Abstract: A new circuit is added to the old electrical circuit including two electrodes underwater positioned very close to a gas exhausting gun gaseous exhaust such as an air gun, wherein the exhaust from the firing gas exhausting gun momentarily blows away the conductive sea water from one or both of the electrodes to produce a high voltage pulse due to the large increase in resistance in the circuit indicating the precise moment of firing of the gas exhausting gun.This new circuit added to the above circuit is a circuit polarity reversing circuit which includes particularly a positive current generator, a negative current generator, and a sea ground for forming a third electron source when any of the two electrodes becomes defective, thus forming a fail-safe system.

Abstract: The invention provides an apparatus (10) and method for measuring the velocity and amplitude of a pressure wave (310) from an acoustic pulse (300) through layers of sediment (140) located below the mudline (130) of the seafloor (120). The apparatus (10) includes an implosive seismic source (30) for injecting acoustic pulses (300) into a region of the sediments (140), a plurality of vertically spaced sensors (50) located vertically below the seismic source (30) for sensing when the pressure waves (130) from the acoustic pulses (300) impact the sensor (50) or the amplitude of the pressure wave (310), and a digital recording system (100) for recording the signals from the sensors (50).

Abstract: New methods are disclosed for detecting the instant of firing of a gas exhausting gun such as an air gun which reduce plating action on two closely spaced apart electrodes submerged underwater very close to the gas exhausting gun exhaust comprising the basic steps of passing a current through the two electrodes, and periodically reversing the current to the two electrodes responsive to a polarity reversing circuit means after (1) a predetermined period of time or (2) after each firing of the gas exhausting gun.Likewise new methods for forming and assembling a fail-safe gas exhausting gun firing detection circuit are set forth in detail.

Abstract: A robust air gun fire time sensor consists of a housing to which is secured a protruding nonmagnetic internal barrel having a bore. The bore is closed at one end by a magnetic end cap defining an air chamber and the bore is in fluid communication with the firing chamber of an air gun. A generator coil surrounds the barrel. A bar magnet is floatingly mounted inside the bore and is urged against a shoulder formed in the end cap. When the air gun is charged with compressed air, some of the air becomes entrapped in the air chamber. When the air gun is fired, the entrapped compressed air in the air chamber pushes the bar magnet away from the shoulder. The collapsing magnetic field creates a transient electric pulse in the generator coil.

Abstract: The invention relates to a marine seismic source which emits an FM signal linearly increasing from 10 Hz to about 100 Hz. The source has a number of transducers which are flexible sleeves containing a pulsing hydraulic fluid.

Abstract: An electro-hydraulic (EH) actuator for converting electrical inputs into hydraulic output signals is described. The actuator features a pressure balanced design which permits operation at high absolute pressures without performance degradation. Internal portions of the EH actuator are filled with a non-conducting fluid, while a flexible diaphragm provides a movable interface between the fluid and the environment in order to equalize the internal and external pressures on the actuator.

Abstract: Apparatus for incremental cylinder length control in hydraulic seismic vibrators having increased frequency range. The vibrator apparatus (10) of the type having a reaction mass (38) and axial cylinder bore (42) utilizes hydraulically movable end sleeves (86 and 96) in each end of the cylinder bore (42) so that the end sleeves (86 and 96) can be controllably positioned thereby to alter the cylinder volume and adjust the hydraulic drive system (18) for maximum efficiency relative to operating frequency.

Abstract: An apparatus for generating P waves and S waves in a ground formation for a geological survey and the like. The apparatus has a percussive device which is driven to abruptly increase water pressure within a bore hole of the ground formation.

Abstract: A compressed-gas seismic energy source suitable for underwater prospecting. The device has two gas storage cylinders placed at the opposite ends of a shuttle. The shuttle seals both storage cylinders when seated at the end of its stroke and releases gas for the desired sonic pulse from both cylinders during its stroke. Design of the device provides for simplicity of operation, ready modification of the sonic signature, and reliability of moving parts.

Abstract: Seismic exploration method in arctic regions involving the generation of a seismic disturbance in the water beneath the ice in areas where conventional marine and land exploration methods are functionally inadequate. Seismic disturbances are generated by an air gun assembly which automatically executes lowering air guns through apertures in the ice and retrieving them while carrying out preventive measures against freeze-ups. Seismic sensing and recording equipment are positioned within an appropriate range to detect seismic data in the form of reflective or diffractive signals generated in response to the seismic disturbance after actuating the air gun array, wherein the seismic data is indicative of sub-surface structural formations existing below the body of water.

Abstract: Methods and devices are disclosed for generating acoustic pulses in a water or land medium, e.g., for use in seismic investigations. The pulse amplitudes, waveshapes, and frequencies can be controlled by signals that may originate at a remote location. Compressed gas is confined at high pressure in a valve chamber (12, 194). An initiating signal causes the opening of a passage (54, 56, 192) from the chamber into the medium to initiate the rise of a pressure pulse therein. A second signal causes the closing of the passage in a manner such that the initial rise of the pressure pulse is limited by the closure of the passage. In one device, the passage is opened by one sleeve valve member (60) and closed by another sleeve valve member (58). In another device the passage is opened by a sleeve valve member (196) whose motion to open the passage is arrested substantially instantaneously by transferring its momentum to a momentum exchange sleeve (246) that is then gradually decelerated.

Abstract: Disclosed herein are improvements in a recoil reducing system of a gas gun which create pulses in a liquid medium by introducing therein gas under high pressure. The release of high pressure gas from the barrel of such a gas gun causes recoil of the barrel. To reduce recoil, a reaction plate is attached to the barrel by metal rods so that the high pressure gas will impinge upon the reaction plate before escaping into the medium, and the force exerted on the reaction plate by the impinging gas will at least partially balance the force of recoil. In a preferred embodiment of this invention, a layer of shock absorbent material is interposed between the reaction plate and the impinging gas to absorb some of the energy of the gas. Flexing of the metal rods is thereby reduced and the life of the rods is extended. Alternatively, the flexing of the rods is reduced by connecting each rod to the reaction plate through a chain link type of connection comprising two rings, each ring passing through the other ring.

Abstract: The invention relates to seismic sources in which a shock wave is produced in a liquid mass by the implosion of a volume of vapor, particularly water vapor. According to the invention, the vapor to be imploded is formed inside a closed, flexible enclosure, surrounding an injection head, fitted with a vapor opening 103 capable of releasing vapor at 5 bars and 170.degree. C., controlled by an electromagnetic valve. Liquid nuclei are advantageously introduced into this vapor by means of a pipe for cold water which is under pressure and under the control of an electromagnetic valve, this water arriving in the cavity in order to exit through spray openings. These nuclei produce a vigorous drop in pressure inside the vapor, and hence an implosion and a shock wave, after which a pipe allows the condensate to be recovered. The invention is of use notably as a seismic marine source.

Abstract: A hydraulic drive system for an underwater vibrator has a hydraulically driven mass for generating a seismic wave into the seabed. The hydraulic drive system for the vibrator is accomplished by filtering sea water, conveying the filtered sea water to the hydraulic pump where the sea water under pressure is supplied through a control valve to the hydraulic vibrator. The output from the control valve is coupled to the sea water. The hydraulic system provides hydraulic fluid which will not need to be cooled, thereby eliminating the normal cooling system along with several necessary accumulators and sump which are used in a closed hydraulic system.

Abstract: The invention relates to the creation of a shock wave within a mass of water by implosion of a vapor bubble.According to the invention, a controlled quantity of liquid water under pressure and which is super-heated relative to the mass of water is released quickly, at a predetermined point of the mass of water, the water advantageously being in the lower vicinity of the left-hand part of the saturation curve (portion B-D). The water liberated in this way expands and vaporizes at least partially in the form of a single bubble, which then implodes suddenly.Application as a marine seismic source.

Abstract: A shuttle valve is slidingly provided within a firing chamber. A shuttle valve actuation control chamber is mounted at each end of the firing chamber. Pressurized air applied to a control chamber at one end of the firing chamber drives the shuttle valve to the opposite end of the firing chamber. An air accumulator chamber having a pressurized-air inlet is mounted adjacent each control chamber. An air passageway having a choke interconnects the firing chamber with the air accumulation chamber. A poppet valve interconnects each accumulator chamber with the adjacent control chamber to selectively apply pressurized air to one or the other of the control chambers. A solenoid vent valve fluidly communicates with each shuttle valve actuation control chamber. A bypass line fluidly interconnects each control chamber with the solenoid vent valve at the opposite end of the firing chamber.

Abstract: The liquid slug projector apparatus (9) comprises a generator (10) having a main housing (13) whose main port (17b) fluidly communicates with a liquid body (12). A first shuttle (26) and a second shuttle (61a) are slidably mounted inside the main housing. The first shuttle forms with the main housing a slug chamber (23) for confining therein a liquid slug (22). Force-producing means (8) cyclically cause the shuttles (26, 61a) to move relative to or in locked condition with each other, thereby applying during each cycle of operation an abrupt propulsion force to the confined liquid slug which becomes expelled as a very high-velocity liquid jet (22a) through the main port.

Abstract: A variable reluctance type firing sensor is mounted on an air gun for providing an electrical signal indicative of the instant of firing of the air gun. The firing sensor has a magnetic circuit which includes a permanent magnet, a pair of pole pieces and an armature including magnetically permeable material and which is free of mechanical restraint in its normal operating position, being held by magnetic attraction in position in the magnetic circuit. The armature freely "floats" on its "magnetic springs" within a thin walled chamber in which it is housed between the pole pieces, assuming a predetermined position of least magnetic reluctance. The armature which is acceleration-responsive is suddenly displaced from its predetermined position upon the firing of the air gun, and thus the reluctance of the magnetic circuit abruptly increases at the instant of firing.

Abstract: There is disclosed apparatus for controlling the precise time of firing of each air gun in an array of air guns employed in marine seismic exploration. For each air gun in the array, the apparatus maintains a record of past measured gun delays, that is the time period expiring between the triggering of an air gun and the time that the gun actually fires. Upon the receipt of a fire command, the apparatus inserts appropriate delays before triggering the individual air guns. In this way the air guns are controlled to fire in a precise predetermined sequence. The air guns may be caused to fire either simultaneously or sequentially so as to exercise effective control over the spectral content and the directionality of the energy generated by the array.

Abstract: A method is described for causing hollow glass spheres to implode on command while deep in the ocean, whereby to produce an acoustic pulse. Specific means for causing the spheres to implode are described. The invention is useful for seismic work.

Abstract: The resistive sensor consists of a pair of electrodes separated by an impervious insulating material. The sensor is mounted adjacent to an exhaust port of an airgun, in the path of the air blast that results when the gun is fired. When the air gun is submerged and not activated, the surrounding water creates a low-resistance path between the electrodes. When the gun is fired, the air blast blows the water away from the electrodes and the resistance between them abruptly increases substantially. A bridge circuit detects the instant of resistance change and generates an electrical transient to mark the time that the gun fired.

Abstract: The device includes two movable members interconnected at their periphery by a flexible membrane defining therewith a tight enclosure of variable volume, a piston slidable in a cylinder integral with one of the two movable members and hydraulically actuated, to move the members apart from each other, a second cylinder separated in two compartments by an inner valve and controlling the actuation of the piston in response to the pressure of the water feeding said second cylinder, two apertures intermittently freed by the valve for releasing the piston and at least one aperture for the discharge of the water from the tight enclosure to the external water body when the piston release allows the two movable members to be urged toward each other, thereby producing an implosion which generates a strong sonic wave.

Abstract: An air gun firing sensor apparatus and system are provided for determining the instant of firing of an air gun by sensing pressure changes within the air gun when it is being fired. A pressure-change-sensitive transducer assembly is inserted into a socket in the housing of a solenoid-controlled valve of an air gun with a passage from the air gun communicating with the transducer for transmitting to the transducer a pressure surge occurring within the air gun whenever it is fired. The transducer assembly has a cylindrical casing with a head mounted at one end. The head includes a plurality of spaced recesses which are adapted to communicate with the passage leading from the air gun.

Abstract: Apparatus for controlling a release of pressurized fluid, to generate an acoustic or shock wave impulse for use in underwater reflection seismic surveys. Compressed air is supplied to the acoustic impulse generator and is used both to provide the compressed air acoustic impulse and to retain two piston members in sealing engagement with each other to maintain the compressed air within the apparatus. The two internal pistons are hollow, open-ended cylindrical members, and are adapted to slide axially within a cylindrical chamber and abutt one another to preclude escape of compressed air. To fine the acoustic impulse generator, compressed air pressure holding the first piston member in position over a series of exhaust ports is suddenly reduced, causing that piston to shift within its chamber, exposing the ports to atmosphere and thereby emitting an acoustic impulse of compressed air.

Abstract: A fluid pulsed generator system including an elongated tubular member of uniform elastic parameters constructed for receiving fluid flow therein and abruptly terminating said flow to create an acoustic pulse containing most of its acoustic energy in the zero to 160 Hertz frequency spectrum. The system generates a directionally distinctive acoustic pulse. The system includes a fluid reservoir adapted for supplying a suitably high fluid pressure for driving a fluid through the elongated tubular member with sufficient velocity to generate an acoustic pulse basically of the classical water hammer variety The device is provided in a marine configuration comprising an elongated acoustic radiating conduit containing the water hammer generated pressure pulse adapted for trailing from a vessel beneath the surface of a body of water.

Abstract: Airgun apparatus are disclosed providing high strength, high pressure and large volume capabilities. An integral high-strength cylindrical housing extends for the full length of the airgun and gives a sleek overall cylindrical configuration. The components of the airgun advantageously are assembled within this cylindrical housing in two groups by sliding them in through the upper or lower end, respectively; moreover, either of the groups of components can be removed independently of the other. The components are pressed firmly together in place within the cylindrical housing by a strong screw-jack type of holding action, and tightening and locking apparatus is included on the airgun itself for enabling the mechanic to tighten and lock the holding means with enormous mechanical advantage.

Abstract: Device for generating acoustic waves by implosion in a fluid medium comprising fluid-operated means to move a piston, having one end face in contact with said fluid, from a retracted position in the enclosure to a spaced apart position of maximum extension towards the exterior of the enclosure or vice versa and intermittent locking means for maintaining the piston at its spaced apart position, said fluid-operated means being actuated by two sources of fluid at different pressures, one of which is said fluid medium and the other a source of lower pressure.

Abstract: In generating seismic waves in earth a generator having a generally elongate, tubular expandable and contractible outer wall portion closed at its upper and lower ends by rigid strength members having separate input and return pressure lines is placed in a well bore, a hydraulic coupling pressure is applied through the input line which causes the expandable wall portion to engage and remain coupled with and in direct contact with the earth wall in the well bore and hydraulic pressure impulses are then cycled through the input and return lines at pressures greater than the coupling pressure to cause further expansion of the expandable wall portion, thereby generating and radiating seismic waves in the earth upon application of each impulse while maintaining the hydraulic coupling pressure sufficient to effectively maintain the outer wall anchored to the wall of the bore hole. The coupling pressure should be sufficient to anchor and couple the transducer to the well bore without any additional anchoring.

Abstract: Disclosed is a seismic source device, known in the industry as an air gun, having internal sleeve and shuttle control for allowing a predetermined discharge of compressed air into water for purposes of seismic exploration. The shuttle engages an internal sleeve having ports that momentarily align with exhaust ports and then moves past, sealing off the exhaust ports before all of the compressed air in the firing chamber of the air gun is exhausted. By preventing further discharge of air with little or no loss in acoustic output, pulses are greatly reduced, thereby enhancing the operation of the entire system. Further by preventing all the air in the firing chamber from being discharged, the system becomes more efficient and more cost effective.

Abstract: A new circuit is added to an electrical circuit including two electrodes underwater positioned very close to an air gun gaseous exhaust wherein the exhaust from the firing air gun momentarily blows away the conductive sea water from one or both of the electrodes to produce a high voltage pulse due to the large increase in resistance in the circuit indicating the precise moment of firing of the air gun free of any uncertainty and mechanical noise which normally affects conventional transducers.This new circuit added to the above circuit is a circuit polarity reversing circuit which includes particularly a positive current generator, a negative current generator, and a sea ground for forming a third electron source when any of the two electrodes becomes defective, thus forming a fail-safe system.

Abstract: Firing of a seismic source of the type called an air gun is detected by means of a fluid pressure sensor located in the housing of a solenoid actuated control valve. Through a pressurized gas support port the pressure sensor is in fluid contact with a shuttle-operating chamber of the air gun, and the sensor detects a surge in fluid pressure resulting from rapid motion of the shuttle. if a misfire or malfunction of the air gun is detected by means of the fluid pressure sensor, the malfunctioning air gun can be shut down by actuating the solenoid valve, which is a novel dual action solenoid valve, thereby preventing pressurized gas from being supplied to that particular air gun. The valve includes a valve stem with radial gas inlet ports and radial triggering ports. A solenoid plunger is movable to close one or the other of the sets of ports.

Abstract: A powerful seismic impulse is generated in a body of water by a slug of water propelled from a seismic source by expanding pressurized gas, but the gas is retained in the source for use in subsequent firings. The seismic energy source, which is called a "hydro gun", is recharged by pumping an incompressible liquid, preferably, water, at high pressure into the gun to compress the retained pressurized gas. The hydro gun includes a firing cylinder, and a piston follower in the firing cylinder divides it into a liquid-charge chamber and a gas-propulsion chamber. The liquid-charge chamber is closed from liquid discharge ports by a shuttle which is held closed by the high pressure of gas in an operating chamber. By pumping an incompressible liquid into the liquid-charge chamber, the follower is forced to compress the pressurized gas which is trapped in the gas-propulsion chamber.

Abstract: Disclosed is a seismic source device, known in the industry as an air gun, having shuttle control for allowing a predetermined discharge of compressed air into water for purposes of seismic exploration. The shuttle is controlled by valve means for closing the exhaust ports before all of the compressed air in the firing chamber of the air gun is exhausted. By preventing further discharge of air, with little or no loss in acoustic output, secondary pulses are greatly reduced, thereby enhancing the operation of the entire system. Further by preventing all the air in the firing chamber from being discharged, the system becomes more efficient and more cost effective.

Abstract: Disclosed is a seismic source device, known in the industry as an air gun, having shuttle and external sliding valve control for allowing a predetermined discharge of compressed air into water for purposes of seismic exploration. The shuttle is controlled by air pressure to move it upward, thereby permitting compressed air in the firing chamber to exhaust through exhaust ports. The external sliding valve had been held in a downward position by air pressure supplied from the firing chamber, compressing a spring. As the firing chamber pressure drops, the compressed spring expands, forcing the sliding valve to move upward, closing the exhaust ports. By preventing further discharge of air, secondary pulses are greatly reduced, with little or no loss in acoustic output, thereby enhancing the operation of the entire system. Further, by preventing all the air in the firing chamber from being discharged, the system becomes more efficient and more cost effective.

Abstract: Disclosed is a seismic source device, known in the industry as an air gun, having shuttle control for allowing a predetermined discharge of compressed air into water for purposes of seismic exploration. The shuttle is indirectly controlled by a moveable plate for closing the exhaust ports before all of the compressed air in the firing chamber of the air gun is exhausted. In one embodiment, the plate is freely moveable; in a second embodiment, the plate is attached to the shuttle. By preventing further discharge of air, with little or no loss in acoustic output, secondary pulses are greatly reduced, thereby enhancing the operation of the entire system. Further by preventing all the air in the firing chamber from being discharged, the system becomes more efficient and more cost effective.

Abstract: A marine seismic source employs a cylindrical gas exploder adapted to be supported from a surface vessel in a submerged state adjacent a marine bottom. The force of expanding gases within the exploder applies a thrust along the exploder longitudinal axis to a ground contact member operatively interconnected with the exploder to produce a seismic signal. The energy producing force is reacted by piston means within the exploder interconnected rigidly with a large area external water interacting disk. The mass of the reaction piston-disk system is sufficiently great so that the slow moving disk experiences viscous damping in the water and thus generates no significant undesirable secondary seismic signal in the water. The exploder may be oriented horizontally for maximum generation of shear waves or inclined at an acute angle to the vertical for generation of a combination of shear waves and compressional waves.

Abstract: An improved seismic prospecting system comprising the use of a closely spaced sequence of source initiations at essentially the same location to provide shorter objective-level wavelets than are obtainable with a single pulse. In a preferred form, three dynamite charges are detonated in the same or three closely spaced shot holes to generate a downward traveling wavelet having increased high frequency content and reduced content at a peak frequency determined by initial testing.

Abstract: An improved air gun consists of an elongated cylindrical housing for containing a volume of compressed air that is closed at each end by end plates. A radially-positioned exhaust port is bored into the wall of the housing. A hollow, cylindrical shuttle, is mounted concentrically inside the housing for linear back-and-forth sliding motion in alternate strokes. The ends of the shuttle are closed by end faces. A radially positioned sealing pad has an orifice that is alignable with the exhaust port is supported by the shuttle. When the shuttle is at either end of a stroke, the sealing pad blocks the exhaust port. The space between each shuttle end face and the respective housing end plates form shuttle-actuation control chambers. A small air leak in each control chamber maintains the residual air pressure therein at ambient when the guns is inactive. To fire the gun, a small quantity of air is diverted by valving from inside the housing to one of the control chambers.

Abstract: A method and apparatus for seismic prospecting which utilizes two transducer plates that are spaced apart, with two sets of bellows placed in between and sealingly attached thereto, to transmit electrically controlled hydraulic pressure signals onto the two plates. When pressure is applied within one set of bellows, the two plates are pushed apart. When pressure is applied within the second set of bellows, the two plates are pulled together. To accomplish this pulling action of the second set of bellows, two closure plates placed between the two transducer plates are used, one attached to one transducer plate and one attached to the other transducer plate. The first closure plate is attached to the first transducer plate in such a manner that it lies between the second transducer plate and the second closure plate. By applying pressure to the second set of bellows that push apart these two closure plates, the two transducer plates are pulled towards each other.

Abstract: Firing of a seismic source of the type called an air gun is detected by means of a fluid pressure sensor transducer in fluid communication with a shuttle-operating chamber of the air gun, and this sensor detects a surge in pressure in a portion of this chamber resulting from rapid motion of the shuttle, thereby producing an electrical signal which provides an accurate indication of the actual time of firing called the "shot instant" of the air gun. The reaction time between the electrical firing command signal and the shot instant is not the same for all air guns in a seismic survey array but may differ from one to another due to variations in the solenoid-actuated valves which trigger the air gun, in tolerances of the air gun parts, frictional effects and slight differences in mass of moving parts, and wear of parts. The method and apparatus as disclosed enables a geophysical survey crew accurately to determine the reaction time of each individual air gun seismic energy source.

Abstract: An exciting method for a logging by means of S wave is provided which includes inserting a wave source into a bore hole containing water and actuating an operating mechanism in the wave source to impart an exciting force to the bore hole wall in the direction perpendicular to the axis of the bore hole, so as to generate the S wave having characteristics of predominant radiation in the direction perpendicular to the axis of the exciting force. The improvement of the invention comprises abruptly ejecting the water at one side of the wave source intersecting the extension of the axis of the exciting force, while, simultaneously at the opposite side of the wave source, abruptly sucking the water of equivalent volume to that ejected at the first mentioned side, whereby a positive and negative pressure change are indirectly applied through the medium of the water to the two respective sides of the bore hole wall intersecting the extension of the exciting force axis.

Abstract: This device comprises two movable elements of rigid material tightly interconnected by means of a deformable membrane forming therewith a tight internal enclosure, means for varying abruptly the volume of said enclosure by successively moving the two elements away from each other, maintaining them in spaced relationship and allowing them to be urged toward each other by the effect of the external hydrostatic pressure, in which the means for moving the two elements away from each other includes two cylinders and at least one piston slidable in one of said cylinders, associated to one of said movable elements and also to a push-member slidable in one of the cylinders and bearing on the other movable element and means for feeding said cylinder with pressurized fluid so as to maintain the elements in spaced relationship or to release them.

Abstract: An underwater transducer which includes a fluid circuit having a valve disposed in a plenum chamber having a small aperture open to the ambient water pressure. Fluid flow into and out of the chamber by way of the valve is governed by controlling the valve opening and closing in accordance with movement of an electrodynamic driver which receives an input signal to be transmitted.

Abstract: An acoustic impulse generator is disclosed for use in a fluid media for oceanographic, seismographic and related applications. The generator includes a housing with a piston slidably disposed therein and a passageway through which a rod attached to the piston moves. A firing chamber is attached to the housing for channeling a quantity of liquid through a nozzle. A diaphragm may be disposed between the housing and the firing chamber with the quantity of liquid being displaced in response to movement of the piston.

Abstract: The invention relates to a device for propelling a liquid projectile to create a shock wave by implosion, said device comprising a cylinder containing two pistons, a reservoir of pressurized fluid acting on the pistons, a stop for stopping the piston, a perforated connecting piece to permit the escape of the propelled liquid and for connecting the cylinder with a return mechanism. The invention is applied to underwater oil prospecting.

Abstract: The invention has application to an implosive sound generator which produces in a body of water a cavity that implodes resulting in a large acoustic impulse. The invention provides means for eliminating or substantially reducing the bubble effect by providing means for absorbing the rebound of the implosion of the cavity and preferably also for cancelling the recoil of the generator. A preferred embodiment of the generator comprises a slug chamber having a primary port. The slug chamber entraps a liquid slug therein when the generator is submerged in a liquid body. Force means propel the liquid slug with sufficient kinetic energy to create in the liquid body a main cavity which is imploded by the hydrostatic pressure head. To reduce or eliminate the rebound of the implosion, there is provided a suction chamber having at least one secondary port communicating with the liquid body near the site of the main cavity.

Abstract: The seismic source consists of a tank for containing a volume of water. The tank is held in firm contact with the ground by suitable weighting means. The tank wall that contacts the ground is thinner than the other walls. The volume of water in the tank is pressurized to one to three atmospheres. An imploder is mounted in the tank, submerged in the water. When the imploder is fired, reducing the tank pressure abruptly, a negative pressure pulse is generated in the water. The negative pressure pulse is transmitted from the water, through the thin ground-contacting wall, to the ground, producing an acoustic pulse whose first motion is one of rarefaction.

Abstract: In the field of seismic exploration, compressed-air guns may be used as sound sources. Known air guns employed complex valving and were wasteful of compressed air. The air gun sound source of this invention is of simple construction and is economical of compressed air.The gun (10) consists of an elongated housing (34) that has at least one radially-positioned exhaust port. The housing is charged with a volume of compressed air. A hollow cylindrical actuator (60) is mounted inside the housing and may be hydraulically or pneumatically driven within the housing in longitudinal strokes. The actuator has at least one radially positioned aperture (88) alignable with the exhaust port. A valve or sealing pad (96) is mounted in each aperture. An orifice (104) is cut into each pad. At one end of an actuator stroke, the valve blocks the exhaust port in the housing.

Abstract: Apparatus for generating a substantially oscillation-free siesmic signal for use in underwater petroleum exploration, including a bag with walls that are flexible but substantially inelastic, and a pressured gas supply for rapidly expanding the bag to its fully expanded condition. The inelasticity of the bag permits the application of high pressure gas to rapidly expand it to full size, without requiring a venting mechanism to decrease the pressure as the bag approaches a predetermined size to avoid breaking of the bag.

Abstract: A source is described capable of generating acoustic signals under water at high cycling rates suitable for providing seismic signals of controlled amplitude and spectral shape and with precise timing for geophysical exploration. The source has a pair of radiating pistons in a housing having a cylindrical sleeve and radial webs. Axial shafts extend outwardly from the pistons and support the pistons in the webs. The peripheral edges of the pistons are in sliding contact with and are guided by the sleeve. The pistons and sleeve define a chamber between the pistons which, under quiescent conditions, contains gas under a low pressure or partial vacuum. The shaft on at least one of the pistons extends into another chamber in the hub of one of the webs.