Abstract:
The present invention relates to an autonomous underwater vehicle (“AUV”) for monitoring underwater fluid currents by detecting electrical currents induced by the flow of a conductive liquid through the Earth&#39;s magnetic field. More particularly, the present invention relates to the gathering of data related to underwater fluid currents and the control of AUV motion during data gathering.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an autonomous underwater vehicle (“AUV”) having control and circuitry for monitoring underwater fluid currents. More particularly, the present invention relates to the gathering of data related to underwater fluid currents and the control of AUV motion during data gathering. 
         [0003]    2. Background of the Invention 
         [0004]    Ocean water is a conductive fluid that moves within the magnetic field of the Earth. As such, an electric current is induced in the water as a result of its movement within the magnetic field. Furthermore, the ocean water does not move uniformly, but rather, moves in linear and non-linear horizontal and vertical fluid currents. By measuring the electrical current in the ocean at a given location, and monitoring changes in this electrical current relative to time and location, the magnitude and direction of fluid currents at a given location of the ocean can be measured. These measurements permit mapping of the velocity of ocean water currents, directions of water currents, and relative velocity of layers of ocean water. Additionally, the measurements provide data for a range of analyses which rely on numerous inputs including ocean water velocity. 
       SUMMARY OF THE INVENTION 
       [0005]    One embodiment of the present invention provides for an underwater vehicle which can be operated within a body of electrically conductive water such as an ocean. The vehicle includes a hull and at least 2 electrodes in contact with the water to measure electrical characteristics of the water and generate information about the water currents in the body of water. The vehicle also includes a propulsion unit for moving the hull through a conductive liquid, and a control system coupled to the electrodes and propulsion unit. The control system is configured to monitor voltages at the electrodes, and to control the propulsion unit such that the electrodes are moved along a reciprocating course during voltage monitoring. The reciprocating course may include a vertical component. The control system may further store the electrode voltages, and transmit signals representative of the motion of the conductive liquid within which the hull resides to a location remote from the vessel. Depending upon the needs of a particular user, the transmitted signals may be representative of data which has had relatively little processing the control system (e.g. raw voltages associated with electrode measurements and vehicle locations) to highly processed data (e.g. actual water current velocity and direction associated with vehicle locations). 
         [0006]    Another embodiment of the invention provides for a sealed vessel having a propulsion unit electrically controlled to move the vessel along a reciprocating course under the surface of the ocean. The vessel includes at least 2 electrodes for monitoring electrical characteristics of the water such as voltage. The electrodes and the propulsion unit are coupled to a controller which controls the propulsion unit, and generates data such as voltage data representative of voltages at the electrodes during motion of the vessel. The controller also generates location data representative of the location of the vessel during generation of the voltage data. 
         [0007]    Another embodiment of the invention provides for a method for monitoring ocean currents. With this method, at least 2 electrodes are moved along a reciprocating course within the ocean. The reciprocating course may have a helical form. Along the path of the electrodes, voltage differences between the electrodes are determined at multiple locations along the path. Based upon these voltage differences, a velocity signal representative of the horizontal velocity of the ocean water is generated for selected locations along the path. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of an AUV adapted to practice the present invention. 
           [0009]      FIG. 2  is a block diagram of a vehicle control system of an AUV adapted to practice the present invention. 
           [0010]      FIG. 3  is a block diagram of a scientific data collection system of an AUV adapted to practice the present invention. 
           [0011]      FIG. 4  is a plan view of a reciprocating course embodying the present invention. 
           [0012]      FIG. 5  is a perspective view of reciprocating courses embodying the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    Referring to  FIG. 1 , an autonomous underwater vehicle (“AUV”) adapted to practice the present invention is shown in perspective view. AUV  10  is a submersible vehicle configured to operate while suspended (e.g. buoyantly suspended) in a volume of liquid, shown as ocean  200 . AUV  10  has a sealed hull  12  that is generally cylindrical in shape. Hull  12  may be configured as a pressure hull having a longitudinal axis. Hull  12  generally has a front end  14  and a rear end  16 , and an exterior wall defining an interior cavity. The interior cavity of hull  12  houses batteries, electronics, controllers, and buoyancy controls. The batteries, electronics, controllers, and buoyancy controls are generally distributed within hull  12  so that AUV  10  has a center of mass that is below the center of buoyancy, thereby stabilizing the AUV in a vertical orientation when suspended in ocean  200 . AUV  10  may optionally be provided with two wings  22  extending generally laterally from hull  12 . 
         [0014]    Hull  12  maybe formed of a fiber reinforced composite matrix, as disclosed in U.S. Pat. No. 7,096,814, which is hereby incorporated by reference in its entirety. In another embodiment, hull  12  may be formed of an aluminum alloy, or another suitable material. AUV  10  is typically suitable for operation to a pressure of 200 bars, corresponding to an ocean depth of approximately 2,000 meters. 
         [0015]    AUV  10  may be provided with stabilization and control fins at rear end  16 . Fins may include a vertical stabilizer  26  having a rudder  28 . Rudder  28  acts as a control surface, thereby providing yaw control of AUV  10 . Rudder  28  may comprise some or all of the surface area of vertical stabilizer  26 . Vertical stabilizer  26  is typically configured in a plane generally perpendicular to the plane of wings  22 . Vertical stabilizer  26  may extend above or below hull  12 . Fins may also include horizontal stabilizers  27 . Horizontal stabilizers  27  are typically configured in a plane generally parallel to the plane of wings  22 . AUV  10  may optionally be provided with an extension  29 . Extension  29  may be a rigid extension, a semi-flexible extension, or a flexible cable. 
         [0016]    A trim control may be used to control the pitch of AUV  10  in a horizontal, “nose up”, or “nose down” orientation. In one embodiment, the trim of AUV  10  within ocean  200  is controlled by shifting an internal weight within hull  12  to move the center of mass of AUV  10  towards front end  14  or rear end  16 . In another embodiment, AUV  10  may be provided with diving planes  24 . Diving planes  24  act as a control surface, thereby providing hydrodynamic trim control of AUV  10 . Diving planes  24  may comprise some or all of the surface area of horizontal stabilizers  27 . If AUV  10  is equipped with diving planes  24 , a second pair of diving planes may optionally be provided at front end  14  of AUV  10 . 
         [0017]    AUV  10  may be provided with a propulsion unit  30 . In one embodiment, AUV  10  is a gliding underwater vehicle or a “glider” as disclosed in U.S. Pat. No. 5,291,847, which is hereby incorporated by reference in its entirety. Propulsion unit  30  may be an autonomous engine as disclosed in U.S. Pat. No. 5,291,847. 
         [0018]    In another embodiment, propulsion unit  30  of AUV  10  may comprise a propeller  36  for propulsion within the ocean. Propeller  36  may be driven by a motor using any type of stored energy, such as electric batteries, compressed gasses, monopropellants, or the chemical reaction of or more two compounds. When provided with a propeller  36 , AUV  10  is capable of horizontal movement within ocean  200 , without an accompanying vertical displacement. Propeller  36  may be a conventional propeller extending from hull  12 . In another embodiment, propeller  12  may be a ducted propeller. In still other embodiments, propulsion unit  30  may incorporate propulsion fins, sometimes referred to as a “fish tail” propulsion system. 
         [0019]    AUV  10  may be provided with a hydrostatic buoyancy control to control depth within ocean  200 , shown as pump  32 . Pump  32  may be configured as a component of propulsion system  30 , or it may be operated independently from a propulsion system. Pump  32  is coupled to an internal bladder  33  and an external bladder  34 . Pump  32  may control the buoyancy of AUV  10  by pumping a control fluid such as mineral oil between internal bladder  33  and external bladder  34 . Movement of the control fluid between internal bladder  33  and external bladder  34  changes the volume of the glider, thereby providing AUV  10  with positive or negative buoyancy. As AUV  10  ascends or descends within ocean  200 , wings  22  permit AUV  10  to glide at a upward angle (arrow  23   a,    FIG. 1 ) or downward angle (arrow  23   b,    FIG. 1 ), thus permitting AUV  10  to change its horizontal position. In another embodiment, buoyancy control of AUV  10  may be provided by a ballast tank configured to be controllably emptied or filled with ocean water. The buoyancy control and trim control may also be combined by providing two ballast tanks, one positioned towards front end  14 , and the other towards rear end  16 . Trim control may be obtained by filling or emptying of the tanks to different levels, thereby altering the center of gravity of AUV  10 . 
         [0020]    In yet another embodiment, AUV  10  may be configured to be substantially neutrally buoyant. A neutrally buoyant AUV  10  may use propulsion system  30 , rudder  28 , and trim control  24  for hydrodynamic maneuvering within ocean  200 , including control of depth within ocean  200 . 
         [0021]    AUV  10  is provided with one or more electrode pairs to measure a voltage gradient. In one embodiment, electrode pairs are silver/silver chloride electrodes. However, other types of reference electrodes known to the art may be used. In a typical embodiment, AUV  10  is provided with a first electrode  90  and a second electrode  92  forming a first pair of electrodes  102 . First pair of electrodes  102  may be positioned substantially transverse to the longitudinal axis of AUV  10 , thereby forming a pair of transverse electrodes  102 . Pair of transverse electrodes  102  may be positioned on wings  22 . Alternatively, pair of transverse electrodes  102  may be positioned on opposing sides of hull  12 . 
         [0022]    AUV  10  may be further provided with a third electrode  94  and a fourth electrode  96  forming a second pair of electrodes  104 . Second pair of electrodes  104  may be positioned substantially parallel the longitudinal axis of AUV  10 , thereby forming a pair of longitudinal electrodes  104 . In one embodiment, both electrodes of pair of longitudinal electrodes  104  are placed on hull  12 . In another embodiment, one or both electrodes of pair of longitudinal electrodes  104  may be towed behind AUV  10  on extension  29 . 
         [0023]      FIG. 2  is an illustrative block diagram depicting a control system for an AUV adapted to practice the present invention. AUV  10  is typically provided with a control computer  50 . Control computer  50  may be a general-purpose computer having a processor and memory as is known in the art. The memory may include a hard disk drive or any type of solid state memory. Control computer  50  is communicatively coupled to propulsion unit  30 , trim control  24 , rudder  28 , and buoyancy control  32 , thereby providing three-dimensional directional control of AUV  10  within ocean  200 . Control computer  50  may thereby direct AUV  10  on one or more reciprocating courses of the present invention. Alternatively, control computer  50  may direct AUV  10  on a non-reciprocating course to change geographical position within ocean  200 . 
         [0024]    Control computer  50  is additionally communicatively coupled to a navigational receiver  52 . In a typical embodiment, navigational receiver  52  is a Global Positioning System (“GPS”) receiver. Alternatively, receiver  52  may be a LORAN receiver or an acoustic receiver. In another embodiment, receiver  52  may include an inertial navigation system. Control computer  50  may thereby receive geographical location information from receiver  52  to determine the location of AUV  10 . Control computer  50  may additionally be communicatively coupled to a science computer  60 . 
         [0025]    Control computer  50  and science computer  60  may also be communicatively coupled to one or more communications links  54 . Communications link  54  may be used to establish a data connection between AUV  10  and a remote computer  68 . Remote computer  68  may be on land, underwater, on a buoy or a ship, or on another object submerged within ocean  200 . In a typical embodiment, communications link  54  is a satellite transceiver capable of establishing a two-way data link with remote computer  68  using the Iridium satellite constellation. Communications link  54  may also be another type of wireless data link. Alternatively, communications link  54  may be a wired data connection capable of use when AUV  10  is removed from ocean  200 . In other embodiments, communications link  54  may be an optical data link or an acoustic data link. 
         [0026]    Communications link  54  may be used to transmit scientific data and AUV status information to remote computer  68 . In a typical embodiment, partially processed data scientific data is periodically transmitted to remote computer  68  using a wireless communications link while AUV  10  is deployed in the ocean, and science computer  60  additionally stores unprocessed data to be downloaded from AUV  10  when the AUV is physically retrieved. Additionally, communications link  54  may be used to provide control computer  50  or science computer  60  with new data collection instructions, navigational information, software updates, or any other programming change. 
         [0027]      FIG. 3  is an illustrative block diagram depicting a data collection system for an AUV adapted to practice the present invention. In a typical embodiment, AUV  10  is provided with a science computer  60 . Science computer  60  may be a general-purpose computer having a processor and memory as is known in the art. The memory may include a hard disk drive or any type of solid state memory. In a typical embodiment, science computer  60  is communicatively coupled to control computer  50 . In another embodiment, a single computational device performs the functions of both control computer  50  and science computer  60 . 
         [0028]    Science computer  60  may be programmed to provide navigational requests to control computer  50 . Navigational requests may include instructions to direct AUV  10  on a reciprocating course at the a location of AUV  10  for data collection purposes. Additionally, navigational requests may include instructions to direct AUV  10  to a location within ocean  200  that is remote from the present location of AUV  10 . 
         [0029]    Still referring to  FIG. 3 , a voltage signal generated by an electrode pair, shown as first electrode  90  and second electrode  92 , forming first pair of electrodes  102 , is received by operational amplifier  110  and amplified. Operational amplifier  110  is coupled to an analog to digital converter  112 . In one embodiment, A/D converter  112  is a 16-bit converter. A digital signal processor  114  may be coupled between A/D converter  112  and science computer  60 . Alternatively, A/D converter  112  may be coupled directly to science computer  60 . The amplified voltage signal is thereby converted to a digital signal, optionally processed, and communicated to science computer  60 . Science computer  60  thereby receives and stores in a memory (not shown) data representing the voltage detected at first electrode pair  102 . Science computer  60  is typically coupled to additional scientific instruments, which generally include a salinity sensor  62 , a temperature sensor  64 , and a pressure sensor  66 . Science computer  60  is typically configured to thereby receive and store scientific data corresponding to ocean water current velocity, salinity, temperature, pressure, and position within ocean  200 . Other configurations for a scientific data collection system will be readily apparent to those skilled in the art. 
         [0030]    Science computer may also be communicatively coupled to navigational receiver  52 . Science computer  60  may thereby receive geographical location information from receiver  52  to determine the location of AUV  10 . Science computer may request control computer  50  to direct AUV  10  to a remote point in ocean  200  as required for scientific data collection or for other purposes, such as instrument retrieval upon the completion of data collection. Science computer  60  may be programmed to collect scientific data along a predefined path within ocean  200 . Alternatively, science computer  60  may be programmed to autonomously collect scientific data within a volume of ocean  200  delineated by positional geographic boundaries. In another embodiment, science computer  60  may be provided with one of more way points within ocean  200 , and directed to collect scientific data while traveling on an autonomously-determined path between the way points. During travel within ocean  200 , science computer  60  may collect and store in memory scientific data from none, some, or all of the scientific instruments and navigational receiver  52  carried by AUV  10 . 
         [0031]    Referring to  FIG. 4 , an AUV  10  having pair of transverse electrodes  102  and pair of longitudinal electrodes  104  is shown in plan view. When a conductor moves within a magnetic field, a voltage gradient is generated. Ocean water is a conductor that is moved through the Earth&#39;s magnetic field by ocean currents. The movement of ocean water thus creates a voltage gradient between two separated points, which is a function of the velocity of the ocean water through the Earth&#39;s magnetic field. Additionally, water at various depths may be moving at different velocities, a phenomena known as current shear. Thus, the difference in the voltage gradient between two depths is representative of the current shear. 
         [0032]    Current shear data may be used to calculate ocean current velocities with respect to a frame of reference that is fixed with respect to the surface of the Earth. To determine ocean current velocities, the velocity of AUV  10  in the fixed reference frame must be determined at the surface of the ocean or at one or more depths. Where there is a known value for the current shear between a first depth with a known ocean current velocity and a second depth with an unknown current velocity, the ocean current velocity at the second depth may be determined by summing the vectors representing the current velocity at the first depth and the current shear. 
         [0033]    In one embodiment, the velocity of AUV  10  with respect to the surface of the Earth may be obtained through closely spaced location readings from navigational receiver  52 . In another embodiment, AUV  10  periodically receives geographical location information using receiver  52  while at or near the ocean surface. Typically, the starting position of AUV  10  prior to data collection using a reciprocating course will be displaced from the ending position. This change in geographical location may be represented as a first vector having a distance and heading. Additionally, AUV  10  may be programmed to collect and store data representative of propelled motion within ocean  200  with respect to an internal frame of reference, which may be represented as a second vector having a distance and direction. The second vector may be subtracted from the first vector to produce a vector representative of the current-induced motion of AUV  10  during data collection, and compared to the sum of individual current shear velocities. 
         [0034]    An AUV  10  adapted to practice the present invention collects a series of voltage signals representative of the current shear at a range of depths in the following manner. The voltage gradient induced by moving ocean water at a location may be measured by one or more electrode pairs. The voltage gradient induced by moving ocean water is perpendicular to the plane defined by the B field vector of the Earth&#39;s magnetic field and the vector direction of ocean water flow. It is understood that if the B field vector and ocean water flow vector are parallel, no voltage gradient is generated by the movement of ocean water. For purposes of the present invention, the field strength of the Earth&#39;s magnetic field may be considered locally invariant where movement of AUV  10  is typically localized within horizontal distances on the order of ten kilometers. 
         [0035]    Movement of AUV  10  through the Earth&#39;s magnetic field also induces a voltage gradient in wires connecting an electrode pair. Linear movement of AUV  10  through the vertical component of the B field vector at a constant velocity will induce a constant voltage in electrode pairs mounted on the AUV. Metallic electrodes placed into a conductive liquid further act as an electrochemical cell, generating a voltage potential. The electrode cell potential is also generally invariant during the measurement process. 
         [0036]    Controller  50  directs AUV  10  on a reciprocating course, shown as a generally circular reciprocating course  204 , by steering the AUV in a course having changes in horizontal heading. Generally, a reciprocating course comprises both forward motion of AUV  10  and at least a 180 degree change in horizontal heading. Preferably, a reciprocating course comprises both forward motion of AUV  10  and a 360 degree change in horizontal heading, wherein the AUV completes a full rotation in a horizontal plane. When AUV is directed on a reciprocating course at a constant depth, a reciprocating course may be a closed course such as a circle, oval, or another two-dimensional shape. A closed reciprocating course may also be closed in three dimensions, that is, the AUV returns to a starting point after changes in both heading and depth. Alternatively, a reciprocating course may be an open course when viewed in either two or three dimensions. An open reciprocating course may be a portion of a circular path, a U shape, a spiral, a helix or corkscrew shape, or any other open shape. The reciprocating courses of the present invention may be any path length and shape providing reciprocating AUV movement sufficient to collect data representative of ocean current velocities. 
         [0037]    Still referring to  FIG. 4 , AUV  10  is buoyantly suspended in ocean water  200 , wherein ocean water  200  has a horizontal water current in an arbitrary direction, shown as first direction  206 . AUV  10  is propelled at a constant forward velocity on a reciprocating course  204 . A generally circular reciprocating course is obtained by propelling AUV  10  at a constant forward velocity and at a constant depth while maintaining a constant rudder angle at rudder  28 . It is understood that such a generally circular reciprocating course is defined from a frame of reference internal to AUV  10 . When AUV  10  is directed in a circular reciprocating course while being advected by a horizontal ocean current, the reciprocating course will be cycloidal when viewed from a frame of reference that is fixed relative to the ocean floor or another fixed geographical location. 
         [0038]    As AUV  10  follows reciprocating course  204 , AUV  10  is continuously advected in first direction  206  by the ocean water current. During horizontal movement wherein the longitudinal axis of AUV  10  is oriented parallel to first direction  206 , a voltage is detected by pair of transverse electrodes  102 . The voltage detected at pair of transverse electrodes  102  comprises a voltage representative of ocean water movement, or ocean movement component, induced by movement of ocean water  200  in first direction  206 . However, the voltage detected at pair of longitudinal electrodes  104  does not comprise an ocean movement component, as pair of longitudinal electrodes  104  is parallel to the direction of the ocean water current. 
         [0039]    When AUV  10  is oriented such that the AUV longitudinal axis is oriented parallel to a second direction  208  and perpendicular to first direction  206 , a voltage is detected by pair of longitudinal electrodes  104 . The voltage detected at pair of longitudinal electrodes  104  comprises an ocean movement component, induced by movement of ocean water  200  in first direction  206 . However, the voltage detected at pair of transverse electrodes  102  does not comprise an ocean movement component, as pair of transverse electrodes  102  is parallel to the direction of the ocean water current. 
         [0040]    As AUV  10  is oriented in and moves in a direction 180 degrees opposite to first direction  206 , the voltage detected at pair of transverse electrodes  102  comprises an ocean movement component that is of the same magnitude, but opposite in sign to the ocean movement voltage detected during travel in first direction  206 . Similarly, as AUV  10  is oriented in and moves in a direction 180 degrees opposite to second direction  208 , the voltage detected at pair of longitudinal electrodes  104  comprises an ocean movement component that is of the same magnitude, but opposite in sign to the ocean movement voltage detected during travel in second direction  208 . 
         [0041]    Because the voltage signal induced by ocean movement changes sign when AUV  10  is directed on opposite headings within a reciprocating course, the locally invariant voltages generated by motion of AUV  10  and the electrode cell potential may be subtracted from the voltage signal detected by one or more electrodes pairs of AUV  10 . Accordingly, the reciprocating courses of the present invention enable separation of the signal representing the voltage induced by ocean water moving through the Earth&#39;s magnetic field from the voltages generated by forward motion of the AUV through the Earth&#39;s magnetic field and the electrode cell potential. 
         [0042]    As AUV  10  changes depth within ocean  200 , voltage signals representative of the relative ocean water current shear between depths may be collected. Where AUV  10  achieves propulsion through buoyancy control, AUV  10  simultaneously changes vertical depth and horizontal position within ocean  200 . Accordingly, the voltage signals representative of ocean water currents may be grouped into depth ranges to determine average ocean water current velocities within stratified depth levels. Where AUV is fitted with a propeller or another propulsion system allowing horizontal travel, AUV  10  may collect data, including voltage signals representative of ocean water current velocity, at one or more substantially constant depths. 
         [0043]    Referring to  FIG. 5 , a variety of reciprocating courses embodying the present invention are shown in perspective views. The paths of AUV  10  are shown with respect to an internal frame of reference, rather than in reference to a fixed point on the ocean floor. It is understood that AUV  10  may be advected by ocean currents, thereby causing deviations from the depicted courses when viewed in a frame of reference external to AUV  10 , i.e. with respect to a fixed point on the ocean floor. AUV  10  is generally disposed in ocean water  200  beneath the ocean surface  202 . 
         [0044]      FIG. 5A  shows a helical path  210  of AUV  10  about a vertical axis  220  perpendicular to ocean surface  202 . According to this embodiment, AUV  10  continuously changes depth while moving forward at a substantially constant velocity between a starting point  230  and an ending point  232 . As AUV  10  does not remain at a constant depth during data collection, voltage readings for a range of depths may be averaged together as AUV  10  changes heading. A helical path may be an open reciprocating course. Alternatively, AUV  10  may be further directed on a return reciprocating path to starting point  230 . 
         [0045]      FIG. 5B  shows a skewed helical path  212  about an axis  222  that is skewed with respect to vertical axis  220 . According to this embodiment, AUV  10  continuously changes depth while moving forward at a substantially constant velocity between starting point  230  and ending point  232 . As AUV  10  does not remain at a constant depth during data collection, voltage readings for a range of depths may be averaged together as AUV  10  changes heading. A skewed helical path may be an open reciprocating course. Alternatively, AUV  10  may be further directed on a return reciprocating path. 
         [0046]      FIG. 5C  shows a discrete-depth reciprocating course  214 , comprising a set of circular reciprocating segments  218  each at a substantially constant depth, wherein each segment  218  is circular about a vertical axis  220  perpendicular to ocean surface  202 . Reciprocating course  214  is shown as an open course having starting point  230  and ending point  232 . According to this embodiment, AUV  10  may be programmed to collect ocean current data at predetermined discrete depths, or AUV  10  may autonomously select certain discrete depths for reciprocating courses upon detection of variations in horizontal current velocities. Once a circular reciprocating course segment  218  is completed at a substantially constant depth, AUV  10  is directed to a new depth. At each discrete depth, AUV  10  is directed in a reciprocating circular course segment  218 . 
         [0047]      FIG. 5D  shows a discrete-depth reciprocating course  216 , comprising a set of circular reciprocating segments  218  each at a substantially constant depth, wherein each segment  218  is circular about an axis  222  that is skewed with respect to vertical axis  220 . Reciprocating course  216  is shown as an open course having starting point  230  and ending point  232 . According to this embodiment, AUV  10  may be programmed to collect ocean current data at predetermined discrete depths, or AUV  10  may autonomously select certain discrete depths for reciprocating courses upon detection of variations in horizontal current velocities. Once a circular reciprocating course segment  218  is completed at a substantially constant depth, AUV  10  is directed to a new depth. At each discrete depth, AUV  10  is directed in a reciprocating circular course segment  218 .