CN109581481B - Portable high-frequency controllable seismic source seismic signal harmonic interference elimination method - Google Patents
Portable high-frequency controllable seismic source seismic signal harmonic interference elimination method Download PDFInfo
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- 230000005284 excitation Effects 0.000 claims abstract description 19
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- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
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Abstract
The invention relates to a portable high-frequency vibroseis seismic signal harmonic interference elimination method, which is constructed according to the signal excitation and acquisition process of conventional vibroseis seismic exploration, and a detector is arranged along the direction of a survey line within 1m from a seismic source substrate. After the seismic source is excited, the first arrival signals are identified and extracted from the signals collected by the specially arranged near-seismic source substrate detectors according to the arrival time difference and the energy difference between the first arrival signals and other seismic waves. And performing cross-correlation processing on the extracted first arrival signals serving as reference factors and the acquired seismic records to obtain the seismic records in the form of wavelets, so that harmonic interference can be effectively eliminated. The method is suitable for eliminating harmonic interference of the portable high-frequency vibroseis seismic signals, the co-axial of the cross-correlation wavelets is more continuous, the seismic phase is clear, the signal-to-noise ratio is obviously improved, and the method is more effective in eliminating the harmonic under the conditions of complex geological conditions and poor coupling of the substrate and the ground. The invention provides effective technical support for shallow high-resolution exploration such as urban underground space exploration.
Description
Technical Field
The invention relates to the field of seismic exploration, in particular to a method for eliminating harmonic interference of a seismic signal of a portable high-frequency controllable seismic source. The method can eliminate the harmonic interference of the seismic signals of the portable vibroseis, and is more effective in eliminating the harmonic under the conditions of complex geological conditions and poor coupling between the substrate and the ground.
Background
A portable high-frequency controllable seismic source is a seismic exploration excitation source which drives a vibration exciter to vibrate at high frequency based on the electromagnetic induction principle. Compared with the conventional hydraulic controllable seismic source, the controllable seismic source has the characteristics of wide excitation signal frequency band, capability of realizing vibration higher than 1000Hz, light volume, flexibility in movement and wide application in shallow high-resolution seismic exploration such as engineering geophysical prospecting and urban underground space detection.
Aiming at the seismic record of the portable high-frequency controllable seismic source, in order to obtain wavelets similar to the pulse seismic source, a preprocessing method of performing cross-correlation on the seismic record and a reference factor is adopted. The conventional method at present takes a seismic source scanning signal or a near-substrate detector signal as a reference factor, and the two methods have the problem of harmonic interference of different degrees through experimental data verification. Particularly, in areas with complex geological conditions, under the condition that the coupling condition of the substrate and the ground is poor, harmonic interference is particularly prominent, the resolution ratio of the seismic signals of the portable high-frequency controllable seismic source is seriously reduced, and further application of the instrument is limited.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a portable high-frequency vibroseis seismic signal harmonic interference elimination method.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for eliminating harmonic interference of a seismic signal of a portable high-frequency controllable seismic source comprises the following steps:
a. in an exploration area, designing an excitation system according to the requirements of conventional seismic exploration, wherein the seismic source parameters of each excitation point are consistent, the scanning signal is s (t), and the seismic source substrate and the ground are kept to form good coupling;
b. designing an observation system according to the requirements of conventional seismic exploration, arranging a plurality of detectors along a measuring line, wherein the distances between the detectors are the same, and keeping the detectors to form good coupling with the ground;
c. when each seismic source point is excited, a detector is arranged in the direction of a measuring line within 1m from the seismic source substrate, and the detector is called a near seismic source substrate detector;
d. seismic waves are excited through a portable high-frequency controllable seismic source, seismic signals are collected through detectors arranged on a survey line and stored by a seismograph, and original uncorrelated seismic records are obtained.
Further, the invention also comprises the following steps:
e. extracting a 1 st signal, namely a near-seismic-source substrate wave detector signal g, aiming at the uncorrelated seismic records obtained from the excitation point Ii(t) of (d). G is prepared fromi(t) performing a cross-correlation operation with the seismic source scanning signal s (t) to obtain
Wherein
The symbol represents a cross-correlation operation;
f. from yjiAnd (t) identifying the first-arrival signals according to the arrival times of the first-arrival signals and other seismic waves. Wherein yj isi(t) the peak point of the wave in the step (t) is regarded as the arrival time of the first-arrival signal, and other seismic waves comprise reflected waves, refracted waves, surface waves and random noise;
g. using the arrival time of the first arrival signal identified in step f as the midpoint, and according to the pulse width of autocorrelation wavelet of scanning signal s (t), yji(t) waveform form and energy ratio requirement, taking windows with same time length on the left and right, extracting first arrival signal to obtain yfi(t) of (d). Wherein, only the first-arrival signal and no other signal are contained in the window, and the signal energy in the window accounts for more than 90% of the energy of the whole first-arrival signal;
h. at this time yfi(t) is in the form of cross-correlation wavelet, and is obtained according to the relation between cross-correlation operation and convolution
Wherein, gfi(t) is a first-arrival signal in the form of a frequency modulated signal, the symbol x represents a convolution operation,
represents the conjugation of the signal;
i. according to the convolution theorem, Fourier transform is carried out on the formula to obtain
Then
Wherein F [. C]Means that the signal is Fourier transformed and then inverse Fourier transformedTo obtain gfi(t)＝F-1[F[gfi(t)]]In which F is-1[·]Representing an inverse fourier transform of the signal;
j. will be gfiAnd (t) taking the seismic record as a reference factor, and performing cross-correlation operation on the seismic record which is not correlated and is obtained by the excitation point I to obtain the seismic record in the form of the wavelet required finally.
The invention has the beneficial effects that: the invention is suitable for eliminating harmonic interference of the portable high-frequency vibroseis seismic signal, and compared with the conventional preprocessing method, the co-axial wavelets of the cross-correlation operation result are more continuous, the seismic phase is clear, the signal-to-noise ratio is obviously improved, and the harmonic elimination is more effective particularly under the conditions of complex geological conditions and poor coupling between the substrate and the ground. The invention provides effective technical support for shallow high-resolution exploration such as urban underground space exploration.
Drawings
FIG. 1a is a portable high frequency vibroseis seismic record processed by conventional methods;
FIG. 1b is a time-frequency curve of the 10 th signal of FIG. 1 a;
FIG. 2a is a portable high frequency vibroseis seismic record processed by the method of the present invention;
FIG. 2b is a time-frequency curve of the 10 th signal of FIG. 2 a.
Detailed Description
The following detailed description is made with reference to the accompanying drawings and examples:
as shown in fig. 1a, fig. 1b, fig. 2a, and fig. 2b, for an example of a seismic record obtained by detecting an underground space by using a portable high-frequency vibroseis in a city in north of China, a method for eliminating harmonic interference of a seismic signal of a portable high-frequency vibroseis related to the present invention is described, which includes the following steps:
a. in an exploration area, designing an excitation system according to the requirements of conventional seismic exploration, setting the distance between excitation points to be 6m, setting the scanning signal of a seismic source to be s (t), setting the frequency band range to be 20-200 Hz, the scanning time to be 10s, and the sampling frequency to be 1KHz, and keeping the seismic source substrate and the ground to form good coupling during excitation;
b. designing an observation system according to the requirements of conventional seismic exploration, arranging 24 receivers along a measuring line, wherein the offset distance is 10m, the distance between the receivers is 2m, and the receivers are required to be well coupled with the ground;
c. particularly, when each seismic source point is excited, a near-substrate detector is arranged at a position 0.5m away from the seismic source substrate along the line measuring direction;
d. after the excitation system and the observation system are set, seismic waves are excited to the earth through the portable high-frequency controllable seismic source, seismic signals are collected through the detectors arranged on the survey line, and the seismic signals are stored by the seismograph according to the sampling rate of 4K, so that original uncorrelated seismic records are obtained;
e. extracting the 1 st signal, namely the near-seismic-source substrate wave detector signal g, from the uncorrelated seismic records obtained from the No. 1 excitation point1(t) of (d). G is prepared from1(t) performing a cross-correlation operation with the seismic source scanning signal s (t) to obtain
Wherein
The symbol represents a cross-correlation operation;
f. from yj1In the step (t), the first-arrival signals are identified according to the time difference between the first-arrival signals and other seismic waves (such as reflected waves, refracted waves, surface waves, random noise and other signals). Wherein yj is1(t) the peak point 0.52ms is considered as the arrival time of the first arrival signal;
g. taking the 0.52ms of the arrival time of the first-arrival signal identified in the step f as a midpoint, extracting the first-arrival signal to obtain yf according to the autocorrelation wavelet pulse width of 8.1ms of the scanning signal s (t) and the waveform shape, wherein the left window and the right window respectively have the length of 4.5ms, so that the window only contains the first-arrival signal and does not contain other signals1(t) of (d). Meanwhile, the signal energy extracted in the calculation window accounts for 91.36% of the whole first arrival signal energy, and meets the requirements of the invention;
h. at this point, extracting the resultant yf1(t) is in the form of cross-correlation wavelet, and is obtained according to the relation between cross-correlation operation and convolution
Wherein, gfi(t) is a first-arrival signal in the form of a frequency modulated signal, the symbol x represents a convolution operation,
represents the conjugation of the signal;
i. according to the convolution theorem, Fourier transform is carried out on the formula to obtain
Then
Wherein F [. C]Which means that the signal · is fourier transformed. Then, performing inverse Fourier transform to obtain gf1(t)＝F-1[F[gf1(t)]]In which F is-1[·]Which represents an inverse fourier transform of the signal.
j. Will be gf1And (t) as a reference factor, and performing cross-correlation operation on the reference factor and the uncorrelated seismic records obtained by the No. 1 excitation point to obtain the seismic records in the form of wavelets required by the invention finally.
The invention is suitable for eliminating harmonic interference of the portable high-frequency vibroseis seismic signal, and compared with the conventional preprocessing method, the co-axial wavelets of the cross-correlation operation result are more continuous, the seismic phase is clear, the signal-to-noise ratio is obviously improved, and the harmonic elimination is more effective particularly under the conditions of complex geological conditions and poor coupling between the substrate and the ground. The invention provides effective technical support for shallow high-resolution exploration such as urban underground space exploration.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (1)
1. A method for eliminating harmonic interference of a seismic signal of a portable high-frequency controllable seismic source is characterized by comprising the following steps:
a. in an exploration area, designing an excitation system according to the requirements of conventional seismic exploration, setting the distance between excitation points to be 6m, setting the scanning signal of a seismic source to be s (t), setting the frequency band range to be 20-200 Hz, the scanning time to be 10s, and the sampling frequency to be 1KHz, and keeping the seismic source substrate and the ground to form good coupling during excitation;
b. designing an observation system according to the requirements of conventional seismic exploration, arranging 24 receivers along a measuring line, wherein the offset distance is 10m, the distance between the receivers is 2m, and the receivers are required to be well coupled with the ground;
c. when each seismic source point is excited, a near seismic source substrate detector is arranged at a position 0.5m away from the seismic source substrate along the direction of a survey line;
d. after the excitation system and the observation system are set, seismic waves are excited to the earth through the portable high-frequency controllable seismic source, seismic signals are collected through the detectors arranged on the survey line, and the seismic signals are stored by the seismograph according to the sampling rate of 4K, so that original uncorrelated seismic records are obtained;
e. extracting the 1 st signal, namely the near-seismic-source substrate wave detector signal g, from the uncorrelated seismic records obtained from the No. 1 excitation point1(t); g is prepared from1(t) performing a cross-correlation operation with the seismic source scanning signal s (t) to obtain
Wherein
The symbol represents a cross-correlation operation;
f. from yj1(t) identifying the first-arrival signals according to arrival times of the first-arrival signals and other seismic waves; wherein, other seismic waves refer to reflected waves, refracted waves, surface waves and random noise signals, yj is obtained1The peak point 0.52ms in (t) is considered as the first arrival signalThe arrival time of (1);
g. taking the 0.52ms of the arrival time of the first-arrival signal identified in the step f as a midpoint, extracting the first-arrival signal to obtain yf according to the autocorrelation wavelet pulse width of 8.1ms of the scanning signal s (t) and the waveform shape, wherein the left window and the right window respectively have the length of 4.5ms, so that the window only contains the first-arrival signal and does not contain other signals1(t); meanwhile, the signal energy extracted in the calculation window accounts for 91.36% of the whole first arrival signal energy;
h. at this point, extracting the resultant yf1(t) is in the form of cross-correlation wavelet, and is obtained according to the relation between cross-correlation operation and convolution
Wherein, gfi(t) is a first-arrival signal in the form of a frequency modulated signal, the symbol x represents a convolution operation,
represents the conjugation of the signal;
i. according to the convolution theorem, Fourier transform is carried out on the formula to obtain
Then
Wherein F [. C]Means for fourier transforming the signal ·; then, performing inverse Fourier transform to obtain gf1(t)＝F-1[F[gf1(t)]]In which F is-1[·]Representing an inverse fourier transform of the signal;
j. will be gf1And (t) taking the obtained seismic data as a reference factor, and performing cross-correlation operation on the obtained non-correlated seismic data of the No. 1 excitation point to obtain the seismic data in the form of the finally required wavelet.
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| CN113050166B (en) * | 2019-12-27 | 2023-04-07 | 中国石油天然气集团有限公司 | Seismic excitation signal correction method and device |
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