Patent Description:
Marine seismic surveys are one type of marine geophysical survey which utilizes sound waves transmitted to the earth's crust and reflected back to recording sensors. The recording sensors may be hydrophones or other sensors in one of a number of towing assemblies, commonly called streamers, that may be towed behind a survey boat. When towed behind the survey boat, the streamer may be submerged. A sound, or other energy, source may also be towed in the water behind the survey boat for transmitting energy waves to be received by the receivers of the streamers. One common application of marine geophysical surveying is oil and gas exploration in marine environments. More particularly, sound waves received during a marine seismic survey may be analyzed to locate hydrocarbon bearing geological structures, and thus determine where deposits of oil and natural gas may be located. In a similar fashion, marine electromagnetic (EM) surveys may be conducted using EM energy transmitted by a submerged antenna and detected by EM receivers.

Remotely operated vehicles (ROVs) may be useful for supporting marine geophysical surveying. For example, an ROV may be deployed to maintain (e.g., clean, repair) a streamer towed behind a survey boat, allowing maintenance of a streamer without reeling the streamer back onto the survey boat. ROVs may also be used for other tasks in marine exploration, such as placing equipment on the seabed.

<CIT> describes an apparatus and methods for deploying, recovering and servicing an AUV. The apparatus includes a linelatch system that is made up of a tether management system connected to a flying latch vehicle by a tether. The linelatch system can be connected to a surface vessel by an umbilical on one end and to an AUV on the other end. In addition to providing a mechanical connection, between the AUV and a surface vessel, the linelatch system can also carry power and data between the surface vessel (i.e. through the umbilical) and the AUV. A position control system which includes a current sensor is provided inside the flying latch vehicle.

<CIT> relates to a system for subsea operations. The system includes a free swimming, submersible garage and docking station, and also an associated free swimming ROV, where the garage and docking station comprises a framework arranged to function as a garage or docking for the free swimming ROV, and where the submersible garage and docking station comprises at least equipment in the form of several thrusters for operation in the vertical and horizontal directions, respectively, units and a steering system for positioning in the water, and also a winch connected to said ROV via a cable for the transfer of electricity and signals.

<CIT> describes a floating sensor system to detect very low frequency pressure signals (down to <NUM>). This system detects pressure fluctuations or pressure signals of interest in the ocean or other body of water in the presence of unwanted pressure signals generated by surface wave induced motion. A drifting sensor surface float follows the surface waves and in turn moves a suspended pressure sensor vertically, such that it detects the wave motion as a change in static pressure which then constitutes a noise source. A correlation circuit and a logic circuit discriminate between a first composite signal, comprised of the pressure signals of interest and wave motion noise, and a second reference signal, comprised only of the wave motion noise to provide an output signal transmitted to a monitoring station.

ROVs may be deployed from a mother vessel equipped with a launch and recovery system (LARS). A LARS can be equipped with active heave compensation (AHC) to keep an ROV docking station, for example, a tether management system (TMS), of the mother vessel stable while a vessel (e.g., the mother vessel) coupled to the ROV docking station is subjected to motion, e.g., heave, roll, and/or pitch, etc. In some situations, launching and/or recovering an ROV, from the ROV docking station, takes place in deep water (e.g., <NUM> meters), away from the influence of free surface water waves. In general, the effects of wave particle motion and/or the wave pressure decay exponentially with water depth and thus, when launching and recovering an ROV in deep water, the vertical motion of the ROV induced by free surface waves can be neglected. The motion of the docking station induced by the effect the motion of the vessel has on the docking station can be counteracted, e.g., by AHC. Counteracting the effect the vessel has on the docking station can allow for improved launching and/or docking of the ROV.

Launching and recovery of an ROV, from the ROV docking station, is not always performed in deep water. In some situations (for example, when an ROV is being used to maintain a streamer being towed behind a survey boat), it may be advantageous to launch and recover an ROV close (e.g., less than ten meters) to the sea surface. In situations where launching and recovery (e.g., undocking and docking) takes place close to the sea surface, the motion of the ROV can be affected by particle motions and/or pressure fluctuations from the free surface waves. As an example, if the free surface waves are large in comparison to the docking depth, the motion of the ROV can be affected by wave particle motion and/or wave pressure. Motion of the ROV during launch and recovery operations can interfere with those operations, possibly damaging the ROV, docking station, and/or LARS. It is therefore desirable to counteract motion of an ROV during launch and recovery operations.

According to embodiments of the present disclosure, techniques are provided to compensate for relative motion between an object connected with a vessel floating on water and an object in the water. The provided techniques include methods, systems, and machine-readable media for compensating for relative motion between an object connected to a vessel and an object in the water. For example, a system operating according to the present disclosure may be configured to minimize relative vertical motion between a docking station connected to a vessel (e.g., a mother vessel) and an ROV in the water.

It is to be understood the present disclosure is not limited to particular devices or methods, which may, of course, vary. This disclosure may be embodied in many different forms and should not be construed as limited to any specific structure or function presented. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used herein, the singular forms "a", "an", and "the" include singular and plural referents unless the context clearly dictates otherwise. Furthermore, the word "may" is used throughout this application in a permissive sense (i.e., having the potential to, being able to), not in a mandatory sense (i.e., must). The term "include," and derivations thereof, mean "including, but not limited to. " The term "coupled" means directly or indirectly connected.

ROVs may be useful for supporting marine geophysical surveying. For example, an ROV may be deployed to maintain (e.g., clean, repair) a streamer towed behind a survey boat, allowing maintenance of the streamer without reeling the streamer back onto the survey boat. ROVs may also be used for other tasks in marine exploration, such as placing equipment on the seabed.

ROVs frequently do not operate independently, but instead are deployed from and supported by another vessel that may be referred to as a "mother" vessel for the ROV. A mother vessel may deploy the ROV, retrieve the ROV, provide control facilities for people to control operation of the ROV, carry spare parts for the ROV, carry detachable equipment of the ROV, carry equipment for repairing the ROV, supply fuel to the ROV, and/or provide electrical power to the ROV. While a mother vessel typically supports operation of the ROV, other vessels may also provide support to an operational ROV. A mother vessel may also be referred to as a support vessel, a launch and recovery vessel, a mother ship, a control vessel, or a control ship.

As mentioned above, a launch and recovery system (LARS) for an ROV can be equipped with active heave compensation (AHC) to keep the ROV docking station (e.g., a tether management system (TMS)), stable while a vessel (e.g., a mother vessel) is moving, e.g., heaving, rolling, and/or pitching, as a result of wave action. These motions of the vessel may be sensed (e.g., by an inertial sensing system) and measured. The motions may also be recorded using a motion recording unit (MRU). An MRU may be mounted on the vessel and located near the LARS or located away from the LARS.

<FIG> illustrates an exemplary mother vessel <NUM> with a LARS <NUM> and an ROV <NUM> operating according to previously known techniques. The LARS <NUM> comprises a crane <NUM>, which comprises one or more actuators (not shown) used to position the crane <NUM>, and a docking station <NUM>. As used herein, a docking station includes any type of ROV docking station, including TMSs, docking stations for tetherless ROVs, and docking stations for ROVs that have tethers managed by devices other than the docking station. The docking station <NUM> is suspended from the tip of the crane <NUM> by one or more cables. Because the docking station <NUM> is heavy, it hangs directly or almost directly beneath the tip of the crane <NUM> and follows the motions of the tip of the crane <NUM>. In <FIG>, the ROV <NUM> is deep (e.g., <NUM> meters or more) under the surface of the water. As previously mentioned above, the wave action at the surface has very little direct effect on the ROV <NUM>, because the ROV <NUM> is deep under the surface, and thus the ROV <NUM> has very little vertical movement with respect to the sea floor <NUM>.

The mother vessel <NUM> in <FIG> is rolling, pitching, and/or heaving, as illustrated by the arrows <NUM> at the bow and stern of the mother vessel <NUM>. The LARS <NUM> of the mother vessel <NUM> is equipped with an AHC (not shown), which sends commands to the one or more actuators of the LARS <NUM>. The commands cause the actuators to counteract the movements of the mother vessel <NUM> by, for example, moving the tip of the crane <NUM> of the LARS <NUM>. The movement of the tip of the crane <NUM> is illustrated by the arrow <NUM>. By counteracting the movements of the mother vessel <NUM>, the AHC allows the docking station <NUM> to remain nearly stationary with respect to the sea floor <NUM> despite the movement of the mother vessel <NUM> caused by the wave action. Launching and recovery (e.g., docking and undocking) operations of the ROV <NUM> are improved by use of the AHC, because the docking station <NUM>, to which the ROV <NUM> docks and undocks, is nearly stationary with respect to the sea floor <NUM>.

<FIG> illustrates an exemplary mother vessel <NUM> with a LARS <NUM> and an ROV <NUM> operating according to previously known techniques. As in <FIG>, the LARS <NUM> comprises a crane <NUM>, which comprises one or more actuators (not shown) used to position the crane <NUM>. The LARS <NUM> also comprises a docking station <NUM> (e.g., a TMS) that is suspended from the tip of the crane <NUM> by one or more cables and follows the motions of the tip of the crane <NUM>. In <FIG>, the ROV <NUM> is relatively near to (e.g., less than ten meters below) the surface of the water. As previously mentioned, the wave action at the surface may have a significant effect on the ROV <NUM>, because the ROV <NUM> is near the surface, and thus the ROV <NUM> may have significant vertical movement with respect to the sea floor <NUM>. The movement of the ROV <NUM> caused by the wave action is illustrated by the arrows <NUM>.

As in <FIG>, the mother vessel <NUM> in <FIG> is rolling, pitching, and/or heaving, as illustrated by the arrows <NUM> at the bow and stern of the mother vessel <NUM>. As in <FIG>, the LARS <NUM> of the mother vessel <NUM> is equipped with an AHC (not shown), which sends commands to one or more actuators (not shown) of the LARS <NUM>. The commands cause the actuators to counteract the movements of the mother vessel <NUM> by, for example, moving the tip of the crane <NUM> of the LARS <NUM>. The movement of the tip of the crane <NUM> is illustrated by the arrow <NUM>. By counteracting the movements of the mother vessel <NUM>, the AHC allows the docking station <NUM> to remain nearly stationary with respect to the sea floor <NUM> despite the movement of the mother vessel <NUM> caused by the wave action. Launching and recovery (e.g., docking and undocking) operations of the ROV <NUM> in this situation are not improved, however, by use of the AHC, because motion of the docking station <NUM>, to which the ROV <NUM> docks and undocks, is reduced while the ROV <NUM> is rolling, pitching, and heaving due to the wave action.

<FIG> illustrates an exemplary mother vessel <NUM> with a LARS <NUM> and an ROV <NUM> operating according to aspects of the present disclosure. As in <FIG> and <FIG>, the LARS <NUM> comprises a crane <NUM>, which comprises one or more actuators (not shown) used to position the crane <NUM>. The LARS <NUM> also comprises a docking station <NUM> (e.g., a TMS) that is suspended from the tip of the crane <NUM> by one or more cables and follows the motions of the tip of the crane <NUM>. As in <FIG>, the ROV <NUM> in <FIG> is relatively near to (e.g., less than ten meters below) the surface of the water. As previously mentioned, the wave action at the surface has a significant effect on the ROV <NUM>, because the ROV <NUM> is near the surface, and thus the ROV <NUM> has significant vertical movement with respect to the sea floor <NUM>. The movement of the ROV <NUM> caused by the wave action is illustrated by the arrows <NUM>.

As in <FIG> and <FIG>, the mother vessel <NUM> in <FIG> is rolling, pitching, and/or heaving, as illustrated by the arrows <NUM> at the bow and stern of the mother vessel <NUM>. The LARS <NUM> of the mother vessel <NUM> is equipped with an active motion compensation system <NUM> that includes an embodiment of the present disclosure. The active motion compensation system <NUM> may receive information regarding particle (e.g., water particle) motion in water surrounding the ROV <NUM> from an MRU <NUM>, inertial sensing system, or other motion sensing system (not shown) on the ROV <NUM>. That is, the active motion compensation system <NUM> may receive information directly regarding the particle motion in the water surrounding the ROV. As used herein, surrounding means within a distance of <NUM> meters from the ROV. Additionally or alternatively, the active motion compensation system <NUM> may receive ROV motion information and/or TMS motion information and use ROV and/or TMS motion information in determining particle motion in the water surrounding the ROV. The information regarding the movements of the ROV <NUM> may be carried via, for example, cables in a tether <NUM>, which may also carry commands to the ROV <NUM> from operators aboard the mother vessel <NUM>. Although the tether <NUM> is shown terminating at the docking station <NUM>, the disclosure is not so limited and embodiments of the present disclosure may be used with a tether <NUM> that connects the ROV <NUM> with the LARS crane <NUM> via the docking station <NUM>. Alternatively or additionally, one or more motion sensors, e.g., an acoustic positioning system <NUM> or optical motion detector (e.g., a laser motion detector) <NUM>, aboard the mother vessel <NUM> may supply information regarding movements of the ROV <NUM> and/or particle motion in the water surrounding the ROV to the active motion compensation system <NUM>. While the laser motion detector <NUM> is shown separated from the crane <NUM>, the disclosure is not so limited, and the optical motion detector <NUM>, such as a laser motion sensor, may be mounted on or near the crane <NUM>.

Additionally or alternatively, the active motion compensation system <NUM> may receive information regarding the motions of the mother vessel <NUM> and/or the motions of the ROV <NUM> and/or the particle motion in the water surrounding the ROV from a motion sensing system. The motion sensing system may generally comprise a computing system, an energy emitter <NUM>, and an energy receiver <NUM>, each of which may be mounted on the mother vessel <NUM> or on the ROV <NUM>. The energy emitter may be, for example, one or more speakers <NUM> for emitting sound waves, one or more antennas for emitting radio waves, or one or more lasers for emitting electromagnetic energy. The energy receiver may be, for example, one or more hydrophones to receive sound waves, one or more antennas to receive radio waves, or one or more optical detectors. The computing system of the motion sensing system may interpret data regarding the received energy to determine motions of the ROV <NUM> and/or the mother vessel <NUM> and/or the particle motion in the water surrounding the ROV. In the invention, the motion sensing system comprises a wave motion sensor <NUM> that senses wave motion and/or particle motion in the water surrounding the ROV and sends data regarding the sensed wave motion and/or particle motion to the active motion compensation system <NUM> via one or more cables <NUM>. The wave motion sensor <NUM> may include, for example, a predominantly neutrally buoyant device (e.g., producing a buoyant force of <NUM> to <NUM> times the weight of the device) equipped with motion sensors that senses particle motion in water near the ROV <NUM> and/or the docking station <NUM>. A second example of a wave motion sensor <NUM> may include a buoyant device equipped with motion sensors that floats on the surface of the water and gathers data regarding water motion at the surface, in which case the computing system of the motion sensing system may interpret the gathered data to determine water motion near the ROV <NUM> and/or the docking station <NUM>. A third example of a wave motion sensor <NUM> may include a buoyant device that floats on the surface of the water that is tethered to a non-buoyant motion sensing device that is suspended near the ROV <NUM> and/or the docking station <NUM>.

Additionally, the active motion compensation system <NUM> may receive information regarding the particle motion in the water surrounding the ROV from a flow sensor (e.g., a Doppler sensor) disposed on the docking station <NUM>. The flow sensor may detect water flow past the docking station <NUM> (e.g., wave-induced water motion), and the active motion compensation <NUM> system may receive the particle motion information via one or more cables and/or the tether <NUM>.

The active motion compensation system <NUM> sends commands to one or more actuators (e.g., motors, not shown) of the LARS <NUM>. The commands cause the actuators to counteract the movements of the mother vessel <NUM> by, for example, moving the tip of the crane <NUM> of the LARS <NUM> to align the movements of the docking station <NUM> relative to the sea floor <NUM> with the movements of the ROV <NUM> relative to the sea floor <NUM>. That is, the active motion compensation system <NUM> compensates for the motion of both the ROV <NUM> and the mother vessel <NUM> and sends commands (e.g., to actuators of the crane <NUM>) synchronizing motions of the docking station <NUM> with motions of the ROV <NUM>. As used herein, "synchronizing motions" means causing the motion of a first object and the motion of a second object to be similar enough to allow easy connection of the first and second objects. For example, a first object may be caused to be displaced within <NUM>% of the displacement of a second object, with a speed of the first object within <NUM>% of a speed of the second object, within one second of a motion of the second object. In some embodiments, "synchronizing motions" refers only to displacements and speeds in a vertical (e.g., perpendicular to a surface of the water) direction. The movement of the tip of the crane <NUM> is illustrated by the arrow <NUM>. The movement of the docking station <NUM> with respect to the sea floor <NUM> is illustrated by the arrow <NUM>. By counteracting the movements of the mother vessel <NUM> and the ROV <NUM>, the active motion compensation system <NUM> allows the docking station <NUM> to remain nearly stationary with respect to the ROV <NUM> despite the movement of the ROV <NUM> and the mother vessel <NUM> caused by the wave action. Launching and recovery (e.g., docking and undocking) operations of the ROV <NUM> are improved by use of the active motion compensation system <NUM>, because motion of the docking station <NUM>, to which the ROV <NUM> docks and undocks, is nearly stationary with respect to the ROV <NUM> while the ROV <NUM> is moving due to the wave action.

<FIG> illustrates a block diagram of an exemplary system <NUM> in which aspects of the present disclosure may be practiced. The system <NUM> includes an ROV <NUM> and a mother vessel <NUM>. The ROV <NUM> is tethered to the mother vessel <NUM> via a tether <NUM> that includes one or more cables (e.g., conductors, fiber-optic cables) that carry commands and data between the ROV <NUM> and the mother vessel <NUM>.

The ROV <NUM> includes one or more motion sensors (e.g., accelerometers) <NUM>, <NUM>, <NUM> that detect and measure motion of the ROV <NUM>. The motion sensors <NUM>, <NUM>, <NUM> may be separate units or may be integrated into a MRU <NUM>. The MRU <NUM> is drawn with dashed lines to show that it is optional. The motion sensors <NUM>, <NUM>, <NUM> and/or MRU <NUM> output signals (e.g., electrical signals, light pulses carried via fiber optics) conveying information regarding the motion of the ROV <NUM>. The signals, which may be digital or analog signals, are conveyed to the mother vessel <NUM> via the cables of the tether <NUM>. The ROV <NUM> also includes at least one motor <NUM>, rudder <NUM>, and/or thruster <NUM> used to maneuver the ROV <NUM>. One or more computers <NUM> may be included in the ROV <NUM> to control the ROV <NUM> and/or communicate (e.g., via the cables in the tether <NUM>) with systems (e.g., systems for controlling the ROV <NUM>) aboard the mother vessel <NUM>. The computers <NUM> may include one or more processors <NUM> and memory <NUM>. The ROV <NUM> may also include one or more water motion sensors <NUM> that may measure motion of particles of water near the ROV <NUM>. The water motion sensors may comprise Doppler motion sensors, flow meters, or other types of motion sensors. The water motion sensor <NUM> is drawn with dashed lines to show that the water motion sensor is optional. The ROV <NUM> may additionally include one or more energy receivers (e.g., hydrophones, light sensors, antennas) for receiving energy emitted from another vessel (e.g., the mother vessel <NUM>) and provide measurements of movements of the ROV <NUM> to the computer(s) <NUM> of the ROV <NUM> and/or an active motion compensation system <NUM>.

The mother vessel <NUM> includes a LARS <NUM>, a control system <NUM> for controlling the ROV <NUM>, and a wave motion sensor <NUM>. The LARS <NUM> includes a crane <NUM>, a control system <NUM>, and an active motion compensation system <NUM>. The control system <NUM> includes an interface (e.g., touchscreen, joystick, and/or keyboard) for accepting commands from an operator who controls the LARS <NUM>. The wave motion sensor <NUM> may comprise a buoy equipped with motion sensors (e.g., an MRU) and tethered to the mother vessel <NUM>, such as wave motion sensor <NUM> shown in <FIG>. Additionally, the optional wave motion sensor <NUM> may comprise a flow sensor (e.g., a Doppler sensor) disposed on a docking station (e.g., a TMS).

The active motion compensation system <NUM> may be an embodiment of the present disclosure. The active motion compensation system <NUM> includes one or more computers <NUM> that control the crane <NUM> and/or communicate with the motion sensors <NUM>, <NUM>, <NUM> aboard the ROV and/or motion sensors (e.g., accelerometers, inertial motion sensors) <NUM>, <NUM>, <NUM> aboard the mother vessel <NUM> and/or the optional wave motion sensor <NUM>. The motion sensors <NUM>, <NUM>, <NUM> detect and measure motion of the mother vessel. The motion sensors <NUM>, <NUM>, <NUM> may be separate units or may be integrated into a MRU <NUM>. The motion sensors <NUM>, <NUM>, <NUM> and/or MRU <NUM> output signals (e.g., electrical signals, light pulses carried via fiber optics) conveying information regarding the motion of the mother vessel. The wave motion sensor <NUM> detects and measures wave action and sends information regarding the wave action to the active motion compensation system <NUM>. The computers <NUM> accept commands from the control system <NUM>, receive measurements of motions of the mother vessel from the motion sensors <NUM>, <NUM>, <NUM>, receive measurements of motions of the ROV from the motion sensors <NUM>, <NUM>, <NUM>, optionally receive measurements of the wave action from the wave motion sensor <NUM>, and then combine the control system commands and motion data (e.g., motion measurements) from the mother vessel <NUM> and ROV <NUM> to determine crane movements that move the tip of the crane <NUM> in alignment with movement of the ROV <NUM> as described above. The computers <NUM> of the active motion compensation system <NUM> then send the determined commands to the crane <NUM> (e.g., to motors and/or actuators) to cause those movements, i.e., to move the tip of the crane <NUM> in alignment with movement of the ROV <NUM> as described above.

According to aspects of the present disclosure, an active motion compensation system (e.g., active motion compensation system <NUM> in <FIG>) may receive information from a control system of an ROV (e.g., control system <NUM>) regarding commanded movements of the ROV (e.g., via connection <NUM>) and use that information in determining commands to send to actuators (e.g., motors of a crane) of a LARS (e.g., LARS <NUM>). The active motion compensation system may vector add or vector subtract the commanded movements from wave-driven movements of the ROV to determine commands to send to the actuators of the LARS. For example, an active motion compensation system may receive information from an ROV control system indicating the ROV is being commanded to rise in the water, and the active motion compensation system may then determine commands to hold the tip of the crane (and the docking station attached to it) relatively still with respect to the ROV so that the ROV can approach the docking station, rather than moving the tip of the crane to raise the docking station in alignment with the rising ROV.

According to aspects of the present disclosure, an active motion compensation system may synchronize motion of a docking station to motion of an ROV in amplitude and/or phase (e.g., amplitude and phase of wave-driven movements of the ROV). In at least one embodiment, this can be accomplished by measuring the motion of the ROV and/or predicting the motion of the ROV for values that can be applied in a control system (e.g., control software) to reduce and/or minimize a residue between the motion of the ROV and the motion of the docking station.

According to aspects of the present disclosure, an active motion compensation system may estimate ROV motion by determining a relationship between a wave (e.g., height, period, direction, etc.) and a motion (e.g., heave) response of the ROV, and calculating the vertical motion of the ROV based at least in part on a measurement of the actual wave. In at least one embodiment, measurement of the actual wave may be accomplished with an optical sensor (e.g., a laser sensor, a camera). In at least one other embodiment, measurement of the actual wave may be accomplished with a buoy equipped with motion sensors floating in the water.

While the above system is described as using motion sensors on board an ROV, embodiments of the disclosure are not limited to using a sensor on board the ROV. In at least one embodiment, direct measurements of the motion of an ROV can be acquired using acoustic positioning systems (e.g., high sampling rate acoustic positioning systems), and/or laser distance measurement systems.

Aspects of the present disclosure can include methods, apparatus, and machine-readable media for motion compensation adapted to reduce and/or minimize relative vertical motion between an object connected to a vessel and an object in the water subject to wave induced motions, as described above.

<FIG> sets forth an operation <NUM> that may be performed by an active motion compensation system, according to aspects of the present disclosure. Operation <NUM> begins at block <NUM>, where the active motion compensation system receives a measurement corresponding to a particle motion in water surrounding an ROV. At block <NUM>, the active motion compensation system synchronizes a motion of a docking station with a motion of the ROV based at least in part on the measurement corresponding to the particle motion.

According to aspects of the present disclosure, the motion of the ROV can be a motion in a vertical plane. For example, motion of an ROV can be measured relative to a sea floor below the ROV.

According to aspects of the present disclosure, an ROV control system may cease sending movement commands to an ROV for a period of time while an active motion compensation system synchronizes a motion of a docking station to motion of the ROV that is caused by wave action.

According to aspects of the present disclosure, an active motion compensation system may receive measurements of motion of an object floating (e.g., a buoy) near the docking station. The active motion compensation system may determine motions of an ROV that is also near the docking station based on the measurements and synchronize (e.g., by commanding movements of a crane) motion of the docking station to the motions of the ROV.

According to aspects of the present disclosure, an active motion compensation system may receive measurements of wave action from sensors on a docking station. For example, a docking station may be equipped with a Doppler sensor and/or a pressure sensor to measure velocity and pressure (both static and dynamic) of water near the docking station to determine wave action. The active motion compensation system may determine motions of an ROV that is near the docking station based on the measurements and synchronize motion of the docking station to the motions of the ROV.

According to aspects of the present disclosure, an active motion compensation system receives measurements of wave action from sensors located at a distance from a docking station. For example, a mother vessel may be equipped with a laser-range finder and/or a video camera to measure wave height and wave frequency or wave length near the docking station to determine wave action. The active motion compensation system may determine motions of an ROV that is near the docking station based on the measurements and synchronize motion of the docking station to the motions of the ROV.

At least one embodiment of the present disclosure can include a non-transitory machine-readable medium storing instructions executable by a processing resource (e.g., a processing system, a CPU) to cause a machine to determine a set of wave properties above an ROV, determine a motion response of the ROV, and calculate a motion of the ROV based at least in part on the set of wave properties and the motion response. In at least one embodiment of the present disclosure, the instructions can include instructions executable by a processing resource to cause the machine to synchronize a motion of a docking station to the motion of the ROV based at least in part on the calculation of the motion of the ROV.

Claim 1:
A method of launching and recovering a remotely operated vehicle (<NUM>) from a docking station (<NUM>) of a launch and recovery system (<NUM>), the method comprising:
deploying the docking station (<NUM>) in the water;
deploying the remotely operated vehicle (<NUM>) in the water;
deploying a sensor (<NUM>) in the water separately from the docking station (<NUM>), the sensor being arranged to sense wave motion and/or particle motion in the water surrounding the remotely operated vehicle (<NUM>);
receiving (<NUM>) from the sensor (<NUM>) a measurement corresponding to a particle motion in the water surrounding the remotely operated vehicle (<NUM>);
subsequent to receiving the measurement, directing movement of the remotely operated vehicle (<NUM>) to dock the remotely operated vehicle with the docking station (<NUM>);
synchronizing (<NUM>) a motion of the docking station (<NUM>) with a motion of the remotely operated vehicle based at least in part on the measurement corresponding to the particle motion; and
ceasing directed movement of the remotely operated vehicle (<NUM>) while receiving the measurement.