Marine seismic system

Abstract

swinging the ship. The system includes a spectrum analyzer and a spectrograph, but it contains nothing that is not known in military sonar systems.--LB 4,509,152 43.30.Yj CHANNEL FORMATION SYSTEM FOR PANORAMIC SONARS Andr• Buhart, assignor to Thomson-CSF 2 April 1985 (Class 367/123); filed in France 7 August 1981With a circular array of hydrophones, this system forms receiving beams in equally spaced directions. Usually it forms twice as many beams as there are hydrophones in the circle. Any given beam contains the signals from all the hydrophones within a 135 ø arc of the array. Shift registers made up of charge-coupled devices provide the time delays that correspond to the displacements of those hydrophones from the chord that subtends that arc. The hydrophone signals are sampled, preferably in analog form, and fed successively to the shift registers by a multiplexer. They are fed in a sequence that causes the resulting beams to step progressively in azimuth.--LB sheet beams, each of which is directed to a separate acousto-optic medium, one rotated 90 ø relative to the other. One beam is doubly diffracted by a pair of signals applied to a surface acoustic wave device (SAW) and the other beam is doubly or singly diffracted by a second SAW device on which two or one signals are applied so that when the diffracted sheet beams are reformed and combined into a detector, the detector outputs the four-or three-product correlated signal.--JWD 4,520,467 43.40.Ph MARINE SEISMIC SYSTEM Albert J. Berni, assignor to Shell Oil Company 28 May 1985 (Class 367/24); filed 18 March 1982 In a conventional marine seismic system the recorded signals contain those reflected from the air-water interface as well as those from the substrate. This patent describes a method for effectively eliminating the reflections from the air-water interface in the recorded data. The method modities amplitude and phase angles of the signals from both pressure and motion sensors in the seismic streamer in such a manner that, when combined, the result is essentially reflection-free, with substantial improvement in signal-to-noise ratio over the seismic band.--SAC 4,510,586 43.30.Yj ARRAY SYSTEM WITH HIGH RESOLVING POWER Georges Grail, Jacques Joseph, and Claude Lemoine, assignors to Thomson-CSF 9 April 1985 (Class 367/87); filed in France 8 January 1982 This line array contains two projectors and many hydrophones for an active sonar. The directional pattern of the projector pair has several lobes of equal amplitude, one of which lies in the direction of the comparatively broad mainlobe of the receiving pattern. Consequently, the width of the overall pattern is determined largely by the transmitting pattern, even though the space between projectors is less than the length of the hydrophone array. The patent covers ratios of projector spacing to array length, which are chosen to yield the best compromises between beamwidth and sidelobe level in the overall pattern. The choice depends on the weighting function that is used for the hydrophone array.--LB 4,5...

Theoretical study on multi‐level source design

“…The three main methods in use are: dual/multi-sensor OBC/OBN (Ocean Bottom Cable/Node) or towed streamer; over-under streamers and slanted/multilevel streamers. The dual/multi-sensor technique takes advantage of the polarity difference between the hydrophone and the velocity sensor and has been widely used (Berni 1985;Barr and Sanders 1989;Barr 1997;Carlson et al 2007;Tenghamn et al 2007;Long et al 2008;Cambois et al 2009a;Goujon et al 2012). Wave-field separation is applied in the over-under method to separate the up-going and down-going (ghost) wavefield.…”

Joint hydrophone and accelerometer receiver deghosting using sparse Tau-P inversion

“…The interference between up-going and down-going wavefields limits the effective bandwidth of the seismic data. Research studies have been performed to use the pressure data ) (P and the particle velocity ) ( z V to remove the receiver ghost (e.g., Berni, 1984;Ruehle, 1984;Robertsson et al, 2001;Carlson et al, 2007). Unlike the pressure data recorded by hydrophones, the particle velocity is measured by geophones that bear the vertical direction (up or down) of the wave propagation.…”

Fidelity and repeatability of wave fields reconstructed from multicomponent streamer data

“…We emphasize that these quantities are derived from the measured components of acceleration. One motivation for recording pressure and the vertical acceleration is to remove the downgoing ghost wave field, reflected at the sea surface, by making use of the complementary ghost responses of the two measurements (Berni ; Robertsson, Kragh and Martin ). Combining data from the two sensors extends the usable seismic bandwidth, improving the acquisition of both low‐frequency, deeply penetrating signal and high‐frequency signal, important for shallow structural resolution.…”