not interfere. Each AUV that receives such signals may be configured to assign a received signal to a specific known emitter.

A TOE pattern is utilized as a way to organize the acoustic emissions of the landed AUVs by TDMA in a series of "time slots," with each time slot devoted to the transmission of one or more AUVs. Such a TOE pattern allows the flying AUVs to exactly recognize each of the transmitting AUVs and subsequently to know the landed AUV position on the seabed. This information will be used to calculate the flying AUVs landing spot. Any of the previously disclosed guidance systems of the present disclosure may use a TOE pattern to assist in the guidance of the flying AUVs to the intended seabed destination. The disclosed TOE pattern may also utilize Space Division Multiple Access (SDMA) principles. In <FIG>, the overall TOE pattern utilizes the SDMA principle because the same TOE pattern is deployed across seismic nodes in different repeating groups of AUVs along the entire length of the deployment line.

For example, <FIG> illustrates a first group of landed AUVs <NUM> on deployment line <NUM>. Each of the AUVs within AUV group <NUM> may form a first TOE pattern. AUV group <NUM> may comprise twelve AUVs labelled A-L, where each AUV is configured to emit an acoustic signal at time interval iA - iL. More or less AUVs are possible for a given TOE pattern. The width "x" of the TOE pattern corresponds to a deployment of the AUV group <NUM> of approximately <NUM> meters (e.g. , in-line intervals of approximately <NUM> meters between each AUV). This distance may vary based on the number of AUVs used and the particular TOE pattern selected. The selection of distance between adjacent nodes and their TOE is performed to guarantee at least a particular desired separation time between the Time of Arrival (TOA) of all received signals by a flying AUV.

In <FIG>, nodes J, K, and L (each a seismic AUV) of AUV group 711are deployed using USBL, and seismic nodes A-I of AUV group 711are deployed using phased array. The disclosed TOE pattern avoids a "tetris effect," in which two different AUVs may reach the same landing point based on the received acoustic signals. For example, a certain deployment line may comprise flying seismic node N, preceding nodes N-<NUM> , N-<NUM>, N-<NUM>, etc., and subsequent nodes N+<NUM> , N+<NUM>, N+<NUM>, etc. If the preceding node N-<NUM> has not landed, flying node N will still naturally take its place at the planned N position thanks to the emissions of N-<NUM>, N-<NUM>, N-<NUM> complying to the "TOE pattern," and leave empty the seabed landing position of N-<NUM>. At some point after landing, seismic node N will start to emit. Seismic node N may start to emit immediately or seismic node N may wait to emit until preceding seismic node N-<NUM> has landed (even if late), or start emitting after a certain time delay (considering that the preceding seismic node N-<NUM> is lost or in failure). In such an event, a subsequently deployed seismic node may or may not be programmed to land at the seabed destination for seismic node N-<NUM>.

At a particular TOE interval, each of the AUVs emit periodically a localization pulse at a given TOE. Two adjacent landed AUVs may have their TOE separated by a different TOE interval. A TOE pattern may be generated during design of the seismic survey (such as by TOE pattern generator software) to ensure the landed AUVs emit a pulse at a TOE interval that ensures that the Time of Arrival (TOA) of two consecutive acoustic pulses on an incoming AUV are separated by at least a predetermined minimum time interval. The uncertainty of the TOA of such pulses may be approximately +/- <NUM>, and thus the TOE interval must account for such uncertainty in the specific TOE pattern. An irregular distribution of TOE intervals may be utilized, such that the TOA of adjacent seismic nodes is always different so that the individual seismic nodes can be recognized. Each of the deployment lines may utilize the same TOE pattern.

The length of the deployment line may be too large to use a single TOE pattern. Multiple TOE groups may be utilized for a particular deployment line, which each group utilizing the same TOE pattern and having the same number of AUVs. The size of the TOE pattern is designed to ensure spatial separation of AUVs having the same emitting scheme in two adjacent TOE patterns. For example, if a deployment line is approximately <NUM>, a TOE pattern may be generated that is approximately <NUM> in length, and thus approximately ten TOE groups may be utilized for the particular deployment line, each with the same number of AUVs. Each of the TOE patterns may be the same and/or identical for the entire deployment line.

<FIG> illustrates a spatial view of one seismic AUV node deployment with repeating TOE patterns. Each group corresponding to the same TOE pattern comprises nodes labelled A-L (each a seismic AUV) and comprises a length of approximately <NUM> meters (as similarly illustrated in <FIG>). The same TOE pattern may be utilized for each AUV group <NUM>, <NUM>, and <NUM>. In other words, the same TOE pattern repeats itself after a predetermined distance (e.g., between different AUV groups) to ensure that the landed AUVs emitting at the same time cannot be received by any flying AUV approaching its landing position. In practice, and depending on the length of the deployment line, more AUV groups may be utilized and employ the same TOE pattern.

As illustrated in <FIG> (which shows a spatial view of the disclosed TOE pattern), seismic nodes A-L of AUV group <NUM> have landed, seismic nodes A-L of AUV group <NUM> have landed, and seismic nodes H-L of AUV group <NUM> have landed, while flying node G (marked as AUV <NUM>) is travelling along the deployment line towards its seabed target in a general direction of path <NUM>. Based on the distance between each seismic node, flying node <NUM> can only receive acoustic signals emitted from those AUVs in group <NUM> (marked by the dashed box in <FIG>). AUV group <NUM> may comprise fewer AUVs than those deployed in the utilized TOE pattern. AUV group <NUM> may comprise previously landed nodes H-L of AUV group <NUM> and previously landed nodes A-E of AUV group <NUM>. As mentioned above, the AUVs within group <NUM> each emit acoustic signals at different TOE intervals. After flying node <NUM> (G) lands, it begins to emit acoustic signals at the predetermined TOE interval. This pattern is repeated until the desired number of AUVs are deployed on the deployment line. In practice, multiple deployment lines are deployed at the same time (such as between two to eight deployment lines) using the same protocol illustrated in <FIG>and<FIG>. As described in <FIG>, the deploying vessel may take one or more serpentine paths through the seismic area to deploy additional sets of deployment lines to achieve a larger width of the seismic survey.

The first plurality of AUVs may be deployed to the seabed without using USBL. In examples not forming part of thr present invention, a ROV may be used to specifically place one or more seismic nodes at their predetermined positions. Those seismic nodes, at some point after being planted on the seabed, may then begin to emit acoustic signals that can be received by traveling AUVs and be guided to their seabed destinations using phased array as described herein. In other words, whether the initial marker / boundary AUVs are guided by USBL (or another guidance system) or planted by an ROV, subsequently deployed AUVs may determine their position by the disclosed phased array approach by receiving acoustic signals from landed AUVs. Still further, the marker / boundary AUVs may not be AUVs or seismic nodes at all and may simply be acoustic tags or other devices that emit acoustic signals according to a disclosed TOE pattern and are planted on the seabed at known/predetermined positions (such as by a ROV).

Many variations in the configurations of the AUV, guidance system, and/or deployment system are within the scope of the invention as defined in the appended claims. For example, the AUVs in the described embodiments are shown being deployed from a surface vessel. However, the same guidance method and system described herein can be utilized for deploying AUVs from a subsea structure, such as a ROV or basket lowered from a surface vessel. Similarly, the AUVs can be recovered in a wide variety of operations known to one of skill in the art, such as being recovered at a subsea location (such as a basket, which can be lowered from and raised to a surface vessel) or travelling back to a surface vessel (such as the deployment vessel) and being recovered by a funnel, basket, or other surface recovery mechanism. As another example, other subsea vehicles can be deployed besides just autonomous seismic nodes, such as drones or vehicles with non-seismic sensors, and a similar guidance system can be used for land seismic and non-seismic sensors, drones, and/or vehicles. The deployment lines may be generally perpendicular and/or parallel to the general travel path direction of the deployment vessel. For phased array techniques, acoustic signals from landed AUVs can be timed according to any number of selected patterns, and a Time of Emission pattern may take many different forms for the AUVs within and between the deployment lines. In some embodiments, USBL is not used at all. It is emphasized that the foregoing embodiments are only examples of the very many different structural and material configurations that are possible within the scope of the present invention, as defined by the appended claims.

Although the invention(s) is/are described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention(s), as presently set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense.

Claim 1:
A method for performing a marine seismic survey in a body of water, comprising
providing a plurality of seismic autonomous underwater vehicles, AUVs, each of the plurality of AUVs including an acoustic emitter and an acoustic receiver;
deploying a first group of the plurality of seismic AUVs (<NUM>; <NUM>, <NUM>; <NUM>; <NUM>; <NUM>) into the body of water and guiding the first group of seismic AUVs to a first plurality of seabed positions in at least one deployment line by using a first guidance system;
deploying a second group of the plurality of seismic AUVs (<NUM>; <NUM>, <NUM>; <NUM>; <NUM>; <NUM>) into the body of water, wherein the acoustic receiver of each of the second group (<NUM>; <NUM>, <NUM>; <NUM>; <NUM>) of AUVs is configured to receive acoustic signals emitted by the previously landed seismic AUVs; and
guiding each of the second group (<NUM>; <NUM>, <NUM>; <NUM>; <NUM>; <NUM>) of seismic AUVs to a second plurality of seabed positions in said at least one deployment line by using their respective acoustic receiver, based on acoustic signals emitted by the acoustic emitters of the first group of seismic AUVs after landing on the seabed;
the method being characterised in that each acoustic receiver comprises a phased array receiver.