Abstract: A seismic source using tuned pulse sources to form an ultra-low frequency (ULF) cluster intended for use in generating seismic energy impulses for marine seismic exploration and more specifically to improved performance by increasing low frequency output to within a range of 1 Hz to 3 Hz to provide greater penetration of the seismic signal through complex overburden such as salt or basalt.

Abstract: This disclosure is related generally to marine surveying. An apparatus for generation of seismic waves in a body of water may include a wave generator. The apparatus may further include a housing defining an internal chamber having an open end. The housing may include baffles positioned between the open end and the wave generator. The housing may further include a vent positioned on an opposite end of the housing from the baffles.

Abstract: Acquiring seismic data using time-distributed sources and converting the acquired data into impulsive data using a multiple-frequency approach. The methods are performed in frequency-source location domain, frequency-wavenumber domain, or frequency-slowness domain. The methods are applicable to single source acquisition or simultaneous source acquisition.

Abstract: A system is provided for component separation. In an embodiment, a light source or other source of electromagnetic energy delivers energy to a volume of tissue. A transducer array or other sensor receives a resulting acoustic signal, and a processing subsystem processes the acoustic signal to separate a direct acoustic return component from a secondary acoustic return component of the acoustic signal. An output and/or storage device presents and/or stores information about the direct acoustic return component, the secondary acoustic return component, or both. Other embodiments include a coded probe, a probe having an isolator that produces a wavefront, a sensor for measuring intensity of an acoustic wave produced by absorbed photons, and a system that receives acoustic signals from surface targets to determine an optical parameter of the volume.

Abstract: In some embodiments, an apparatus, system, and method may operate to determine the density of drilling fluid associated with photon activity in the drilling fluid using an array of nuclear detectors. Further activity may include determining acoustic impedance of the drilling fluid as a combination of the density and acoustic velocity. Additional apparatus and systems, as well as methods, are disclosed.

Abstract: Embodiments of the present disclosure relate to a drilling fluid system that includes a conduit configured to convey a fluid from a first sub-system of the drilling fluid system to a second sub-system of the drilling fluid system, an ultrasonic measurement system configured to determine a flow rate of the fluid in the conduit, and a controller configured to receive feedback from the ultrasonic measurement system and to adjust one or more operating parameters of the drilling fluid system based at least on the feedback.

Abstract: Apparatus for the generation of pressure waves for seismic surveys in marine environment comprising a cylinder (3), defining an axis, in which a striker piston (1) and a pump piston (2) are situated, each having two respective opposite sides with respect to said axis, of which a side of the striker piston (1) situated in front of the pump piston (2) is defined first impact side, and a side of the pump piston (2) in front of the striker piston (1) is defined second impact side, the pump piston (2) and the striker piston (1) sliding in the cylinder (3) in a direction parallel to the axis, and the pump piston (2) and striker piston (1) being such as to strike against each other, by means of the first and the second impact sides, the striker piston (1) being driven by activation means pressing on the side opposite to its own impact side, wherein the cylinder (3) comprises, at one of its ends, a chamber (15) having a diameter larger, smaller or equal to that of the portion of cylinder (3) in which the striker pist

Abstract: A source element for generating seismic waves includes a housing; a partitioning element placed inside the housing and configured to split the housing in a closed chamber and an opened chamber; and a valve in fluid communication with the closed chamber and configured to supply high-pressure air to the closed chamber to make the partitioning element oscillates. An oscillation of the partitioning element generates low-frequency seismic waves.

Abstract: A marine vibratory sound source for producing swept or pulse coded signals in a body of water and within geological structures beneath a body of water, primarily for seismic exploration of the strata beneath the bottom of the water. More particularly, a high power, servo controlled hydraulic, sound source that delivers fluid alternatively to first and second actuator pistons to move the actuator pistons to a forward and an aft position thereby axially vibrating a piston shaft having cone-shaped pistons for vibrationally moving water out and in through a plurality of ports for propagating vibratory sound. The sound source having a position sensor to determine a center point of travel and by tracking the position sensor air pressure in hollow stationary cone-shaped bulkheads is modulated to maintain the travel of the cone-shaped pistons at an equal distance in the fore and aft directions from the determined center point.

Abstract: A technique includes obtaining data indicative of images of a marine seismic source event, which are acquired by underwater cameras and processing the data to determine an attribute (a seismic bubble volume or motion, as non-limiting examples) that is associated with the seismic source event.

Abstract: Seismic sources including a steerable submersible float and related methods are provided. A seismic source includes a submersible float and a plurality of individual sources. The submersible float is configured to control at least one of a depth and a horizontal position of the submersible float by adjusting angles of one or more rotatable surfaces attached to the submersible float. The individual sources hang under the submersible float and are configured to operate at a depth larger than the depth of the submersible float.

Abstract: The maximum output of a seismic source array may be reduced by activating the individual seismic sources within these seismic source array in a pattern that is extended in time rather than by the presently employed conventional simultaneous activation of a large number of individual seismic sources. Methods are disclosed which take data shot with patterned sources and may use a sparse inversion method to create data with the about same image quality as that of conventional sources. In this manner the output of the maximum impulse of a seismic source array may be reduced by an amplitude factor of about 10 in the examples shown here, corresponding to a reduction of about 20 dB while maintaining virtually the same seismic image quality. The disclosed methods may be used in combination with any simultaneous sourcing technique. In addition, the disclosed methods may be used with a plurality of source arrays.

Abstract: The invention concerns a device for emitting seismic waves designed to operate by being towed by a vessel, characterized in that it comprises means capable of discharging compressed air under high pressure into water, to generate a bubble (44) of a general annular shape.

Abstract: Air bubbles may be used to reduce radiated underwater noise. Two modalities of sound attenuation by air bubbles were shown to provide a reduction in radiated sound: bubble acoustic resonance damping and acoustic impedance mismatching. The bubbles used for acoustic resonance damping were manifested using gas-filled containers coupled to a support, and the acoustic impedance mismatching bubbles were created using a cloud of freely-rising bubbles, which were both used to surround an underwater sound source.

Abstract: The invention relates to a base structure for an off-shore wind power installation having preferably three base piles, each of which is of a length such that when installed at an installation location it extends from a seabed to above a sea level, wherein the base pile has a driving pile which is guided in its interior at least portion-wise for anchoring in the seabed, and at least one support structure for mounting the wind power installation. Furthermore at least a portion of the base pile has a wall comprising a plurality of layers, wherein there is provided al least an inner layer and an outer layer, between which, is arranged at least one intermediate layer which has a sound-reducing core material, in particular concrete. The invention also relates to a method and an apparatus of reducing noise emissions when erecting a base structure.

Abstract: Methods and apparatus for controlling seismic source firings are disclosed. The methods and apparatus enable firing of seismic sources to increase pressure wave amplitude. Some methods and apparatus reduce ghosting and align first pressure peaks of multiple seismic sources. The multiple seismic sources may be fired sequentially according to active feedback mechanisms. Controlling the firing of the seismic source facilitates more accurate seismic data and a more consistent seismic source signature.

Abstract: The present invention provides an apparatus and a method for reducing wing-tip vortex energy during seismic exploration. The apparatus includes a vortex concentrator of deployed proximate a tip of a hydrofoil and a vortex reducing device deployed proximate the vortex concentrator.

Abstract: Methods and apparatus for attenuating waves in a bore hole, and seismic surveying systems incorporating the same. In one embodiment, an attenuating device includes a soft compliant bladder coupled to a pressurized gas source. A pressure regulating system reduces the pressure of the gas from the gas source prior to entering the bladder and operates in conjunction with the hydrostatic pressure of the fluid in a bore hole to maintain the pressure of the bladder at a specified pressure relative to the surrounding bore hole pressure. Once the hydrostatic pressure of the bore hole fluid exceeds that of the gas source, bore hole fluid may be admitted into a vessel of the gas source to further compress and displace the gas contained therein. In another embodiment, a water-reactive material may be used to provide gas to the bladder wherein the amount of gas generated by the water-reactive material may depend on the hydrostatic pressure of the bore hole fluid.

Abstract: Methods and apparatus for attenuating waves in a bore hole, and seismic surveying systems incorporating the same. In one embodiment, an attenuating device includes a soft compliant bladder coupled to a pressurized gas source. A pressure regulating system reduces the pressure of the gas from the gas source prior to entering the bladder and operates in conjunction with the hydrostatic pressure of the fluid in a bore hole to maintain the pressure of the bladder at a specified pressure relative to the surrounding bore hole pressure. Once the hydrostatic pressure of the bore hole fluid exceeds that of the gas source, bore hole fluid may be admitted into a vessel of the gas source to further compress and displace the gas contained therein. In another embodiment, a water-reactive material may be used to provide gas to the bladder wherein the amount of gas generated by the water-reactive material may depend on the hydrostatic pressure of the bore hole fluid.

Abstract: Methods and apparatus for suppression of wave energy within a fluid-filled borehole using a low pressure acoustic barrier. In one embodiment, a flexible diaphragm type device is configured as an open bottomed tubular structure for disposition in a borehole to be filled with a gas to create a barrier to wave energy, including tube waves. In another embodiment, an expandable umbrella type device is used to define a chamber in which a gas is disposed. In yet another embodiment, a reverse acting bladder type device is suspended in the borehole. Due to its reverse acting properties, the bladder expands when internal pressure is reduced, and the reverse acting bladder device extends across the borehole to provide a low pressure wave energy barrier.

Abstract: A method of detecting a marine gas seep that includes: deploying a local probe on or near the seafloor; producing bubbles in water near or within the local probe; detecting the bubbles; producing data indicating the relative concentration of dissolved gas in the water; and associating elevated dissolved gas concentrations with the presence of a nearby marine gas seep. Another aspect of the invention involves an apparatus configured to carry out the inventive method. Preferred embodiments of the invention utilize an ultrasonic transducer to both produce bubbles and detect them.

Abstract: A sound mitigation system and method reduce the transmission of acoustic output from explosions underwater. The system is submerged to bottom terrain of a body of water and has at a series of gas-generating devices providing volumes of gas that are fed to refractory heat resistant tubing assemblies and flexible general tubing assemblies. The heat resistant and general tubing assemblies extend between adjacent gas generating devices and are provided with at least one row of holes to vent bubbles of gas and form a virtually continuous curtain of bubbles rising to the surface of the water between detonating explosives and areas of interest. The curtain of bubbles mitigates the effects of the explosions on marine mammals and endangered, threatened, or protected species within an area adjacent to the explosions.

Abstract: A method and apparatus for in-situ characterization of downhole fluids in a wellbore using ultrasonic acoustic signals. Measurements of the speed of sound, attenuation of the signal, and acoustic back-scattering are used to provide qualitative and quantitative data as to the composition, nature of solid particulates, compressibility, bubble point, and the oil/water ratio of the fluid. The tool generally comprises three sets of acoustic transducers mounted perpendicular to the direction of the flow. These transducers are capable of operating at different frequencies so that the spectrum of the acoustic signal can be optimized. The apparatus is capable of operating downhole to provide real time information as to conditions in the well.

Abstract: A valving system is disclosed which generally comprises a body including an inlet and an outlet where the inlet is disposed in fluid communication with a fluid flow passage and the outlet is disposed in fluid communication with a pressurized fluid member, the body further defining an internal bore in which is slidably disposed a piston moveable between a first and a second position such that fluid communication between the fluid flow passage and the fluid flow member is established when the piston is disposed in the first position but not in the second position, an apparatus and to move the piston from the first position to the second position so as to interrupt fluid flow from the fluid flow passage to the fluid member.

Abstract: A system and method for periodically providing information about subsurface formations in a marine environment using a non-towed seismic signal source (3) and a static array of seismic signal receivers (4) is disclosed. The seismic signal source (3) comprises a support frame (10) and a line (7) attaching the support frame to a stationary platform (2), wherein the line (7) restrains the support frame (10) in a position that is static in relation to the formation (8). The seismic signal source (3) includes eight air guns (12) attached to the support frame (10) such that the air guns (12) are discharged to provide a tapered, heavy centered, point source seismic signal at a specific location relative to the formation (8) that is reflected to the static array of seismic signal receivers (4) such that changes in the formation characteristics may be observed over time.

Abstract: A well tool in accordance with the invention comprises an attenuation device which attenuates tube waves associated with an elastic wave emission and/or reception set (1, 12). The attenuation device comprises a bubble generator (2) which releases into the well a gas not readily soluble in the well fluid, slightly overpressured in relation to the hydrostatic pressure, in the form of calibrated bubbles which greatly attenuate the parasitic tube waves. The attenuation device is placed above or below the elastic wave emission and/or reception set having a plurality of pickups whose signals are acquired by a local electronic module (14) and/or a source of elastic waves such as a vibrator. A bubble trap (17) is preferably associated with the bubble generator (2) in order to limit the volume of gas to be generated in situ. The invention is applicable to VSP type seismic prospecting and acoustic logging.

Abstract: A pneumatic gun having a fast-acting sliding sleeve valve member reciprocating between two axial positions, first to open an exhaust port for the explosive release of gas from a pressurized charge chamber in a stationary housing while simultaneously closing a pressurized intake port to said chamber, and then to close said exhaust port while simultaneously opening said pressurized intake port for recharging said charge chamber, all for the purpose of generating repetitive trains of impulsive sounds at a rapid rate with increased efficiency. The sliding valve member comprises a sleeve and may include a piston in a cylinder within the housing. The sliding valve member has a sealing flange which forms a lip seal with a stationary annular mating surface of the gun to close an exhaust port. A wall of the charge chamber is provided with an intake port in communication with a source of high-pressure gas.

Abstract: A pneumatic gun or air gun having a fast-acting sliding valve reciprocable between two axial positions to close or open intake and exhaust ports in a charge chamber in a housing. The sliding valve comprises a piston internal to the housing and may include a piston in a cylinder within and extending beyond the housing. The sliding valve has a sealing flange which forms a lip seal with an annular mating surface of the housing to close an exhaust port. Air accelerating from the gun may be radial from an equatorial exhaust port or may be axial from an end of the charge chamber. The charge chamber is provided with an intake port in selective communication with a source of pressurized gas, thereby to facilitate rapid charging rates. The intake port is closed when the exhaust port is opened by the sliding action of the valve member, and is opened when the lip seal is formed to close the exhaust port.

Abstract: A sleeve air gun for releasing compressed air into water. The air gun housing has a chamber enclosed with an end cap. The end cap is engaged with the air gun housing with a retainer that is light weight and expedites the engagement and disengagement of the end cap and housing. The retainer can comprise a light weight ring that engages the housing and end cap. The retainer uniquely permits larger diameter air guns to be constructed without disproportionately increasing the weight of the air gun. The larger diameter air gun expedites the discharge of compressed air from the air gun, which maximizes the acoustic pulse generated in the water.

Abstract: An air gun for releasing compressed air into the environment. Two opposing shuttle valves selectively open ports to release compressed air more quickly from the air gun. A centering mechanism returns the first and second shuttle valves to the initial position. The centering mechanism can comprise a pressure compensation system or mechanical stop for positioning the first and second shuttles at the selected position.

Abstract: Seismic airgun arrangement for attenuating unwanted oscillations in the emitted signal. The airgun has one or more outlet ports (9) for exhausting air in a generally radial direction from a central axis of the airgun (10), and a perforated screen (20) of plate material is provided around the airgun for the attenuation mentioned. The volume generally delimited within the screen (20) is significantly smaller than the maximum bubble size which is normally generated by the airgun (10). The screen (20) has an open side or end (20A) at a part of the screen that is adapted to face at least partially downward in the normal operative position of the airgun (10). At least edge portions of the screen along the open side or end (20A) are located substantially directed opposite the outlet port or ports (9).

Abstract: A marine seismic signal source apparatus and method that maximizes the usable acoustical (db) energy of the array signature in a lower frequency bandwidth. The apparatus forms a three dimensional 2.times.4.times.2 array having a plurality of 8 air guns of identical firing chamber size (10 cubic inch) operably arranged in pairs at different water depths. Firing of the guns in a top to bottom time delayed sequence shifts the frequency domain of the peak acoustical db signal to concentrate the usable seismic energy in the deeper earth formation penetrating range. The frequency boundaries of the bandwidth of the occurrence of the peak 6 db increment of acoustical power are lowered and compressed into a narrower bandwidth by the firing sequence.

Abstract: A patient monitoring system utilizes a transmitter associated with each patient. The transmitter is worn by a patient and includes sensors operative to monitor vital signs of the patient. The transmitter transmits an allocated RF frequency which is particularly associated with that patient. A series of antennas are incorporated in a building, each antenna having its own signature signal. As the patient moves throughout the building, the antennas pick up the signals from the patient's transmitter and combines the antenna signature signal with the transmitted patient signal. This combined signal is then analyzed at a central location to determine the exact location of the patient due to the antenna signature signal which is modulated on the transmitted patient signal. Transmitted patient data is also decoded at the central station to provide a signal indicative of the vital signs of the patient.

Abstract: The present invention is directed to a method and apparatus for substantially suppressing the undesired recoil derivative from the explosive discharge of high pressure gas from an airgun while still providing for useful optimized pressure pulses.

Abstract: A process for degassing a coupling liquid is disclosed, comprising adding to said coupling liquid at least one chemical substance readily taking up gas in a sufficient quantity to absorb said gas substantially completely. This chemical substance is preferably a sulfite of alkaline- or alkaline-earth metal. The invention makes it possible to obtain pressure values of the pressure waves greater than those obtained by conventional physical degassing.

Abstract: The present invention is directed to a method of modifying or reshaping the acoustical signature created by the explosive, underwater release of a highly pressurized gas. More specifically, the present invention is directed at a method for modifying the asymmetric and cuspate nature of the acoustical signature derivative from the generation of a primary pulse so as to allow for the beneficial superimposition of a second wavelet of opposite phase.

Abstract: A towable marine seismic source apparatus for producing a high resolution seismic signal at relatively shallow depths for engineering surveys is disclosed. The apparatus support frame operably mounts a plurality of eight identical chambered air guns in a 2.times.4.times.2 configuration to provide a tapered, heavy centered point source. The cylindrical air guns are positioned in a horizontal orientation at a predetermined depth of 1 to 3 meters and are synchronized to fire substantially simultaneously to achieve maximum peak energy output. Two chamber sizes of individual air guns (4 cu. in. & 10 cu. in.) are in a desired range and may be preferably employed in the array configuration to produce the seismic signal having distinct signature characteristics.

Abstract: The novel method substantially reduces the pressure pulse, generated by a first radial motion of a body of water, by changing the radial motion into axial motion. The change from radial motion into axial motion is produced by generating a second radial motion of opposite phase within the body of water.The method can be used to substantially reduce the pressure pulse, generated by the implosion of a body of water, by generating an explosion in the body of water. It can also substantially reduce the pressure pulse generated by an explosion within a body of water, by generating an implosion of the body of water. The method can further be used to generate within a body of water an impulsive acoustic signal by sequentially generating within the body of water a first explosion and a second explosion. The apparatus comprises a signal chamber which contains a first charge of gas. A normally-closed valve maintains the signal chamber closed and has a discharge port into the water.

Abstract: The present invention comprises an apparatus and method for producing a high resolution acoustic signal from a single point source while achieving a commercially acceptable secondary bubble suppression. More specifically, the present invention comprises first and second explosive generators which sequentially create two explosions or one explosion and injection, within the body of water; said first explosion producing within the body of water a powerful acoustic pulse in an expanding cavity of very low pressure, said second explosion or injection establishing hydrostatic pressure within the cavity about the same time the volume of the cavity reaches its maximum volume, thereby substantially reducing the secondary pressure pulses.

Abstract: The novel method substantially reduces the pressure pulse, generated by a first radial motion of a body of water, by changing the radial motion into axial action. The change from radial motion into axial motion is produced by generating a second radial motion of opposite phase within the body of water.The method can be used to substantially reduce the pressure pulse, generated by the implosion of a body of water, by generating an explosion in the body of water. It can also substantially reduce the pressure pulse generated by an explosion within a body of water, by generating an implosion of the body of water. The method can further be used to generate within a body of water an impulsive acoustic signal by sequentially generating within the body of water a first explosion and a second explosion. The apparatus comprises a signal chamber which contains a first charge of gas. A normally-closed valve maintains the signal chamber closed and has a discharge port into the water.

Abstract: A water gun seismic source for use in underwater environments has a sleeve valve (100) for opening a jet aperture (37, 101) to enable jets of pressurized water to be emitted for the generation of a seismic signal. The water is pressurized by a drive piston (3) which is reciprocated to a cocked position for pressurizing the water for the jets. A compressed air operated cocking mechanism (4, 7, 8, 76 or 110-199 or 200-260) is coupled to the piston for cocking it. The cocking mechanism may utilize cocking piston (7) slideable on a shaft (4) connected to the drive piston (3) which cocking piston is returned to a position where any load due to such cocking piston is decoupled from the shaft. The sleeve valve (100) may be biased to close the jet aperture ports (101) by compressed air and opened with high timing resolution when the pressurized water held back by the sleeve valve is applied to actuate it (via 40, 41, 50 & 43).

Abstract: The invention is a method of shaping the spectrum of a seismic source signature. Energy is concentrated in the range below a selected frequency and attenuated in the range above the selected frequency by activating a plurality of sources asynchronously within a time window of selected duration. In a preferred embodiment, the frequency spectrum is smoothed by firing a second plurality of sources within a second time window having a time delay from the first time window equal to substantially the time between the initial firing of a source and the first positive zero-crossing of the signature.

Abstract: The novel method substantially reduces the pressure pulse generated by an implosion of a cavity within a body of water by aborting the implosion. The abortion of the implosion is produced by generating within the cavity an explosion at the instant that this cavity attains its maximum volume.The method can also be used to generate within a body of water an impulsive acoustic signal by generating a first explosion within the body of water to produce therein a powerful pressure pulse and a cavity of very low pressure, and then generating a second explosion within the cavity so as to establish hydrostatic pressure inside the cavity while the volume of the cavity remains within a few percent of its maximum volume.

Abstract: A method of providing a marine seismic signal comprising the steps of: arranging a plurality of seismic sources into a seismic array having at least two seismic subarrays with each subarray having a plurality of seismic sources, towing the seismic array behind a vessel and operating the plurality of seismic sources such that the seismic array satisfies a predetermined relation which is a function of the operating pressure, gun volume and towing depth of the respective seismic sources in the respective subarrays.

Abstract: Disclosed is an underwater seismic energy source which includes a plurality of airguns. Each of the airguns has substantially the same size, weight and external configuration, but the internal capacities are configured such that when the guns are fired the primary pulses interfere constructively and the bubble pulses interfere destructively. Each of the airguns is connected in the same way to an individual tow line, each having the same length. When the airguns are towed, they are maintain substantially the same depth, even without flotation devices such as Norwegian buoys or rigid floats.

Abstract: An acoustic energy source or gun for use in an aqueous environment such as in a borehole, a well, or in open water. The apparatus, when lowered into a water occupied borehole or the like, functions to create a series of acoustic impulses without forming bubbles, as a result of the water rapidly infilling an implosion cylinder or chamber. A piston rod assembly is reciprocally mounted in each acoustic chamber and is actuated by a power source to trigger the desired sound creating series of impulses.

Abstract: In the art of acoustic well sounding a gas-gun for the sudden discharge of a measured quantity of compressed gas, comprised of two chambers, viz. a discharge chamber closed at one end by a poppet, and on the opposite end by a power-head, the latter a cylinder including a sealed piston, with the poppet connected by sealed piston rod penetrating the cylinder head, and terminated at the piston. The entire assembly to be so proportioned that regardless of the position of the piston a gap remains between the piston and the cylinder-head penetrated by the piston rod. Means for connecting this gap to the inside of the discharge chamber through a check valve permits gas flow from the discharge chamber to the gap, but not in the reverse direction, and means for venting the gap to the atmosphere. A passage from the opposite side of the piston to the axial outlet of the discharge chamber, a spring or a positive locking device for pressing the poppet against the valve seat.

Abstract: Apparatus for forming a downwardly directed beam of acoustic wave energy in a body of water, comprising a source of acoustic wave energy such as a water gun, supported at a selected depth in the body of water. Means are provided above and around the source in the form of a series of concentric circular tubes of selected diameters and spacing so that the enveloping surface is a paraboloid. A large number of small perforations are spaced along these horizontal tubes through which compressed gas, which is supplied to the tubes, can escape and form spaced rising columns with small gas bubbles in the volume of water above the paraboloid. The highly reflecting contact surface between the water within the paraboloid and the gas-water mixture above the paraboloid causes downward reflection of seismic energy from the source in the form of plain waves of seismic energy.

Abstract: A seismic source drives one or more jets of high velocity water into an underwater environment and then terminates the jets by means of a valve member, the motion of which is controlled to obtain precisely timed high energy seismic pulses to provide reflected signals from which high resolution seismograms may be obtained when the signals are processed.

Abstract: A moving seismic source system for the use in water-covered areas comprising a conventional source and streamer cable means with multiple receiver, and additionally includes between the source and receivers a volume of the body of water containing a small percentage of free gas to form a gas-water mixture. The volume of gas-water mixture is of select size and shape to form an interface with the gas-free water to form, for example, a paraboloid which acts to reflect and attenuate acoustic waves that impinge on the interface and so minimizes extraneous seismic noise.