DE1473952A1 - Method and device for seismic soil investigation - Google Patents

Description

Method and device for seismic soil investigation

Finding relates generally to seismic prospecting, particularly seismic prospecting with a plurality of seismic vibrators with mutual delays sum emitting a directed beam seismic energy in a plurality of different frequencies; In particular, the invention relates to seismic prospecting using a plurality of frequencies, where the energy is impulsive or in short wave trains of the The respective frequency is sent out and the recorded signals of different frequencies are combined into a temporally superimposed recording.

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Seismic prospecting includes determining the

mutual arrangements of structures in the ground. At the seismic prospecting are thrown back or Broken sound waves are used to determine the position of Schlchtgrensen between the different soil layers. At the usual seismic prospecting is a load of dynamite detonated near the surface of the earth, and it is time

measured, in which the resulting seismic wave has a certain * reached the subterranean layer and after the reflection on The layer boundary at a receiver on the earth's surface arrives. The receiver is commonly referred to as a geophone. If you know the speed of sound in the ground or calculated, one can calculate dl depth from the measured Laufselt at which dl well was reflected and from this dl Depth of the reflective layer. Generally there it has sahi-rich reflective layers, and therefore the geophone draws a look! reflected waves. Dl depth a number of layers can thereby be determined on a single villain.

Dynamite loads are loaded with success on a large scale uses, but there are a number of disadvantages associated with it. On the one hand, the ground is destroyed at the point of fire, a Shot cannot be repeated. The sound waves go away from the shot in all directions, so it will Energy sent in unnecessary directions. In addition, waves that are sent out in more than one direction can to one and the same geophone and can there

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even arrive at the same time, so that it becomes difficult to determine the direction and depth of the reflective layer. • Finally, the sharpness of the detected waves is limited because of the natural frequencies generated by the shot will.

Seismic '.' Rushes can also be generated by dropping heavy masses. However, this method has most of the disadvantages associated with gunshot wave generators, because the sound waves emanate in all directions, the ground is destroyed, and frequencies are generated which are limited by natural frequencies of the earth.

Another sound source is formed by a circular plate which is forced into contact with the surface of the ground by the weight of a truck under which the plate can be placed. The plate is then excited to vibrate at a continuously changed frequency. With this sound source, the floor is not damaged. ,

In accordance with the present invention , a number of seismic vibrators are used which correspond to those described in the pending application of Park H. Miller, Jr. dated June 25, 1962 (Serial No. 2o4 739 - method and device for geophysical prospecting) or those from the application filed at the same time by Park H. Miller Jr., Dv / ight C. Pound and Herschel R. Snodgrass (seismic vibration transmitter) . In the present study, a plurality of such vibration transmitters is used in a certain geometrical manner

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Arrangement, preferably along a straight line with equal distances from one another, applied; The transmitters are preferably synchronized in such a way that they emit a directed sound wave beam with a certain mutual phase shift at one of several frequencies.

Each transducer is preferably made up of a strong annular plate held in contact with the ground surface by means of a clamp underneath the plate. The clamp is connected to the plate via a tension member. The tension in the connecting link is varied sinusoidally and thereby exerts a sinusoidally changing force on the soil surface eus. This force moves the surface of the ground and creates pressure waves, that is, seismic waves, which are radiated into the ground.

In the present system , the various encoders are

preferably driven under the action of a control system which sufans a chain of pulses to the various transmitters, each pulse train being fed to the respective donors to different tents. The various transmitters therefore generate essentially the same wave series of seismic oscillations with mutual phase shifts. This distorts an overall picture of seismic waves with directivity.

They send the seismic waves one «from each several »distant points in the ground. The waves are reflected on different layers and on • recorded at a receiving station. The reflections of the waves

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from all donors are picked up at the same tent and generate a signal that is a combination of all reflected represents waves. In order to highlight a particular layer, the combined cells are used for a particular reffecion set to a maximum by changing the phase position of the waves sent by certain encoders. The phase position for this setting to the maximum can then be used as a display for the direction of the combined sound waves can be measured - and from this the apparent inclination of the selected layer. The directivity thus fulfills two functions: highlighting a selected layer and determining its relative inclination. Each function has a special meaning.

• *

The detectors or receivers can also have certain phase relationships with one another and thus a directional characteristic exhibit. According to the invention, a look! Using geophones, which is preferably in a straight, equally spaced sequence ans -, are ordered «and the signals from the respective geophones receive mutual phase delay by suitable means, see above that the recorded signals practically collide. The for such a coincidence gives the delay required Direction of the reflected signal to

The direction of the emitted beam, the direction of the reflected signal and the time span swiscben emission and Reception of the waves are determined by the mean speed of sound and the depth and inclination of the reflective layer and therefore these values can, if the distance »wipe

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the transmitter and the receiver arrangement is known will. From the measured mutual phase difference between vultures for set to maximum value, combined recorded vibrations, their different arrival times at their recipients and the transit time of the light the speed of sound and the inclination and depth of a certain layer can be precisely determined.

An essential one? Feature of the invention are the measures for . Temporal summary of the recorded signals. This is achieved by operating the encoders one after the other * at a number of specific frequencies, with the length of the V / ell trains of the respective Fr.eQ.ue.nEen la being essentially the same. The wave trains recorded for the successive frequencies are then summed up and form a result- '·. rendes signal which had been auegesandt over a longer period of time in a short period in each WEI (1enzügen ,, summarizes the information contained. Ia individual provides through the application of suitable narrow band filter through which tfahl certain preferred frequencies and Wellenzuglän-

> ■

By appropriately setting the control system, the resulting reading creates a strong peak or "mark" for each reflective layer that is relatively little disturbed by floor noise or by reflections from layers outside the rays. This allows deep reflections . · Animal layers from the surrounding noise level · - j are lifted.

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The invention thus provides a system for seismic prospecting in which the transmitters determine seismic energy can conduct reflective layers. A method of seismic prospecting is also given, according to which the .Ve 11 en are passed through the mutual phase position of a plurality of encoders. The mutual phase relationships The transmitters are also changed in order to give a maximum value to the waves coming from a bec: guiding reflective layer and recorded at the receiving station. S: The relative phase position of the encoders that are used for it is necessary to reach the maximum value, the time difference between the arrival of the maximum value signal at two receiving stations and the transit time of the waves between the sensors and The receiving stations measured an indication of the wave speed and the inclination and depth of the particular layer to obtain.

The invention also provides a system with which the incoming seismic signal by multiple frequency technology can be summarized. The system also allows the intercepted signals from deep reflective layers to be emphasized from the ambient noise level will. The measurements are reproducible, multiple shots are possible, and the recordings have high fidelity. The frequencies used in the system according to the invention can be set in such a way that floor noise is suppressed, that interference effects are observed and that the transmittance and reflectivity of the xu determining layers can be monitored.

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Further features and advantages of the invention emerge from the following description and the associated drawings, which show the following »»:

FIG. 1 shows, in simplified form, partly in section, partly schematically, a preferred arrangement of seismic transmitters and receivers in an embodiment of the invention and the paths of the seismic waves for a signal of the recorded reflected waves that is brought to the maximum value;

FIG. 2 shows a part of FIG. 1 enlarged, successive therein Transmitter and the delay of seismic waves for maximum value signals recorded reflected Y / ellen;

3 shows the arrangement of transmitters and receivers according to FIG. 1 and the movement of waves from a specific transmitter and their reflection to successive receivers;

Fig. 4 shows a part of Fig. 3 enlarged, namely successive receivers and the time delay of waves arriving at successive receivers;

Fig. 5 is a schematic representation of the geometry of the invention ;

6 shows a schematic plan view of a two-dimensional arrangement of transmitters and their position on the receivers;

Figure 7 is an end view of Figure 6 in the direction 7-7;

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Fig.8 is a schematic representation of the geometry of the arrangement according to the invention according to Figure 6 and Figure 7;

Fig. 9 shows schematically that for the signal superimposition recording system used again;

Flg.1ο shows a scheme for one in the system according to Fig.9 usable filter;

Fig. 11 shows a schematic image of the filter naoh Fig * 1ο dar;

Fig. 12 is a circuit diagram for another filter design (for use in the system of Fig. 9);

Fig. 13 shows vibrations generated according to the invention dar and

Fig. 14 shows sum signals generated by a single reflector with different frequency selection will.

Flg.1 shows in general the geometric arrangement of seismic transmitters and receivers, as they are in the present one Invention is applied. In the preferred embodiment shown in FIG. 1, there are a number of seismic transmitters Io arranged at equal mutual distances along an approximately straight line 11, and in the same direction 11 are a number of seismic receivers or pickups 12, also designed with the same mutual distance. The line 11 runs, generally speaking, in the ground surface

As stated above, any seismic transducer 10 can be configured as described in the pending application by Miller (Serial No. 2o4 739) or in the simultaneous registration of

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Hillor, Found, and Snodgrass is described and drawn. Each receiver 12 can be one or more common geophones include that convert the recorded sound waves into corresponding electrical display signals that are further processed and registered in a recording system 13.

The transducer described in the two current patent applications has an annular shape printed against the surface of the earth Plate that is moved mechanically at set frequencies. More precisely, the plate is; via a tension member with eir.er well connected bracket set in the earth. The train in this tension member is changed periodically and on this A quasi-sinusoidally variable force effect caused in the floor under the plate. The force presses the soil practically sinusoidally alternating and creates a downward gradient from the plate into the soil Blast wave. In a given anchorage hole, these encoders can be used for a long time without any noticeable change of the pressure wave emitted and without changing the structure of the soil in the vicinity of the encoder. The givers will generally in fast-drilled anchor holes from about 15 cm (6 inches) in diameter and about 3 m (10 feet) deep arranged. They can easily be taken out and moved to another location.

In the present arrangement, the encoders are operated in accordance with a certain mutual excitation or phase position, so that the combination of all the encoders

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generated waves produces a beam concentration and directional characteristic. The transmitters 1o are controlled by a main control system 14, which is preferably implemented like that according to the application filed at the same time by Dwight C. Found (control device for seismic sensors). As stated in Pound's application, the encoders are operated at a number of frequencies. The donors are in a tent point excited at the same frequency, but their phasing may be different, determined by that Main control system 14. The encoders are preferably excited by wave trains of defined, limited length, the stimulating wave trains are of the same length for all encoders. Each encoder therefore delivers a pressure wave that coincides with the pressure wave every other encoder exactly matches, but has a different phase position or operating time. According to the invention the main control system sets the mutual phase relationship or delay between the pressure waves emitted by the respective transducers, which are transmitted by a receiver 12 Caused recorded associated reflected waves for mutual amplification.

In reflection seismics, the pressure waves of the seismic transmitter 1o are radiated downwards and to the various Soil layers reflected. As shown in Fig.1, can the waves are reflected from the top 16 of the layer 18. This layer can be between the overlying one Layer 2o and an underlying layer 22 are and

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end at an abutting layer 24. BIe Reflection will caused by a change in the refractive index between the layer and the layer 18.

As can be seen from Fig.1, the length of the path depends on the Encoder 1o to the reflective layer delimits 16 and back to a receiver 12 from the relative position of the encoder so that each of the waves emanating from one of the donors after their reflection at the boundary layer 16 simultaneously at one certain receiver 12 arrives .. A determination of this mutual delay is then an element of the information required to determine the inclination of the reflective Layer boundary 16 can be used. The inclination is the angle between the layer boundary and the horizontal.

Bas can be explained by considering the path length of two specific donors 1o 12 to a predetermined recipient _t If, for example, recognizes the path from the central transducer Se and the adjacent generator S, up to the central receiver R ₈ regarded as one, that the path length from the transmitter S ^ to the receiver R ₈ after reflection at the layer boundary 16 by the amount Δ. D is greater than the distance from the encoder Se to the receiver Rg. If the main control system is set correctly, the encoder S _K sends its pulse sequence to the time ΔΤ- later from al3 of the encoder S ₄ , so that the waves from the encoder S ^ im At the moment _{when encoder S 5} starts sending, the path Λ Β has been covered to have. The time & T_ calls a phase difference between

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seismic waves emitted by successive sensors. The tent d T_ is therefore a MaQ for the

Phase difference between the two encoders. The tent ΔΤ_

is determined by observing the response of the receiver Rg to the pressure waves sent by the sensors S and Se and by making the two waves coincide. This is done by adjusting the main control system, as described in the aforementioned pending simultaneous application by Pound, in order to achieve a delay time which causes a maximum large reflection signal to arise at the receiver Rg, whereby the mutual amplification of the waves is indicated. The amplitude of the combined intercepted waves reflected from the selected layer can be recorded as a function of the delay, and the delay causing a largest signal is measured. The delay AT ₈ then becomes the distance 4, D by the velocity ν seismic waves in the ground using the equation

iiD ^a ν / ΛΤ _β

Put in relation.

Di'e delay for brought to the maximum value intercepted Signals indicates the direction of the wave traveling from the transmitter to the receiver after reflection at the layer boundary 16.

This is shown more clearly in Fig. 2. For the sake of simplicity, it is assumed that the paths from the various transmitters to the receivers are essentially parallel to one another. This" Assumption is sufficiently fulfilled for all practically occurring measurements, because the gap between the sensors In general

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my very small 1st compared to the depth of the reflective layer boundary 16. The distance between the transmitters is located la while the interest reflective layer boundaries usually several hundred fceter (several thousand feet) are generally about 15 m (5o feet) below the surface. Under this assumption, geometrical considerations show that the angle 6 between the path of the pressure waves and the normal to the line 11 is determined by measuring the phase relationship or the delay AT. can be determined because this angle S is determined by the following expression:

ο = arc sin -,

CS

where AS is the distance

means between neighboring donors.

1 also shows that there are similar geometrical relationships in the direction and the relative travel time of the waves from a specific transmitter over the reflective layer boundary 16 to successive receivers. on in this way the time difference in the arrival of the wave at successive receivers can be measured. the Time difference ΔΤ can be used to determine the angle £ between serve the incoming wave and the normal to the earth's surface, because

ν, AT

arc sin —-. ,

4R

where i \ R means the distance between neighboring receivers .

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The relationships are clearly shown in FIGS. 3 and 4, where the waves from the transmitter Sc run from the reflective layer boundary 16 to the successive receivers Rg and Rg. How in optics can the geometrical relationships be determined when the encoder S _{c is} at the location of its mirror image S? relocated.

It is within the scope of the invention, the time difference 4T in in exactly the same way as ΔΤ. The captured Signals can be delayed from one another at the respective receivers and then combined, the delay so it is set to produce a maximum value of the combined captured signal. This delay is then a measure for / IT. The delay can be brought about electronically or mechanically by adding every signal that is picked up. is recorded for itself and then the recording media are shifted against each other until a maximum value is reached.

In addition, it is within the scope of the invention to set the delay on the transmitter in order to reach the maximum value of the captured Kprabinationssignals; however, since the receivers are relatively close to one another, it has proven to be useful to set the delay at the transmitter to a maximum for a single received signal, preferably the signal at the central receiver R _Q.

In practical operation it has been found to be useful not to combine the signals from the various receivers it is better to register each one individually as a function of time.

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s trier en and then the time difference between the arrival of the reflections on the observed layer for the respective

To measure recipients *.

The assignment of a particular reflected signal to the reflective layer under consideration is given below in connection with the illustration of the preferred method for achieving it discussed sharp signals.

Assuming that the transmitters have a small mutual distance compared to the distance from the reflective layer, and assuming that the same applies to the receiver, the geometric relationships are represented as shown in FIG. The angles cf and t can be determined as described above, and the distance between the transmitters and receivers can be measured. The waves emanating from all the transmitters 1o are deflected from practically one and the same point 26 on the reflector 16 to the receivers 12. With respect to the line 11, the reflector 16 is inclined by the angle 0. V / eil when the angle of incidence of the waves is equal to the angle of exit 1 , the angle j6 has the size of half the difference between C and O , that is:

Furthermore, it follows from geometrical considerations that the speed ν is also determined from easily measurable quantities can be:

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AR AS

where χ the

Distance between the donors and the receivers is and t is the time between the transmission of the pressure waves by the transmitter and the reception of the waves reflected by the reflector 16.

This 7 / ert the speed can be used "in order, O, and to determine, in conjunction with the previously mentioned relations, the angle £ 0th In a similar way, the distance h between the connecting line of transmitters and receivers up to the reflection point 26 can be determined trigonometrically, as can R_ as the distance on the connecting line between the transmitters 1o and the base of the perpendicular from the reflection point 26 to the connecting line.

It should be noted that the relationships given so far for determining inclination, depth and speed only apply approximately and under the restrictive

conditions, i.e. as long as the distance between encoders and Receivers are small compared to the depth of the reflective layer. The arrangement described can similarly can also be operated under conditions in which more precise relationships are appropriate, which can be derived from the precise geometric relationships. However, the above-mentioned relationships have the advantage of being simple and general to be applicable.

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However, the information obtained so far (using the arrangement shown in Fig. 1) does not indicate the actual inclination and depth of the layer boundary 16. So far is rather only the position of the layer opposite the line 11 in that of the line and a normal on the Schlchtgrenie defined level given. The actual inclination dor Sehloht is given by the dihedral angle enclosed by the layer and the horizontal, and the true depth let the vertical distance from the ground surface. Around To determine sizes, one can determine the angle of the plane of the recorded reflected Y / ellen with respect to the vertical. This can be done by pivoting the arrangement by 90 ° and the The same measurement is carried out; this results in the apparent inclination of the layer in another Level. The true slope and depth can then be calculated trigonometrically.

In addition, the encoder arrangement can also be designed two-dimensionally and in two directions with delay adjustment, for the simultaneous formation of a recorded maximum signal. Such a two-dimensional arrangement is shown in FIG. according to which the encoder 10 * designed in the form of a rhombus one diagonal of which coincides with line 11, while the diagonal 11 * is perpendicular to the line 11. The geometric considerations for inclination and depth with respect to line 11 are the same as in FIG. 1. For the 7 makes it easier to understand the further dimension geometric relationships.

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Figure 7 is a side view of that shown in Figure 6 from line 7-7. In this view, the encoders 12 are superimposed in the central encoder St. The same settings for the delay time or the mutual phase position are made, as described above in connection with the encoders 10; the reflected signals picked up by a receiver 12 are in phase for all waves that are emitted by the respective transmitters 10 '. According to the information given with i'ig.1, the angle of the path from the transducer ^10f to the reflector 16 and further to the feeders 12 can be determined by this delay with the aid of the same relationship, that is to say

arc sin

where O is the angle between the normal to the line 11 and the direction of the square from the encoders 10 ', 4l' is the delay between the excitation of successive encoders and Λ S ^{1 is} the distance between adjacent encoders 10 'in the direction of the Line 11 _% is. The speed ν is the same as that according to the arrangement shown in rig.1.

We.-zi the same conditions are made as before, i.e. that the transducers are close together compared to the depth of the reflector 16, the path is the reflected reflected 7 / ellenwJe shown in Fig. 8. Since the receiver and transmitter are in 8 are at the same location, the wave path runs in a line that is perpendicular to the reflector

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runs as drawn in Fig.8. The inclination 0 ^{% of} the reflector is equal to the angle O in this arrangement:

With this additional information, the information may consist of the collinear array £ eir.üß Fig.1 used v / ground to the actual depth h ^ · _Γ of the reflector and the actual inclination angle of the reflector as well as the true brushing, that is, the impact of the boundary layer on the soil surface.

It should also be noted that the lines 11 and 11 * do not necessarily run horizontally, because the surface of the earth is also is not level everywhere. The position of these lines against the horizontal can be determined by the usual surveying methods be determined, and determining the true depth 'inclination and deleting can then be carried out using the necessary corrections in the previous determination of the lines and 11 · occur.

A linear arrangement of nine encoders is shown in FIG such an arrangement has proven to be extremely useful proven. A relatively large number of donors improved

Provides the alignment of the seismic waves. A large number of also reduces the impact of surface or other localized anomalies by averaging these perturbations. A individual encoders or a small number of encoders could be caused by local disturbances that could lead to incorrect measurements, to be influenced in high chew; Errors in a Kessung

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but masked by the influence of a large number of correct measurements. On the other hand, there is a point of decreasing return signals, beyond which there is an additional gain not worth the additional equipment and the associated cost and increase in complexity. It has been shown that more than five encoders provide the required accuracy ensure that with more than fifteen donors the additionally gained directivity is relatively low. Hence, the number of nine or eleven donors is preferred. Its odd number of donors · is expedient because it is a middle encoder results as the origin of the measurement. As said above, the distance between neighboring encoders is selected to be around 15 to 3o meters (5o to 100 feet). The distance between neighboring receiving stations can be chosen to be just as large. It is desirable to keep the distances small compared to the depth of the reflective layer of interest so that the derived simplified relationships remain valid. Fig. 1 shows the use of fifteen receiving stations. It has It has been found to be expedient to use between fifteen and twenty-five receiving stations, which are also between 15 and 30 meters (50 to 100 feet) apart.

With any seismic system, the ground must have a certain hatred in terms of energy supplied and measured by the tent, the energy required to make a certain reflective layer to reach and from there su a receiving station su get. Single pulses of seismic energy can be used in the manner indicated above; in their preventive execution

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form, however, the invention makes use of wave trains, because on these catfish additional energy over a longer period of time Period of time can be fed to the ground. On the other hand, although a continuous signal would still have more energy in could bring the ground to a confusing reception signal lead, because the waves would be reflected continuously by a large number of reflectors, and those of interest reflective layer would no longer be recognizable. The arrival time of the iVelle must be related to its launch tent. Therefore it is preferred to use trains of limited length. More precisely, wave trains of different frequencies are used according to the invention, and the recordings made at the respective frequencies are combined in a certain way in order to sharpen the resulting combined signal, that is to say to make it to be shortened significantly compared to the transmitted wave train.

The effect of noise can be reduced significantly by picking up each frequency through its own narrow band filter. It would be possible to make the noises by applying cross-correlation techniques, According to the invention, however, it is preferred to use simple in £ aehe filters that are effective at the right time. When using wave trains of limited length, the output of such filters gradually increases, reaching a climax at of the last oscillation of the wave train and then gradually decreases. An essential feature of the invention is the Combination of the outputs of the filters with all frequencies In

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the fact that all signals are in phase at a given time, namely at the time of the last transmitted wave, and that all signals cancel each other out on average at all other times, so that a sharp combined signal is produced.

The frequencies used are given below. They are controlled by the encoders 1o, from the main control system 14, as described in the referenced Pound patent application. The reflected waves of each frequency are recorded by all recipients 12.

Fig. 9 reproduces part of the recording system 13 which includes only one receiving channel. The entire recording system Figure 13 contains duplicates of the circuit shown in Figure 9 for each. Receiver 12. That of a receiver 12 when hit reflected waves generated electrical signal is fed to a filter 28, which is precisely adjusted to the waves to let through the frequency transmitted by the encoders for the wave train that has just been recorded. That passed by the filter 28 Signal is then registered by a recording device 3o. So that the event recorded by the device 3o Can be related to the running time of the waves from the named encoders, the rotation of the recording device is on the main control system connected either by the main control system controls the start of the recording or by doing the recording cyclically, e.g. by using a Magnetic drum recording and deployment of the main control system operation at a certain point in time of the recorder

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syklus, for example by closing a Uikroschalters mounted at a certain location of the Aufzeichnertrommel. It is also possible to install a receiving station in the center of the transmitter arrangement in order to measure the time of transmission of the seismic waves and to use the output of this receiver to control the timing of the recording device. On ^ jZiLT * case will be in some known, useful way

3o

the time of the recording made in your device at the time of triggering the seismic impulses related, so that a record of the recorded waves as a function of the Time and with the V / ellenaussendzeitzeit as a reference point wonr.-un y / ird. For each frequency switched on by the main control system 14, a frequency setting switch 31 switches components into the Filter 28 to tune the filter to this frequency. At the same time, the frequency setting switch is controlled via a shaft 33 connected to a switch 32, which switches the output of the filter 28 to a recorder 3o, which then the signal for the records the frequency used. It follows that the reflected signal has a frequency associated with it Recorder 3o is recorded. The individual recorder can be implemented by having its own track on a single one Recording magnetic drum.

Since every recording is a measure of the seismic wave recorded as a function of time and in relation to a reference point, E.g. the stimulation time of the encoder to send a specific frequency, the records can be arranged so that the reference points coincide and the

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Records can then be combined. The recordings recorded in each of the recorders 3o can be combined by a reading device 34, which can be designed as a single pick-up head which covers all of the recording tracks on the drum of the recording device, and the combined signal is then sent to the sum signal recorder 36 as a function of the time. The sum signal recorder 36 produces a separate record for each Ecipfänerkanal, which are all related to the same excitation time of the transducers and thereby allow the time difference between the arrival of various reflections at the respective geophones to be measured.

It has been found to be expedient to use a so-called functional filter in the form of a narrow band filter with adjustable frequency and Q-switch as the filter. The Filier is based on the analog simulation of the differential equation of a damped linear oscillator, which is excited with an input signal of resonance frequency. The frequencies and G values are set in such a way that a filter curve is achieved which approximates the correlation function for the specific V / ell train in terms of frequency and length. The differential equation is:

φ ♦ co ² «- ω * FCt).

where F (t)

represents the input function containing a sought seismic reflection signal, characterized by the effective

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Resonance filter frequency mixed with different levels of noise. A conversion results

4 , 2 "

lF (t) -

which can be built according to the representation in Fig.io.

Note that for a 100 Hz signal, Cc is 628 while a coefficient potentiometer only gives numbers from 0 to 1. For this reason the U> setting is actually • / I000, and both such settings are followed by integrants with a gain of 1ooo for compensation. For this reason, the integration capacitors do not need to be excessively large either.

The preferred basic circuit diagram is shown in FIG. 11.

The filter has amplifiers 38, 40, 42 and 44. The amplifiers 38, 40 and 42 can be designed as small, conventional functional amplifiers with a frequency range from 0 to 10 kHz will. The amplifier 44 can be a symmetrical emitter follower with one output low impedance. The amplifier 38 forms a :. Great of a summing amplifier 46, about each of the Input resistors 48 and 5o an input signal is supplied and. which has a feedback resistor 52. Potentiometer 54 is used to set the frequency and is between the Output of the summing amplifier 46 and an integrating amplifier 56, the input resistors 58 and 6o, an amplifier

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and a feedback capacitor 62. The exit of the amplifier 56 is switched to a further potentiometer 64

given, which is also used to adjust the frequency. The output from the frequency regulator 64 leads to a potentiometer 66, which represents a quality setting, and in an input resistor 68, which is part of an integrator 7 o which also includes amplifiers 42 and 44 and rack coupling capacitor 72. The signal from the Quality setting 66 is applied to integrator 56 via a resistor 6o. The output of the integrator is 7o then the pilter exit, which led to a recorder 3o v / ird. It is also fed back to the input of amplifier 46.

The operation of the amplifier results from Fig.io, the represents a functional description of the filter. The function filter is normally set so that the gain in filter output over the duration of an individual is idealized The reflection signal and the fading of the filter after the signal has disappeared result in an approximately triangular envelope. The amplifier 46 sums its input signals -F (t) and χ and inverts the sum to a signal F (t) - x. The potentiometer 54 (with the appropriate gain) multiplied the sum with 60> to obtain a signal jF (t) - x | Cü. The integrator 56 adds this signal to one for -Tj -jf characteristic signal to a signal & (t) - xJW- -q -j ^

to achieve which, as stated above, is equal to - ■ = - £;

fc ^ dt ^

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de * Integrator 56 integrates it to "a signal u ~ 77, -JF SU access, which is then multlpllsiert from the potentiometer 64 (with suitable Verstftrkungsgrad) with CO; the resulting signal corresponds to - «J | . This signal, multiplied by 1 / Q, which is used by the Q (quality) potentiometer 66, supplies an input signal for the integrator 56. It is further integrated to form the signal x, which corresponds to the filter output and also to the input signal of the amplifier 46.

The filter 28 is tuned by adjusting the potentiometer 54 and 64. The setting can be made by moving the frequency adjustment switch 31 can be made to deliver the appropriate frequencies, or the switch can have various predetermined ones Connect elements to the potentiometers 54 and 64, the elements being designed so that certain frequencies be achieved. The graduation 66 can be done in a similar manner be made.

The function filter described in connection with FIGS. 10 and 11 has independent frequency and quality setting. In a seismic system, however, the frequency sequences and cycle numbers applies in such a way that all pulse trains have approximately the same duration (period χ number of pulses = constant), it is expedient to use a filter in which the quality setting proportional to the frequency 1st, while the frequency division is independent of Q. This can be achieved with a filter as shown in Fig.12.

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A filter similar to FIG. 12 is described in an article by FT May and BA Dandl ("Active Filter Element and Its Application to a Fourier Comb", REVIEW OF SCIENTIFIC INSTRUCTIONS ₁ April 1961, Volume 32, No. 4, page 387). This circuit requires only a single frequency setting instead of the two frequency settings of the filter according to FIGS. 10 and 11 and ensures the required frequency dependency in the Q setting. The bandwidth and gain are practically the same in this circuit as in the circuit according to FIGS. 10 and 11, the associated relationships are:

resonance

• C1 / 2

^R f

»Τ

Λ \ ■ tap on Rj bandwidth on long wave train a

Reinforcement at f _{D £} , _eftwte _. * n long '.Vellenzug » ^ L

itesonans *

₁ C ₁

Bas Q _1, controlled by χ , only needs to be set once for a certain period of time in the pulse train, and the only control that requires a switching process during the seismic investigation is the one-of-a-kind frequency (oO setting. The setting M can therefore be made in order to achieve the required quality (Q) at a certain frequency for a veilensug of the length used so that the required rise and fall of the filter output is achieved

009808/0379

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Setting the tap · ·. then delivers the required quality (Q) for all other frequencies, as determined by the setting * , where Q is also influenced by the setting - \ and is therefore frequency-dependent. This creates a Q that increases with the frequency, which is desirable in view of the normally higher attenuation in the transmission of seismic waves of higher frequency.

The filter according to Flg.12 can be used particularly advantageously in switching elements of a filter 28, because only a single element, namely R _f , has to be switched. This means that the frequency switch 31 simply _{switches on different values of R f in} order to change the frequency of the filter, being at the same time as switch 32 which connects the filter to another recorder 3o (corresponding to a different channel or a different track of a multi-track recorder). \

The filter technique known as delay filtering is to be regarded as an alternative to the function filters described. Delay or propagation time filtering can be used to highlight a signal of known frequency and duration as it is. This is achieved by recording the unfiltered signal coming from the geophone and performing repeated additions of the recording with successive taps of one period, two periods, three periods, etc. The number of summands is equal to the number of cycles in the original input signal. The IkH can be satisfactorily either through

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speaking rotations of the drum or by rotating the recording heads can be achieved. The η records can • each be contained in a special recording track and all tracks can ianr. simultaneously from a single pick-up head read v / ground to get the desired output signal.

Time-of-flight filtering was applied to each frequency record of each geophone. If the range used is η periods long, the envelope curve resulting from the η-fold addition of the recording would be triangular with a peak height. η be units. The length of the envelope would correspond to twice the pulse length. The resulting signal would be essentially equivalent to the recording made by a recorder 30 in the circuit of Figure 9 and can be used in a similar manner. This means that the resulting signals for all frequencies can be combined with the correct phase. Time-of-flight filters have the advantage that the envelope curve breaks off sharply outside of a time span which corresponds to twice the wave length, but it has the disadvantage of a longer processing time.

An essential prerequisite for successful work of the device according to FIG. 9 is that the recorded wave trains for all frequencies are combined in the temporal relationship be, in which the recorded wave trains that the sent Correspond to wave trains without passage through the ground, are in phase during a period of each wave train, more precisely beeps that they are in phase during the period that

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corresponds to the last period of each transmitted wave train. The "temporal relationship in which the recorded wave trains, which correspond to the emitted ϊ / ell trains without passing through the ground , are in phase during a period of each wave train " means and includes that relationship in which all phase shifts in the system itself are taken into account, but in which the phase shifts are excluded, which have been generated by the passage of the waves through the ground . That is the temporal relationship in which the signal peaks of all the respective signals written down on the respective recorders 3o coincide in time, who.η the detector reacts to the emitted seismic waves. tslbar reacts without the waves penetrating the ground hacö.'i. This can be achieved by appropriately setting the main control system so that each transmitted wave train ends with an end wave at the correct time in the operating cycle of the system, i.e. at a specific time after a reference level:; 3 or reference time. This reference quantity is the reference quantity for the recorder 3o, and if the final period of each pulse series expires in the correct time interval after the reference quantity for each frequency and the reference quantities for the recordings made by all recorders 3o are combined, then the recorded waves at the various frequencies all be in phase at the time corresponding to the arrival of the final period of the respective wave trains sent out from the various deflectors .

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The recordings produced by the respective recorders 3o are made with matching reference values. This is done by appropriately programming the main control system achieved. This setting of the main control system is made before the respective seismic operations achieved simply by using a test receiver at the central encoder 1o, such as it will be explained later.

The frequency summing technique is shown in Fig. 13. All Records in this figure are taken directly from the field records. In the study selected here, six frequencies were used, namely 9o, 79, 53, 57, 46 and 35 Hz. The data on the respective recording

3o The traces of writing obtained by the device are in A, B, C, D, E and F. reproduced. Each of these writings is using one Narrowband filter 28 was created »that was switched over to tune to the respective frequency. Magnetic writings are normally produced in the recording devices 3o. In Fig. 13 they are redrawn as writings from an oscilloscope.

The summation of signals A, B, C, D, E and F by the Reading device 34 recorded in totalizer 36, 1st reproduced as letter Q. The delay between the encoders was set to 3 msec; this delay left that The maximum value of the signals in the time range around 1 second occurs. LiIt this delay and with frequency summing become two Reflectors Visible in the area around 1 see, marked as signal peaks 74 and 76 in the letter G.

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Linzel writes and the frequency search according to I i ^. 13 graphically represent the effect of the frequency adjustment technique. Obviously none of the writings A, B, C, D, E and F clearly show the position of the reflective layers. The summation wrote G on the other hand clearly shows the reflective layers in largely the same way as they can be seen in conventional seiscograms. The characteristic small wave (wavelet) that indicating a reflective layer is known as that layer's reflection mark. Since the Suir.mler record largely What a common seismic record looks like, it can be interpreted in the usual way. The way and way in which this seismic record was obtained however, the highlighting of certain reflective layers under conditions where conventional seismic techniques would have failed. In particular, 1st to see how very close adjacent reflective layers can be separated.

The dissolution effect with frequency summation is most evident when comparing it with monochromatic signals among the same conditions. The letter H in Flg. 13 belongs to one 80 Hz recording (8 periods, unfiltered) using the same arrangement of transmitters and receivers as with frequency summation recording. The delay time of the primary sources favors the area around in both cases 1, oh see. The signals in this time range are controlled by the Frequency summing technlk well resolved while in the

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monochromatic wrote due to overlaps and interference to be veiled. In particular, the sharp resolution of the closely spaced signals 74 and 76 is in dor. Frequency summation (G) to be observed compared to the relatively long, undifferentiated pulse train in the L.o..ochroir.atic writing (H).

Ls ^ "ibt an ar ...: a number of criteria, which an optimal identification to let win. The sign must be sharp and clear. To get us a sharp mark ai'csen the recorded, reflected by a certain yeast reflector .Yelle trains each other for a short period of time amplify while they are in all other time periods wipe out. It has been shown that the linear I reque.iz distribution generally has small side lobes, highlighting the main peak. The strongest side lobes are caused by the beat frequency, which results from the general frequency difference. These Kebenzipfel caused by the beat frequency can, however, be elimited by a suitable choice of the length of the '.

r.iniert. A "linear frequency sequence" is intended to express be that there is a number of frequencies at which adjacent frequencies each have equal frequency differences differentiate. A linear sequence in which one or more terms of the regular episode are omitted.

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The following criteria are important for extraction usable 2 characters:

1. A high average frequency should be used v / earth for good resolution; the higher the frequency used, the sharper the main peak of the summation record. However, the frequency is limited by the physical properties of the encoder and the soil.

The higher frequencies can only be broadcast with difficulty and effectively forwarded.

2. A wide frequency range should be used, ranging from the highest to the lowest values at which good radiation and transmission is possible. A large area is required to shrink the side lobes.

3. For general depreciation the side lobe is

a large number of different frequencies are required.

The number of frequencies used should be compatible with the cost of the field equipment and operation. With a set of fixed frequencies achievable by programming or simply selecting with switches, shots with a number of different frequencies should take little more time than doffing the same number of shots with a small number of frequencies. A large number of frequencies would offer the fundamental advantage of having an almost continuous series of waves with closely spaced, fixed frequencies. Omitting one or more frequencies in order to bypass certain annoying outstanding noise peaks would be possible without

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that the income would be deteriorated too much. Additional frequencies on either end of the main episode would become one Selection of the frequency range for adaptation to the special field conditions.

4. It is necessary to have function filter outputs of approximately the same amplitude in order to have a uniform display of all frequencies in the record. Outputs with the same amplitude can either be set by setting the Amplification or multiple shooting can be achieved when certain frequencies are transmitted with high attenuation. The use of a filter whose Q increases with frequency, e.g. the Fllteis according to Flg. 12, helps maintain alignment represents the amplitude of the normally more attenuated signals of a higher frequency.

5. A linear frequency distribution generally provides small side lobes, apart from the large beat frequencies * - that result from the constant frequency interval. These side lobes are to the side at J-y seconds do3 central character, where Af means the constant frequency difference. With a large number of frequencies you can these side lobes are kept away from the central sign.

6. The length of the transmitted wave trains should be sufficiently large so that a good signal / fluff ratio results; but the length must be less than -r ^ y so that the Side lobes remain outside the boundaries of the emitted wave eye.

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7. The frequencies must be selected so that the recorded waves can only be in phase during one of their periods. Especially during the the period belonging to the last period of the corresponding transmitted wave train.

8. The frequencies must be chosen so that the frequencies of the floor noise and all other interfering noises, be lenders the 60 Hz * frequency, can be omitted. Ground noise is from the seismic transducers in the upper ones Noise caused by layers of soil. With the usual Soisaiki sessions, the floor noise often covers the wanted one Reflection signals because it arrives at the same time and with a comparable amplitude. The in the present invention preferred donors give very little floor noise; moreover, the floor noise after it la general random occurs, somewhat reduced by the diversity of the transmitters, moreover the Bodane noise is generally present in a limited frequency range, for example at Io to 30 Hz, and the effect of floor noise can therefore be reduced considerably by not using this frequency for measurement. This can be done by a suitable choice of the filters 28 and by not sending out waves with the same frequency as the floor noise.

In summary, the summation character has a width that is durih the average frequency determines 1st, and the sidelobes become smaller as the frequency range increases. The number the frequencies is apparently not critical, a larger one

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However, number reduces the kebon tips. The exact size the frequencies are not critical, except that they should be chosen so that the signals are never in phase, except once within the total time spent by the outgoing signals.

Empirical studies have a linear distribution of the Make frequencies appear more favorable than other distributions examined. An unsatisfactory fact of the linear distribution is the appearance of two strong sidelobes that from the common difference or the beat frequency between the individual frequencies. These two side lobes can be filtered out or otherwise significantly reduced are, depending on the applied filter process, by choosing a length of the emitted wave train and a frequency difference combination, through which the side lobes are brought beyond the temporal boundaries of the wave train. The minimization of the side lobe is achieved if a transit time filtering is carried out before the frequency summation to merge the pulses is made; a reduction in size of the side lobes is brought about by function filters.

Let us now assume a linear distribution with fifteen frequencies, which has a frequency interval of J * f Hz. If long wave trains of these frequencies are summed up, beats with a beat frequency, ^ f, result. The time interval between in-phase beat peaks ^is -si

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In a seismic recording created by the summation of waves of constant amplitude, a series of large in-phase peaks appears with time intervals -gj>, separated by areas of considerably lower oscillation, which have been created by the addition of random phases.

It is now assumed that instead of wave tails, more constant Amplitude wave trains are to be combined which have such phase · lSije, Fora and length that the by adding the waveform obtained around a peak in various curves ait phase equality is centered and a period of time is

2
1I of amplitudes of less than -yr » duration, which is the type of waveform appearing at the filter output. In this way only one central peak with phase equality would be produced, while the neighboring phase equality peaks are either absent or negligibly small, and the weak oscillations surrounding the central single character decrease in amplitude with the distance from the central peak.

The criterion of the recording that the length of time that the

2 rubberized shaft is less than -n means for that

Case of the delay filtering, that the time span of the input pulses for the transit time filtering is smaller than -J- * . In this case the side lobes are eliminated. When using function filters before summing, the Kr It er lim would say that the input pulses for the function filter cover a time span of less than -yj and further that the constriction Im output of the function filter within a time -n Im '. would decrease substantially to zero. When applying function

009808 / 03-79. bad ordinal

The tip of the love would filter at - ~ γ seconds after the Main peak can be reduced considerably but not eliminated.

The actual length T of the wave train is given by the relationship

where η is the number of periods

per pulse and f is the frequency in Hz. According to the criterion, this length should be less than -n . If you allow that

1 η + m

where m is a positive,

is not necessarily an integer constant, the criterion is met.

For an example, m = 1 is chosen. The number of periods and the frequencies result in the following picture:

21 periods with 99 Ha 2o periods with 94.5 Hz 19 periods with 9o Hz 18 periods with 85.5 Hs 17 periods with 81 Hz 16 periods with 76.5 Hz 15 periods with 72 Hs 14 periods with 67.5 Hs 13 periods with 63 Hs 12 periods with 58.5 Hz 11 periods with 54 Hs Io periods with 49.5 Hs 9 periods with 45 Hz 8 periods with 4o, 5 Hz 7 periods with 36 Hz

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15 frequencies η + 1 f At = 4, 5 Hz T ₉₉ - O, 212 see T ₅₆ * O, 194 sec Means ^a 67 , 5 Hz

0.222 sec

One of the many advantages of the fifteen frequencies is that when one or more frequencies are omitted, in order to avoid certain background noise frequencies, only low Effects on the representation of the recording would appear. At both ends of the frequency sequence can additional frequencies can also be added, and the distribution can be shifted to higher or lower frequencies without serious disturbances to the recording.

Investigations with a single reflector and the set of frequencies given above led to the result shown by the letter A of FIG. The effect of a suitable frequency selection can be graphically represented by the plot 3 in Fig. 14, which was obtained with a low distribution of eight frequencies between 24 and 1o1 Hs . The interval -t of 11 msec led to strong H- lobes at 90 msec, while the interval At of 4.5 msec, which was used in the production of the plot A, would cause meo lobes to arise 222 msec away from the main peak, so? .u far outside than that with noticeable

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Amplitude when using pulse lengths of 194 to 212 msec could appear.

A sequence of frequencies which has been found to be very useful in practice is the linear distribution of fifteen frequencies starting at 18 Hz and having a difference Δ t of 4.5 Hz between adjacent frequencies. The skin train with 18 Kz is four periods long and at 81 Hz 18 periods long; Corresponding numbers of periods apply to the frequencies in between, in order to allow wave trains of approximately even -L <length to arise.

Provided that the frequencies for pulse summation are selected, there are two critical settings left for the Obtaining an optimally good frequency summation step. On the one hand, there is the time control for the use of the pulse in order to achieve that the central! Main peaks of the recorded filter outputs are recorded in phase for summing at all frequencies. On the other hand, it concerns the setting of the amplitude of the individual frequencies.

Fixing "the pulse onset times at each frequency is of great importance. Experience has shown that the application is satisfactory if it is determined in the range of a millisecond or better. The operating time is for each frequency set by the main control system as described earlier. When the time for a worried system once set, it usually does not need to be readjusted, except if there are extreme changes the field conditions.

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The operating time must be the main or central peaks of the function filter outputs bring to coincidence. It includes all phase shifts in the system, including those of the encoder itself. Sin satisfactory method of determining the Frequency application times consists of placing a geophone in the Ground next to one of the givers and then the giver with stimulate and record the different frequencies; the geophone signal is generated by the usual geophone amplifier recorded with the function filter 28 matched to the respective frequency. The runtime settings are changed until the required frequency peaks appear clearly on the writing. Those determined in this way Frequency bet pages can then be used for all subsequent shots.

In a preferred embodiment of the invention is used as a recorder, a magnetic drum with a plurality of Recording channels axially offset on the drum surface; the drum rotates at a constant speed and provides a recording time of a few seconds. A certain point in the recorder circulation can be used as a reference point or "No Deco" can be used. This point can be replaced by a Timestamp to be identified and marked that occurs at the Recording drum is attached, e.g. by means of a microscope holder, which closes a circle, which becomes active at this point in the cycle and delivers a reference pulse, which indicates the reference values or the no-decompression limit. As all recording channels are on the same drum, identify

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net this impulse the same point in the orbit each Recording channel and therefore any signal recorded at one of the frequencies. The reference pulse can then be the Main control system to initiate its work. So that the recorded signals in the respective channels in the correct mutual phase relation to Summarizing the pulses according to the invention, the Beginning of the wave emitted by the seismic transducers, for example, can be set with respect to the reference mark by means of a customary adjustable transit time mechanism through a monostable multivibrator with adjustable Switching time or an oscillator and counter that are operated as an electronic clock generator. A different one Delay for each frequency ensures that the signals in the respective channels are correctly timed with respect to the time stamp, so that the signals of all channels can be summed to form the summarized one described above Record. For this reason, from sich & US the reference marks for the respective channels coincide, if all channels are registered on the same drum.

»As mentioned above, the synchronization carried out in this way enables the respective recorded files to be summarized or recorded trains in the catfish, which has previously been referred to as "a temporal relationship in which the recorded wave trains, which correspond to the transmitted wave trains without passing through the ground, during a Period of each wave train are in phase ", in particular during the last period.

009i0t / 0379

It has previously been found that the best recordings seem to be obtained with filter outputs that have approximately the same amplitude. A factor of 2 for the amplitudes has proven to be permissible.

If the amplitudes are adjusted so that the outputs have approximately the same amplitude, then there must be multiple of Interference phenomena caused by reflections are carefully excluded. Accordingly, the amplitude setting for a given frequency should be based on an averaging of amplitude over a considerable part of the time scale and not on a single reflection signal. Furthermore, in the case of a relatively strong increase in the attenuation of the high frequencies with increasing depth two or more series of different settings for the amplitude relationships can be made. When the gain adjustment has been made - either for the entire time span or for several separate time intervals - it should not be changed during the seismic measurement even if it appears that, for certain reflectors, a certain frequency has unusually low or high amplitudes. The unusually low or high amplitudes may be due to interference between two or more reflectors.

It is in the nature of frequency summation recording that that these interference effects maintain their instantaneous amplitude, so that the interfering reflectors are their own Write characters with the correct spacing.

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It has already been mentioned that a certain dependence of the recorded amplitude on the frequency can occur varies with the running time. This dependence on the frequency is caused by processes during generation and transmission and the reflection evoked. In some areas the high frequencies are increasingly weakened relatively more, while in other areas they get away with equally good relative strength. Under test conditions, where the amplitudes of the reflections at high frequencies require special amplification, it is sometimes useful trigger the high frequencies more frequently before merging them with the lower frequencies.

It is often possible to adjust the recorded signals by adjusting them of the encoder output or the gain in the various recording channels. However a limit is formed by the performance of the transducers and amplifiers used. There is a practical one Limit on the amount of energy that can be radiated by a transducer of reasonable size when one is inside the elastic limit of the soil that wants to remain with which it is connected. The reinforcement can only make up for that so far there is a reasonable signal / bulk ratio. In addition, the amplifiers used must not be excessive Cause phase shift, otherwise the signals of the different frequencies cannot be combined correctly will. Under such circumstances, the received signals equalized by multiple triggers at the higher frequencies

009808/0379 _BAD original

will be. That is, some channels can use the same Frequency are charged. Every received signal this Frequency can then be written in its own recording channel. These different channels would then together contain the matched signal of this frequency, which can be summed with the signals of the other frequencies were. This multiple omission at a given frequency improves the signal-to-noise ratio without the encoder or overloading the display system.

This alignment of the signals not only enables the best Summary of the impulses but it is also used for retention the fidelity of the recording. This is often important because - as the expression suggests - the labeling for each reflective layer is characteristic of that layer on different seismograms. That enables a Correct assignment of seismic records from different locations in an area so that the different layers in a geophysical study of a larger area with donors and receivers in a number of different locations were designed, can be properly classified.

The term "fidelity" used here for a seismic recording is based on the use of the Expression used when playing music. The precision The reproduction of the seismic characteristics, like the fidelity of the musical reproduction, depends on the extent to which a uniform frequency response is achieved.

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The teianitchen characters are made according to their shape and structure Qls detected coming from a certain layer boundary. The shape and structure of a certain observed reflection symbol depend not only on the reflection properties of the boundary layer but also on the transmission properties of the path of the wave between transmitter and receiver. Sin mechanism or process that is responsible for the upright Preservation of a frequency spectrum of constant amplitude over Different paths ensures that the reflective marks have the same shape and structure across these different ones Lurchlafivrege are retained, which then gives the character a Characteristic of the individual reflection layer boundary is. A device or procedure such as multiple incremental triggering at higher frequencies that is the relatively strong one Able to compensate for the attenuation of the high frequencies and maintain a constant amplitude of the frequency spectrum at the receiver, guarantees the fidelity to the characters and thus provides optimal recognizability. The one described above A system which provides the separate treatment of each of the frequency components is particularly suited to the selective multiple triggering required to achieve the smooth frequency curve for fidelity.

Ed is to be noted that the procedure of the Laufieitelnetstellung and dl · Combination of wave trains by frequency summers are different things that are of importance in themselves. The combination of the two, however, provides an improved selection of information and makes it possible to

009808/4379

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Identify bare reflective layers. The technique of summing provides sharper formation characters lower background noise than could be achieved with the previously known methods. However, the addition of the runtime adjustment also makes it possible to add characters identify which 30nst is covered by other reflections are. In order to highlight certain reflectors, it is generally necessary to take several measurements with different Make run time values and determine the run time setting that results in a Llaxiraal value of the reflector character of interest.

The combined record obtained by the frequency summing method is similar in appearance to the so-called "Ricker Wavelet" and to that obtained by autocorrelation techniques achievable characters. The narrow character width that the high average frequency is achieved, which makes this system possible, leads to a better tent and thus depth resolution than with the usual systems with drop weight or dynamite are possible. The high signal / noise ratio, achievable by the narrowband function filter and the frequency summation ame t ho de, leads to particular clarity of the Reflexion peaks and the ability to work in a noisy environment. The alternatives for the Choice of frequencies makes it possible to avoid ambient noise with strong peaks, to reduce floor noise, to make special interference studies of thin reflective layers uni. > contends for other notable advantages. the

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Accurate · lateral synchronization and good reproducibility of the signal characteristics make repeated signal triggering possible and ensures good reproduction fidelity of the recordings. The ability to generate and maintain a uniform amplitude of the recorded signal over the frequency spectrum used (by selective multiple triggering at each frequency) allows the production of high fidelity reflective characters and allows easy recognition and identification of the reflective layer boundary. The basic features of the alignment of the beam and .icr selectivity for the reflecting horizon, which is a result of the delay time adjustment or phase adjustment of the various encoders, allow a further adjustable magnification of the reflection symbols.

These features allow seismic records to be made that can be used to analyze subterranean details with good resolution and high accuracy.

In these seismic recordings there is, however, one more quantity compared to the usual recordings. With each attuned reflection mark its time displacement or run tent value is associated with said distance encoder - makes possible receiver, the time shift at the receivers and the duration of the signal, the direct determination of the average wave velocity and depth, and projected onto the surface position of the reflector and the angle of inclination of the reflective surface.

009808/0379

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Separate the reflection mark with the one described above Technique of combining impulses is obtained, η one learns the tuning of the running time preferably through Back and forth adjustment of the running time setting before making the setting at which the symbol for the special highlighted reflector has reached its maximum value. Under certain circumstances it may be preferable to do this Signal for a single pulse or wave train Bring a single frequency to the maximum value. In any case, there can be a number of different terms be introduced, usi the identification and application of those Allow transit time that is the maximum value of the recorded Sijnals for the special reflector.

If the running time is not set, it can d: .s resulting seismogram like an ordinary seismogram uses v / earth. The speed can be determined by other measurements, such as the speed log or by setting the running time in adjacent areas

'For clear geological areas, i.e. with approximately parallel stratifications, the entire recording area can be accommodated on a representation by arranging properly tuned successive sections, where the detuned sections are discarded. The writings can then, if desired, be represented by the Comparison of a variable and the density or other catfish.

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In more difficult areas where highly variable I. 'angle of observation occur and especially when appearing more positive and negative 17 angles, the reflectors can best by a ssris of episodes with duration matching the positive and negative values of the detuning in separate foI- £ 2-i include. For example, in the case of Hessen in the lütte a Kulde separate individual records ge-Eiaclit v / ground from the opposing inclined elites of L'ulde, a record for a succession of positive Lnu-T times and another sequence for negative running times.

Preferred embodiments of the invention have been described in detail above; however, deviations are still possible within the scope of the invention. For example, the wool trains can be made at different frequencies in certain _; Sequences with only short intervals between the pulses are sent if the sequence of frequencies is chosen so that mutual interference (cross-channel fe-ci-through) is kept as small as possible. It is also necessary to program the entire sequence in advance, with the instructions being fed to the main control system by means of punched tape. As mentioned above, the cultifrequency approach enables the identification of interference patterns which indicate the relative distance between reflectors. Further modifications of the arrangements described above are possible without departing from the scope of the invention. . ₍

Patent claims !

009-08 / 03ΪΙ]

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Claims (13)

Claims 1. Procedure for seismic prospecting in which in seismic waves are emitted across the ground from a number of distant points and all of the seismic waves reflected from reflective layers in the ground Waves are combined and recorded at the receiving station, characterized in that the transmission is seismic Waves from certain points (1o) is delayed to a maximum value of the combined. seismic rushes, which are thrown back from a selected layer (16). 2. A method for seismic prospecting according to claim 1, characterized in that the relative phase position of the seismic waves is varied from certain points (1o) are radiated out to a maximum value of the combined seismic reflected from the selected layer (16) get bark. . 3. A method for seismic prospecting according to claim 1 or 2, characterized in that the ground is seismic V / ellen of a certain frequency and for a certain limited time. 4. A method for seismic prospecting according to any one of claims 1 to 3, characterized in that seismic waves hit the ground at each of an odd number of one another distant points (1o) are fed. BAD CFu G ^ 'AL 009808/0379 " ⁵⁵ " U73952 5. A method for seismic prospecting according to any one of claims 1 to 4, characterized in that the ground is seismic Waves are fed at each of more than five distant points (1o). 6. A method for seismic prospecting according to claim 5, characterized in that the ground seismic walls to each of about eleven distant points (1o). 7. A method for seismic prospecting according to any one of claims 1 to 6, characterized in that the ground is seismic Waves at each of a number of points arranged on a straight line (11) (collinear) with mutual spacing (1o) zOöe led, and that the combination of all seismic V / ellen on one in the straight line extension of the row of dots (collinear) arranged receiving station (12) is added. 8. A method for seismic prospecting according to any one of claims 2 to 6, characterized in that the ground seismic waves ^{are fed to each of a number of points (1ο 1} ) which are arranged in a two-dimensional order, and that the relative phase position of the seismjs chen waves is varied, which ^{are radiated from certain points (1o f} ) in order to obtain a maximum value of the combined seismic waves reflected from a selected layer (16) « 009808/0379 ■ BAD ORi " ⁵⁶ 'H73952 9. A method for selsmjs chen prospecting according to claim 8, characterized in that seismic waves are fed to the ground at springs at a number of points (10 ') which In Rhoaben shape (S ^ to SA) are arranged. 1, o. Method for seismic prospecting according to one of Claims 1 to 9, characterized in that the relative Phase position of the supplied seismic waves for the case of the "received Llaxiinalv / erts of the combined captured seismic 7, 'ellen is measured. 11. The method for seismic prospecting according to claim 1o, characterized in that seismic waves hit the ground * from. Points are supplied from, the mutual distance from the depth of the selected layer (16) can be neglected. 12. A method for seismic prospecting according to any one of claims 1 to 11, characterized in that at the same time the combination at at least two receiving stations (12) of all seismic waves reflected back to the stations by reflective layers in the ground, so that the Difference between the arrival tent and the maximum value combined captured seismic waves' at each of the aforementioned stations is measured, and that the transit time of the above-mentioned combined seismic waves that have been brought to their maximum value for the distance from points (1o) BAD ORiGIMAL 009808/0379 H73952 up to the stations (12) is measured, whereby from the relative phase position for the brought to maximum value, combined captured waves, from the difference in the arrival time of the brought to maximum value, combined captured waves and from the passage show the inclination and the depth of the selected layer (16) can be determined. 13. A method for seismic prospecting according to claim 12, wherein the seismic waves hit the ground at each of a number on a straight line (11) (collinear) with mutual spacing arranged first points (1o), characterized in that further seismic waves hit the ground at each a number of spaced-apart straight lines on a second straight line that adjoins the arrangement of the first points Points are supplied so that the combination of all further seismic waves at at least one receiving station (12) which are thrown back to the station by reflective layers in the ground, is intercepted so that the relative phase position of the other seismic waves, which are sent out at the respective further points, is changed by one. .: To obtain the maximum value of the combined captured seismic waves which are reflected by the selected layer (16) and that the relative phase position is measured which is necessary to achieve the maximum value of the combined, additional captured seismic waves .. ■,] _{B; X)} oa ^^ AL .ι 009808 / 03.79