Abstract: A system to extend transducer arrays from the hull of a vessel while it is underway provides for increased array gain, volumetric aperture (very large aperture arrays), and rejection of hull-bound noise for submarines, surface ships, weapons, and unmanned underwater and surface vehicles. A plurality of arms extend radially outwardly from the hull of a submarine, and passive and/or active elements of the arrays are mounted around the hull on the arms, trail in the water from the arms, or extend between different ones of the arms or between arms and the hull. The system of arms and the array are folded into elongate recesses in the hull to lower noise during higher speed transit by the submarine. The arrays can be made up of sensors and/or projectors of radar, sonar signals, optical energy, vibrational energy, magnetic influence, temperature, etc., and combinations of these sensors.

Abstract: The location of a submerged tow vehicle (LOST) system provides a device for accurately determining a position of an underwater vehicle towed by a surface craft or aircraft, such as a helicopter. The LOST system utilizes five sources of input data to compute a best estimate of the towed vehicle's position. These are (1) high resolution bathymetry data in an area of the towed vehicle's transit, (2) ocean depth at a position of the towed vehicle, (3) the towed vehicle's velocity over sea bottom, (4) a slant range from the towed vehicle to a known reference point, and (5) a position and course of the towing vehicle. The LOST system is comprised of a slant range updater, a maximum likelihood estimator, a constrained adaptive tracker and a slant range corrector.

Abstract: A low friction surface is provided to hose-shaped acoustic envelopes for towed sonar arrays. The low friction surface permits multiple envelopes that are in intimate, parallel contact or that are crossed-over one another, to slide easily relative to one another, enhancing their deployment. The low friction surface is accomplished by blending particles of a low friction material with a base material. The mixture is heat extruded into pellets and the pellets are heat extruded into a hose of desired size. The exterior surface of the resulting hose is then subject to axially aligned abrasion to both expose the particles close to the exterior surface of the hose, and to create axially aligned micro-grooves in this surface. The micro-grooves allow water to enter and lubricate the boundary that is present, which is typically either another hose surface or the metal or other surface of an array deployment vehicle.

Abstract: A towed body yaw angle sensor arrangement used to sense the angle between the axis of a tow fish and the flow of water. The water flow vector is used as the reference for correcting towed body yaw so that a magnetic compass in the towed body is aligned with the towed arrays streaming in the water flow. A yaw angle in the towed body with respect to the flow will cause errors for target bearing and skew the arrays relative to each other which will also cause errors. The flow sensor must be in the free flow off the towed body and ideally the sensing part is aligned with water current flow. Also provided is a method for sensing and correcting a yaw angle.

Abstract: A drag antenna for a sonar system for detecting and/or locating sources of sound in water includes at least two acoustically sensitive lines positioned side-by-side and laterally spaced apart during a trailing operation. The lines are secured to each other at the leading ends and at the trailing ends by respective connecting element in order to lower the production costs for the drag antenna and to achieve a sufficiently constant lateral spacing between the acoustically sensitive lines.

Abstract: The invention relates to towed acoustic transmitters forming an underwater vehicle which is itself intended for towing a linear acoustic receiving array (105). It consists in placing the vertical faired acoustic array (303) of such a transmitter at the very rear of the underwater vehicle, and in balancing the weight of this array by a faired ballast (313) situated at the very front thereof. These two parts are joined by a girder (310) of small cross-section, and the center of gravity of the whole is situated at the front of this girder and beneath it. The vehicle is towed by a cable (101) fastened to the vehicle by a hook (314) fixed to a swivel joint (315) above the center of gravity. It makes it possible to facilitate the operations of submersion and fishing-out of the whole while also achieving a greater depth of submersion.

Abstract: A self-powered towed underwater sensor is provided. The sensor has a shied casing which encloses an electric generator. The generator is connected to an impeller that is located at the midpoint of the casing. The impeller is covered by a shroud which minimizes the disturbance of the water by the impeller. The casing contains a shield which absorbs electromagnetic radiation produced by the generator. The shield is placed around the generator. A towed cable is connected to the forward end of the casing. The towed cable is made of a material having a high tensile strength to facilitate towing. A fiber optic cable is located within the towed cable and runs the length of the cable, specifically for transmission of received data from the attached sensor to the towing craft. The use of fiber optics prevents interference by electromagnetic radiation in the environment through which the cable passes, and there is no power lead that could conduct interference into the array.

Abstract: A towed array includes an array of N hydrophone groups and one or more nocoustic sensor modules structurally connected in-line with the array of hydrophone groups. The hydrophone groups and non-acoustic sensor module(s) are coupled to a common data transmission line. Each of the hydrophone groups defines a portion of an acoustic aperture occupying a specified length of the towed array. Each non-acoustic sensor module has a length that is n times the specified length where n is a whole number multiple of the total number of hydrophone groups.

Abstract: A method and system are provided for frequency filtering compressional wave nergy. An elastic cylinder is filled with a fluid that is selected based on a fluid density .rho..sub.i and a dilatational wave phase velocity c.sub.i thereof. When the elastic cylinder so-filled is subjected to a compressional wave propagating in a fluid environment, a first radial resonance frequency of the elastic cylinder is controlled by the fluid density .rho..sub.i and the dilatational wave phase velocity c.sub.i. Further tuning of the first radial resonance frequency can be achieved by adjusting the radial wall thickness of the elastic cylinder.

Abstract: A dual zero velocity towed array system for use in an ocean environment crises a plurality of towed array subsystems and a deployment vessel. Each towed array subsystems comprises a rear drogue, an elongated communication cable having mounted thereon at least one acoustic sensor. The deployment vessel deploying the towed array subsystems. The deployment vessel moving in a forward direction through the ocean environment at a selected forward motion rate and alternatingly deploys the at least one acoustic sensor and communication cable of alternate ones of the towed array subsystems during successive iterations. In each iteration the deployment vessel deploys one of the towed array subsystems rearwardly at a deployment rate corresponding to the forward motion rate, thereby to maintain the at least one acoustic sensor and communication cable in a stable position in the ocean environment.

Abstract: Disclosed is an inverse method for measuring the breathing wave speed in a iquid-filled cylindrical shell. The model used with this method is based on an experimental configuration where a shell is attached to a mechanical shaker at the forward end, which initiates longitudinal wave propagation. The resulting spatial field in the shell consists of extensional and breathing waves. End-mounted accelerometers and force transducers are used to measure the extensional wave speed. Once this is accomplished, transfer functions between five equally spaced hydrophones that are in the fluid and a forward accelerometer are recorded. These data are then combined to yield a closed form value of the complex, frequency-dependent breathing wave speed. The experiment included to validate this method is extremely easy to implement and can be executed in a short period of time.

Abstract: A zero velocity towed array system for use in an ocean environment includes towed array subsystem and a deployment vessel. The towed array subsystem comprises a rear drogue, an elongated communication cable having mounted thereon at least one. acoustic sensor. The deployment vessel deploys the towed array subsystem. While the deployment vessel moves in a forward direction through the ocean environment at a selected forward motion rate, it deploys the acoustic sensor and communication cable rearwardly at a deployment rate corresponding to the forward motion rate, thereby to maintain the acoustic sensor and communication cable in a stable position in the ocean environment.

Abstract: A method for determining the position of seismic equipment wherein acoustic transmitters transmit spread spectrum sequences which are received by the seismic sensors in the equipment whose position has to be determined. By collecting and processing the signals thus produced, it is possible to determine the position of seismic equipment with reference to each individual sensor in the seismic equipment each time a measurement is take. The already existing conventional seismic sensors which are provided in a streamer are used to record the transmitted spread spectrum signals. By calculating time differences between the sensors' reception of a spread spectrum signal it is possible to calculate the position of the seismic equipment.

Abstract: Method and apparatus are disclosed for reducing breathing-wave induced no in a liquid-filled elongate hose housing a hydrophone array. The arrangement involves sensing radial strain induced in the hose wall by the breathing waves (created as the hose is drawn longitudinally through water) and subtracting a multiple of the sensed value thereof from the array hydrophone output. Arrangements for measuring the breathing-wave-induced wall strains include (1) relative phase shifts in light passing through the sensing arm of an optical fiber interferometer, and (2) signal currents generated from piezolectric polymer both of which are disposed inside the hose wall surrounding a hydrophone.

Abstract: A system for compensating for noise induced in a sensor data stream from a sensor array towed by a towing device includes a towing device motion data input receives a towed motion data stream representative of towing motion of the towing device. A sensor array input for receiving the sensor data stream. An adaptive filter connected to the towing device motion data input and the sensor array input for receiving the towed motion data stream from the towing device motion data input and the sensor data stream from the sensor array input and for generating a corrected sensor data stream representing sensor array data with ship motion noise attenuated therefrom.

Abstract: A method for compensating for lateral distortion in a moving linear array using a frequency domain beamformer, comprising the steps of measuring the instantaneous lateral distortion of the linear array at discrete points along the array, corresponding to array element locations, calculating a shading weight for each of the discrete points along the array, corresponding to array element locations based on the instantaneous lateral distortion at each said point and calculating the compensated beam magnitude by multiplying said shading weight into the frequency domain beamformer equation.

Abstract: One or more slave acoustic transponders are secured to selected parts of a seismic bottom cable whose location is imperfectly known. A master transponder broadcasts an interrogation pulse from each of a number of different, known locations distributed along a line of survey. In response to an interrogation pulse, a slave transponder emits an encoded signal that is received by the master transponder. The acoustic flight time between each pulse broadcast and encoded-signal reception constitutes a range measurement to the participating slave transponder. Resolving a gather of several range measurement from different known broadcast locations, focussed on an identifiable transponder, defines the transponder location.

Abstract: A method and apparatus for detecting, processing and tracking sonar signals o provide bearing, range and depth information that locates an object in three-dimensional underwater space. An inverse beamformer utilizes signals from a towed horizontal array of hydrophones to estimate a bearing to a possible object. A matched field processor receives measured covariance matrix data based upon signals from the hydrophones and signals from a propagation model. An eight nearest neighbor peak picker provides plane wave peaks in response to output beam levels from the matched processor. A five-dimensional M of N tracker identifies peaks within the specified limit of frequency, bearing change over time, range and depth to specify an object as a target and to display its relative range and depth with respect to the array of hydrophones.

Abstract: A system for target detection and localization with an algorithm for performing target motion analysis (TMA) using data from a passive sonar array and which works directly with beam spectra to estimate the target track. The system determines when the coordinate trajectory of a hypothesized target aligns with the coordinate trajectory of an actual target and operates by forming long-term integrated spectral values from short-term values of frequency and angle coordinate values. The hypothesized target track that yields the maximum long-term integrated spectral value is used as the estimate of the true target track. A track generator is used to generate hypothesized target tracks for a search grid in the form of vectors that are clocked downward in a chain of latches. The latches are connected through computational elements, which are supplied with non-acoustic data, and RAMs to a summation pipeline, the RAMs being supplied with data from an array's sonar processor.

Abstract: The present invention provides a method for on-line real-time processing of processing navigational data for determining the location of sensor and receiver points in a navigational network having a number of different types of devices. Observations from these devices are obtained using a coordinate system that follows appropriate nominal sailing lines. Outlying observations are discarded using w-statistics for the observations. Any correlated observations such as compass azimuths are uncorrelated. The uncorrelated observations are then sequentially processed in an extended sequential Kalman filter, which provides the best estimate of the station coordinates. These estimated coordinates are then used to determine the location of the source and receiver points.

Abstract: A magnetic heading sensor alignment and roll reducing device is provided. A enerally cylindrical assembly has a first end and a second end. Each end has a plurality of grooves located equiangularly on a circle with the center thereof located at the cylindrical assembly's center longitudinal axis. Bearings, positioned at and supported by the first and second ends, support a magnetic heading sensor at either end thereof. The bearings provide the sensor with rotational freedom about the center longitudinal axis. A counterweight is affixed to the sensor such that its center of gravity and the sensor's center of gravity are located at a common axial loci. A plurality of longitudinal spring strips are provided to fit into corresponding ones of the grooves on the first and second ends of the cylindrical assembly. The spring strips cooperate with the inner surface of a tubular housing when the device is inserted therein. All materials used to construct the device are non-magnetic.

Abstract: A system for storing and deploying a number of elements sequentially in connected but spaced-apart relationship is described. Adjacent elements are joined together temporarily by connectors which overlay adjacent elements. The connectors are bound to the elements by a plurality of cables, one of which is wound around each element and the overlying connectors. One end of each cable is connected to the element around which it is wound and the other end is connected to the next preceding element. When tension is applied between the cable of the first element and the last element, for example, by connecting an underwater tug to the cable and connecting a drogue to the last element, the cables unwind one by one releasing the connectors and extending the elements in a straight line, spaced apart by the length of the connecting cables.

Abstract: The apparatus and method for determining the direction of an incoming sonar ignal using a towed array having at least two auxiliary transducers positioned along the array. Each auxiliary transducer contains a plurality of small transducers. By summing the output from each of the small transducers, thereby forming the outputs of the auxiliary transducers, and combining the output of the auxiliary transducers with the output of the towed array, the direction of arrival of a sonar signal impinging upon the towed array is determined.

Abstract: The invention provides a floatation apparatus for maintaining a longitudinal object at a constant depth below the water surface in a body of water. Several airtight chambers are connected in a serial connection to form a string of air tight chambers. A one-way check valve is installed in the chamber at one end of the string while the other end chamber is connected to a nose piece. Air is continuously supplied to the check valve connected to the end chamber. A separate one-way check valve is installed between each pair of adjacent chambers in the string in a manner that air can pass between only in the direction from the air source to the nose member. The floatation apparatus is pivotaly connected to the longitudinal object at more than one place by means of parallel links.

Abstract: A termination assembly is disclosed providing a substantially watertight, yet field serviceable interface to a plurality of electrical splices. The termination assembly includes a housing having an anchor portion for receiving and fixing a multi-transmission line cable therein, a ported sleeve for cradling the transmission lines, and a shell for providing field access to the splices between the transmission line in the interior of the housing. A resinous epoxy, together with O-ring seals and heat shrink tubing provide redundant protection against the invasion of water into the housing along the transmission lines.

Abstract: The system comprises measuring means and carrying or supporting means (6), to which the measuring means are fixed. The carrying means are dragged underwater by a helicopter (2) via a cable (4). The carrier means, equipped with measuring means, have a hydrodynamic shape such that they remain at a substantially constant depth when dragged underwater by means of the cable.Application to marine soundings.

Abstract: A system for measuring the speed in water of an underwater towed array has towbody connected in close proximity to the array by means of a rope drogue. The towbody has a freely turning propeller that turns a shaft that has a rotor magnet. Magnetic pulses from the rotor magnet are converted first to an electrical and then to an acoustical signal. The acoustical signal from the towbody is received by the towed array and converted back to an electrical signal that is transmitted along a line to a ship that is towing the array. The ship then displays the detected speed and/or utilizes the information received for control purposes.

Abstract: A towed streamer having a buoyant core, a data bearer layer surrounding the buoyant core, an inner jacket layer formed of a resilient material surrounding the data bearer layer, and an outer jacket layer surrounding the inner jacket layer, wherein a series of longitudinally positioned strength members are embedded in the inner jacket layer to extend along the streamer to transmit tension along the streamer while the streamer is held in the inner jacket layer.

Abstract: A linear hydrophonic antenna with an associated portside/starboard ambiguity removing device comprises three streamers placed in an equilateral triangle, with a center distance of the order of a third of the wave length which corresponds to the center frequency received. The density of the median streamer is notably greater than the common density of the other two streamers. Channels are formed in a standard way, and the received signals are phase shifted then added up so that the directivity associated with each channel shows a zero, either at portside or at starboard, the direction of which remains fixed despite the roll.

Abstract: In a method of formation of channels for a sonar, after having sampled at a frequency T=1/4f.sub.0 (where f.sub.0 is the receiving center frequency of the sonar) the signals from the hydrophones of the sonar and having translated them to baseband, the signals thus translated are subsampled with a period T.sub.SE =kT (wherein k is an integer) substantially equal to 1.25 B, where B is the reception bandwidth of the sonar. A first set of signals is subsampled at identical times to form a frontal sector. Two further sets of signals are subsampled with delays between the signals from two adjacent hydrophones equal to T, which determines two side sectors adjacent to the frontal sector. The subsampled signals are then transmitted serially by the towing cable of the sonar device towed array and are processed in FFT circuits which allow to form in each sector a set of channels covering the sector.

Abstract: A magnetic heading sensor alignment device for an acoustic towed line array s described. It includes a generally cylindrical non-magnetic piece having a longitudinal opening along its central axis to accommodate the heading sensor. A plurality of longitudinal non-magnetic strips or springs are provided around the cylindrical piece by securing them at the ends of the cylindrical piece to form a cage. This provides a spring-like action when the alignment device including the heading sensor is inserted inside the hose of the towed line array and thus keep the heading sensor aligned during the deployment of the acoustic towed array.

Abstract: Apparatus and method for transmitting and receiving hydroacoustic pulses used to determine the spatial separations between pairs of such apparatus. According to a preferred embodiment, the apparatus transmits hydroacoustic pulses having a selected shape and frequency at specific times and also determines the time of arrival of received hydroacoustic pulses having a known shape and carrier frequency. Included is a transducer for converting the hydroacoustic energy received from a body of water into electrical energy and for converting electric pulses into hydroacoustic pulses which are then coupled into the body of water. Electric pulses having a selected shape and carrier frequency are digitally synthesized in response to a count comparator.

Abstract: An acoustic array, useful for sonar, comprises a plurality of transducing ements which are free floating and not connected to each other. Means are provided for locating the position of each of the transducer elements. The acoustic array may be one-dimensional, that is, a line array, a two-dimensional array, or a three-dimensional array. In another embodiment of the acoustic array, the transducing elements are free-floating but connected to each other by a flexible tether, which limits the range of separation of one transducing element from any of the others. The locator comprises a centrally located element to which there are attached three horizontal rigid arms. On the end of each arm is a high-frequency acoustic transducer. Periodically, each of the transducers transmits a high-frequency broadband pulse. The pulse from each of the three transducers is unique and identifiable.

Abstract: A device for seismic exploration is in the form of a towed streamer. The streamer is easily managed, is very flexible and has a low weight so that it may be towed with moderate tractive forces. The streamer includes a cable with an inner core, one or more layers of insulated conductor pairs and an outer low-friction protective coating. Both the core and the outer low-friction protective layer are of an acoustically substantially inert material of low specific gravity. Seismic signals are obtained series connected gimbal-mounted geophones arranged in strings connected to the cable at positions spaced longitudinally thereof.

Abstract: A submarine drone has special hydrodynamic performance features for operag as a moving underwater platform for underwater transport of a barrel stave type sonar receiving transducer and a pole type sonar transmitting transducer with highly precise vertical alignment. The body of the submarine comprises a generally spherical pressure hull for containing propulsion plant and electronic components. The barrel stave transducer is affixed about the upper half of the pressure hull. An acoustically transparent false wall forms a spherical hydrodynamic wall over the pressure vessel and transducer. The false wall also forms a tail cone projecting from the rear side of the submarine. The tail cone contains an annular channel which takes in boundary layer water from the spherical portion of hydrodynamic wall and conducts it back to a pump jet at the extreme rear of the tail cone. A fixed tail boom emerges from the center of the pump jet structure and extends rearwardly.

Abstract: A mobile sonar surveillance system having a fully populated circular shaped orizontal receiving array steered in edgefired directions with overlapping coverage of beams. The array has a plurality of hydrophones randomly spaced and mounted on a series of parallel lines in the same horizontal plane and is suitable for towing by a single small ship. For alignment of a received signal one or more single beams suitable for rotation can be steered azimuthally with the proper set of synchronized variable delays. These beams will retain approximately the same parameters as they rotate.

Abstract: Apparatus for monitoring the laying of a deep sea cable or flexible pipeline (1) from a vessel (22). The apparatus comprises a sleeve threaded on the cable or flexible pipeline and having sliding means (4) tangential to said cable or pipeline and measuring means (3A) for measuring variables indicative of the position of the sleeve and for transmitting their values, positive buoyancy means (8) mechanically connected to the sleeve, an auxiliary small chain (19) suspended from the sleeve and extending down to the sea bed, the mass per unit length of the chain, and the masses and volumes of the sleeve and of the positive buoyancy means being such that the sleeve is maintained around that part of the cable which is situated at a substantially constant height above the sea bed (21), which height is relatively small compared with the depth of the sea bed.

Abstract: A means for extending the useful aperture of a multi-hydrophone towed array by using the overlap of the successive positions of the array hydrophones as the array moves forward through the water. The overlap information is used by an overlap correlator to provide phase correction factors for a synthetic aperture signal processing scheme. The overlap correlator continues to refine the correction factors using later in time hydrophone measurement data.

Abstract: A system for acoustically positioning a noisy platform. An array of transponders, adapted to be deployed in a region of water, is provided. A transducer is mounted on the noisy platform and another transducer is mounted on a relatively quiet vehicle tethered to the platform. A first means is provided for transmitting acoustical energy from the transducer on the noisy platform to said array and from said array to said transducer on said vehicle for measuring the distance from said noisy platform to said quiet vehicle via said transponders in said array. A second means is provided for transmitting acoustical energy from the transducer on said vehicle to said array and back to said vehicle for measuring the distance said vehicle is from the transponders in said array. Calculating means is coupled to said first and second means for determining the location of said noisy platform relative to said array.

Abstract: A method for determining the position of a marine seismic receiver cable of the type which is towed behind a seismic survey vessel through the sea, wherein the azimuth and the distance from the vessel to points along the seismic receiver cable are measured, and the coodinates of these points are calculated on the basis of these values. A hydroacoustic measurement method is utilized, based on a super-short baseline system integrated with a gyrocompass, for measuring the azimuth and distances in accordance with signals from transponders, beacons, responders and/or similar instruments installed on or within the seismic receiver cable.

Abstract: A method and device are provided for determining by acoustic telemetering the position of immersed objects with respect to a ship having a location assembly connected thereto including two acoustic transmission-reception assemblies and a towed locating base including two other assemblies offset laterally with respect to the path of the ship, in which method two measuring cycles are carried out successively, the first one consisting in determining by acoustic telemetering the position of the mobile locating base with respect to the locating base fixed to the ship, while the second consists, still using acoustic telemetering, in determining the position of the towed objects with respect to the mobile locating base. Then the coordinates of all the towed objects are determined with respect to the ship.

Abstract: A cable wiper assembly for airborne sonar includes a housing suspended from a hoist used to rapidly raise and lower a sonar transducer at the end of a cable. The wiper assembly is interposed ahead of the cable-directing sheaves forming part of the hoist to strip away the sea water which adheres to the cable as it is pulled from the ocean. The cable wiper housing includes a series of internal grooves each of which contains and secures one wiper stage. Each stage includes a washer-like wiper of elastomeric material whose internal diameter is just slightly smaller than the cable diameter carried in a shallow cup-shaped holder having an internal port significantly larger than the cable diameter and secured by means of an upper washer-member overlying the wiper whose internal diameter is slightly larger than the diameter of the cable.

Abstract: A marine cable system including one or more elongated cable sections whose buoyancy may be independently controlled. Each section is associated with a pump and a variable volume, elongated bladder. In one embodiment, one reservoir containing buoyant fluid is included, and fluid from the reservoir is pumped between adjacent sections to inflate or deflate the associated bladders. In another embodiment, a rigid reservoir containing compressed gas is included in each section. The associated pump releases gas from the reservoir to inflate the bladder, or pumps gas from the bladder into the reservoir when desired. The pumps are operated in response to control signals from a remote control unit, such as one aboard a vessel towing the cable. One or more depth sensors may be attached in or near each section. Depth information from the sensors may be supplied to the control unit for use in generating the pump control signals. The buoyant fluid is entirely contained within the cable.

Abstract: A bi-planar pontoon paravane is towed by a marine vessel and controls the depth and position of a towed seismic source array. The bi-planar pontoon paravane is made up of a buoyant bridge with right and left wings attached to the long sides of the bridge, the wings projecting into the water and, in concert, providing a side force. The paravane is towed by a tow line connected to an adjustable bridle which in turn is connected to the paravane. Remote adjustment of the bridle is provided by an hydraulic valve on the vessel controlling an hydraulic motor and gear arrangement on the paravane to adjust the bridle. Adjustment of the bridle adjusts the angle of attack of the paravane. The paravane provides a housing formed below the bridge and between the two wings for housing the seismic source array. A boom on the vessel is attached to the seismic source array, through the bridge, when the assembly is to be placed in or removed from the water.

Abstract: A towed underwater transducer assembly includes a spherical housing (10) suspended from a towing vehicle at the end of a cable (12). The housing includes mounting brackets (26, 28) located less than one-half of the circumference of the housing apart along a meridian of the housing (10) centered in the direction of tow with a bridle cable (24) extending between the mounting brackets including a turnbuckle (32) to adjust its tension and a mechanical stop (30). A grooved pulley wheel (22) is mounted at the end of the towing cable (12) with the bridle cable (24) riding in the groove and the pulley wheel (22) free to seek a position along the bridle cable (24) such that the projected line of the tow cable (12) passes essentially through the geometric center of the spherical housing (10) thereby causing the spherical housing (10) to maintain an essentially vertical orientation irrespective of variations in the speed of tow.

Abstract: The positions of seismic subarrays are determined using special hydrophones in a streamer cable which listen for acoustic signals generated from each seismic subarray.

Abstract: A hydrophone section for a seismic streamer towed array in which the hydrophones 2 are arranged in groups of not more than 7, the spacing of the hydrophones within each group being such that each group has an overall length l=0.8-1.2 m. The hydrophone mounts 5 and mechanical spacers 3 are attached at their periphery to aramid fibre strainwires 4. The hydrophone mounts and mechanical spacers are acoustically open structures.

Abstract: A method for determining the absolute geophysical location of a streamer using reference signal source(s), or alternately detector(s), of unknown location. The absolute geophysical location of a seismic streamer is determined by the optimal sequential use of the field measurements of reference signal travel time, streamer magnetic heading and conventional navigational measurement. The absolute location determination is accomplished in three steps. Each step solves for one aspect of streamer location by optimally utilizing one of three types of field measurement. This procedure requires no a priori knowledge of the absolute location of the reference signal source(s), or alternately detector(s).

Abstract: Method and apparatus are provided for locating a towed float relative to the towing vessel. The method determines the range from at least two known spaced apart locations on the towing vessel to the float and determines the position of the float from the intersection of the at least two ranges. The apparatus includes a microwave transceiver selectably interconnectable with a plurality of microwave antennas at known spaced apart locations on a towing vessel, a microwave transponder on each float whose locations is to be determined, and suitable controller and/or computer means to calculate ranges and intersections of ranges.

Abstract: Apparatus and method are provided for locating seismic sources suspended below a float, seismic streamer cables and other towed seismic apparatus relative to a towing vessel. The range and bearing from a selectively energizable acoustic source on or near the float, cable or apparatus to the towing vessel is measured by an acoustic phased array.