United iStates Patent £191
`Silverman
`
`(54):: METHOD. OF THREE DIMENSIONAL
`SEISNUCPROSP~G
`
`[76]
`
`Inventor: Daniel Silverman, 5969 S.
`Birmingham St., Tulsa, Okla. 74105 ·
`[21]11 Appl~ No.: 844,355
`[22]:: . Filed:
`Oet. 21, 1977
`
`Related U.S. Application Data
`Continuation-in-part of Ser. No.6~ 7,857, Sep. 29, 1975,
`Pat. No. 4,064,481, which is a continuation-in-part of
`Ser. No. 407,646, Oct. 18, 1973, Pat. No. 3,984,805.
`Int. CJ.2 ..•...........................•................ G01V 1/36
`U.S. Cl •..................... 340/15.5 CP; 340/15.5 CC
`Field of Search ................. 340/15.5 CC, 15.5 CP
`
`Referenees Cited
`U.S. PATENT DOCUMENTS
`7/1967 Silverman ..................... 340/15.5 CP
`1/1974 Sorkin .......................... 340/15.5 CC
`5/1915 Anstey et al ................. 340/15.5 CP
`
`3,332;Sll
`3,786;409
`3,885;225
`
`[5:1]
`[5~]
`[5.8]
`[56]:
`
`[11]
`
`(45]
`
`4,159,463
`Jun.26, 1979
`
`Primary Examiner-Nelson Moskowitz
`[57)
`ABSTRACf
`A method of seismic prospecting involving at least a
`first and second spaced apart vibratory sources, cotem(cid:173)
`poraneously vibrating with the same or different refer(cid:173)
`ence signals, and recording into a common geophone at
`a point distant from both sources. The method involves
`recording at least two records, one record includes the
`first vibrator V1 responsive to a first reference signal Rl
`and the second vibrator V2 responsive to a second
`reference signal R2. In the second record the second
`vibrator repeats the reference signal R2, while the first
`vibrator is responsive to the first reference signal Rl,
`but in opposite phase, -Rl. When the two received
`records are added, the components due to the first vi(cid:173)
`brator are in opposite phase or polarity, and cancel,
`leaving only the part due to the second vibrator. When
`the two records are subtracted, the part due to the sec(cid:173)
`ond vibrator cancels, and all that remains is the part due
`to the first vibrator.
`
`22 Claims, 3 Drawing Figures
`
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`VI
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`V2
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`PGS Exhibit 1003
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`
`PGS Exhibit 1003
`PGS v. WG
`
`

`
`U.S. Patent
`
`Jun. 26, 1979
`
`Sheet 2 of 2
`
`4,159,463
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`FIG. 3.
`
`PGS Exhibit 1003
`PGS v. WG
`
`

`
`1
`
`4,159,463
`
`METHOD OF TIIREE DIMENSIONAL SEISMIC
`PROSPECTING
`
`CROSS-REFERENCE TO RELATED PATENTS 5
`Tliis application is a continuation-in-part of my co(cid:173)
`p~nding application Ser. No. 617,857, filed Sept. 29,
`1975 entitled, "Vibratory and Processing Systems for
`Vibratory Seismic Operations", now U.S. Pat. No.
`4,064,481 which was a continuation-in-part of the then
`copending application Ser. No. 407,646, ftled Oct. 18,
`1973, now U:S. Pat. No. 3,984,805.
`
`2
`drawings, in which: at least two vibratory sources, or
`vibrators, VI and V2 are operated cotemporaneously,
`recording into each of a plurality of geophones in a
`selected linear, or aerial array.
`The principle of separation can be described as fol-
`lows:
`Consider a single first vibrator VI operating, respon(cid:173)
`sive to, or under the control of, a fust reference signal,
`Rl. This signal Rl can be a conventional swept fre-
`10 quency signal, of a selected frequency range, starting
`time Tl, and time duration Dl. The vibrator can be
`phase-controlled (as conventionally operated) or non(cid:173)
`phase-controlled. The reference signal can also be a
`BA€KGROUND OF THE INVENTION
`pseudo-random, . or other type of reference signal that
`1. Field. of the Invention
`15 can be used to control the vibrator.
`This.invention lies in the field of seismic geophysical
`The vibrator VI is operated responsive to Rl, and the
`seismic wave is detected and ·forms a first received
`prospecting. More particularly itisinvolved with vibra-
`signal, Sl.
`tory sources, which are programmed by reference sig-
`nals:
`The vibrator is operated a second time with the same
`Still more particularly it is concerned with aerial 20 Vl, however, this time the polarity of the reference
`signal is reversed or inverted. Let us call this - Rl.
`coverage, currently known as Three Dimensional Map-
`ping, or 3D seismic operations, in which a plurality of With this inverted reference signal, the received signal
`spa.ced apart seismic sources are used, recording into at
`will be identical to Sl only opposite, or inverted in
`least one common geophone line.
`polarity, or -Sl,. ·
`Still more. particularly, the invention involves meth- 25 Now, if these two records are added, the Sl and -Sl
`ods ·of separating, in the data processing, the seismic
`will cancel each other, and all that will remain will be
`waves progressing separately from two simultaneous
`noise. On the other hand, if the second record - Sl is
`vibratory sources at spaced-apart points, to a common
`reversed in polarity, the result will be identical (to an
`receiver.
`approximation) to the first record. Now the sum of
`2.J)escription of the Prior Art
`30 these two records will be 2 Sl, and the signal to noise
`li1 ~e prior art it ~ been the en~ire practice, in
`ratio will be greater by V2.
`To make use of this principle, consider a second vi-
`vibratory source operations, to use a smgle source re-
`cording into a plurality of receivers. Even though a
`brator V2 at point P2 spaced apart from PI, and respon-
`pllirality of vibratory sources may be used, so as to
`sive to a second reference signal R2. The operation of
`pro\'ide greater energy, all of the son:ces are placed 35 the two vibrators is cotemporaneous, that is, the two
`clo~ to ea':h other, and all are sync~ro~zed to the same
`durations Dl and 02 overlap in time. They can both
`reference stgnal .. Thus all of the setSmtc energy travels
`start at the same time or different times. Preferably the
`by .a common path to the receivers or s~nsors. .
`two durations Dl and D2 should be equal, although
`More recently there ~ been some mteres~ m the
`they need not be. If Rl and R2 are the same, it is then
`simultaneous us~ of a p~urality of spaced a~art vtbr~tory 40 preferable that they start at different times.
`sources each wtth a different reference stgnal. S~ver-
`On the first record Sl there will be two components,
`man.in U.S. Pat. No. 3,984,805 uses ~on-synchromzed,
`one due to Rl, through Vl, and the other due to R2
`through V2 On the second record S2 there will be two
`non-phase-controlled spaced-apart vtbrators, and sepa-
`component~ one part due to - Rl th;ough Vl and the
`rates the seismic components in the received signal on
`the. basis of correl~tion ':"ith the separate reference sig- 45 other part, ltke on Sl, of R2 through V2.
`'
`nals. Anstey et al m thetr u~s. Pat. No. 3,885,225 uses
`This situation can be represented by the following
`separate reference s~gnals in separate f~equency ba_nds,
`table:
`and separates .the stgnal components m the recetved
`signal on the basis of correlation with the corresponding
`reference signals.
`ful this invention the method of separation of the
`seismic waves from the twa or more sources is by a
`different method.
`
`SO
`
`Vibrator
`Vibrator
`VI
`V2
`Record Sl
`R2
`Rl
`R2
`-Rl
`Record S2
`2R2
`0
`First Stock Sum of (Sl) + ( +S2)
`55 =Se~c~on~d~S~toc~k~S~urn~o~f(~S~l)~+~(-~S2~)------~2~R~l------~O---
`
`SUMMARY
`Itiis a primary object of this invention to provide a
`system of 3D seismic operations using vibratory sources
`in which a plurality of spaced-apart vibrators can be
`used. simultaneously, with the same or different refer-
`ence. signals.
`.·.
`ILis a further object of this invention to provide a
`method of separating the seismic waves received. from
`each of. a plurality of spaced-apart vibrators, by a can(cid:173)
`celling process.
`These and other objects and advantages ofthis inven- 65
`tion. and a better understanding of the principles and
`details ofthe invention will be evident from the follow(cid:173)
`ing description taken in conjunction with the appended
`
`60
`
`Thus, by stacking (SI)+(S2) the components of Rl
`cancel and all that is left is R2, and by stacking
`(S2) + (-S2) the R2 cancels out, and all that is left is Rl.
`This type of operation can be expanded to 3, 4, 5, or
`more vibratory sources, as will be fully explained in
`connection with FIG. 1. Also the more vibrators, the
`more repetitions, of the vibrators are required, such as 2
`repetitions for 2 vibrators; 4 repetitions for 3 vibrators;
`8 repetitions for 4 vibrators, 16 repetitions for 5 vibra(cid:173)
`tors, and so on.
`Getting this many repetitions is no great problem,
`since with 3 or 4 synchronized vibrators 10-20 repeti-
`
`PGS Exhibit 1003
`PGS v. WG
`
`

`
`4,159,463
`
`4
`and R2 are different, then a further "cleaning up" of the
`record can be done by correlation with the appropriate
`reference signal.
`A further development of this invention involves
`"inverting" or "changing the polarity" or "phase shift(cid:173)
`ing by 180"," portions of one of the two reference sig(cid:173)
`nals. This is accomplished by modifying or altering the
`reference signal to have two or more portions, or ele(cid:173)
`ments, in half of which the signal is inverted. With two
`vibrators the total duration of the one or more elements
`that are direct (non-inverted) must be equal to the total
`duration of the elements which are inverted.
`R1 is "modified" as above to :RI, and V1 is controlled
`by RI, while V2 is controlled by R2. The record when
`correlated with RI will produce R1 and cancel R2,
`while correlating by R2 will produce R2 and cancel Rl.
`
`3
`tions are required to get sufficient energy. Thus when
`the vibrators are used singly, at spaced locations, the
`number of repetitions are likely to be 3, 4, or 5 times this
`many, depending on the number of vibrators.
`Of course the real value of this operation of miltiple, S
`ndependent, spaced vibrators lies in the fact that with a
`single linear array of geophones and say three spaced
`vibrators, aligned transverse to the line of the array,
`three times the area of subsurface coverage will be
`provided at much less than three times the cost of 1 10
`vibrator.
`It will be clear also that instead of a single vibrator at
`each transverse position, two or more synchronized
`vibrators can be used.
`When I speak of "reference signal," I mean a time 15
`function, for controlling a vibratory source. This can be
`a conyentional swept frequency signal of selected fre(cid:173)
`BRIEF DESCRIPTION OF THE ORA WINGS
`quency band, starting time, and time duration. It can
`FIG. 1 indicates schematically the process of coding
`also be a pseudo-random signal, or any selected signal,
`20 transmitted and received signals for operation with
`which the vibratory source can follow.
`two-to-five spaced sources.
`The vibratory source can be the conventional phase
`controlled vibrator, or it can be non-phase controlled. It
`FIG. 2 illustrates a second method of coding trans-
`can follow a sinusoidal reference signal, or a square
`mitted and received signals.
`FIG. 3 illustrates in plan view one method of field
`wave reference signal.
`When two vibrators are spaced apart with respect to 25 operations.
`each other, they are far enough apart so that they can be
`DESCRIPTION OF THE PREFERRED
`considered to be generating independent seismic signals
`EMBODIMENTS
`which travel by different paths to the receivers, sensors,
`Referring now to the drawings, and in particular to
`or geophones.
`When vibrators are spaced apart and generate sepa- 30 FIG. 1, there is shown in outline, the manner of operat-
`ing with up to 5 spaced apart vibrators V1, V2, V3, V4,
`rate seismic signals, and operate cotemporaneously, at
`least some part of their seismic signals overlap in time,
`VS, responsive respectively to five separate reference
`and it becomes important to be able to separate the two
`signals, R1, R2, R3, R4, RS. The column spaces 1, 2, 3,
`seismic signals, for purposes of determining 3 dimen-
`... 16 between the vertical lines 34, represent separate
`sional structure. This is the objective to which this 35 records, the numbers at the tops of the columns 1-16
`invention is directed.
`being the successive record numbers. These represent
`In this invention it is important to "invert" or change
`the records made with the vibrators at the same points
`the "polarity" of a reference signal, such that when one
`P.1, P2, P3, P4, P5, respectively, on a repetitive basis.
`No attempt will be made to go into detail of how
`record is made with the reference signal in "normal
`polarity," and another record is made in "inverted po- 40. vibrators are constructed, or used, or operated, since all
`larity" or "opposite polarity" or "opposite phase" then
`of this is well known, and need not be repeated. U.S.
`Pat. No. 3,984,805, which is made part of this applica-
`in stacking these 2 records, the result would theoreti-
`cally be zero. In a practical case the two records may
`tion by reference, explains the use of vibrators. A fur-
`not completely cancel because of variation in phase shift
`ther reason for not going into greater detail on the vi-
`in the vibrators, and other well known reasons. How- 45 brators is because this invention is not limited to any
`ever, in general, the repeatability of seismic records is
`particular type of vibratory source, provided it will
`good, so that if the two records are added, they will
`follow the applied reference signal, both in a direct and
`substantially cancel each other, except for noise, while
`in an inverted polarity manner.
`if they are subtracted, the result should be substantially
`Consider the case first of two vibrators V1 and V2,
`double the amplitude of the first record. Here subtrac- 50 responsive to reference signals R1, R2 respectively.
`This is included in the dashed box 35. In record 1, R1
`tion means addition in opposite, or inverted, phase or
`drives V1 in direct polarity (as represented by the up-
`polarity.
`pointing arrow 30). Also R2 drives V2 in direct polar-
`It becomes important therefore, in using this inven-
`tion, to drive the vibrator with a reference signal, either
`ity. In the second record R1 drives V1 and R2 drives
`in normal polarity, or in inverted polarity. Also, in 55 V2 in opposite or reversed polarity. Or putting it an-
`stacking received records there must be capability to
`other way, -R2 drives V2.
`stack the received signals, or records, or traces, in nor-
`It will be seen (inside box 35) that if records 1 and 2
`mal polarity or inverted polarity.
`are stacked, or added, in direct polarity, R1 will be in
`So if there are two vibrators V1 and V2 responsive to
`phase on both records, while R2 will be in opposite
`reference signals R1 and R2 respectively, to be able to 60 phase, or polarity, on the two records, and will cancel.
`separate the two seismic signals on a record, involves
`Conversely if record 2 is inverted and stacked, with
`recording two records. In the first record the two vibra-
`record 1, R1 will be out of phase and R2 will be in
`tors respond to the two signals R1 and R2 directly. On
`phase.
`the second record V1 responds to (- R1) and V2 to R2.
`Consider the case of 3, vibrators V1, V2, V3 respon-
`By directly stacking the two records, the V2 record is 65 sive to R1, R2, R3 respectively, as outlined in dashed
`produced, and by inverting the second record and
`box 36. In recording records 1, 2, 3, 4, R1 is in direct
`stacking, the V1 record is produced. This can be done
`polarity on all four records, while R2 is in direct polar-
`even if R1 and R2 are the same reference signal. If R1
`ity in records 1 and 3, and in reversed, or inverted polar-
`
`PGS Exhibit 1003
`PGS v. WG
`
`

`
`4,159,463
`
`6
`The portion 64 of the record represents R2, and is in the
`same polarity as R2.
`Consider that reference signals R1 and R2 are identi(cid:173)
`cal. Then if 81 is correlated with R2, (or Rl) the com(cid:173)
`ponent of V2 will be reproduced while the correlation
`of Rl with components of Vl will cancel to zero. This
`is because in half the duration of V1 the polarity of the
`record is the same as R1, and half the time it is inverted,
`so that in the summation of the products in the correla(cid:173)
`tion process, half the products will be positive and half
`will be negative, and thus the sum will be zero.
`On the other hand when 81 is correlated with R1, the
`portion of the record due to V1 will be reproduced in
`the correlogram, while the part due to V2 will be can(cid:173)
`celled.
`This can be illustrated clearly by stating that:
`correlation Rl * R1 will produce a correlogram
`correlation Rl * R1 will produce zero.
`
`5
`ity in records 2 and 4, while R3 is indirect polarity on
`records' 1 and 2 but in reverSed polarity on records 3
`and4.
`If the 4 records.are stacked directly, (that is, without
`any inverted records) Rl will be in phase on all 4 re- S
`cords and will sum to amplitude 4, while both R2 and
`R3 will be direct on 2 .records and inverted on two
`records and will be cancelled. If the records are stacked
`by inverting records 2 and 4, then R2 will be in phase on
`all.4 and will sum to amplitude 4, while Rl and R3 will 10
`cancel. If the records are stacked by inverting records 3
`and 4, then .R3. will be in phase on all records and will
`add to amplitude 4, while R1 and R2 will cancel.
`Thus three separate vibrators can use three similar, or
`different, reference signals and can be operated at 15
`spaced· points, and, by recording at least 4 repetitive
`records; in, proper codes of polarity, of reference sig(cid:173)
`nals, each of the three seismic waves received cotempo(cid:173)
`raneously can.be separated by stacking the 4 records in
`3 different codings, related to the codes of polarity by 20
`Thus even with the same reference signal, R1, and
`which the records were recorded.
`coding one vibrator in a particular time and polarity
`By similar reasoning, the dashed box 37, involving
`manner, will permit separating the two seismic signals.
`the recording of 8 records with 4 vibrators illustrates
`While the modification RI(t) shows abrupt reversals
`how· the 4 separate seismic signals can be separated. 25 of phase, in order to satisfy the limitations of the vibra-
`tor, it may be desirable to taper the amplitude to zero at
`Also box 38 covering 16 repetitions illustrates the han-
`dling of 5 vibrators spaced apart, with the same or dif-
`each reversal time, as shown in Box E.
`ferent reference signals.
`This method can be expanded to more than two vi-
`Of course, after the two, three, four or five stacks or
`brators by using the type of coding illustrated in FIG. 1;
`additions are made, the resulting stacked records must 30 that is, with three vibrators on the same or different
`reference signal R1, one modified signal would have,
`be correlated with the proper reference signal in accor-
`dance with the • reference signal which is enhanced by
`like IU, 4 segments, successive ones direct, inverted,
`the stacking.
`direct, inverted. The third vibrator would have a differ-
`It is not necessary to use box 35 with two vibrators.
`ent modified signal JU, which would have two equal
`Box 40; illustrates how R4 through V 4 and RS through 35 segments, the one direct and the other inverted, and so
`VS can be used with 16 repetitions. If two vibrators are
`on.
`used, the number of repetitions (records) must be an
`The method of FIG. 2 has an important advantage in
`even number, so. that multiples of box 35 can be used.
`that each record has all the coding to separate the two
`The order ··in which the records are recorded is not
`or more signals, and does not require stacking to do the
`important. For example, in using R1 and R2 for 16 40 separation. Thus a system in which correlation is done
`before stacking, can handle this type of coding and
`records, 8 records can be run with both R1 and R2 in
`standard or normal, or direct polarity, and then 8 re-
`separation. Thus, while each vibrator may have the
`cords are run with R2 in inverted polarity.
`same basic reference signal, they have different time
`Another embodiment based on this principle of can-
`and polarity coding on their particular reference sig-
`cellation is illustrated in FIG. 2.
`45 nals.
`Here are shown S boxes A, B, C, D, and E. Box A, SO,
`While phase coding may have been used to separate
`represents the ·envelope of an analog sweep reference
`signals on the basis of correlation, this system offers a
`signal• R1. T represents the starting time, and 81 the
`type of time and phase coding that not only distin-
`duration of the signal. The arrow 52 indicates standard
`guishes against the differently coded signals, but if they
`so have the same time duration, reduces the correlograms
`pqlarity, while 54 represents inverted polarity.
`of the discarded signal to zero.
`·This.reference signal has been changed, or modified,
`in. accordance with box B, into 4 serial time segments,
`While this description has been directed to a basic
`54, 55; 56, 57, all of equal time duration. This is a modi-
`array of two spaced vibrators and one distant receiver,
`tied reference signal RI, which will operate through
`it can be modified to include almost any conceivable
`Vl. This is the reference signal R1 with 2, 4, or more SS vibratory system array. In FIG. 3 is shown one array
`which has many operational and economic advantages
`segments, half of which, 54, 56, are in direct polarity per
`arr.ows 52, .. and the other half of which, 55, 57, per ar-
`(refer to Anstey U.S. Pat. No. 3,885,225).
`rows 54; are inverted polarity. Box C represents a sec-
`Here a system 80 is shown with a line of geophones
`ond reference signal R2 operating through V2. R2 can
`90, along a l~e 93, and a vibrator 83. The result would
`be different from; or similar to, Rl. R2 is .run in normal 60 be a plurality of subsurface reflection points 95. If an
`additional line 94 is to be surveyed, the entire operation
`polarity.
`Box D represents a received record of V1 operated
`is repeated along the line 94, (not shown) with vibrator
`by IU, ·and, V2 operated by R2. This record is labelled
`at 84, to produce subsurface reflection points 92, by
`81, and consists of two seismic waves; which are super-
`travel along the paths like 96, 97, etc. However, the
`imposed, but for purposes of clarity, are shown side by 65 same reflection points 92 can be recorded with geo-
`side; labelled V1 and V2. V1 is a replica of Box D hav-
`phones 90 along line 93, as shown, with vibrator 85.
`ing .4 time segments 60, 61, 62, 63, coded in time and
`Thus by running vibrators 83 and 85 simultaneously,
`pqlarity, identically to lU, from which it was derived.
`and separating the seismic signals by the means of this
`
`PGS Exhibit 1003
`PGS v. WG
`
`

`
`4,159,463
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`to
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`25
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`20
`
`7
`invention the two line coverage can be obtained simul(cid:173)
`taneously without moving the line of geophones 90.
`Also, in accordance with Ser. No. 617,857 now U.S.
`Pat. No. 4,064,481, the received signals can be digitized
`to 1 bit, and the reference signals can be digitized to I 5
`bit, and correlations can be made on a 1 bit by l bit basis.
`This method is sensitive to phase reversals, or inver(cid:173)
`sions, and therefore, the use of l bit digitizing eliminates
`problems of amplitude variations in the cancelling pro-
`cess.
`While I speak of received records, in practice what
`are stacked are received traces. The nomenclature
`"stacking records" includes also "stacking traces."
`The type of seismic operations illustrated in FIG. 3 is
`often called 3 Dimensional profiling, since the subsur- 15
`face reflection points 95, 92, which are mapped simulta(cid:173)
`neously, and the corresponding deeper and/or shal(cid:173)
`lower reflection points occupy a three-dimensional vol(cid:173)
`ume related to the two-dimensional array of surface
`f
`Th"
`. al
`"b
`d
`.
`t"
`v1 rators an
`rece1vers.
`1s type o opera 10n 1s
`so
`called broadline proflling, since it maps a wider area
`than the subsurface line 95. Another way of describing
`this type of operation is that it provides subsurface cross
`dip information, as well as inline dip information, pro-
`viding true dip of subsurface reflecting horizons.
`The type of operation shown in FIG. 3 can be carried
`out with conventional explosive shots, or vibrators
`recorded successively, rather than cotemporaneously.
`But such a successive operation consumes a greater 30
`operating time than does the simultaneous, or cotempo-
`.
`raneous operation of this method.
`If the separated vibrators are using the same refer(cid:173)
`ence signal it may be desirable to delay the initiation
`times. If they are using different reference signals this 35
`delayed initiation is not necessary.
`A vibrator driven by an alternating reference signal
`creates a pulsating, or reversing, or alternating pressure
`on the earth. This creates a seismic wave in the earth, as
`is well known. This process can also be described by 40
`saying that the vibrator radiates seismic energy, or seis(cid:173)
`mic waves, into the earth at the source point, or that it
`irradiates the earth with seismic waves.
`While the invention has been described with a certain
`degree of particularity, it is manifest that many changes 45
`may be made in the details of construction and the ar(cid:173)
`rangement of components without departing from the
`spirit and scope of this disclosure. It is understood that
`the invention is not limited to the embodiments set forth
`herein for purposes of exemplification, but is to be lim- so
`ited only by the scope of the attached claim or claims,
`including the full range of equivalency to which each
`element thereof is entitled.
`What is claimed is:
`1. A method of seismic prospecting in which a plural- 55
`ity of seismic vibratory sources, at a plurality of spaced
`source points, cotemporaneously radiate seismic signals
`into the earth, each source responsive to an individual
`reference signal; the seismic signals which travel by
`different paths and are received at a receiver and form 60
`a single composite received signal, comprising the steps
`of·
`'(a) repeating said radiations from said spaced sources
`a plurality of times, each source using its same
`reference signal on each repetition and forming a 65
`plurality of composite received signals; each com(cid:173)
`posite received signal including a component from
`each of said sources;
`
`8
`(b) on each repetition of said sources coding the
`transmission from: none, or some, but not all of said
`sources, in a selected first manner;
`(c) making at least one selected stack of said plurality
`of composite received signals, with none, or some,
`but not all of the individual composite received
`signals in said at least one stack being coded in a
`second manner, related to said frrst manner;
`whereby the result of said at least one stack is the
`summation of the repeated transmission compo(cid:173)
`nents from a selected one of said plurality of spaced
`sources.
`2. The method as in claim 1 in which said coding in
`said first manner involves inverting the polarity of at
`least one of said individual reference signals on a se(cid:173)
`lected basis; and said coding in a second manner in(cid:173)
`volves inverting the polarity of at least one selected
`composite received signal in said stack, in a selected
`manner.
`3. The method as in claim 1 including the step of
`making as many selected stacks with corresponding
`selected coding, as there are spaced sources and source
`points; whereby the contribution received signal from
`each source point to said composite signal can be deter(cid:173)
`mined.
`4. The method of seismic prospecting comprising;
`(a) providing a frrst selected reference signal Rl(t)
`fora vibratory source, of selected time duration Dl;
`(b) inverting the polarity of said reference signal
`during a selected portion of said duration Dl to
`form a frrst modified reference signaliU(t);
`(c) radiating a frrst seismic signal into the earth re(cid:173)
`sponsive to said frrst modified reference signal,
`Rl(t) at a frrst point on the earth;
`(d) receiving the seismic signal radiated at said first
`point,' at a second point distant from said first point,
`to provide a frrst received signal; and
`. (e) correlating said frrst received signal with said
`modified first reference signallU(t).
`5. The method as in claim 4 in which said selected
`portion of said duration Dl is Dl.
`6. The method as in claim 5 in which said selected
`portion of said duration Dl comprises a plurality of
`spaced time segments;
`whereby the sum of the plurality of spaced time seg(cid:173)
`ments when said reference signal is inverted equals
`the sum of the time segments when said reference
`signal is not inverted.
`7. The method of seismic prospecting comprising;
`(a) providing a f1rst selected reference signal Rl(t) for
`a vibratory seismic source, of selected time dura(cid:173)
`tion 01;
`(b) inverting the polarity of said reference signal
`during a selected portion of said duration Dl to
`form a first modified reference signal Rl(t);
`(c) radiating a frrst seismic signal into the earth re(cid:173)
`sponsive to said first modified reference signal,
`lU(t) at a frrst point on the earth;
`(d) radiating a second seismic signal of time duration
`02 into the earth responsive to a second reference
`signal R2(t) co-temporaneously with said first seis(cid:173)
`mic signal, at a second point on the earth spaced
`from said first point;
`(e) receiving the seismic signals radiated at said flfSt
`and second points, at a third point distant from said
`first and second points, to provide a first composite
`received signal, which includes components of
`both said first and second seismic signals; and
`
`PGS Exhibit 1003
`PGS v. WG
`
`

`
`4,159,463
`
`15
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`25
`
`40
`
`55
`
`9
`(f) correlating said first composite received signal
`separately both with said modified ftrst reference
`signal IU(t), and
`with. said .second reference signal, R2(t).
`8. The method as in claim 7 in which said first and 5
`second. reference signals are the same.
`9. The method as in claim 7 in which said first and
`second reference signals are different.
`10. The method as .in claim 4 in which said modifica(cid:173)
`ti0n. comprises 4 equal time segments, with alternate 10
`segments of direct and inverted polarity.
`11. The method as in claim 4 in which said modifica(cid:173)
`tion. comprises 2 equal. Segments, one of said segments
`direct, and the other ofinverted polarity.
`12. In the.method of seismic prospecting in which at
`least a first and a second seismic source cotemporane(cid:173)
`ously radiate into the earth, first and second vibratory
`seismic signals responsive respectively to a first and to a
`second reference signal, at flr