Abstract: Sonar array cable is typically provided in lengths comprising hydrophone ays and associated electronics and transmitter can components, each cable length or section having one of each of these components housed therein. These sections are relatively stiff and unbendable, requiring that they be connected with relatively bendable intermediate segments. These intermediate segments are susceptible to excessive bending that can lead to failure of the wiring provided therebetween. The wiring in these intermediate bendable segments is provided in the form of a coil, each of which coils is rigidly connected to the transmitter and electronics in one cable section, and the other end of the coil being connected electrically to the wiring associated with the hydrophone array in an adjacent cable section.

Abstract: A chain of elongate components (10, 20) are connected end-to-end. Each component (e.g. 10) comprises a sheath (1) closed at its ends filled with a dielectric liquid (e.g. kerosene). Sound detectors are located in the liquid as are electric conductors for conveying signals therefrom. The ends are closed by means including an electric connector. At least one of a pair of mating end portions includes a valve (14, 24) which releases the dielectric liquid from inside the sheath into the interstices between the mated pair. A bleed screw can be used to ensure no air remains. This arrangement minimises pressure differentials around the join between two adjacent elongate components and facilitates use of the chain at great depths.

Abstract: A composite hydrophone array assembly is made from a compliant mandrel such s a hollow tube and at least one wrap of piezoelectric film adhered to the compliant hollow tube at a plurality of locations thereon. Each location defines a composite hydrophone channel. The centers of adjacent hydrophone channels are separated along the length of the compliant hollow tube. To shade a hydrophone channel, the wall thickness of the hollow tube can be varied along its length, the circumferential area of coverage of the wraps of piezoelectric film can be varied along their length, the longitudinal lengths of the wraps of piezoelectric film are varied, or a combination of these approaches can be used. Unwanted noise is rejected by eliminating hydrophone channel grating lobes and overlapping portions of the wraps of piezoelectric film of the adjacent hydrophone channels to create a wavenumber response for the composite hydrophone array that significantly reduces array grating lobes.

Abstract: Disclosed is a vibration isolation module for a towed hydrophone streamer comprising: (1) a first transition unit, an outboard end of the first transition unit capable of receiving a first tension member, the first tension member terminating within the first transition unit, an inboard end of the first transition unit capable of receiving second and third tension members, the second tension member entering, looping back and exiting the inboard end of the first transition unit, the third tension member terminating within the first transition unit and (2) a second transition unit, an outboard end of the second transition unit capable of receiving a fourth tension member, the fourth tension member terminating within the second transition unit, an inboard end of the second transition unit capable of receiving the second and third tension members, the second tension member entering, looping back and exiting the inboard end of the second transition unit, the third tension member terminating within the second transi

Abstract: A towed streamer including a hydrophone (1) supported, in a filler (4) being either liquid or semi-liquid such as a gel having wave damping properties, within a housing (2). The housing (2) is in the form of a tube whose ends are closed by closures such as rigid plugs (3). Where liquid is used wave damping baffles such as open cell foam structures are provided. A rigid shielding arrangement in the form of reinforcing strips (5) can be provided to shield the hydrophone from bulge waves.

Abstract: An integrated module coupler for a towed hydrophone streamer and a method of transmitting towing forces and electrical signals therethrough.

Abstract: A connector for attaching equipment to an underwater cable includes a cylindrical race having a plurality of sections pivotably connected by a hinge. The sections can pivot about the hinge to enable the race to be opened and detached from the cable. The hinge includes a plurality of sockets and a hinge pin rotatably received in the sockets. The hinge pin can preferably be retracted from the sockets to unlock the hinge and inserted into the sockets to lock the hinge. A retaining member prevents the hinge pin from falling out of the sockets when the hinge pin is retracted.

Abstract: An electro-acoustical transducer arrangement for underwater antennas comprised of a plurality of hydrophones (10) which are arranged at equal distances in a linear array, and are to be disposed vertically above each other on a support. For reasons of a simplified assembly along with good receiving properties, the hydrophones (10), together with a reflector (11) disposed behind them in the direction of incoming sound, are embedded in an acoustically transparent rigid cast enclosure (20) of an elastomer, preferably polyurethane, which can be worked in a casting process. The connecting lines (12) of the hydrophones (10) of the enclosure 20 are combined in a common plug (13), which is accessible on a front end of the rigid cast enclosure (20). The rigid cast enclosure (20) is provided with devices for fastening the enclosure to the support.

Abstract: A towed streamer including buoyant core (1), and strength members (3) to transmit tension along the streamer. Strength members (3) are arranged so that the streamer is compliant for a predetermined elongation of the streamer. Members (3) are embedded in an inner jacket (5) surrounded by an outer jacket (6). The assembly is encased in an extruded outer jacket (2). Braided data bearers (4) can be provided between the inner jackets (5, 6). Strength members (3) can be braided with interstices impregnated with gel. Where the strength members (3) are of non-compliant material, the braid is initially compliant where the streamer is slightly elongated but becomes non-compliant as the streamer elongates further. Alternatively a combination of compliant (3) and non-compliant members (14) can be used where the compliant members (3) only become engaged after a predetermined elongation of the streamer.

Abstract: A Vibration Isolation Module (VIM) for a towed acoustic streamer includes cylindrical masses attached at regular spacing to a central core of viscoelastic damping material, which may be extruded over a snubbed elastic strength member. Further snubbed elastic strength members may be attached around the outer diameter of the masses. Viscous "dash-pot" type dampers are installed within the masses. The space between the masses is filled with open cell plastic foam, around which is wrapped a layer of power and data cables. A jacket of damped thermoplastic is extruded over the cable layer and caps containing a fluid filling valve are attached at each end of the module, and the interior void is filled with a low density, high viscosity fluid. The "dash-pot" type dampers can be replaced by a stocking which, under extension, compresses the foam and forces fluid through pores of the foam, thus simulating the viscous damping of the "dash-pot" type dampers.

Abstract: The device comprises instruments for collection and recording of signals in seismic exploration of the substratum off-shore. The device is designed as a pole which is adapted to be forced down into the seabed and comprises a pointed lower end (7), an intermediate approximately cylindrically shaped main portion (6), a vibration-absorbing spacer (14) between the pointed end (7) and the intermediate main portion (6). The other end of the intermediate main portion (6) is connected to a top part (8) designed for inserting/pulling and other ways of handling the device. The pointed end (7) at least comprises geophones (15-17) and a hydrophone (23) is placed in the vicinity of the upper end of the device. The majority of the device's other instruments are placed in the intermediate main portion (6). The device is connected to a main cable (4) which extends to a seismic ship (29, 31).

Abstract: This invention provides an apparatus including a plurality of omnidirectional hydrophone sensors in a particularly configured array comprised of ring members which are carried between a plurality of tensioned cables, the cables being tensioned by an anchor weight at the bottom end of the array and a capsule float at the top end, the configuration enabling simplified signal processing techniques to achieve sound source discrimination in both azimuth and elevation within an underwater environment.

Abstract: Disclosed is an encapsulated hydrophone assembly for use in a towed hydrophone array. The assembly comprises (1) a hydrophone element having a hydrophone electrical conductor, (2) an insulated input electrical lead and an insulated output electrical lead coupled to the hydrophone electrical conductor, (3) an electromagnetic shield surrounding the hydrophone element and the hydrophone electrical conductor, the input electrical lead and the output electrical lead extending from the electromagnetic shield and (4) a layer of encapsulating material surrounding the hydrophone element, the hydrophone electrical conductor, a portion of the input electrical lead, a portion of the output electrical lead and the electromagnetic shield to thereby form the hydrophone assembly.

Abstract: Disclosed is a towed hydrophone streamer module comprising: (1) an elongated, fluid-resistant jacket having a substantially circular cross section, the water resistant jacket having mating connectors at ends thereof, (2) a plurality of sensors distributed in a spaced-apart relationship within the jacket, (3) a data bus positioned along a length of the jacket and terminating in electrical contacts in the mating connectors and (4) a plurality of cylindrical, fluid-resistant electronics housings disposed within the jacket in a spaced-apart relationship along a length thereof, each of the plurality of housings having a circuit board therein and spanning a length thereof and end caps at ends thereof, one of the end caps having electrical contacts coupled to components on the circuit board, a center-line of the housings substantially in alignment with a center-line of the jacket, the components coupling the plurality of sensors to the data bus for electrical communication therewith.

Abstract: A coupling for joining sections of an underwater towed acoustical array iudes male and female couplers. The male coupler has an annular end portion with an axial bore that receives a first towed array section and a first connector and an annular body integral with and extending coaxially from the annular end portion. An outer groove is disposed around an outer circumference of the annular body. The female coupler has an annular end portion and an axial bore that receives a second towed array section and a second connector and a cup-shaped body portion integral with and extending from the annular end portion. The cup-shaped body portion has an inner groove disposed on the inner surface and an aperture through the cup-shaped body portion communicating with the inner groove. The inner groove is located so as to be in registry with the male coupler outer groove when the annular body is inserted into the cup-shaped body portion to form an annular channel.

Abstract: A submerged cable is fitted with one or more tethered transducers that are otatably supported on the cable between clamped collars spaced apart to receive a standoff device. The device has pivotably connected flat portions which define semi-circular lower parts to so receive the cable. Upper triangular panel portions can be spread apart to receive the cable, and clamped together by a clevis that is connected to a riser or tether for the transducer.

Abstract: A self-orienting seismic detector for detecting vertical acceleration regardless of the device's horizontal orientation. The detector comprises a housing fitted with diaphragms capable of generating signals. A mass is internally suspended within the housing between the diaphragms by means of a filament which is connected at each of its ends to one of the diaphragms. Vertical motion of the detector causes internal displacement of the mass within the housing. Motion by the mass within the cylinder is translated by the filament to the diaphragms which generate signals which may then be recorded. The detector may be incorporated within or attached to an undersea cable to form a seismic detection system primarily suitable for placement on an ocean bottom, but which may be employed in a towed array. In a primary embodiment, the detector is sealed from external pressure changes such that the stresses placed upon the detector's diaphragms will be governed by particle acceleration changes rather than pressure changes.

Abstract: An improved hydrophone body, suitable for forming an array of towed hydrophone bodies or "fish", formed by placing an acoustic shield or scatterer in the nose and tail sections of the hydrophone body to reduce noise coupling from the cable into the hydrophone sensor. This resulting hydrophone has significantly reduced background noise interference.

Abstract: The current invention discloses a construction of a hydrophone body and hydrophone sensors which provides a significantly enhanced wide band frequency sensor capability within the construction of a sensor array towed in a cable. This construction extends a tuned resonator or sensor along the hydrophone body and into an adjacent section of interconnecting cable. This elongated sensor, in the form of a tubular sensor, provides an enhanced, very low frequency sensing capability within the overall hydrophone array, supplementing the frequency range of the encased hydrophone sensor.

Abstract: Disclosed is a vibration isolation module for a towed hydrophone streamer comprising: (1) a first outboard transition unit having an outboard end and an inboard end, the outboard end of the first outboard unit capable of receiving a first tension member, the first tension member terminating within the first outboard unit, the inboard end of the first outboard unit capable of receiving second and third tension members, the second tension member entering, looping back and exiting the inboard end of the first outboard unit, the third tension member terminating within the first outboard unit and (2) a first inboard transition unit having an outboard end and an inboard end, the outboard end of the first inboard unit capable of receiving the second and third tension members, the second tension member passing through the first inboard unit, the third tension member terminating within the first inboard unit, the inboard end of the first inboard unit capable of receiving a fourth tension member, the fourth tension mem

Abstract: A marine seismic bottom geophone anchor and coupling device comprising two rectangular fabric sections attached along their edges and along a plurality of lines between edges to form a plurality of pockets. The pockets are filled with a weighting material. Connecting means are provided so that when the combined fabric sections are wrapped around a marine seismic bottom geophone, it will be held in a generally cylindrical form to simultaneously anchor the geophones and associated cables at a desired marine bottom location, isolate the sensors from noise sources, and provide good coupling to the marine bottom for receiving desired seismic signals.

Abstract: An extendible linear sonar array for an Autonomous Underwater Vehicle (AUV) comprises a linear hydrophone array fixed in the nose of the AUV and two hydrophone array segments mounted at the leading edge of stabilization fins extendible from and retractable into the AUV. The stabilization fins are pivoted to move between extended and retracted positions where, in the extended position, the movable arrays together with the fixed nose array form a linear sonar array with extended width. In the retracted position, the stabilization fins with the hydrophone arrays pivot and fold back into stow channels in the AUV body. The stabilization fins may include movable control surfaces to control the attitude of the AUV, or the stabilization fins can be rotated when in the extended position to provide attitude control.

Abstract: A method for reconnection and connection of sensor groups, especially hydrophone groups or channels in a seismic cable, where the active sections in the seismic cable are connected with electronic modules or one another via connector plugs, is based on the principle that a specific number of hydrophone groups are connected symmetrically on each side of each electronic module. The number of connected hydrophone groups on each side is identical and constitutes at least one respective active section. A summation of a set of hydrophone groups in a section is performed automatically by connecting this section with another section or by connecting a respective section and the electronic module.

Abstract: The present invention discloses an apparatus for rotatably attaching a sensor to a cable. A cable mount having a groove about a substantial portion of its periphery is fixedly placed on the cable. A sensor mount having a key adapted to slide along the groove is rotatably placed on the cable in a manner which enables the key to remain in the groove when the sensor mount rotates about the cable.

Abstract: A pulsed-transmission, narrow-band sonar system has a first antenna array ich is unshaded and a second array partitioned into four parts, the center two of which are electrically connected in parallel and the outer two of which are connected in series.

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: In a preferred embodiment, an accelerometer sensor system, including: a housing structure; a first acceleration sensor disposed in the housing structure at a first selected location along the vertical axis of the housing structure, the first acceleration sensor providing a first output; a second acceleration sensor disposed in the housing structure at a second selected location along the vertical axis, the second acceleration sensor providing a second output; and apparatus to combine the first and second outputs of the first and second acceleration sensors such as to simulate the output from a virtual acceleration sensor located at any selected location on the vertical axis, allowing one to reduce noise induced by pitch motion, at any desired frequency or across a desired frequency band.

Abstract: A side looking sonar transducer having a plurality of active elements forming an elongated active radiating, or receiving surface wherein the active elements at the ends of the transducer have a lesser depression angle than the active elements at the middle. This arrangement provides an energy distribution which allows for a greater depth of focus.

Abstract: A marine seismic cable section with stress members and internal wiring located within the cable section in a manner which reduces internal bending stresses upon the cable section when wound upon a storage reel. Stress members are at least near a horizontal plane passing through and at approximately equal distances from the center line of the cable section. Internal wiring is located in a vertical crisscrossing pattern down the length of the cable section. In one important embodiment, the cable section contains an elastomeric filler material to retain and support stress members, internal wiring and other internal components at their desired location and to prevent damage to internal wiring and components due to external stress when the cable section is wound on a cable reel. Stress relief sections are also provided to further reduce bending stress within the seismic cable section in other embodiments.

Abstract: A jacket for a liquid filled towed array is formed from a composite material formed from short lengths (typically 2-4 mm) of reinforcing fibre (1) which are mixed with a thermoplastic material (2) to form the jacket (3). The reinforcing fibre (1) is preferably either glass fibre, aramid fibre, or carbon fibre or a mixture thereof and provides the desired high Tensile Modulus. The thermoplastic material (2) provides a relatively high level of viscoelastic damping (that is a high, or at least medium, Loss Tangent). The fibres (1) and thermoplastic material (2) are mixed, or compounded, by the material supplier and the material for the jacket (3) provided in granular form to the extrusion contractor. The manufacture of the jacket (3) is undertaken by normal extrusion processing.

Abstract: A marine seismic seabed cable for use on or near the seabed includes at least one pulling cable, a data cable, and a sleeve which surrounds the data cable and the pulling cable. Groups of geophones and position metering instruments are placed along the cable with the position metering instruments and geophones being disposed in a geophone sphere. The geophone sphere and the pulling cables are to a substantial degree mechanically isolated from each other so that, for example, shocks and signals against the seabed cable will only be transferred to a minor extent to the geophone sphere.

Abstract: An acoustic sensor module, contains groups of single sensor elements within a fluid-tight enclosure. The enclosure is bounded by a reinforced hose wall and module end caps at either end of the module. The sensors are mounted in the center of the enclosure using tubular foam spacers; smaller cylindrical foam spacers fill the central space between sensors. Radial stiffness is provided to the spacers by thin annular rings held in place by fine strength cords. Thin flexible wires connect the sensor elements of each group to the preamplifying/multiplexing electronic package, the connecting leads therefrom being brought out to the outer surface through a division between spacers. Data and power cables are spirally wrapped around the outer diameter, with an over-wrap of fine fiber or plastic tape to lock them into position. The connecting leads to the electronic packages are then spliced into their respective data/power cables.

Abstract: Hydrophone transducer elements are mechanically isolated from one another vibration by suspending them in a urethane matrix molded into a cylindrical shape. A metal ring is mechanically locked in an annular slot defined by the cylindrical shaped matrix. The ring is used to mechanically support the assembly for towing. The transducer elements are electrically connected to one another and to an electrical cable independently of this mechanical support.

Abstract: Seismic streamers (detection cables) used in the reception of reflection signals during seismic surveys at sea, where the streamer is towed behind a vessel, are constructed with an external, tubular cover (1) of a flexible plastic material. In order to reduce the noise produced by movement of the streamer through the water the external cover (1) is constructed with continuous longitudinally extending grooves (3) in its longitudinal direction, and preferably regularly disposed circumferentially around the entire periphery of the cover (1).

Abstract: A reception system including a central core (5) formed of a traction cable (6) and a harness (7) of conducting wires. A fibrous or porous acoustic screen (8) made, for example, from a fibrous or porous material is formed around the core. Sensitive elements are arranged outside this screen, with discontinuous inner electrodes (9) connected to the different wires of the central harness (7), and a common outer electrode (13). A pipe made of a piezoelectric material (12) is formed therebetween. The whole is covered with a protective sheath (2). With such a multi-layered sensitive structure, the manufacturing process of the reception system can be simplified.

Abstract: A borehole cable includes a plurality of geophone-containing modules spaced apart along the cable by a plurality of conduit sections and designed for acoustic, thermal and pressure imaging of the subsurface. Each cable conduit section comprises an inner core of flexible tubing and an outer wall of interlock completely surrounding the core. The inner corrugated core is designed to compress under the external pressure applied by the formation in which it is deployed. The percent of core compression is controlled by adjusting the composition and structure of the inner core and the outer interlock wall. Compression of the inner core beyond a predetermined limit causes the interlock to form a rigid outer wall preventing further compression. The pressure at which the inner core begins to compress and the percent of compression at which the outer wall locks is determined by their material composition, wall thickness and pre-compression during manufacturing.

Abstract: The invention provides a seismic transmitter source system which includes a floatation device that contains a plurality of air tight chambers in a serial connection. A separate one way check valve is placed between each adjacent pair of the chambers. Pressurized air is continuously supplied to an end chamber. The one-way check valves enable the air to pass to the remaining chambers in one direction. A transmitter subarray containing a plurality of spaced apart transmitters is suspended from the floatation device by means of severasl pivotly connected links. The front end of the transmitter array is connected to a point near the front end of the floatation device. During operation, the seismic transmitter source system is pulled from a tow point located at the front of the floatation device, pulling both the floatation device and the transmitter subarray in substantially a horizontal straight line position while maintaining the transmitter subarray at a near constant depth below the water surface.

Abstract: A seismic receiver array device for shallow water and near-shore operations which is comprised of an elongated low-profile, flexible casing having a plurality of geophones and hydrophones spaced along its length, and the geophones and hydrophones are electrically connected to a transmitter for transmitting the seismic impulses into a master receiver. Spikes are extended downwardly at spaced intervals along the length of the casing and a setting tool is provided to releasably anchor the spikes into the earth below a body of water.

Abstract: A hydrophone is provided for use with a hydrophone array enclosed in a streamer cable that is deployed in a body of water. The active transducer elements of the hydrophone are electrically isolated from the sealed metal case in which they are mounted. The signal input and output terminals are protected from short-circuiting due to water invasion of a faulty streamer cable jacket.

Abstract: A vertical hydrophone array and a system of multiple arrays are disclosed. The vertical hydrophone array includes multiple groups of hydrophones mounted along a cable. A floatation device is coupled to the cable at one end, and an anchor is coupled to the cable at another end via a remotely controllable release. Depth transducers and position transponders are preferably mounted along the cable to provide precise depth and position indication to the surface. The release allows for retrieval of the array while leaving the anchor behind, thus reducing the potential for array damage. In the system including multiple arrays, a central positioning anchor is disclosed, through which tensioning cables pass. Each tensioning cable is connected to the float end of a vertical array, so that tension of the tensioning cable allows for control of the angle of the sensor array from the vertical. A clamp is preferably provided so that the position of the array may be held without maintaining tension thereon from the surface.

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: Longitudinal shocks and longitudinal emotional disturbances are reduced between members attached to opposite ends of a vibration isolation module. An elongate, essentially cylindrically shaped cord extends the length of the module and is fabricated from a compliant and dissipative material. At least one cord-like essentially nonextensible member is wound about the core in a helical fashion with at least one symmetrically located pitch reversal, and with attachment to the core at least at the ends and pitch reversal points. Longitudinal shocks and motional disturbances are translated by the essentially nonextensible cord-like member into torsional shear strains in the compliant core. The dissipative characteristics of the core material coupled with the nonlinear relationship between longitudinal and torsional strain produce a tensile shock absorber with both damping and a spring constant that increases with longitudinal strain.

Abstract: A sonar transducer wherein a plurality of transducer modules are affixed along the length of a mounting member in the form of an elongated bar. The bar is contained within a protective housing and the mid point of the mounting member is affixed to the back wall of the housing in a manner that the mounting member stands off from the back wall of the housing. The mounting member is cantilevered on either side of the mounting position and is totally enclosed within the outer housing which is affixed along its entire length to a host structure so as to isolate and protect the alignment of the transducer modules from distortions.

Abstract: A towed array of hydrophone modules employs bladders that are mounted to bulkheads at the ends of the hose sections. The bladders are configured and pressurized so that pressure waves produced by the oscillatory motion of the bulkhead are suppressed by the bladders thereby significantly diminishing noise due to the breathing waves.

Abstract: A large eddy break-up device for towed acoustic arrays for reducing the f noise due to the (TBL) around the towed array is described. It includes two identical halves, each having a circumferential airfoil and two flat flanges which are used to secure it to a coupling on the towed acoustic array and also to integrate the two halves using fasteners. The circumferential foil interferes with the flow noise and large eddys are broken up into easily dissipating small eddys of higher frequency.

Abstract: A magnetic coupler and the use of such couplers to place a plurality of etroacoustic transducers around a lengthy single conductor trunk cable is described. The magnetic couplers are used to place the electroacoustic transducers in any randomly selected configuration. They allow the use of a single conductor trunk cable so as to facilitate the deployment of the system at a relatively low cost.

Abstract: A transducer array designed for towing at an extended distance behind a sace vessel includes electroacoustical transducer elements connected in opposition to the active elements of the array. A surrounding acoustic isolation structure effectively isolates the dummy transducer elements from the ambient noise field while permitting cancellations of self-induced noise.

Abstract: Seismic cable shielding method and apparatus. Shielding is obtained by switching unused wire pairs to ground via a roll-along switch which is connected to system ground. Grounding of the unused conductors in the cable is accomplished by ground connections at the roll-along switch. By grounding the unused conductor pairs (all pairs except those required for the sensor signals) within the cable, partial shielding is provided between the active wire pairs and cross-talk is reduced to a negligible level. Additional wire pairs are hardwired to system ground and distributed uniformly throughout the cable cross section to form an interstitial shield.

Abstract: A marine geophysical prospecting system employs a hydrophone streamer cable containing electromagnetic field sensors, modified to be towed at a preselected distance above the sea floor by a first marine vessel senses electromagnetic energy from selected substrata beneath bodies of water. The voltage between sensors may be amplified by amplifiers in the cable or by amplifiers aboard the towing vessel. Optionally, a second similarly modified cable is preferably located above the near-bottom cable. Both cables may also contain hydrophones and/or accelerometers, as well as depth and position sensors. Optionally, a second vessel tows at least one conventional seismic source to create compressional energy which propagates downwardly through the water into the substrata beneath the body of water. At appropriate porous subsurface formations, the acoustic energy is converted to electromagnetic energy.

Abstract: A sonar array which is operable at a broad range of frequencies, has a high free-field voltage sensitivity and is operable at high hydrostatic pressures. The array includes sensor elements made of a piezoelectric material, a backing plate which supports the sensor elements, a dielectric-elastic insulator positioned between the sensor elements and the backing plate, and backing blocks corresponding, respectively, to the sensor elements, each backing block positioned between a corresponding sensor element and the insulator. The sensor elements are arranged in staves, the staves forming four separate quadrants, the sensor elements in each stave being arranged in parallel and series combinations, so that the sonar array is operable between a frequency range of 10 kHz to above 100 kHz, each stave has a free-field voltage sensitivity of -186 dB re 1V/.mu.