(19)
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`(12)
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`(cid:6)(cid:27)&(cid:11)(cid:11)(cid:12)(cid:19)(cid:16)(cid:11)(cid:12)(cid:16)(cid:12)(cid:24)(cid:12)(cid:6)
`EP 1 850 151 B1
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`(11)
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`EUROPEAN PATENT SPECIFICATION
`
`(45) Date of publication and mention
`of the grant of the patent:
`10.08.2011 Bulletin 2011/32
`
`(21) Application number: 07113031.4
`
`(22) Date of filing: 28.09.1999
`
`(51) Int Cl.:
`G01V1/38(2006.01)
`
`(54) Control system for positioning of marine seismic streamers
`
`Steuerungssystem zur Positionierung mariner seismischer Streamer
`
`Système de contrôle de la position des flûtes sismiques marines
`
`(84) Designated Contracting States:
`FR IT NL
`
`(30) Priority: 01.10.1998 GB 9821277
`
`(43) Date of publication of application:
`31.10.2007 Bulletin 2007/44
`
`(62) Document number(s) of the earlier application(s) in
`accordance with Art. 76 EPC:
`99943180.2 / 1 119 780
`
`(73) Proprietors:
`• WesternGeco Seismic Holdings Limited
`Road Town,
`Tortola (VG)
`Designated Contracting States:
`IT NL
`• Services Pétroliers Schlumberger
`75007 Paris (FR)
`Designated Contracting States:
`FR
`
`(72) Inventors:
`• Hillesund, Oyvind
`N-1312, Slependen (NO)
`• Bittleston, Simon
`Bury St Edmunds, Suffolk IP29 5GR (GB)
`
`(74) Representative: Suckling, Andrew Michael
`Marks & Clerk LLP
`4220 Nash Court
`Oxford Business Park South
`Oxford
`OX4 2RU (GB)
`
`(56) References cited:
`WO-A1-97/30361
`US-A- 5 138 582
`US-A- 5 790 472
`
`US-A- 4 890 568
`US-A- 5 532 975
`
`
`• COURT I.: "Applications of Acoustics to
`Streamer/Source Positioning" SEG EXPANDED
`ABSTRACTS, 1 January 1989 (1989-01-01), pages
`610-612, XP002480425
`
`Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent
`Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the
`Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been
`paid. (Art. 99(1) European Patent Convention).
`
`Printed by Jouve, 75001 PARIS (FR)
`
`EP1 850 151B1
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`PGS Exhibit 1093, pg. 1
`PGS v. WesternGeco (IPR2014-00689)
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`EP 1 850 151 B1
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`Description
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`BACKGROUND OF THE INVENTION
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`[0001] This invention relates generally to systems for controlling seismic data acquisition equipment and particularly
`to a system for controlling a marine seismic streamer positioning device.
`[0002] A marine seismic streamer is an elongate cable-like structure, typically up to several thousand meters long,
`which contains arrays of seismic sensors, known as hydrophones, and associated electronic equipment along its length,
`and which is used in marine seismic surveying. In order to perform a 3D marine seismic survey, a plurality of such
`streamers are towed at about 5 knots behind a seismic survey vessel, which also tows one or more seismic sources,
`typically air guns. Acoustic signals produced by the seismic sources are directed down through the water into the earth
`beneath, where they are reflected from the various strata. The reflected signals are received by the hydrophones, and
`then digitized and processed to build up a representation of the subsurface geology.
`[0003] The horizontal positions of the streamers are typically controlled by a deflector, located at the front end or
`"head" of the streamer, and a tail buoy, located at the back end or "tail" of the streamer. These devices create tension
`forces on the streamer which constrain the movement of the streamer and cause it to assume a roughly linear shape.
`Cross currents and transient forces cause the streamer to bow and undulate, thereby introducing deviations into this
`desired linear shape.
`[0004] The streamers are typically towed at a constant depth of approximately ten meters, in order to facilitate the
`removal of undesired "ghost" reflections from the surface of the water. To keep the streamers at this constant depth.
`control devices known as "birds", are typically attached at various points along each streamer between the deflector and
`the tail buoy, with the spacing between the birds generally varying between 200 and 400 meters. The birds have hydro-
`dynamic deflecting surfaces, referred to as wings, that allow the position of the streamer to be controlled as it is towed
`through the water. When a bird is used for depth control purposes only, it is possible for the bird to regularly sense its
`depth using an integrated pressure sensor and for a local controller within the bird to adjust the wing angles to maintain
`the streamer near the desired depth using only a desired depth value received from a central control system.
`[0005] While the majority of birds used thus far have only controlled the depth of the streamers, additional benefits
`can be obtained by using properly controlled horizontally steerable birds, particularly by using the types of horizontally
`and vertically steerable birds disclosed in our published PCT International Application No. WO 98/28636. The benefits
`that can be obtained by using properly controlled horizontally steerable birds can include reducing horizontal out-of-
`position conditions that necessitate reacquiring seismic data in a particular area (i.e. in-fill shooting), reducing the chance
`of tangling adjacent streamers, and reducing the time required to turn the seismic acquisition vessel when ending one
`pass and beginning another pass during a 3D seismic survey.
`[0006]
`It is estimated that horizontal out-of-position conditions reduce the efficiency of current 3D seismic survey
`operations by between 5 and 10%, depending on weather and current conditions. While incidents of tangling adjacent
`streamers are relatively rare, when they do occur they invariably result in prolonged vessel downtime. The loss of
`efficiency associated with turning the seismic survey vessel will depend in large part on the seismic survey layout, but
`typical estimates range from 5 to 10%. Simulations have concluded that properly controlled horizontally steerable birds
`can be expected to reduce these types of costs by approximately 30%.
`[0007] One system for controlling a horizontally steerable bird, as disclosed in UK Patent GB 2093610 B, is to utilize
`a manually-operated central control system to transmit the magnitudes and directions of any required wing angle changes
`to the birds. While this method greatly simplifies the circuitry needed within the bird itself, it is virtually impossible for this
`type of system to closely regulate the horizontal positions of the birds because it requires manual input and supervision.
`This becomes a particularly significant issue when a substantial number of streamers are deployed simultaneously and
`the number of birds that must be controlled goes up accordingly.
`[0008] Another system for controlling a horizontally steerable bird is disclosed in our published PCT International
`Application No. WO 98/28636. Using this type of control system, the desired horizontal positions and the actual horizontal
`positions are received from a remote control system and are then used by a local control system within the birds to
`adjust the wing angles. The actual horizontal positions of the birds may be determined every 5 to 10 seconds and there
`may be a 5 second delay between the taking of measurements and the determination of actual streamer positions. While
`this type of system allows for more automatic adjustment of the bird wing angles, the delay period and the relatively long
`cycle time between position measurements prevents this type of control system from rapidly and efficiently controlling
`the horizontal position of the bird. A more deterministic system for controlling this type of streamer positioning device is
`therefore desired.
`[0009]
`It is therefore an object of the present invention to provide for an improved method and apparatus for controlling
`a streamer positioning device.
`[0010] An advantage of the present invention is that the position of the streamer may be better controlled, thereby
`reducing the need for in-fill shooting, reducing the chance of streamer tangling, and reducing the time needed to turn
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`PGS v. WesternGeco (IPR2014-00689)
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`EP 1 850 151 B1
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`the seismic survey vessel.
`[0011] Another advantage of the present invention is that noise in marine seismic data associated with streamer
`position over-correction and streamer positioning errors can be significantly reduced.
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`SUMMARY OF THE INVENTION
`
`[0012] The present invention involves a method of controlling a streamer positioning device configured to be attached
`to a marine seismic streamer and towed by a seismic survey vessel and having a wing and a wing motor for changing
`the orientation of the wing. The method includes the steps of: obtaining an estimated velocity of the streamer positioning
`device, calculating a desired change in the orientation of the wing using the estimated velocity of the streamer positioning
`device, and actuating the wing motor to produce the desired change in the orientation of the wing. The present invention
`also involves an apparatus for controlling a streamer positioning device. The apparatus includes means for obtaining
`an estimated velocity of the streamer positioning device, means for calculating a desired change in the orientation of
`the wing using the estimated velocity of the streamer positioning device, and means for actuating the wing motor to
`effectuate the desired change in the orientation of the wing. The invention and its benefits will be better understood with
`reference to the detailed description below and the accompanying figures.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`Figure 1 is a schematic diagram of a seismic survey vessel and associated seismic data acquisition equipment;
`
`Figure 2 is a schematic horizontal cross-sectional view through a marine seismic streamer and an attached streamer
`positioning device;
`
`Figure 3 is a schematic vertical cross-sectional view through the streamer positioning device from Figure 2; and
`
`Figure 4 is a schematic diagram of the local control system architecture of the streamer positioning device from
`Figure 2.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`[0014]
`In Figure 1, a seismic survey vessel 10 is shown towing eight marine seismic streamers 12 that may, for
`instance, each be 3000 meters in length. The outermost streamers 12 in the array could be 700 meters apart, resulting
`in a horizontal separation between the streamers of 100 meters in the regular horizontal spacing configuration shown.
`A seismic source 14, typically an airgun or an array of airguns, is also shown being towed by the seismic survey vessel
`10. At the front of each streamer 12 is shown a deflector 16 and at the rear of every streamer is shown a tail buoy 20.
`The deflector 16 is used to horizontally position the end of the streamer nearest the seismic survey vessel 10 and the
`tail buoy 20 creates drag at the end of the streamer farthest from the seismic survey vessel 10. The tension created on
`the seismic streamer by the deflector 16 and the tail buoy 20 results in the roughly linear shape of the seismic streamer
`12 shown in Figure 1.
`[0015]
`Located between the deflector 16 and the tail buoy 20 are a plurality of streamer positioning devices known as
`birds 18. Preferably the birds 18 are both vertically and horizontally steerable. These birds 18 may, for instance, be
`located at regular intervals along the streamer, such as every 200 to 400 meters. The vertically and horizontally steerable
`birds 18 can be used to constrain the shape of the seismic streamer 12 between the deflector 16 and the tail buoy 20
`in both the vertical (depth) and horizontal directions.
`[0016]
`In the preferred embodiment of the present invention, the control system for the birds 18 is distributed between
`a global control system 22 located on or near the seismic survey vessel 10 and a local control system located within or
`near the birds 18. The global control system 22 is typically connected to the seismic survey vessel’s navigation system
`and obtains estimates of system wide parameters, such as the vessel’s towing direction and velocity and current direction
`and velocity, from the vessel’s navigation system.
`[0017] The most important requirement for the control system is to prevent the streamers 12 from tangling. This
`requirement becomes more and more important as the complexity and the total value of the towed equipment increases.
`The trend in the industry is to put more streamers 12 on each seismic survey vessel 10 and to decrease the horizontal
`separation between them. To get better control of the streamers 12, horizontal steering becomes necessary. If the birds
`18 are not properly controlled, horizontal steering can increase, rather than decrease, the likelihood of tangling adjacent
`streamers. Localized current fluctuations can dramatically influence the magnitude of the side control required to properly
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`PGS v. WesternGeco (IPR2014-00689)
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`EP 1 850 151 B1
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`position the streamers. To compensate for these localized current fluctuations, the inventive control system utilizes a
`distributed processing control architecture and behavior-predictive model-based control logic to properly control the
`streamer positioning devices.
`[0018]
`In the preferred embodiment of the present invention, the global control system 22 monitors the actual positions
`of each of the birds 18 and is programmed with the desired positions of or the desired minimum separations between
`the seismic streamers 12. The horizontal positions of the birds 18 can be derived, for instance, using the types of acoustic
`positioning systems described in our U.S. Patent No. 4,992,990 or in our PCT International Patent Application No. WO
`98/21163. Alternatively, or additionally, satellite-based global positioning system equipment can be used to determine
`the positions of the equipment. The vertical positions of the birds 18 are typically monitored using pressure sensors
`attached to the birds, as discussed below.
`[0019] The global control system 22 preferably maintains a dynamic model of each of the seismic streamers 12 and
`utilizes the desired and actual positions of the birds 18 to regularly calculate updated desired vertical and horizontal
`forces the birds should impart on the seismic streamers 12 to move them from their actual positions to their desired
`positions. Because the movement of the seismic streamer 12 causes acoustic noise (both from seawater flow past the
`bird wing structures as well as cross current flow across the streamer skin itself), it is important that the streamer
`movements be restrained and kept to the minimum correction required to properly position the streamers. Any streamer
`positioning device control system that consistently overestimates the type of correction required and causes the bird to
`overshoot its intended position introduces undesirable noise into the seismic data being acquired by the streamer. In
`current systems, this type of over-correction noise is often balanced against the "noise" or "smearing" caused when the
`seismic sensors in the streamers 12 are displaced from their desired positions.
`[0020] The global control system 22 preferably calculates the desired vertical and horizontal forces based on the
`behavior of each streamer and also takes into account the behavior of the complete streamer array. Due to the relatively
`low sample rate and time delay associated with the horizontal position determination system, the global control system
`22 runs position predictor software to estimate the actual locations of each of the birds 18. The global control system
`22 also checks the data received from the vessel’s navigation system and the data will be filled in if it is missing. The
`interface between the global control system 22 and the local control system will typically operate with a sampling frequency
`of at least 0.1 Hz. The global control system 22 will typically acquire the following parameters from the vessel’s navigation
`system: vessel speed (m/s), vessel heading (degrees), current speed (m/s), current heading (degrees), and the location
`of each of the birds in the horizontal plane in a vessel fixed coordinate system. Current speed and heading can also be
`estimated based on the average forces acting on the streamers 12 by the birds 18. The global control system 22 will
`preferably send the following values to the local bird controller: demanded vertical force, demanded horizontal force,
`towing velocity, and crosscurrent velocity.
`[0021] The towing velocity and crosscurrent velocity are preferably "water-referenced" values that are calculated from
`the vessel speed and heading values and the current speed and heading values, as well as any relative movement
`between the seismic survey vessel 10 and the bird 18 (such as while the vessel is turning), to produce relative velocities
`of the bird 18 with respect to the water in both the "in-line" and the "cross-line" directions. Alternatively, the global control
`system 22 could provide the local control system with the horizontal velocity and water in-flow angle. The force and
`velocity values are delivered by the global control system 22 as separate values for each bird 18 on each streamer 12
`continuously during operation of the control system.
`[0022] The "water-referenced" towing velocity and crosscurrent velocity could alternatively be determined using flow-
`meters or other types of water velocity sensors attached directly to the birds 18. Although these types of sensors are
`typically quite expensive, one advantage of this type of velocity determination system is that the sensed in-line and
`cross-line velocities will be inherently compensated for the speed and heading of marine currents acting on said streamer
`positioning device and for relative movements between the vessel 10 and the bird 18.
`[0023] Figure 2 shows a type of bird 18 that is capable of controlling the position of seismic streamers 12 in both the
`vertical and horizontal directions. A bird 18 of this type is also disclosed in our PCT International Application No. WO
`98/28636. While a number of alternative designs for the vertically and horizontally steerable birds 18 are possible,
`including those utilizing one full-moving wing with ailerons, three full-moving wings, and four full-moving wings, the
`independent two-wing principal is, conceptually, the simplest and most robust design.
`[0024]
`In Figure 2, a portion of the seismic streamer 12 is shown with an attached bird 18. A communication line 24,
`which may consist of a bundle of fiber optic data transmission cables and power transmission wires, passes along the
`length of the seismic streamer 12 and is connected to the seismic sensors, hydrophones 26, that are distributed along
`the length of the streamer, and to the bird 18. The bird 18 preferably has a pair of independently moveable wings 28
`that are connected to rotatable shafts 32 that are rotated by wing motors 34 and that allow the orientation of the wings
`28 with respect to the bird body 30 to be changed. When the shafts 32 of the bird 18 are not horizontal, this rotation
`causes the horizontal orientation of the wings 28 to change and thereby changes the horizontal forces that are applied
`to the streamer 12 by the bird.
`[0025] The motors 34 can consist of any type of device that is capable of changing the orientation of the wings 28,
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`PGS v. WesternGeco (IPR2014-00689)
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`EP 1 850 151 B1
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`and they are preferably either electric motors or hydraulic actuators. The local control system 36 controls the movement
`of the wings 28 by calculating a desired change in the angle of the wings and then selectively driving the motors 34 to
`effectuate this change. While the preferred embodiment depicted utilizes a separate motor 34 for each wing 28, it would
`be also be possible to independently move the wings 28 using a single motor 34 and a selectively actuatable transmission
`mechanism.
`[0026] When the bird 18 uses two wings 28 to produce the horizontal and vertical forces on the streamer 12, the
`required outputs of the local control system 36 are relatively simple, the directions and magnitudes of the wing movements
`required for each of the wings 28, or equivalently the magnitude and direction the motors 34 need to be driven to produce
`this wing movement. While the required outputs of the local control system 36 for such a two full moving wing design is
`quite simple, the structure and operation of the overall system required to coordinate control of the device is relatively
`complicated.
`[0027] Figure 3 shows a schematic vertical cross-sectional view through the streamer positioning device shown in
`Figure 2 that will allow the operation of the inventive control system to be described in more detail. The components of
`the bird 18 shown in Figure 3 include the wings 28 and the body 30. Also shown in Figure 3 are a horizontal coordinate
`axis 38 and a vertical coordinate axis 40. During operation of the streamer positioning control system, the global control
`system 22 preferably transmits, at regular intervals (such as every five seconds) a desired horizontal force 42 and a
`desired vertical force 44 to the local control system 36.
`[0028] The desired horizontal force 42 and the desired vertical force 44 are combined within the local control system
`36 to calculate the magnitude and direction of the desired total force 46 that the global control system 22 has instructed
`the local control system to apply to the streamer 12. The global control system 22 could alternatively provide the magnitude
`and direction of the desired total force 46 to the local control system 36 instead of the desired horizontal force 42 and
`the desired vertical force 44.
`[0029] While the desired horizontal force 42 and the desired vertical force 44 are preferably calculated by the global
`control system 22, it is also possible for the local control system 36 in the inventive control system to calculate one or
`both of these forces using a localized displacement/force conversion program. This type of localized conversion program
`may, for instance, use a look-up table or conversion routine that associates certain magnitudes and directions of vertical
`or horizontal displacements with certain magnitudes and directions of changes in the vertical or horizontal forces required.
`Using this type of embodiment, the global control system 22 can transmit location information to the local control system
`36 instead of force information. Instead of the desired vertical force 44, the global control system 22 can transmit a
`desired vertical depth and the local control system 36 can calculate the magnitude and direction of the deviation between
`the desired depth and the actual depth. Similarly, instead of transmitting a desired horizontal force 42, the global control
`system 22 can transmit the magnitude and direction of the displacement between the actual horizontal position and the
`desired horizontal position of the bird 18. One advantage to this alternative type of system is that the required vertical
`force can be rapidly updated as the local control system receives updated depth information from the integrated pressure
`sensor. Other advantages of this type of alternative system include reducing communication traffic on the communication
`line 24 and simplifying the programming needed to convert the measured vertical and/or horizontal displacements into
`corresponding forces to be applied by the birds 18.
`[0030] When the local control system 36 has a new desired horizontal force 42 and desired vertical force 44 to be
`applied, the wings 28 will typically not be in the proper orientation to provide the direction of the desired total force 46
`required. As can be seen in Figure 3, the wings 28 introduce a force into the streamer 12 along an axis perpendicular
`to the rotational axis of the wings 28 and perpendicular to the streamer. This force axis 48 is typically not properly aligned
`with the desired total force 46 when new desired horizontal and vertical force values are received from the global control
`system 22 or determined by the local control system 36 and some rotation of the bird 18 is required before the bird can
`produce this desired total force 46. As can be seen, the force axis 48 is directly related to the bird roll angle, designated
`in Figure 3 as ϕ.
`[0031] The local control system 36 optimizes the control process by projecting the desired total force 46 onto the force
`axis 48 (i.e. multiplying the magnitude of the desired total force by the cosine of the deviation angle 50) to produce an
`intermediate desired force 52 and then adjusting the wing common angle α (the angle of the wings with respect to the
`bird body 30, or the average angle if there is a non-zero splay angle) to produce this magnitude of force along the force
`axis. The calculated desired common wing angle is compared to the current common wing angle to calculate a desired
`change in the common wing angle and the wing motors 34 are actuated to produce this desired change in the orientation
`of the wings.
`[0032] A splay angle is then introduced into the wings 28 to produce a rotational movement in the bird body 30 (i.e.
`to rotate the force axis 48 to be aligned with the desired total force 46). The splay angle is the difference between the
`angles of the wings 28 with respect to the bird body 30. As the bird body 30 rotates and the force axis 48 becomes more
`closely aligned with the desired total force 46, the bird roll angle and the bird roll angular velocity are monitored, the
`splay angle is incrementally reduced, and the common angle is incrementally increased until the intermediate desired
`force 52 is in the same direction and of the same magnitude as the desired total force. The local control system 36
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`EP 1 850 151 B1
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`carefully regulates the splay angle to ensure that the streamer is stable in roll degree of freedom. The calculated common
`wing angle and the splay angle are also regulated by the local control system 36 to prevent the wings 28 from stalling
`and to ensure that the splay angle is prioritized.
`[0033] When using the type of birds described in our published PCT International Application No. WO 98/28636, where
`the bird 18 is rigidly attached, and cannot rotate with respect, to the streamer 12, it is important for the control system
`to take the streamer twist into account. If this is not taken into account, the bird 18 can use all of its available splay angle
`to counter the twist in the streamer 12. The bird 18 will then be unable to reach the demanded roll angle and the generated
`force will decrease. The inventive control system incorporates two functions for addressing this situation; the anti-twist
`function and the untwist function.
`[0034]
`In the anti-twist function, the streamer twist is estimated by weightfunction filtering the splay angle measurements
`instead of simply averaging the splay angle measurements to improve the bandwidth of the estimation. The anti-twist
`function engages when the estimated twist has reached a critical value and it then overrides the normal shortest path
`control of the calculated roll angle. The anti-twist function forces the bird 18 to rotate in the opposite direction of the twist
`by adding +/-180 degrees to the demanded roll angle. Once the twist has been reduced to an acceptable value, the anti-
`twist function disengages and the normal shortest path calculation is continued.
`[0035] The untwist function is implemented by the global control system 22 which monitors the splay angle for all of
`the birds 18 in each streamer 12. At regular intervals or when the splay angle has reached a critical value, the global
`control system 22 instructs each local control system 36 to rotate each bird 18 in the opposite direction of the twist. The
`number of revolutions done by each bird 18 is monitored and the untwist function is disengaged once the twist has
`reached an acceptable level.
`[0036] Figure 4 is a schematic diagram of the architecture of the local control system 36 for the bird 18. The local
`control system 36 consists of a central processor unit 54, having EEPROM 56 and RAM 58 memory, an input/output
`subsystem 60 that is connected to a pair of motor drivers 62, and an analog to digital conversion unit 66. The motor
`drivers 62 are connected to and actuate the wing motors 34 to produce the desired change the orientation of the wings
`28 with respect to the bird body 30.
`[0037] The wing motor 34/wing 28 units are also connected to wing position indicators 64 that sense the relative
`positions of the wings and provide measurements to the analog to digital conversion unit 66 which converts the analog
`wing position indicator 64 measurements into digital format and conveys these digital values to the central processor
`unit 54. Various types of wing position indicators 64 can be used, including resistive angle or displacement sensors,
`inductive sensors, capacitive sensors, hall sensors, or magneto-restrictive sensors.
`[0038] A horizontal accelerometer 68 and a vertical accelerometer 70, placed at right angles with respect to one
`another, are also connected to the analog to digital conversion unit 66 and these accelerometers convey measurements
`that allow the central processor unit 54 to determine the roll angle and roll rate of the bird 18. An angular velocity vibrating
`rate gyro (rategyro) can also be used to measure the roll rate of the bird 18. A temperature sensor 72 is connected to
`the analog to digital conversion unit 66 to provide temperature measurements that allow the horizontal accelerometer
`68 and the vertical accelerometer 70 to be calibrated.
`[0039] A pressure sensor 74 is also connected to the analog to digital conversion unit 66 to provide the central processor
`unit 54 with measurements of the water pressure at the bird 18. To calculate an appropriate depth value, the measured
`pressure values must be filtered to limit the disturbance from waves. This is done in the inventive control system with a
`weightfunction filter that avoids the large phase displacements caused by mean value filters. Instead of using an instan-
`taneous depth value or simply calculating an average depth value over a given period of time (and thereby incorporating
`a large phase displacement into the depth value), the inventive control system uses a differentially weighted pressure
`filtering scheme. First the pressure values are transformed into depth values by dividing the pressure sensor reading
`by the seawater density and gravitational acceleration. These depth values are then filtered using a weight function filter.
`Typical incremental weighting functions values range from 0.96 to 0.90 (sample weights of 1.0, 0.9, 0.81, 0.729, etc.)
`and the filter will typically process depth values received over a period of at least 100 seconds.
`[0040] The central processor unit 54 is also connected to a RS485 communications unit 76 that allows information to
`be exchanged between the local control system 36 and the global control system 22 over the communication line 24
`that passes through the streamer 12. The RS485 bus may, for instance, utilize Neuron chips that communicate using a
`Local Operating Network protocol to control the data transfer.
`[0041] Preferably, the central processor unit 54 and associated components comprise a MicroChip 17C756 processor.
`This type of microprocessor has very low power requirements, a dual UART on-chip, 12-channel, 10 bit ADC on-chip,
`908x8 RAM, 16kx16 ROM, and 50 digital I/O channels. The software running on the central processor unit 54 will typically
`consist of two units, the local control unit and the hardware control unit. It is typically not possible to pre-load both of
`these program units into the EEPROM 56 and it is possible to update these program units without having to open the
`bird 18. The on-chip memory may thus only initially contain a boot-routine that enables the loading of software units into
`the external memory via the RS485 communication unit 76. The external program memory (EEPROM 56) will typically
`be a nonvolatile memory so that these program units do not have to be re-loaded after every power down.
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`PGS Exhibit 1093, pg. 6
`PGS v. WesternGeco (IPR2014-00689)
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`5
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`10
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`15
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`25
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`35
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`45
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`55
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`EP 1 850 151 B1
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`[0042] The central processor unit 54 must be able to run the local control system software fast enough to secure the
`sampling frequency needed for effective local bird control. This may mean, for instance, a