Ex. PGS 1005
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`Uite Mates atent
`
`.,
`
`[72] inventor
`
`Ronald M. Hedberg
`18 Whittier St., Cambridge, Mass. 02140
`No‘ 375511: 1969
`[2]]
`l e
`0v‘
`’
`[22]
`[45] Patented May 25, 1971
`Continuation of application Ser. No.
`645,643,.lune 13, 1967.
`
`[541 MARINE SEISMIC EXPLORATION
`13 claims’ 13 Drawing Figs_
`
`U.S. ...................................................... ..
`114/237, 181/0‘5VM, 340/15-5MC
`
`[111 3,58 1 ,273
`
`6/1967 Ballard ....................... ..
`3,325,778
`3,331,050 7/1967 Kilmer et al. ............... ..
`Primary Examiner-Richard A. Farley
`Assistant Examiner—Daniel C. Kaufman
`Anomey__spen_y and Zoda
`
`340/7
`340/7
`
`v
`
`‘
`
`ABSTRACT: Continuous marine seismic explorations are car
`ried out by providing echo detecting means with control
`means fonmaintaining the echo detecting‘means in ?xed or
`predetermined positions and at spaced points in two dimen
`mom of a horizontal plane, and by generating echo producing
`impulses at one or more Spaced points located in fixed or
`predetermined relative positions with respect to each other
`
`[5 l]
`
`56
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`
`and in Said p]ane_ In [his way’ a Set of records may be obtained
`lllt.
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`. . . . . . . . . . . . . . . . . .._. ................. .. G01‘!
`define the Seismic interfaces of the prospect under sul'.
`Fleld Of Search .......................................... ..
`MRC; 114/237; 181/5 VM vey in two intersecting vertical planes. Thereafter, by produc
`C, ed
`ing successive sets of such records, quadratic surfaces in
`R f
`e erences It
`which the true inclinations of interfaces may be determined
`UNITED STATES PATENTS
`over an extended area are obtained in a single traverse
`Re25,204 7/1962 Becker . . . . . . .
`. . . ..
`thereof. At the same time, the accuracy of the records ob
`3,019,412
`1/1962 Crawford ................... ..
`tained is materially increased.
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`mined points spaced apart in two directions to provide a cross spread" within a horizontal plane. For this purpose the
`
`equipment used preferably also includes means for maintain
`ing the impulse generating and echo receiving means in such
`fixed or predetermined relative positions during survey as to
`' assure the accuracy of the records produced, and may it‘
`desired embody means for controlling the record producing
`means so as to compensate for any dislocation or deviation of
`the impulse generating and echo producing means from such
`predetermined positions.
`Accordingly, it is possible to generate a set of echo produc
`ing impulses from which accurate records may be obtained by
`energizing one or more impulse sources located at the desired
`and predetermined points which may be spaced with respect
`to each other in two directions in a horizontal plane above the
`area under survey. When such sources are energized succes
`sively and in such a manner as to permit a separate record of
`the echo or re?ected waves derived from each of the spaced
`20
`impulse sources to be produced, or to permit resolution of the
`reflections from a single impulse source into two distinct
`nearly vertical planes containing the points of re?ection, so
`that these planes are oriented at a substantial angle to each
`other, or so that these planes are widely spaced, it is then
`possible to survey the area with greatly increased speed and
`accuracy. Thus, each record of the set of echoes obtained
`froni multiple sources will indicate the profile of the area and
`strata under survey in a substantially vertical plane passing
`through the echo producing strata. Because the separation of
`the l'e?ection points is sufficient to permit resolution of the
`positions of seismic horizons outside the plane of traverse of
`the survey ship, the true inclination of re?ecting strata may be
`determined. Repeated sets of such records obtained by re
`peated operations carried out in a single traverse of the area
`under survey will thus serve to indicate the structural configu
`ration of the entire area with greater accuracy than has been
`possible heretofore.
`The equipment employed in accordance with the present in
`vention further serves to coordinate the individual records of
`each set of impulses whereby the nature of the structure in
`dicated by any set of impulses can be quickly and easily deter
`mined.
`
`30
`
`35
`
`40
`
`25
`
`1
`MARINE SEISMIC EXPLORATION
`
`RELATED APPLICATION
`
`This application is a continuation of copending application
`Ser. No. 645,643, ?led June 13, 1967.
`Preferred equipment used for obtaining such records in
`cludes steerable means such as paravanes for maintaining the
`impulse generating devices and echo responsive elements in
`known or predetermined relative positions when producing
`the successive sets of records. Furthermore, when inscribing
`such records, the individual records of each set may be
`brought into registry with each other so as to facilitate correla
`tion and interpretation of the records obtained.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of Invention
`This invention relates to methods and means for use in
`marine seismic exploration and is directed particularly to
`systems and equipment whereby records may be obtained to
`indicate the pro?le of the area under survey as a series of sub
`stantially vertical orthogonal sections proceeding in the
`direction in which said area is traversed.
`2. Description of the Prior Art
`It has been common practice heretofore to carry out marine
`seismic surveys by employing a number of hydrophones that
`are connected by electrical conductors to recording equip
`ment, and are towed behind a boat moving over the area to be
`surveyed. The hydrophones are thereby stretched out in a
`straight line or “spread," after which an echo producing im
`pulse, such as an explosive blast, spark or the like, is generated
`at a point along or beside the spread of hydrophones. The
`resulting echoesfrom the surface ahd underlying strata are
`recorded to indicate the pro?le and/or character of the area
`being surveyed.
`Such systems serve to produce a record which indicates the
`pro?le of the strata in a single, substantially vertical plane
`beneath the “spread" and it is therefore necessary to traverse
`the area under survey repeatedly in order to obtain a complete
`record of thearea and a clear indication of the various slopes,
`inclinations, and contours of the bottom and underlying strata
`in the area. Even then the records obtained are frequently
`limited and inaccurate and .present dif?cult problems in the
`coordination and reconciling thereof. Typical methods and
`equipment heretofore suggested for use in marine seismic sur
`veying are those shown and described in the following U. S.
`Pats:
`'
`Paslay 2,456,696
`'
`Paslay et al.
`2,729,300
`Hersey et al.
`3,065,815
`Loper et al.' 3,124,781
`Strange 3,133,262
`
`45
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`FliG. I is a diagrammatic top plan view of one arrangement
`of impulse producing and echo receiving means embodying
`the present invention;
`FIG. 2 is a block diagram illustrating the manner in which
`the equipment of FIG. I is employed;
`F1tG.3 is a plan view of the block illustrated in FIG. 2;
`FIG. 4 is a diagrammatic illustration of recording equipment
`adapted for use in accordance with the present invention;
`FIG. 5 is a view similar to FIG. 4 illustrating a further step in
`the [recording of impulses in accordance with the present in
`vention;
`E6. 6 is a plan view illustrating an alternative arrangement
`of the impulse producing and echo receiving means which
`may be employed in the practice of the present invention;
`FiG. 7 is a block diagram similar to FIG. 2 indicating the
`mariner in which the equipment of FIG. 6 operates;
`FIG. 8 is a diagrammatic plan view of a further alternative
`arrahgement of elements embodying the present invention;
`FIG. 9 is a diagrammatic illustration of a condition which
`maybe encountered in the prior art;
`FIG. 10 is a plan view of a part of the equipment of the
`present invention;
`FIGS. 11 and 12 are side views of alternative embodiments
`of tiiat part of the equipment shown in FIG. 10; and
`FIG. 13 is a diagrammatic illustration of one type of control
`system which may be employed in the practice of the present
`Invention.
`
`Roever 3,189,870
`.
`'
`In some instances “cross-spread" arrangements of impulse
`generating means and geophones have been used in seismic
`prospecting on land. However, cross spreads in marine areas
`have not heretofore been practical because of the problems of
`handing a main cable of the requisite length, and because of
`the transverse spread required to obtain meaningful results;
`the problems of deploying such an array and the problems of
`adapting cross spreads to a “continuous pro?ling” operation.
`Frequent displacement of the elements in marine areas with
`respect to each other during the survey and under the in
`?uence of ocean currents, tides, wave motion and other
`forces, as well as the surveying problems of knowing the exact
`location of an intersection of individual pro?les, have com
`pounded the above problems.
`
`55
`
`65
`
`SUMMARY OF THE INVENTION
`In accordance with the present invention, improved and
`more complete records indicating the structural con?guration
`in three dimensional space of an area under marine survey are
`obtained rapidly and accurately by locating and maintaining
`the hydrophones or other echo responsive means at predeter
`
`70
`
`75
`
`Ex. PGS 1005
`
`

`
`3
`DESCRIPTION OF THE PREFERRED EMBODIMENT
`
`3,581,273
`
`10
`
`25
`
`In that form of the invention chosen for purposes of illustra
`tion in FIGS. 1 to 5 and 13 of the drawings, the surveying
`equipment is moved continuously over an area to be surveyed
`by means of a boat or other towing means 2 from which a “~
`spread" 4 of hydrophones or other echo responsiveelements 6
`extend rearwardly in a straight line. The hydrophones 6 may
`be of any suitable or preferred type and the spread 4 may be of
`a usual form including from, say, 96 to I20 hydrophones per
`group and comprised of several groups that are connected by
`electrical conductors in cable 10 to a recording equipment 12,
`carried by the boat 2.
`In accordance with the present invention, at least one, and
`preferably two, additional cables 14 and 16 are towed by the
`boat 2 and as shown in FIG. 1, these cables are caused to
`spread outward at opposite sides of cable 10 by means of
`paravanes 18a and 18c respectively. In a similar way, a
`paravane 18b may be connected to the cable 10 of the spread '
`4. Each paravane is provided with rudders or other steerable
`means which are operable to maintain the paravanes in sub
`stantially ?xed, or predetermined positions with respect to the
`other paravanes of the assembly. The paravanes 18a, 18b, and
`18c may thus be located and controlled so as to take up posi
`tions which may be a quarter mile or more apart and posi
`tioned so as to de?ne a line 22 extending transversely, and
`preferably at right angles, to the cable 10 and at right angles to
`the direction of transverse of the assembly over the area under
`survey.
`Each of the paravanes 18a, 18b and 180 may be con
`structed, as shown diagrammatically in FIG. 13, so as to posi
`tion, or be provided with, an echo responsive element,
`designated 6, and also to position or be provided with an im
`pulse generating device, designated at 24. For purposes of il
`lustration and discussion it is hereafter indicated that each
`paravane 18a, 18b and 180 has an echo responsive element 6
`and an impulse generating device 24 carried thereby. The im
`pulse generating devices may be of any suitable or preferred
`type such as a gun for exploding gas or other combustible
`charges, or a device for producing an electric are, or striking
`an anvil and if-desired, the impulse generating device may be
`allowed to drift along its cable to the paravane thereon to
`cause it to be actuated. However, for niost purposes, it is
`preferable to actuate the impulse generating devices and to
`receive the re?ected or echo responses by means of electrical
`connections through cables 10, 14 and 16. In any event, the
`present invention employs an arrangement wherein the echo
`responsive elements are located at fixed or predetermined
`points spaced apart in two directions within a substantially
`horizontal plane above the area under survey whereas the im
`pulse generating devices are located at one or more spaced
`and predetermined points with respect to at least some of the
`echo responsive elements to establish an effective “cross
`spread" arrangement of the elements which may be moved
`continuously over the area under survey in carrying out the
`survey.
`As shown by way of illustration in FIGS. 1, 2 and 3, the
`equipment may be'towed along a survey line 26 by a boat 2
`?oating on the surface 28 of the ocean or other body of water.
`For simplicity of presentation, the area under survey is
`represented as overlying a single seismic interface 30 includ
`ing an upthrown block 32, a transverse fault plane 34, and a
`downthrown block 36, all of which are located some distance
`below the ocean ?oor 20. The spread of echo responsive ele
`ments 6 on cable 10 extend in a straight line behind the boat 2
`and are held on the survey line 26 by the paravane 18b,
`whereas cables 14 and 16 are caused to spread out laterally
`from the cable 10 by the paravanes 18a and 18c until they are
`spaced apart a distance of, say one-quarter to one-half mile, or
`sufficient to permit separate recording of echoes from points
`in the area under survey which are spaced apart transversely
`of the line of transverse without confusion or suppression of
`such echoes in the records produced. When the cables and
`
`4
`.
`paravanes, with their impulse generating devices and echo
`responsive elements are thus deployed, the imptilse' generating
`devices are ?red in a predetermined manner to 'obtain a set of
`records from the echo responsive means.
`In a typical operation, the impulse generating devices 24 as
`sociated with the paravanes 18a, 18b and 18c may be actuated
`one after the other in a known sequence with a delay between
`the shots as the spread is moved over the area under survey.
`The delay between successive impulses need only be about I
`to 10 seconds or suf?cient to prevent confusion in the records
`as to which generating devices 24 produce a given trace on the
`recording equipment 12. This is effected through the coor
`dination of the ?ring circuit control device 13 and the record
`ing equipment 12. Thus, the device 24 associated with the
`paravane 1817 located on or adjacent cable 10 may be
`detonated or otherwise actuated to produce elastic waves that
`spread downward and outward in all directions. The waves
`represented by the limiting rays’40 and 42 are re?ected from
`the points 40a and 42a on the seismic interface and are
`received as echoes by the hydrophones 6x and 6y respectively
`on cable 10. In this way a record is caused to be produced in
`the conventional manner of the prior art upon an instrument
`44 of the recording equipment 12.
`At the same time, the vertical ray 46 will be re?ected from
`the point 46a on the interface and may be received by the
`echo responsive element 6 which is on or adjacent the
`paravane 18b, The latter echo responsive element is con~
`nected to instrument 44 and additionally to an instrument 48
`of the recording equipment 12 by a switch 50 and thereby
`serves to produce the central trace 52 on the record of instru
`ment 48 as shown in FIG. 4. In a like manner and at the same
`time, the inclined rays 54 and 56 generated by the device 24
`associated with the paravane 18b will be re?ected from the
`points 54a and 56a on the seismic interface to the echo
`responsive elements 6 associated with the paravanes 18a and
`180 respectively. The dominant echoes thus re?ected will
`serve to produce the two traces 58 and 60 on the record of in
`strument 48 as shown‘ in FIG. 4. “Normal move'out cor
`rections” for the slant ray path are applied later in the data
`processing phase. When the dominant re?ections of the elastic
`waves thus generated by the device 24 of paravane 18b have
`attenuated sufficiently, switch 50 of instrument 48 is opened
`and switch 62 is closed. Shots are then ?red by the impulse
`generating devices 24 associated with the paravanes 18a and
`18c respectively and the rays 64 and 66 re?ected vertically
`from the points 64a and 660 on the interface serve to actuate
`the echo responsive elements 6 associated with paravanes 18a
`and 18c to cause the additional traces 68 and 70 to be
`recorded by the instrument 48 as shown in FIG. 5. Further
`more, if the paravanes 18a and 180 are so closely spaced with
`respect to the desired depth of penetration as to interfere with
`each other, it is then desirable to ?re and receive re?ections
`from paravane 18a, with suf?cient time for attenuation before
`?ring at paravane 180. In any event, the operations of the ?r
`ing and recording equipment are so synchronized that the shot
`instants recorded by the traces 52, 58 and 60 first produced on
`the instrument 48 are caused to register with the traces 68 and
`70 provided on said instrument by subsequent shots. In this
`way the successive traces are brought into parallelism so as to
`simplify the relating of the various traces with respect to each
`other.
`When such a set of tracings is completed, the switch 62 is
`opened and switch 50 is again closed whereby the equipment
`is restored to its original condition for repeating the cycle of
`operations. The cycle is repeated at predetermined intervals
`or as often as desired while the boat 2 and the assembly of im
`pulse generating and responding means travel along the survey
`line 26 as shown in FIGS. 2 and 3. Each record produced as
`described above and as shown in FIG. 5, serves to indicate the
`pro?le and nature of the seismic interface taken on a substan
`tially vertical orthogonal plane passing through the line 22 at
`right angles to the survey line 26 along which the assembly is
`towed. The successive records obtained by repeating the cycle
`
`35
`
`40
`
`45
`
`55
`
`65
`
`75
`
`Ex. PGS 1005
`
`

`
`3,581,273
`
`20
`
`25
`
`30
`
`35
`
`40
`
`5
`of operations correspond to successive vertical sections taken
`on the line 22a, 22b, 220, etc. of FIG. 3 and will be spaced
`apart distances lengthwise of survey line 26 which are depen
`dent upon the speed of travel of the boat 2 and its array of
`sound generating devices and echo responsive elements and
`the frequency at which the successive cycles are initiated. At
`the same time, the recording instrument 44 serves to produce
`a record of the pro?le of the seismic interface as represented
`by a vertical plane passing through the cable 10 of the conven
`tional hydrophone spread 4. As a result, the two records ob
`tained indicate pro?les at right angles to each other and afford
`much more complete information which, in turn, permits
`more accurate interpretation regarding the seismic interface
`than has been possible of attainment heretofore. Thus the data
`so obtained permits determination of true inclinations of the
`seismic interface and the azimuth of linear features.
`Moreover, all this information is obtained by a ‘single traverse
`of the area under survey whereby much less time is required
`for completing the survey of any desired plot or zone under in
`vestigation.
`The systematic and coordinated operation of the equipment
`described above may be attained by the use of any suitable or
`preferred control mechanism, such as that set forth in US.
`Pat. No. 3,065,815 for example. Further, although the equip
`ment shown and described herein employs analog recording
`on paper, it is well known in the art to employ other recording
`means and methods such as magnetic tape or the like adapted
`for use in conventional data processing systems.
`The method of determining and recording the character ofa
`seismic interface may be varied if desired. Thus, for example,
`after recording the dominant re?ections resulting from a shot
`or impulse generated at 18b, the cable 10 can be connected to
`a different recorder and a single shot or “broadside”
`generated at 18a. The data obtained and recorded as received
`from the hydrophones of the spread 4 and cable 10 can then
`be electronically processed to give stacked continuous pro?le
`representative of a plane passing nearly vertically through the
`line 72 from which elastic waves from the source 18a are
`re?ected to the hydrophones 6 on cable 10.
`In a similar way, elastic waves may be generated at 18c and
`re?ected to the hydrophones on cable 10 to obtain a record
`representing the seismic interface in a vertical plane passing
`through the line of re?ections 74 of waves passing to the cable
`10. It will thus be apparent that the equipment disclosed in
`FIGS. 1 to 5 is capable of being used in various ways.
`It is also possible to present the echo responsive elements in
`various arrangements extending in two directions within a
`horizontal plane above the surface of the area under survey.
`Thus as shown in FIGS. 6 and 7, the boat 2 may be used to tow
`a longitudinal spread 4 of hydrophones 6 secured to a cable
`I0. A cross or transverse spread may then be used and em
`body a cable 80,having hydrophones 82 carried thereby. The
`cross spread is preferably maintained in a position at right an
`gles to the longitudinal spread 4 by paravanes 81a and 81c and ,
`if desired intermediate connectors 86 may be employed. The
`cable 80 of the cross spread is connected to the recording
`equipment on the boat 2 by electrical cables 84.
`When using the arrangement shown in vFIG. 6, a single im
`pulsegenerating device 88 may be used and as shown in FIG.
`7, the impulse generator may be located at the intersection of
`the two spreads 4 and 80 or at any other point spaced horizon
`tally from multiple points on the two cable spreads. The elastic
`waves generated at 88 travel downwardly and outwardly and
`are represented by their limiting recordable ray paths, 83, 85,
`87 and 89. The rays are re?ected from seismic interface 30 at
`points 830, 85a, 87a and 89a and detected by the hydrophones
`at the distal ends of seismic cables 4 and 80. Elastic waves
`re?ected at the intersection of nearly vertical planes through
`seismic cables 4 and 80 with the seismic interface 30 and con
`tained within the points 83a, 85a, 87a and 89a are detected by
`hydrophones 6 and 82. Data obtained from cables 4 and 80 is
`transcribed by conventional means on separate recorders and
`the cycle is repeated with the generation of another impulse at
`
`6
`88v when the re?ected energy is suf?ciently attenuated or
`when the survey ship has proceeded along its traverse a
`desired distance. Thus it is possible to carry out repeated cy
`cles to obtain records of the re?ected impulses representing a
`plurality in intersecting vertical planes, thereby de?ning the
`true inclination of the seismic interface of the area under sur
`vey, whereas it has heretofore only been possible to determine
`the apparent inclination in two dimensions while making a sin
`gle traverse.
`In a like manner, other two dimensional arrangements of
`sensing elements within a horizontal plane can be provided by
`the use of multiple spreads connected to recording instru
`ments for developing three dimensional records of the pro?les
`of areas under survey. As shown in FIG. 8, such spreads may
`be arranged in three parallel lines extending parallel to the
`direction of transverse of the area under survey, and the three
`records which are obtained can be utilized to establish a three
`dimensional pro?le or the seismic interface of the area under
`survey.
`In any of the various forms and arrangements employed in
`the practice of the present invention, it is desirable to establish
`and maintain the impulse generating means and the sensing or
`echo responsive means in ?xed and predetermined relative
`positions during the recording operations. This may be
`achieved to the extent heretofore accomplished in conven
`tional seismic surveys by the use of conventional paravanes.
`However, as shown in FIG. 9, the use ofa conventional spread
`of hydrophones, located in a single dimension of a horizontal
`plane, is subject to error due to the set and drift or displace
`ment of the spread by marine currents at the successive times
`when shots or impulses are generated for recording purposes.
`In accordance with a preferred embodiment of the present
`invention it is possible to overcome the foregoing source of
`‘error and to compensate for any deviations of the paravanes,
`elements or devices from predetermined positions. Thus, as
`shown in FIGS. 10, 11 and 12, the cable 90 by which any por
`tion of the arrangement of impulse generating and echo
`sensing means is supported may be provided with one or more
`paravanes 92 located at suitable points in the assembly. These
`paravanes are provided with rudders and elevators or other
`steerable means, diagrammatically indicated at 94 in FIG. ll,
`12 and 13. In addition, the paravanes are provided with radar
`re?ectors or the like 96 by which the position of the paravane,
`and the various elements or devices connected thereto, can be
`established and maintained. For this purpose, as represented
`in FIG. 13, a radar control means 98 carried by the towing
`ship is arranged to respond to signals re?ected from the radar
`re?ector 96 on the paravane. The responses thus obtained are
`utilized as correction factors and are transmitted to a steering
`motor 100 through cable 102 to actuate the steering motor
`100. In this way, the various paravanes may be controlled to
`maintain them in predetermined and accurate positions with
`respect to each other. The seismic means are thereby held in
`such consistent and related positions during traverse of the
`area under survey that the records obtained will be capable of
`ready and accurate correlation and interpretation.
`The mechanical and electrical devices employed in the
`paravane control equipment illustrated in FIG. I3 may be of
`any conventional type known in the industry and exempli?ed
`by those shown and described in US. Pat. Nos. 2,960,960;
`2,997,689 and 3,125,980. In a similar way, the recording in
`struments represented in FIGS. 4 and 5 may be any of those
`known and conventional types now employed or acceptable in
`the art of seismic recording and surveying equipment.
`It will thus be apparent that the various elements and com
`binations employed in the practice of the present invention
`are capable of many variations and changes in the application
`thereof. For example, the present invention may be used in ac~
`curately charting the ocean ?oor or for locating submerged
`bodies. In view thereof, it should be understood that the par—
`ticular embodiments of the invention shown in the drawings
`and described above are ‘intended to be illustrative only and
`are not intended to limit the scope of the invention.
`Iclaim:
`
`45
`
`50
`
`55
`
`60
`
`65
`
`70
`
`75
`
`Ex. PGS 1005
`
`

`
`3,581,273
`
`20
`
`8
`means responsive to deviation of said position indicating
`means from said predetermined position are connected to said
`actuating means to correct such deviation.
`8. Equipment as de?ned in claim 6 wherein said vehicle
`means include paravanes having rudders and provided with
`signal reflectors connected thereto, a source of signal impul
`ses, and rudder actuating means responsive to deviation of
`said signal reflectors from predetermined positions with
`respect to said source of signal impulses to correct such devia
`tion.
`9. Equipment as defined in claim 1 wherein a plurality of
`spaced impulse generating devices are provided, and means
`are employed for successively actuating the same.
`10. Equipment as de?ned in claim 9 wherein means'are pro
`vided for actuating said impulse generating devices succes
`15
`sively to produce a separate record of the impulses received
`by said echo responsive elements from each of said impulse
`generating devices.
`11. Equipment as de?ned in claim 10 wherein means are
`provided for successively producing sets of records, each of
`which sets includes a record of of the echoes received by said
`echo responsive elements following the generation of an im
`pulse by each of said impulse generating device.
`12. A method for conducting marine seismic exploration
`comprising the steps:
`providing a plurality of echo responsive elements;
`arranging the echo responsive elements into a horizontally
`extending array, with the elements disposed in predeter
`mined space relationship with respect to each other in
`two directions within the horizontal plane;
`towing the array of echo responsive elements over a surface
`to be explored by means of a vessel;
`maintaining the predetermined space relationship of the
`echo responsive elements by vehicle means; and
`maneuvering the.vehicle means to correct any deviations of
`the positions of the echo responsive elements of the
`predetermined spaced relationship thereof.
`13. The method as de?ned in claim 12 wherein a plurality of
`impulse generating'rneans are employed and are actuated at
`successive intervals to produce a set of records indicating the
`characteristics of the area under survey in an orthogonal plane
`substantially normal to the predetermined direction of move
`ment over said area.
`
`7
`1. Equipment for use in marine seismic surveying, including
`a plurality of echo responsive elements; a vessel for towing
`said echo responsive elements; vehicle means associated with
`said echo responsive elements to maintain said echo respon
`sive elements in a predetermined array, wherein said elements
`are spaced apart in two directions in a generally horizontal
`plane; said vehicle means operable to correct the positions of
`said echo responsive elements in response to signals trans
`mitted between said vessel and said vehicle means; at least one
`impulse generating device located in a predetermined position
`with respect to said array and spaced apart in two directions
`from at least a portion of said echo responsive elements; and
`means for separately recording the echoes of each impulse
`generated by said device and received by said echo responsive
`elements as the separately resolved dominant re?ections from
`points located in two distinct planes disposed at an angle to
`each other and positioned substantially vertically with respect
`to said horizontal plane.
`2. Equipment as 'de?ned in claim 1 wherein said echo
`responsive elements are arranged in at least two substantially
`straight lines in said common horizontal plane.
`3. Equipment as de?ned in claim I wherein said echo
`responsive elements are arranged in two straight lines extend
`ing substantially at right angles to each other in said common
`horizontal plane.
`4. Equipment as de?ned in claim 1 wherein said echo
`responsive means are located in at least two parallel rows ex
`tending longitudinally of the direction of traverse of the area
`under survey.
`5. Equipment as de?ned in claim 1, wherein the echo
`responsive elements are so arranged and the re?ections so
`recorded as to yield substantially parallel records suf?ciently
`displaced in two directions of a horizontal plane to reveal any
`differences in travel time due to inclination of the strata
`beneath the area under survey.
`6. Equipment as de?ned in claim 1 wherein said vehicle
`means are connected to said impulse generating devices and
`