Abstract:
Certain aspects of the present disclosure generally relate to motion compensation between water-borne objects, and, more particularly, to synchronizing motion between a remotely operated vehicle (ROV) and a docking station of a launch and recovery system (LARS). An exemplary method includes receiving a measurement corresponding to a particle motion in water surrounding an ROV and synchronizing motion of a docking station with a motion of the ROV based at least in part on the measurement corresponding to the particle motion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present Application for Patent claims priority to U.S. Provisional Application No. 62/185,819, filed Jun. 29, 2015, which is assigned to the assignee of the present application and hereby expressly incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    Field of the Disclosure 
         [0003]    Certain aspects of the present disclosure generally relate to motion compensation between water-borne objects, and, more particularly, to synchronizing motion between a remotely operated vehicle (ROV) and a docking station of a launch and recovery system (LARS). 
         [0004]    Description of Related Art 
         [0005]    Marine seismic surveys are one type of marine geophysical survey which utilizes sound waves transmitted to the earth&#39;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. 
         [0006]    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. 
         [0007]    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., 100 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. 
         [0008]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. 
           [0010]      FIG. 1  illustrates an exemplary mother vessel with a LARS and an ROV operating according to previously known techniques. 
           [0011]      FIG. 2  illustrates an exemplary mother vessel with a LARS and an ROV operating according to previously known techniques. 
           [0012]      FIG. 3  illustrates an exemplary mother vessel with a LARS and an ROV operating according to aspects of the present disclosure. 
           [0013]      FIG. 4  a block diagram of an exemplary system in which aspects of the present disclosure may be practiced. 
           [0014]      FIG. 5  sets forth an example operation for motion compensation between water-borne objects, in accordance with certain aspects of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    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. 
         [0016]    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. 
         [0017]    The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. 
         [0018]    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. 
         [0019]    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. 
         [0020]    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. 
         [0021]      FIG. 1  illustrates an exemplary mother vessel  102  with a LARS  104  and an ROV  106  operating according to previously known techniques. The LARS  104  comprises a crane  110 , which comprises one or more actuators (not shown) used to position the crane  110 , and a docking station  120 . 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  120  is suspended from the tip of the crane  110  by one or more cables. Because the docking station  120  is heavy, it hangs directly or almost directly beneath the tip of the crane  110  and follows the motions of the tip of the crane  110 . In  FIG. 1 , the ROV  106  is deep (e.g., 100 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  106 , because the ROV  106  is deep under the surface, and thus the ROV  106  has very little vertical movement with respect to the sea floor  116 . 
         [0022]    The mother vessel  102  in  FIG. 1  is rolling, pitching, and/or heaving, as illustrated by the arrows  108  at the bow and stern of the mother vessel  102 . The LARS  104  of the mother vessel  102  is equipped with an AHC (not shown), which sends commands to the one or more actuators of the LARS  104 . The commands cause the actuators to counteract the movements of the mother vessel  102  by, for example, moving the tip of the crane  110  of the LARS  104 . The movement of the tip of the crane  110  is illustrated by the arrow  112 . By counteracting the movements of the mother vessel  102 , the AHC allows the docking station  120  to remain nearly stationary with respect to the sea floor  116  despite the movement of the mother vessel  102  caused by the wave action. Launching and recovery (e.g., docking and undocking) operations of the ROV  106  are improved by use of the AHC, because the docking station  120 , to which the ROV  106  docks and undocks, is nearly stationary with respect to the sea floor  116 . 
         [0023]      FIG. 2  illustrates an exemplary mother vessel  202  with a LARS  204  and an ROV  206  operating according to previously known techniques. As in  FIG. 1 , the LARS  204  comprises a crane  210 , which comprises one or more actuators (not shown) used to position the crane  210 . The LARS  204  also comprises a docking station  220  (e.g., a TMS) that is suspended from the tip of the crane  210  by one or more cables and follows the motions of the tip of the crane  210 . In  FIG. 2 , the ROV  206  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  206 , because the ROV  206  is near the surface, and thus the ROV  206  may have significant vertical movement with respect to the sea floor  216 . The movement of the ROV  206  caused by the wave action is illustrated by the arrows  218 . 
         [0024]    As in  FIG. 1 , the mother vessel  202  in  FIG. 2  is rolling, pitching, and/or heaving, as illustrated by the arrows  208  at the bow and stern of the mother vessel  202 . As in  FIG. 1 , the LARS  204  of the mother vessel  202  is equipped with an AHC (not shown), which sends commands to one or more actuators (not shown) of the LARS  204 . The commands cause the actuators to counteract the movements of the mother vessel  202  by, for example, moving the tip of the crane  210  of the LARS  204 . The movement of the tip of the crane  210  is illustrated by the arrow  212 . By counteracting the movements of the mother vessel  202 , the AHC allows the docking station  220  to remain nearly stationary with respect to the sea floor  216  despite the movement of the mother vessel  202  caused by the wave action. Launching and recovery (e.g., docking and undocking) operations of the ROV  206  in this situation are not improved, however, by use of the AHC, because motion of the docking station  220 , to which the ROV  206  docks and undocks, is reduced while the ROV  206  is rolling, pitching, and heaving due to the wave action. 
         [0025]      FIG. 3  illustrates an exemplary mother vessel  302  with a LARS  304  and an ROV  306  operating according to aspects of the present disclosure. As in  FIGS. 1 and 2 , the LARS  304  comprises a crane  310 , which comprises one or more actuators (not shown) used to position the crane  310 . The LARS  304  also comprises a docking station  320  (e.g., a TMS) that is suspended from the tip of the crane  310  by one or more cables and follows the motions of the tip of the crane  310 . As in  FIG. 2 , the ROV  306  in  FIG. 3  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  306 , because the ROV  306  is near the surface, and thus the ROV  306  has significant vertical movement with respect to the sea floor  316 . The movement of the ROV  306  caused by the wave action is illustrated by the arrows  318 . 
         [0026]    As in  FIGS. 1 and 2 , the mother vessel  302  in  FIG. 3  is rolling, pitching, and/or heaving, as illustrated by the arrows  308  at the bow and stern of the mother vessel  302 . The LARS  304  of the mother vessel  302  is equipped with an active motion compensation system  303  that includes an embodiment of the present disclosure. The active motion compensation system  303  may receive information regarding particle (e.g., water particle) motion in water surrounding the ROV  306  from an MRU  324 , inertial sensing system, or other motion sensing system (not shown) on the ROV  306 . That is, the active motion compensation system  303  may receive information directly regarding the particle motion in the water surrounding the ROV. As used herein, surrounding means within a distance of 30 meters from the ROV. Additionally or alternatively, the active motion compensation system  303  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  306  may be carried via, for example, cables in a tether  322 , which may also carry commands to the ROV  306  from operators aboard the mother vessel  302 . Although the tether  322  is shown terminating at the docking station  320 , the disclosure is not so limited and embodiments of the present disclosure may be used with a tether  322  that connects the ROV  306  with the LARS crane  310  via the docking station  320 . Alternatively or additionally, one or more motion sensors, e.g., an acoustic positioning system  326  or optical motion detector (e.g., a laser motion detector)  314 , aboard the mother vessel  302  may supply information regarding movements of the ROV  306  and/or particle motion in the water surrounding the ROV to the active motion compensation system  303 . While the laser motion detector  314  is shown separated from the crane  310 , the disclosure is not so limited, and the optical motion detector  314 , such as a laser motion sensor, may be mounted on or near the crane  310 . 
         [0027]    Additionally or alternatively, the active motion compensation system  303  may receive information regarding the motions of the mother vessel  302  and/or the motions of the ROV  306  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  330 , and an energy receiver  332 , each of which may be mounted on the mother vessel  302  or on the ROV  306 . The energy emitter may be, for example, one or more speakers  326  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  306  and/or the mother vessel  302  and/or the particle motion in the water surrounding the ROV. The motion sensing system may optionally comprise a wave motion sensor  350  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  303  via one or more cables  352 . The wave motion sensor  350  may include, for example, a predominantly neutrally buoyant device (e.g., producing a buoyant force of 0.9 to 1.1 times the weight of the device) equipped with motion sensors that senses particle motion in water near the ROV  306  and/or the docking station  320 . A second example of a wave motion sensor  350  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  306  and/or the docking station  320 . A third example of a wave motion sensor  350  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  306  and/or the docking station  320 . 
         [0028]    Additionally or alternatively, the active motion compensation system  303  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  320 . The flow sensor may detect water flow past the docking station  320  (e.g., wave-induced water motion), and the active motion compensation  303  system may receive the particle motion information via one or more cables and/or the tether  322 . 
         [0029]    The active motion compensation system  303  sends commands to one or more actuators (e.g., motors, not shown) of the LARS  304 . The commands cause the actuators to counteract the movements of the mother vessel  302  by, for example, moving the tip of the crane  310  of the LARS  304  to align the movements of the docking station  320  relative to the sea floor  316  with the movements of the ROV  306  relative to the sea floor  316 . That is, the active motion compensation system  303  compensates for the motion of both the ROV  306  and the mother vessel  302  and sends commands (e.g., to actuators of the crane  310 ) synchronizing motions of the docking station  320  with motions of the ROV  306 . 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 10% of the displacement of a second object, with a speed of the first object within 10% 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  310  is illustrated by the arrow  312 . The movement of the docking station  320  with respect to the sea floor  316  is illustrated by the arrow  328 . By counteracting the movements of the mother vessel  302  and the ROV  306 , the active motion compensation system  303  allows the docking station  320  to remain nearly stationary with respect to the ROV  306  despite the movement of the ROV  306  and the mother vessel  302  caused by the wave action. Launching and recovery (e.g., docking and undocking) operations of the ROV  306  are improved by use of the active motion compensation system  303 , because motion of the docking station  320 , to which the ROV  306  docks and undocks, is nearly stationary with respect to the ROV  306  while the ROV  306  is moving due to the wave action. 
         [0030]      FIG. 4  illustrates a block diagram of an exemplary system  400  in which aspects of the present disclosure may be practiced. The system  400  includes an ROV  402  and a mother vessel  404 . The ROV  402  is tethered to the mother vessel  404  via a tether  406  that includes one or more cables (e.g., conductors, fiber-optic cables) that carry commands and data between the ROV  402  and the mother vessel  404 . 
         [0031]    The ROV  402  includes one or more motion sensors (e.g., accelerometers)  450 ,  452 ,  454  that detect and measure motion of the ROV  402 . The motion sensors  450 ,  452 ,  454  may be separate units or may be integrated into a MRU  456 . The MRU  456  is drawn with dashed lines to show that it is optional. The motion sensors  450 ,  452 ,  454  and/or MRU  456  output signals (e.g., electrical signals, light pulses carried via fiber optics) conveying information regarding the motion of the ROV  402 . The signals, which may be digital or analog signals, are conveyed to the mother vessel  404  via the cables of the tether  406 . The ROV  402  also includes at least one motor  458 , rudder  460 , and/or thruster  462  used to maneuver the ROV  402 . One or more computers  464  may be included in the ROV  402  to control the ROV  402  and/or communicate (e.g., via the cables in the tether  406 ) with systems (e.g., systems for controlling the ROV  402 ) aboard the mother vessel  404 . The computers  464  may include one or more processors  466  and memory  468 . The ROV  402  may also include one or more water motion sensors  470  that may measure motion of particles of water near the ROV  402 . The water motion sensors may comprise Doppler motion sensors, flow meters, or other types of motion sensors. The water motion sensor  470  is drawn with dashed lines to show that the water motion sensor is optional. The ROV  402  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  404 ) and provide measurements of movements of the ROV  402  to the computer(s)  464  of the ROV  402  and/or an active motion compensation system  414 . 
         [0032]    The mother vessel  404  includes a LARS  410 , a control system  440  for controlling the ROV  402 , and an optional wave motion sensor  428 . The LARS  410  includes a crane  412 , a control system  430 , and an active motion compensation system  414 . The control system  430  includes an interface (e.g., touchscreen, joystick, and/or keyboard) for accepting commands from an operator who controls the LARS  410 . The optional wave motion sensor  428  may comprise a buoy equipped with motion sensors (e.g., an MRU) and tethered to the mother vessel  404 , such as wave motion sensor  350  shown in  FIG. 3 . Additionally or alternatively, the optional wave motion sensor  428  may comprise a flow sensor (e.g., a Doppler sensor) disposed on a docking station (e.g., a TMS). 
         [0033]    The active motion compensation system  414  may be an embodiment of the present disclosure. The active motion compensation system  414  includes one or more computers  416  that control the crane  412  and/or communicate with the motion sensors  450 ,  452 ,  454  aboard the ROV and/or motion sensors (e.g., accelerometers, inertial motion sensors)  418 ,  420 ,  422  aboard the mother vessel  404  and/or the optional wave motion sensor  428 . The motion sensors  418 ,  420 ,  422  detect and measure motion of the mother vessel. The motion sensors  418 ,  420 ,  422  may be separate units or may be integrated into a MRU  424 . The motion sensors  418 ,  420 ,  422  and/or MRU  424  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  428  detects and measures wave action and sends information regarding the wave action to the active motion compensation system  414 . The computers  416  accept commands from the control system  430 , receive measurements of motions of the mother vessel from the motion sensors  418 ,  420 ,  422 , receive measurements of motions of the ROV from the motion sensors  450 ,  452 ,  454 , optionally receive measurements of the wave action from the wave motion sensor  428 , and then combine the control system commands and motion data (e.g., motion measurements) from the mother vessel  404  and ROV  402  to determine crane movements that move the tip of the crane  412  in alignment with movement of the ROV  402  as described above. The computers  416  of the active motion compensation system  414  then send the determined commands to the crane  412  (e.g., to motors and/or actuators) to cause those movements, i.e., to move the tip of the crane  412  in alignment with movement of the ROV  402  as described above. 
         [0034]    According to aspects of the present disclosure, an active motion compensation system (e.g., active motion compensation system  414  in  FIG. 4 ) may receive information from a control system of an ROV (e.g., control system  440 ) regarding commanded movements of the ROV (e.g., via connection  442 ) and use that information in determining commands to send to actuators (e.g., motors of a crane) of a LARS (e.g., LARS  410 ). 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. 
         [0035]    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. 
         [0036]    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. 
         [0037]    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. 
         [0038]    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. 
         [0039]      FIG. 5  sets forth an operation  500  that may be performed by an active motion compensation system, according to aspects of the present disclosure. Operation  500  begins at block  502 , where the active motion compensation system receives a measurement corresponding to a particle motion in water surrounding an ROV. At block  504 , 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. 
         [0040]    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. 
         [0041]    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. 
         [0042]    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. 
         [0043]    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. 
         [0044]    According to aspects of the present disclosure, an active motion compensation system may receive 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. 
         [0045]    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. 
         [0046]    Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of this disclosure. 
         [0047]    The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Various advantages of the present disclosure have been described herein, but embodiments may provide some, all, or none of such advantages, or may provide other advantages.