Abstract:
Apparatus and methods are described for remotely controlling position of marine seismic equipment. One apparatus comprises a source connected to a tow member; and an adjustment mechanism connected to the source and the tow member, the adjustment mechanism adapted to actively manipulate an angle of attack of the source. It is emphasized that this abstract is provided to comply with the rules requiring an abstract, which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
This is a continuation of U.S. application Ser. No. 11/055,169, entitled “Apparatus and Methods for Controlling Position of Marine Seismic Sources”, filed Feb. 10, 2005 now abandoned, in the name of the inventor Rune Toennessen (“the &#39;169 application”). The earlier effective filing date of the &#39;169 application is hereby claimed for all common subject matter. The &#39;169 application is also hereby incorporated by reference in its entirety for all purposes as if expressly set forth verbatim herein. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to the field of marine seismic instruments and methods of controlling same. More specifically, the invention relates to apparatus and methods for remotely controlling position marine seismic instrumentation, as well as related systems, methods, and devices. 
   2. Related Art 
   Marine seismic exploration investigates and maps the structure and character of subsurface geological formations underlying a body of water. For large survey areas, a single vessel may tow one or more seismic sources and one or more seismic streamer cables through the water. Alternatively, a tow vessel may either be a “pure” source vessel (meaning it only tows seismic sources) or a “pure” streamer (receiver) vessel, in which case two or more vessels may be used. In any case the seismic sources may comprise compressed air guns or other means for generating acoustic pulses in the water. The energy from these pulses propagates downwardly into the geological formations and is reflected upwardly from the interfaces between subsurface geological formations. The reflected energy is sensed with hydrophones attached to the seismic streamers, and data representing such energy is recorded and processed to provide information about the underlying geological features. 
   Three-dimensional (3-D) seismic surveys of a grid provide more information regarding the subsurface formations than two-dimensional seismic surveys. 3-D surveys may be conducted with up to twelve or more streamers that form an array covering a large area behind the vessel. The streamers typically vary in length between three and twelve kilometers. Tail buoys attached at the streamer distal ends carry radar reflectors, navigation equipment, and acoustic transponders. Hydrophones are positioned along each streamer. The in-line interval between each receiver, or receiver group, ranges between about 3 and 25 meters, with 12.5 meters comprising typical interval spacing. 
   Since the grid is often much wider than the array, the tow vessel must turn around and tow the array in laps across the grid, being careful not to overlap or leave large gaps between the laps across the grid. 
   A multiple streamer array requires deflectors near the vessel to pull the streamers outwardly from the direct path behind the seismic tow vessel and to maintain the transverse or crossline spacing between individual streamers. The same is true for multiple sources being towed behind a tow vessel when no streamers are present. Deflectors rely on hydrodynamic lift created by forward motion through the water to pull the streamers and/or sources outwardly and to maintain the transverse position relative to the vessel path. 
   In 4-D geophysical imaging, a 3-D seismic survey is repeated over a grid that has been previously surveyed. This series of surveys taken at different times may show changes to the geophysical image over time caused, for example, by extraction of oil and gas from a deposit. 
   It is important that the source members being used to generate the acoustical pulses be located as closely as possible to the same location as in previous surveys over the same grid. This has been difficult to accomplish in a marine survey because the acoustical source members are typically towed behind the tow vessel in source arrays, which are subject to wave and current movement. 
   In addition to the deployment and operation difficulties associated with towing multiple streamers and/or multiple source arrays, conventional techniques limit the ability to position source arrays and streamers in different relative positions and orientations. Source array design is limited by the tow configuration. Each towed source array is also subject to crosscurrents, wind, waves, shallow water, and navigation obstacles that limit the coverage provided by the survey system. 
   Attempts to control the location of seismic sources and source arrays have included attaching distance ropes running to lateral passive deflectors and tow cables; use of active (steerable) deflecting members attached to the source tow cables in front of the source arrays, or mid-way or at the aft end of the source arrays; and use of passive lateral deflectors equipped with a winch located near the front of the source. WO2004092771 A2, published Oct. 28, 2004, (the &#39;771 application) discloses the latter two options. By attaching one or more steerable deflecting members to the front, rear, or mid-section of one or more source arrays, or a winch to the front of the source that acts on a passive lateral deflector, the source array locations may be controlled. Another method and device employs a source array comprising a rigid bar mounted under a rigid or semi-rigid float member, with the seismic source members, for example air-guns, hanging below the rigid bar.  FIGS. 1A and 1B  illustrate plan and side-elevation views, respectively, of this source array  100 . Source array  100  comprises a rigid steel or aluminum member  8  rigidly mounted to a rigid or semi-rigid float  10 , which floats near surface  12  of the ocean or other water body. Multiple source members  14  are hung by chains or other means  16  from member  8 , and source array  100  is towed behind a seismic vessel (not shown) by a strength-taking source umbilical  2  that is attached to a tow bridle having two elements, a front element  4  attached to a front  5  of member  8 , while a second bridle element  6  is attached proximate a mid-section  7  of member  8 . The lengths of bridle elements  4  and  6  determines the orientation, or so-called angle of attack of member  8  and float  10  toward the incoming flow, F. Therefore, member  8  and float  10  function as a low aspect ratio hydrofoil creating lateral lift that enables source array  100  to be laterally deflected. However, this method and apparatus offers no possibilities for remotely adjusting the angle of attack. 
   The previous attempts have not provided optimal control of the location of the source arrays under towing conditions. While these techniques are improvements in the art, further improvement is desired. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, apparatus, systems and methods are described for actively controlling position of marine seismic sources and source arrays that reduce or overcome problems with previous apparatus and methods. Apparatus and systems of the invention comprise a source array, sometimes referred to herein as a gun-array, the source array comprising one or more source members, sometimes referred to herein as air-guns. As used herein the term “source array” is meant to be broader than the term gun-array, which those skilled in the art will recognize as meaning one or more air-guns. The term “source member” is meant to be broader than the term air-gun, and is meant to include all acoustic sources, including, but not limited to, air-guns, oscillating members, vibration members, explosive charges, percussion devices, and the like. Thus, in the same way that a gun-array includes one or more air-guns, a source array comprises one or more source members. The terms gun-array, gun-string and sub-array are also often used interchangeably in the art to call out an assembly of components, including an array of air-guns, one or more floats, chains, hang plates, everything required to position the gun-array and have it functioning. The term source array will be used herein for this assembly. Finally, the terms “source”, “seismic source”, and “marine seismic source” are used interchangeably herein, unless a specific embodiment requires a different meaning, and means one or more source arrays comprising some or all source members (e.g., air-guns) fired at the same time. A source may comprise from one to ten source arrays, more typically one to four source arrays. In this regard, the art distinguishes between dual source and single source. Dual source systems comprise two sources, each of say three source arrays, where each source is located offset to the centerline. A single source may comprise three source arrays where the center of the source is located at the centerline. 
   A first aspect of the invention is an active, position controllable marine seismic apparatus comprising: 
   a source array connected to a source tow member; and 
   an adjustment mechanism connected to the source array and source tow member, the adjustment mechanism adapted to actively manipulate an angle of attack of the source array. As used herein, “actively manipulate” means controlling the angle of attack either directly or indirectly in response to, and/or in anticipation of, an undesirable change in movement of the source array. “Controlling” may be performed locally on the source array, or remotely through any type of communication system. “Angle of attack” means, when referring to a seismic source array, the angle that the body of the source array makes relative to the direction of flow of water past it, sometimes referred to as the flow vector. This may also be described as the angle that the body of the source array makes relative to its direction of travel through the water. The flow vector may or may not be parallel to the tow member. 
   The adjustment mechanism may be connected to the source array at one or a plurality of tow points located on the source array, and may include a towing harness. The tow point may be located at a front end of the source array, or at a position between the front end of the source array and a rear end of the source array. The adjustment mechanism may comprise a deflecting member positioned between the float and one or more of the source members, and may further comprise a rigid moment-transfer member having first and second portions, which may or may not be ends, the first portion connected to the source tow member, the second portion connected to a tow point on the deflecting member through a swivel joint, where the swivel joint may be a hinged joint, ball joint, or equivalent function joint. The adjustment mechanism may further comprise an actuator mounted on the deflecting member near the tow point and adapted to actuate the rigid moment-transfer member. The rigid moment-transfer member may be a solid member or hollow, and the solid and hollow members may be cylindrical members, parallelepiped members, or equivalent functional members. The rigid moment-transfer member may also be a telescoping member, an I-beam, or other equivalent functional configuration. 
   The adjustment mechanism may comprise either a low or high aspect ratio deflecting member positioned between, or in front of a float and one or more source members. In this arrangement, the adjustment mechanism may include a bridle system, and a rotatable connector may be operatively connected to the deflecting member and adapted to function with the bridle system. The rotatable connector may be positioned on the deflecting member approximately at a mid-section of the deflecting member. A local controller may be mounted on the apparatus, the local controller adapted to receive a signal from an on-board controller on a tow vessel or other remote controller and send a signal to the local controller, which then operates an actuator and rotatable connector. The bridle system may comprise a front bridle leg attached to a front end of the deflecting member, and an aft bridle leg comprising a loop that passes through the rotatable connector, and thus the bridle system may be remotely controllable. The bridle system may include a frame that is connected to a front end of the deflecting member via a swivel joint and adapted to pivot about the swivel joint, and the frame may attach to an aft bridle leg comprising a loop that passes through the rotatable connector. The frame may be a triangular frame, or any other shaped frame that performs the equivalent function of moving the bridle legs when actuated. Another alternative is to replace all or substantial portions of the bridle legs with linear actuators. In this latter embodiment, the adjustment mechanism may be a combination of a frame, linear actuators, and a high aspect ratio deflecting member, as further explained herein. 
   The source array may comprise a float and one or more source members attached to the float. 
   Apparatus of the invention may further comprise a local controller mounted on the source array, the local controller adapted to receive a signal comprising a desired angle of attack from a remote controller, inform the adjustment mechanism of the desired angle of attack, and signal an actuator to move the adjustment mechanism accordingly. The adjustment mechanism may further comprise a sensor able to measure the actual, or “real” angle of attack of the source array and report this data to the remote controller. Alternatively, rather than sensing and using the real angle of attack of the source array, which may be difficult to measure, the orientation of a component of the source array may be sensed, for example the orientation of the source tow member, the position of an actuator, or the like, and this data used to control the adjustment mechanism. 
   The term “deflecting member” is to be distinguished from the term “deflector.” As used herein a “deflecting member” is a member that is a component of and deflects a source. Deflecting members useful in the invention may comprise a low aspect ratio member or a high aspect ratio member. The deflecting member may be suspended between the float and one or more of the source guns, or the deflecting member may be rigidly attached to the float. In any case, the deflecting member may be positioned between the float and some or all of the source members, in front of the source array, or at the aft end of a source array. The term “deflector” means a discrete device or apparatus connected to the source via an active or passive tow cable. Systems of the invention may include deflecting members but not deflectors, deflectors but not deflecting members, or both deflecting members and deflectors. 
   Another aspect of the invention are systems comprising a tow vessel, a seismic source connected to the tow vessel by a source tow member, and a remotely controllable deflector. Systems of the invention may comprise many alternative arrangements for connecting the tow vessel, source, and deflector, and all are considered within the scope of the invention. As used herein the terms “active” and “passive” refer to the ability and non-ability to communicate, respectively, of a connection between a tow vessel and a source, between a tow vessel and a deflector (with or with out streamers), and between a source and a deflector (with and without streamers). “Tow member”, as used herein, may be an active or passive connection device, and may be a strength-taking component or non-strength-taking component. A strength-taking component is one that is intended to pull, or help pull any of a source array, a deflector, and/or a streamer. The term “umbilical” when used without qualification means an active, power and/or data transmitting tow member that is substantially non-strength-taking; in other words an umbilical can withstand some tension, but is not meant to pull a source array or deflector, unless it is a strength-taking umbilical. Any combination of remotely controllable deflector being connected to and towed by the tow vessel, or towed by the source with and without connection to the tow vessel, and any practical combination of passive tow member with an umbilical, using both wherein at least one is a strength-talking tow member, or using only a strength-taking umbilical if desired, are intended to be within the invention. For example, the following non-limiting embodiments are considered within the invention, wherein the deflector is remotely controllable (wire or wireless) in each:
         deflector connected to and towed by the tow vessel with a passive strength-taking tow member, and either 1) a strength-taking umbilical connecting the deflector to the source, or 2) a combination of a passive, strength-taking tow member and an umbilical;   deflector connected to and towed by the tow vessel with a strength-taking umbilical, and a passive tow member extending from the deflector to the source;   deflector connected to and towed by the source by a strength-taking umbilical, with no direct connection to the tow vessel;   deflector connected to and towed by the source by a combination of a strength-taking passive tow member and an umbilical; and   deflector connected to and towed by the source by a passive, strength-taking tow member, with an umbilical connecting the deflector to the tow vessel.
 
Notice that embodiments wherein the remotely controllable deflector is not directly mechanically connected to the tow vessel are considered within the invention. There may be wireless or other non-mechanical transmission between the deflector and tow vessel in such embodiments, and the mechanical connection between deflector and source could be two fold, either a combination of passive, strength-taking tow member (for example chain, or rope) and an umbilical for transmitting electrical power and/or signals, or a single strength-taking umbilical able to take the loads and to transmit electrical power and/or signals. Data transmission and electrical power could go from vessel to source via umbilical and further to deflector via umbilical.
       

   The remotely controllable deflector may be any type of deflector, including wing and boom arrangements, and door-type deflectors, both of which are known in the art, as long as the deflector is, or is modified to be, remotely controllable. One useable deflector comprises a principal wing-shaped body shaped to produce in use a sideways force which urges the marine seismic source laterally with respect to the direction of movement of the towing vessel, a boom extending rearward from the principal wing-shaped body, and an auxiliary wing-shaped body, smaller than the principal wing-shaped body, secured to an end of the boom remote from the principal wing-shaped body and shaped so as to produce in use a sideways force in generally direction opposite to that produced by the principal wing-shaped body, and comprising a remotely operable means for adjusting an angle between the boom and the principal wing-shaped body to vary the sideways force produced by the principal wing-shaped body. Another deflector useful in the invention is a modified “door” type deflector, comprising a plurality of passive hydrofoils mounted within a frame, and at least one active hydrofoil mounted in the frame aft of the passive hydrofoils, the active hydrofoil adapted to be moved and change an angle of attack of the deflector using an actuator and controller positioned in the frame, and through remote communication between the controller and the tow vessel via an umbilical. 
   Another aspect of the invention comprises methods of remotely controlling position of marine seismic sources, one method comprising actively controlling an angle of attack of a marine seismic apparatus relative to a reference using an adjustment mechanism connected to the apparatus and a tow member. One method of the invention includes sensing the angle of attack (or sensing a parameter indicative of the angle of attack, such as an actuator position) to obtain an acquired value, comparing the acquired value to a desired value and adjusting the adjustment mechanism accordingly. As with the apparatus of the invention, rather than sensing and using the real angle of attack of the source array, which may be difficult to measure, the orientation of a component of the source array may be sensed, for example the orientation of the source tow member, and this data used to control the adjustment mechanism. In other methods of the invention, where the apparatus is a source array comprising a float and one or more source members generally below the float, the method further comprises providing a deflecting member positioned between, in front, or behind the float and one or more of the seismic signal guns, towing the apparatus with a tow vessel using a tow member, and transferring moment from a rigid moment-transfer member having first and second portions to the deflecting member, the first portion connected to the tow member, the second portion connected to a tow point on the deflecting member through a swivel joint. Further methods of the invention include actuating the rigid moment-transfer member using an actuator mounted on the deflecting member near the tow point; controlling the actuator using a local controller mounted on the apparatus; and sending a signal from the tow vessel to the local controller and sending a signal from the local controller to the actuator. Other methods of the invention include towing the apparatus with a tow vessel using a tow member wherein the tow member comprises a bridle system, and transferring moment from the bridle system to the deflecting member. Further methods of the invention include actuating the bridle system using one or more actuators mounted on the deflecting member near a tow point on the deflecting member. Actuators may be rotatable or linear, for example hydraulic or pneumatic cylinders connecting each bridle member to the deflecting member. Actuators may be actuated using a local controller mounted on the apparatus. A local sensor may sense the position or status of an actuator and feed this information back to the local and/or remote controllers. The local controller may receive a signal from the tow vessel and send a signal to the actuator. 
   Another method of the invention is used to remotely control position of a marine seismic source, one method comprising towing a source using a first strength-taking umbilical connected to a tow vessel, and remotely controlling an angle of attack of a deflector connected to the source by a second umbilical, and connected to the tow vessel by a passive, strength-taking tow member, the deflector positioned laterally from the source during seismic shooting. Alternatively, a method of remotely controlling position of a marine seismic source comprises towing a marine seismic source array using a strength-taking umbilical connected to a tow vessel, and remotely controlling position of a deflector connected to the tow vessel by a second umbilical, and connected to the marine seismic source array via a passive, strength-taking tow member, the deflector positioned laterally from the source array during seismic shooting. In these methods one may sense the angle of attack to obtain an acquired a value, compare the acquired value to a desired value, and adjust the deflector accordingly, or sense a parameter indicative of the angle of attack, such as an actuator position known by experience or experiments to indicate the relationship between the actuator position and the resulting angle of attack. The deflector may be adjusted by using an actuator mounted on the deflector. The actuator may be actuated using a local controller mounted on the deflector, which can send a signal from the tow vessel to the local controller and send a signal from the local controller to the actuator. 
   Further advantages and features of the invention will be apparent upon review of the brief description of the drawings, the detailed description of the invention, and the claims which follow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The manner in which the objectives of the invention and other desirable characteristics can be obtained is explained in the following description and attached drawings in which: 
       FIGS. 1A and 1B  illustrate schematic plan and side-elevation views, respectively, of a prior art marine seismic steering apparatus and method; 
       FIGS. 2A and 2B  illustrate schematic plan and side-elevation views, respectively, of a first position controllable marine seismic apparatus and method of the invention; 
       FIG. 3  illustrates a schematic side-elevation view of a second position controllable marine seismic apparatus and method of the invention; 
       FIG. 4  is a schematic diagram of a process control scheme useful in the present invention for controlling position of seismic sources using the apparatus and systems of the invention; 
       FIGS. 5A-C  illustrate schematic plan views of position controllable marine seismic apparatus and methods of the invention employing bridle systems as part of the adjustment mechanism; 
       FIGS. 6A-C  illustrate schematic plan views of position controllable marine seismic apparatus and methods of the invention employing frames as part of the adjustment mechanism; 
       FIG. 7  illustrates a schematic aerial plan view of a system of the invention; 
       FIG. 8  illustrates a prior art wing-type deflector useful in the invention; 
       FIG. 9  illustrates a schematic plan view, with portions cut away, of a prior art door-type deflector; 
       FIG. 10  illustrates a schematic plan view, with portions cut away, of the door-type deflector of  FIG. 9  modified in accordance with the invention; and 
       FIGS. 11A-F  are simplified schematic diagrams illustrating six non-limiting alternative tow member arrangements. 
   

   It is to be noted, however, that the appended drawings are not to scale and illustrate only typical embodiments of this invention, and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
   The present invention relates to various apparatus, systems and methods for controlling position of one or more marine seismic components. The terms “controlling position”, “position controllable”, “remotely controlling position”, “remotely adjustable”, and “steering” are generally used interchangeably herein, although it will be recognized by those of skill in the art that “steering” usually refers to following a defined path, while “controlling position”, “position controllable”, and “remotely controlling position” could mean steering, but also could mean merely maintaining a relative position, for example relative to one or more reference points, such as natural or man-made objects, or merely deflecting an object. As “position controllable” and “controlling position” are somewhat broader terms than “steering”, these terms are used herein, except when specific instances demand using more specific words. One aspect of the present invention relates to position controllable apparatus. Other aspects of the present invention, which are further explained below, relate to methods for remotely controlling or adjusting position of marine seismic sources. 
   As an example,  FIGS. 2A and 2B  illustrate plan and side-elevation views, respectively, of a first position controllable marine seismic source array  200  and method of the invention. (The same numerals are used throughout the drawing figures for the same parts unless otherwise indicated.) Source array  200  comprises a plurality  202  of source members  14 , for example compressed air guns, which are fired to generate acoustical waves that are reflected from the subsurface geological features back to receivers (not shown) during a seismic exploration. Source members  14  may be other acoustical-wave generation device, such as explosives, percussion devices, and the like. Source array  200  is towed after a seismic vessel (not illustrated) with a strength-taking umbilical  2 . Source members  14  may be suspended from chains or other means  16  beneath a plate, beam or similar member  8  that is rigid in at least the lateral plane. Member  8  is in turn suspended from chains or other means  18  beneath a float  10 , or alternatively fixed tightly to float  10 . Float  10  may be flexible, semi-flexible or rigid. A rigid body  204 , illustrated in  FIGS. 2A and 2B  as a solid cylindrical rod (although other shapes are possible), is fixed to member  8  by a swivel connection  206 , which may be a hinge, ball joint, or other type of equivalent function joint. Swivel connection  206  allows rigid body  204  to swing side-to-side as illustrated by double-headed arrow, S, in  FIG. 2A . Alternatively, rigid body  204  may comprise a frame (as depicted in and further explained in relation to  FIG. 6 ) or some other structure able to swing and able to transfer moment from umbilical  2  to member  8 . An actuator  208  may be actuated by a motor,  209 , which is in turn controlled by a local controller  210  to ensure that swivel connection  206  comprises a stiff connection and adjusts swing position, S, of rigid body  204  based on one or more signals given from a vessel or other signal source (not illustrated) through strength-taking umbilical  2 . As rigid body  204  swings, the orientation of a tow-point  210  changes. The tension from strength-taking umbilical  2  is transferred into a moment on member  8  that causes source array  200  to position itself with an angle of attack (α) with respect to incoming flow, F. This positioning, and change of position, causes source array  200  to position or re-position itself, typically laterally, although other movements are possible. 
     FIG. 3  illustrates a schematic side-elevation view of a second position controllable marine seismic source array  300  and method of the invention. Comparing embodiment  300  with embodiment  200  of  FIG. 2 , note that member  8  in  FIG. 2  is replaced with a plate or hydrofoil-shaped body  302  having a higher aspect ratio (ratio between height and length) that may result in better deflection performance. However, note that deflection of member  302  need not be identical to the deflection of the source array it is associated with, that is, the angle of attack of plate or hydrofoil  302  may be different than the angle of attack of the source array. This is true whenever a deflection member has a length different than the length of the source member. Plate or hydrofoil-shaped body  302  is illustrated as suspended between float  10  and a hang plate  304 , however, body  302  could also be in front of or behind float  10  and source members  14 . Swivel connection  206  is provided, as in embodiment  200  of  FIG. 2 , as are actuator  208 , motor  209 , local controller  210 , and rigid body  204 , which may be mounted onto plate or hydrofoil-shaped body  302  using any suitable means, such as bolts, screws, weldments, and the like. A towing harness  306  connects strength-taking umbilical  2  and rigid body  204 . 
     FIG. 4  is a schematic diagram of a control scheme useful with all apparatus and methods of the present invention, for example those depicted in  FIGS. 2 ,  3 ,  5 ,  6 ,  8 ,  10 , and  11 , and is not limited to any particular apparatus or method of the invention. A positioning unit  11 , mounted for example on source array  200  ( FIG. 2A ) transmits position of source array  200  to a navigation system  17  located on the tow vessel (not illustrated). Navigation system  17  provides the location information received from positioning unit  11  to an on-board controller  32 . On-board controller  32  may be a computer, a distributed control system, an analog control system or other control device known to those having ordinary skill in the art. On-board controller  32  may communicate with a local controller  210  through umbilical  2 , but may alternatively communicate through a wireless transmission. Umbilical  2  contains conductors for providing power and control signals to and from plate or hydrofoil-shaped body  302 . Local controller  210  sends a signal to an electric motor  31  that moves actuator  208 , which in turn moves plate or hydrofoil-shaped body  302 . When plate or hydrofoil-shaped body  302  moves, the lateral force imparted against it by the water steers source array  200  to the desired position. Sensors  28  may detect the angular position of plate or hydrofoil-shaped body  302  and send this information back to local controller  210  and, optionally, to on-board controller  32  where it may be displayed for an operator to read. 
     FIGS. 5A and 5B  illustrate schematic plan views of a third position controllable marine seismic apparatus  500  and method of the invention. Apparatus  500  builds on prior art apparatus  100  depicted schematically in  FIG. 1 , modified to make the bridle system remotely adjustable. A source array, illustrated by member  8  only, is towed behind a seismic vessel (not illustrated) by strength-taking umbilical  2 . A bridle system comprised of a front bridle leg  4  and aft bridle legs  6   a  and  6   b  is used in order to achieve the desired angle of attack of member  8 . Bridle legs  4 ,  6   a , and  6   b  may be the same or different in composition and may be wires, cables, ropes, or any other material that can function as described. Each of bridle legs  4 ,  6   a , and  6   b  are connected to strength-taking umbilical  2  at a point  9 . Front bridle leg  4  connects to member  8  at a front point  5  and is substantially always taught. Aft bridle legs  6   a  and  6   b  are routed through member  8  in a loop as illustrated in  FIGS. 5A and 5B . Position control (starboard or port, as illustrated by the labeled arrows) is achieved by maintaining one of bridle legs  6   a  and  6   b  taught ( 6   a  is taught in port position,  6   b  is taught in starboard) while its complement bridle leg is slack. Positioned on member  8  approximately at its mid-section (could be anywhere along member  8 ) is a rotatable member  207 , for example a motor- or winch-driven pulley or equivalent functioning means, that acts on bridle legs  6   a  and  6   b  so as to rotate member  8  as illustrated by double-headed arrow S in order to achieve the desired angle of attack. A local controller  210  that communicates with an on-board controller  32  ( FIG. 4 ) on the seismic vessel through umbilical  2  controls a motor  209 , which in turn moves actuator  208 , and rotatable member  207 . Alternatively, rather than a motor- or winch-driven rotatable actuator, one may simply employ a linear actuator, for example an electric, hydraulic or pneumatic jack connected to a point between bridle legs  6   a  and  6   b  to maintain one leg taught. Another alternative to using a rotatable actuator would be to use a pair linear actuators, for example a pair of hydraulic or pneumatic piston/cylinder actuators, one each directly on bridle legs  6   a  and  6   b , similar to the arrangement illustrated in and discussed below in relation to  FIG. 6C , which illustrates a high aspect ratio plate or hydrofoil. The arrangement of embodiment  500  of  FIG. 5A  may be employed as well with a high aspect ratio plate or hydrofoil as depicted schematically in  FIG. 5C . This figure illustrates embodiment  500 ′, including a high aspect ration plate or hydrofoil  302  moved to starboard deflecting position. All other elements in embodiment  500 ′ of  FIG. 5C  are equivalent to those of embodiment  500  depicted in  FIG. 5A  except that bridle legs  6   a  and  6   b  may be shorter in embodiment  500 ′ than in embodiment  500 . The same alternative arrangements may be employed in embodiment  500 ′ as were discussed in relation to embodiment  500  of  FIGS. 5A and 5B , including replacing the rotatable actuator with a linear actuator, employing a frame, and employing a pair of linear actuators. 
     FIGS. 6A and 6B  illustrate schematic plan views of a fourth position controllable marine seismic apparatus  600  and method of the invention. An adjustable bridle system comprising bridle legs  6   a  and  6   b , rotating member  207 , actuator  208 , motor  209 , and local controller  210  are illustrated, with both bridle legs  6   a  and  6   b  remaining substantially taught. Bridle legs  6   a  and  6   b  are connected to a stiff frame  602  at points  608  and  606 , respectively, and to strength-taking umbilical  2  at point  604 , so that frame  602  may pivot about a swivel joint  610 , which may be a hinge, ball joint, or other equivalent function joint, positioned at front end of member  8 . An alternative (not shown) is to replace the combination of rotating member  207 , actuator  208 , and motor  209  with a linear actuator as discussed above in relation to  FIGS. 5A and 5B . Another alternative is to replace bridle legs  6   a  and  6   b  with linear actuators, but closer to the frame  602 , as illustrated in schematic plan view in embodiment  600 ′ of  FIG. 6C . Embodiment  600 ′ includes a pair of piston/cylinder actuators  208   a  and  208   b . Cylinder  208   a  is attached to plate or hydrofoil  302 , while its corresponding piston  208   c  is attached to frame  602  at point  606 . Similarly, cylinder  208   b  is attached to plate or hydrofoil  302  and piston  208   d  is attached to frame  602  at point  608 . 
   Referring now to  FIG. 7  there is illustrated a schematic plan view of a marine seismic system  700  and method of the invention. Illustrated schematically is a tow vessel  702  following a desired path, which may be straight or curved, and one seismic source  703  of a dual seismic source (the other source not shown) showing a line of symmetry  705  between the two sources. Source  703  comprises three passive, non-steerable source arrays  707 , each source array  707  connected to tow vessel  702  through its own strength-taking umbilical  2 , and a deflector  704  that is connected to seismic source  703  through an umbilical  706 . Alternatively umbilical  706  may be a passive, strength-taking member such as a rope, wire, or equivalent passive connector, while deflector  704  is towed by use of a separate strength-taking umbilical  3 . Many arrangements are possible, and are discussed separately and in detail in reference to  FIGS. 11A-F . By adjusting its angle of attack, deflector  704  changes its lateral position, and this change in position deflects seismic source  703  away from or back to a path  701  (shown as straight but could be curved), as desired by the seismic survey team. In case of a dual source system, there would be one source/deflector system as shown in  FIG. 7  on each side of the symmetry line  705 . In case of a single source system (see  FIGS. 11A-F ) the source is positioned with its center at the symmetry line  705  and with one deflector on each side enabling positioning to either side of the symmetry line. 
   Deflectors useful in the invention may be any type of deflector able to adjust its angle of attack, including so-called free-flying deflectors, and non-free-flying deflectors that have streamers or other trailing, drag-producing means. As used herein the term “free-flying” means a deflector that is towed but does not have suspended to its tail end a streamer or other drag-producing device. In some situations it might be desired to include a stabilizing tow member to an otherwise free-flying deflector. 
     FIG. 8  illustrates a schematic cross-section view of a prior art free flying deflector  800  useful in the invention known under the trade designation “MONOWING”, available from WesternGeco L.L.C., Houston, Tex. This particular embodiment of the deflector includes a main hydrofoil  810 , a boom  812  rigidly fixed to main hydrofoil  810 , and a so-called boom-wing  814  mounted near a rear end  815  of boom  812 . By rotating boom-wing  814  as depicted by double-headed arrow R, it creates lift force in either positive or negative direction. As illustrated in  FIG. 8  a negative lift force  816  is achieved. However, this lift translates into a moment that translates into a change of the orientation of main hydrofoil  810 . The orientation, or angle of attack α, of main hydrofoil  810  is important, as the lift force  818  of main hydrofoil  810  is directly proportional to α, and proportional to the square of the magnitude of the inflow velocity (indicated by arrow F). An actuator  820  that communicates with a local controller  210  may adjust the orientation of boom-wing  814 . Communication with tow vessel  702  ( FIG. 7 ) is available through any of the combinations of strength-taking umbilicals and non-strength-taking umbilicals discussed herein (see discussion of  FIGS. 11A-F ). Local controller  210  may also communicate with on-board controller  32  ( FIG. 4 ) and/or other remote controller(s) via wireless transmission. Deflectors useful in the invention may be suspended from or attached rigidly to a float on the sea surface. 
     FIG. 9  illustrates a schematic plan view, with portions cut away, of a prior art, so-called “door” deflector  900 . This deflector is often used to deflect a marine seismic source to a nominal position. Three passive hydrofoils  910  (only the top ends of which are viewable in this view) are suspended between a pair of plates, a top plate  912  and a bottom plate  911 , the latter of which is viewable through the portions of top plate  912  that are cut away. In three dimensions this comprises an array of hydrofoils with end plates  912  and  911  at the top and bottom of each hydrofoil  910 . A towing bridle or harness comprising four legs is required: a front leg  930  and an aft leg  931  are illustrated attached to top plate  912 . Two additional bridle legs  930 ′ and  931 ′, one forward and one aft, attach to bottom plate  911  but are not shown in this view. All four bridle legs come together in one point  913 . Attached to bridle legs  930 / 931 / 930 ′/ 931 ′ is a passive, strength-taking tow member  3 , from which door  900  is towed by a tow vessel. The angle of attack α of door  900  is referenced to the inflow water velocity vector, F, approaching door  900  and the relative lengths between the front and aft bridle legs determine the angle α. As position of door  900  is a function of the angle of attack, α, the position of the door is not remotely adjustable. 
     FIG. 10  illustrates a schematic plan view, with portion cut away, of a door-type deflector  950  of the invention, which is similar to deflector  900  of  FIG. 9 , but modified in accordance with the invention to make its angle of attack remotely controllable. Aft bridle legs are not required and a unit  951  is included that includes a hydrofoil  814  with similar function as boom-wing  814  of  FIG. 8 . The function of hydrofoil  814  is not to produce lift as the hydrofoils  910  ( FIG. 9 ), but to create a smaller lift force  816  that causes modified door  950  to orient itself with the desired angle of attack α relative to incoming water flow velocity vector, F. As the total lift  952  is a function of angle of attack α, total lift  952  may be adjusted by adjusting the orientation and hence the lift of hydrofoil  814 . The angle of attack (orientation) of hydrofoil  814  may be adjusted by an actuator  208  that is operatively coupled to a motor  209  and local controller  210 . Local controller  210  may communicate with on-board controller  32  ( FIG. 4 ) on the tow vessel through strength-taking umbilical  3 , or through umbilical  706  and strength-taking tow-member  2  (not illustrated). Local controller  210  may also communicate with on-board controller  32  and/or other remote controller(s) via wireless transmission. 
     FIGS. 11A-F  illustrate six non-limiting embodiments of how one may arrange active, strength-taking tow members, passive strength-taking tow members, and umbilicals (recall as defined herein an umbilical is non-strength-taking unless indicated otherwise). In each of  FIGS. 11A-F , tow vessel  702  and seismic source  703  are indicated as being connected by a strength-taking umbilical  2 . It will be understood that the functions of strength-taking umbilical  2  could be divided into a passive, strength-taking tow member and an umbilical in each of  FIGS. 11A-F . 
     FIG. 11A  illustrates an embodiment wherein a tow vessel  702  tows a single seismic source  703  and deflectors  704   a  and  704   b . Tow vessel  702  and each deflector  704   a  and  704   b  are connected using respective passive, strength-taking tow members  3   a  and  3   b . Source  703  is connected with deflectors  704   a  and  704   b  using respective active, strength-taking tow members  706   a  and  706   b.    
     FIG. 11B  illustrates an embodiment identical to that of  FIG. 11A  except that active, strength-taking tow members  706   a  and  706   b  are replaced by a combination of a passive, strength-taking tow members  706   a  and  706   b  and umbilicals  706   a ′ and  706   b′.    
     FIG. 11C  illustrates an embodiment that might be viewed as the reverse of that of  FIG. 11A . Tow members  3   a  and  3   b  are now active, strength-taking tow members, while tow members  706   a  and  706   b  are passive, strength-taking tow members. 
     FIG. 11D  illustrates an embodiment where there is no direct mechanical connection between tow vessel  702  and deflectors  704   a  and  704   b . In this embodiment active, strength-taking tow members  706   a  and  706   b  connect source  703  with deflectors  704   a  and  704   b , respectively. The deflectors in this case are remote controlled either through communications links in  706   a ,  706   b , and  2 ′ or through wireless transmission. 
     FIG. 11E  illustrates another embodiment where there is no direct mechanical connection between deflectors and tow vessel. Passive, strength-taking tow members  706   a  and  706   b  connect between deflectors  704   a  and source  703 , and deflector  704   b  and source  703 , respectively. Umbilicals  706   a ′ and  706   b ′ provide power and optionally communication and data transmission links, and may include other utilities such as compressed air, and the like. 
     FIG. 11F  illustrates an embodiment where source  703  tows deflectors  704   a  and  704   b  through passive, strength-taking tow members  706   a  and  706   b , respectively. Umbilicals  3   a  and  3   b  function as power and, optionally, communications links between deflectors  704   a ,  704   b , respectively and tow vessel  702 . 
   In use the position of a deflecting member on a source, or deflector associated with a source via umbilicals and/or passive tow cables, is actively controlled by GPS or other position detector sensing the position of the source or deflector and feeding this data to a navigation system. Navigation may be performed on board a tow vessel, on some other vessel, or indeed a remote location. By using a communication system, either hardwire or wireless, information from the remote controller is sent to one or more local controllers on deflectors and/or deflecting members of sources. The local controllers in turn are operatively connected to adjustment mechanisms comprising motors or other motive power means, and actuators on the deflectors and/or deflecting members, which function to move a wing, plate or hydrofoil, or a bridle system, depending on the adjustment mechanism used. This in turn adjusts the angle of attack of the deflector or deflecting member, causing it to move the source as desired. Feedback control may be achieved using local sensors on the deflectors or deflecting members, which may inform the local and remote controllers of the position of a swivel connector, a wing or hydrofoil, the angle of attack of a deflector or wing or hydrofoil of a particular boom wing, a position of an actuator, the status of a motor or hydraulic cylinder, the status of a bridle system, and the like. A computer or human operator can thus access information and control the entire positioning effort, and thus obtain much better control over the seismic data acquisition process. 
   Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.