Abstract: The present invention relates to a system for acquisition and separation of the effects of simultaneous sources of electromagnetic field. According to the invention the system comprises an array of n pick-ups (1a . . . 1e) connected to registration means (2), the minimum number n of pick-ups per array being equal to 2s+2, where s is equal to a number of simultaneous sources to be analysed.

Abstract: A sound wave receiving device associated with a probe lowered into a well at the end of a cable and applied against the wall of the well by opening anchorage arms. In the part of the probe in contact with the wall of the well there is disposed at least one receiver assembly comprising a sensor case connected by a resilient sheath and a sleeve, movable along a cylinder integral with the body, to the rod of a piston sliding in said cylinder. A hydraulic and/or pneumatic system is provided for placing the case in contact with the wall and increasing the force of application of said case.

Abstract: In a method of locating and orienting a first direction linked to the position and to the orientation of an autonomous first mobile object (M), such as a ship towing a marine geophysical prospecting cable, and a second direction formed by a non-autonomous second mobile object (Bj), such as a buoy at the trailing end of the towed cable, and at least one reference point on the first mobile object relative to a fixed reference radionavigation system comprising at least two reference beacons (Si, Si+1) the first mobile object (M) and the second mobile object (Bj) are respectively provided with a first communication device (MI) providing communications between the first mobile object (M) and the reference beacons (Si, Si+1) and a second communication device (MJ) providing communications between the first mobile object (M) and the second mobile object (Bj). They are further provided with a communication device (BIJ) providing communications between each reference beacon (Si, Si+1) and the second mobile object (Bj).

Abstract: The invention relates to a method and apparatus for processing data from a seismic survey.In accordance with the invention, the data is regrouped to form a plurality of seismic images (A1, A2, A3, B1, B2, B3, C1, C2, C3). These images being defined by image elements defined in spatial position with respect to an operation direction (D) and having a grey level of predetermined amplitude, the method consisting for each pair of images (Ai,Bj) of carrying out processing by correlation of the amplitude of the grey levels, in order to establish an intercorrelation coefficient and to compensate the localization errors in the position of the images.Application to mono-, bi- or tri-dimensional marine geophysical prospecting.

Abstract: A suspended structure for coupling a seismic source to the walls of a borehole, in particular for underground prospecting purposes, the structure comprising top (14) and bottom (16) elongate plug elements having transverse dimensions substantially equal to the inside dimensions of the borehole (10), defining therebetween a substantially closed space (32), and suspension elements (30, 50) connecting the bottom plug element to the top plug element without isolating said space from the surrounding walls of the borehole, a seismic source (34) suitable for acting in said space, with the top and bottom plug elements opposing said action in the longitudinal direction of the borehole so that said action is applied essentially against the walls (10) of the borehole level with said space.Applicable to underground prospecting together with pick-up means.

Abstract: A system is provided for transmitting energy to an apparatus, such as a pulsed or vibratory seismic source, lowered inside a well or drill hole. It includes a structure anchorable in a well, mobile means whose linear displacement with respect to the anchorable structure causes the creation of energy and means for accumulating the energy created, a rigid column connected to said mobile means and drive means disposed outside the well for moving the rigid column linearly. The mobile means and the accumulation means may be formed by a weight and a device for raising this latter or else by a hydraulic system including a linear pump.

Abstract: The invention permits the measurement of the propagation anisotropy of a transverse wave between two given reference points of a non-isotropic medium (M), particularly a shear wave in a stratified or fissured rock.According to the invention: a source (S) and two detectors (G.sub.1, G.sub.2) are arranged along a single ray vector, the detectors being positioned at the location of respective reference points; the source is excited by an excitation signal producing a transverse wave in the medium; the respective resultant measurement signals produced by each of the detectors are received; from the excitation signal and the measurement signals the transfer function of the medium along each of the respective source-detector paths is determined; the differential transfer function of the medium between the two reference points is deduced.

Abstract: To help a user program a computer target system to solve problems, the computer system is provided with predefined capabilities and the user is provided with a knowledge system that includes knowledge about applying the capabilities to effectively and efficiently solve the user's problems. The knowledge system provides automatic programming for solving problems within a particular domain, rejects problems that cannot be solved using the available capabilities of the target computer, and explains how and why a certain program was generated or why a program cannot be generated to solve a given problem.

Abstract: A device is provided, associated with a computer, for controlling data transfers between a data acquisition device and a recorder-reader. The device comprises logic gates for the selective connection of said acquisition device with said recorder and an intermediary memory of sufficient capacity for at least one series of signals issued from the computer. The device is adapted to supply said signals to the control inputs of said logic gates.

Abstract: A device for determining the position in the water of an elongate element (a seismic streamer for example) towed while submerged, by means of measuring elements such as compasses and pressure gauges spaced apart along said elongate element. Said compasses and pressure gauges are disposed inside profiled bodies firmly secured to sleeves fixed about said elongate element and transmit the measurements, by means of a hertzian wave transmission assembly, to a sensor inside the elongate element, which is connected by a transmission cable to a reception assembly connected to a central unit installed in the towing ship.

Abstract: In a method and device for the study of surface layers and subjacent layers of interest, the device comprises receivers and at least two transmission sources spaced at a distance such that a set of traces produced by one of the transmission sources does not interfere with a set of traces produced by the other transmission source when the two sets of traces are on the same time-section.

Abstract: A device for supplying electric power to electronic apparatuses of a seismic streamer of great length, comprises an electric feeding assembly associated with each electronic apparatus and including three voltage transformers whose primary windings are respectively fed from a generator with a different phase of a three-phase current, and whose secondary windings are respectively connected to three rectifier bridges supplying the required DC voltage to the electronic apparatus.

Abstract: A mixed device for successively generating in the earth, at the same location, longitudinal and shear waves is disclosed. The device comprises in association a target coupled to the earth surface and having a first striking face substantially parallel thereto and at least one second striking face substantially perpendicular to said first striking face. A guide tube is adapted to be positioned above the first striking face and perpendicularly thereto, and a movable weight is slidable in the guide tube and adapted to strike the first striking face. At least one hammer is articulated to a support rigidly secured to the guide tube and adapted to strike one second striking face of the target. Directional coupling means connect the guide tube to the target in such a manner that the weight sliding in the guide tube directly impinges the first striking face, but such that the guide tube is substantially released from the effect of the hammer impact on a second striking face.

Abstract: In a method of geophysical prospection a transmitter dipole and a receiver dipole which is sensitive to an electromagnetic field are positioned in cooperation with the subsoil. An impulsive excitation current is applied repeatedly to the transmitter dipole, the excitation current comprising a group of pulses of alternate polarity, each followed by zero current. The transient signal, which is produced thereby at the output of the receiver dipole, is repeatedly detected, and the transient signals are processed to obtain a figurative representation of the transient phenomenon which facilitates geophysical interpretation. Time intervals which are consecutive to excitation pulses and simultaneously with the excitation zero current are defined, these time intervals being of a predetermined duration, chosen to substantially cover all the useful parts of the transient phenomenon.

Abstract: A device is provided for interconnecting a series of data acquisition apparatuses. Each of the apparatuses collect signals and transmit them to a remote central receiving and recording system. In order to sequentially transmit the signals thereto on reception of an order from said central system, the apparatuses are subdivided into a plurality of groups having the same number m of apparatuses. The groups comprise cable sections of substantially equal length interconnecting the acquisition apparatuses in such a manner that the apparatuses of the same rank of each group are connected in parallel by the same transmission cable to the central system.

Abstract: The present invention relates to a method for initiating an underwater implosive seismic source which comprises the steps of: measuring the instantaneous pressure at the location of the source; determining, from this measured pressure, the bubble period separating the firing signal from the implosion peak of the shock wave; and initiating the source with a delay or advance of a value equal to the difference between the bubble period corresponding to the instantaneous pressure and that corresponding to the mean pressure. The invention also provides a device for carrying out this method which device comprises; means for measuring the instantaneous pressure in the neighborhood of the source; comparator means (C5) for comparing this pressure with a mean value; and time delay means (C3, C4) for delaying a firing signal (S1) by a value which is a function of the result of this comparison.

Abstract: Water inflow inside a seismic streamer may create parasitic electric connections between lines supplying current to the electronic devices of the streamer and lines transmitting seismic informations, thus damaging the electronic apparatus and making these informations inaccurate. In accordance with the invention streamer sections including sections of supply lines and transmission lines are provided with water inflow detection assemblies, each comprising a closed circuit element surrounding the supply lines, a conducting line connected to a DC voltage generator, and means for detecting any DC voltage therebetween resulting from parasitic connections between the supply lines and the closed circuit element, created by a water inflow.

Abstract: A device for preventing secondary impacts of a mass against a target member, as used in particular for generating shear waves in the earth, is provided. The mass is secured at the end of a pivotable rigid arm actuated by driving device, and the driving device adapted to block the fall of the rigid arms, comprises a cam co-operating with a pawl when it registers therewith and with a flat part of the cam with the registering conditions occurring only after the first impact of the mass and its bounce against the target member.

Abstract: An amplification and sampling device for multiplexed analog signals comprises a continuous chain of amplification elements, means for giving to each of said elements a gain selected from a predetermined set of values, sample-and-hold units for memorizing the amplified voltages available at the output of said elements, means for correcting the drift or noise voltage of the amplification chain and selection means for applying to the amplification chain the samples of the multiplexed analog signals or the voltages memorized in the sample-and-hold units, in accordance with the voltage level obtained at the output of the amplification chain as compared with reference voltages.

Abstract: In a method of geophysical prospection a transmitter dipole and a receiver dipole which is sensitive to an electromagnetic field are positioned in cooperation with the subsoil. An impulsive excitation current is applied repeatedly to the transmitter dipole, the excitation current comprising a group of pulses of alternate polarity, each followed by zero current. The transient signal, which is produced thereby at the output of the receiver dipole, is repeatedly detected, and the transient signals are processed to obtain a figurative representation of the transient phenomenon which facilitates geophysical interpretation. Time intervals which are consecutive to excitation pulses and simultaneously with the excitation zero current are defined, these time intervals being of a predetermined duration, chosen to substantially cover all the useful parts of the transient phenomenon.