Ocean vibroseis seismic data processing method based on frequency domain cross correlation

Abstract

The invention is applicable to the technical field of geophysical exploration, and provides an ocean vibroseis seismic data processing method based on frequency domain cross-correlation, which comprises the following steps of: acquiring a seismic detector receiving signal u (t) and a scanning signal sw (t), and performing preprocessing operation on the u (t) and the sw (t); converting u (t) and sw (t) to a frequency domain by using RFFT to obtain frequency domain signals U (omega) and SW (omega); calculating a conjugate product S (omega) of the U (omega) and the SW (omega); calculating a power spectrum SW (omega) 2 of the scanning signal, and correcting S (omega) to obtain Z (omega); and converting the Z (omega) back to the time domain by using RIFFT to obtain final seismic channel time domain data z (t). The method is high in calculation efficiency, effectively eliminates interference of scanning signals, and has higher practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of geophysical exploration, and in particular relates to a method for processing marine vibroseis seismic data based on frequency domain cross-correlation. Background Art

[0002] In marine vibroseis seismic exploration, the vibrator transmits a known sweep signal (such as a sinusoidal sweep signal) through a vibrating plate. Receivers record a received signal that contains a mixture of the subsurface response and the sweep signal. Traditional time-domain cross-correlation methods, which directly calculate the convolution or correlation between the received signal and the sweep signal, suffer from the following problems:

[0003] (1) Low computational efficiency: Time domain correlation requires a large number of multiplication and addition operations, which takes a long time to process large-scale data;

[0004] (2) Weak anti-interference ability: After the scanning signal is superimposed on the noise, the time domain correlation is difficult to completely eliminate the influence of the scanning signal;

[0005] (3) Limited accuracy: The time domain method is susceptible to signal aliasing and noise interference, resulting in inaccurate extraction of underground medium response.

[0006] Some existing methods attempt to use frequency-domain transformation techniques, but these methods fail to fully integrate the conjugate properties of the scanned signal with power spectrum compensation mechanisms, resulting in phase distortion or energy attenuation in the correlation results. Therefore, an efficient and high-precision frequency-domain cross-correlation method is urgently needed to address these technical challenges. Summary of the Invention

[0007] The purpose of the embodiments of the present invention is to provide a method for processing marine vibroseis seismic data based on frequency domain cross-correlation, aiming to solve the problems raised in the above background technology.

[0008] The embodiment of the present invention is implemented as follows: a method for processing marine vibroseis seismic data based on frequency domain cross-correlation, comprising the following steps:

[0009] Step 1: Obtain the geophone received signal u(t) and the sweep signal sw(t), and perform preprocessing operations on the geophone received signal u(t) and the sweep signal sw(t) to remove environmental noise and irrelevant interference;

[0010] Step 2: Use fast Fourier transform (RFFT) to convert u(t) and sw(t) into the frequency domain to obtain frequency domain signals U(ω) and SW(ω);

[0011] Step 3: Calculate the conjugate product S(ω) of U(ω) and SW(ω);

[0012] Step 4: Calculate the power spectrum of the sweep signal |SW(ω)|2 , and correct S(ω) to get Z(ω);

[0013] Step 5: Use RIFFT to convert Z(ω) back to the time domain to obtain the final seismic trace time domain data z(t).

[0014] Step 6: Output the results.

[0015] Further technical solution, said step 2 includes the following specific steps:

[0016] Step 2.1: Calculate the discrete Fourier transform of the signal;

[0017] RFFT is used to convert the seismic detector received signal u(t) and the scanning signal sw(t) into frequency domain signals U(ω) and SW(ω), respectively. The formulas are as follows:

[0018] U(ω)=RFFT[u(t)]

[0019] SW(ω)=RFFT[sw(t)]

[0020] Step 2.2: Calculate the magnitude and phase of the signal;

[0021] Calculate the magnitude and phase of U(ω) and SW(ω) to prepare for subsequent frequency response calculations:

[0022]

[0023] Where Im represents the real part; Re represents the imaginary part; ω is the angular frequency, in rad / s; for; is the phase angle.

[0024] Further technical solution, said step 3 includes the following specific steps:

[0025] Step 3.1: Calculate the conjugate of SW(ω) conj[SW(ω)], which is calculated as follows:

[0026]

[0027] Where, e is the base of natural logarithm, j is the imaginary unit;

[0028] Step 3.2: Calculate the conjugate product;

[0029] Calculate the conjugate product S(ω) of U(ω) and SW(ω):

[0030] S(ω)=U(ω)·conj[SW(ω)].

[0031] Further technical solution, said step 4 includes the following specific steps:

[0032] Step 4.1: Calculate the power spectrum of the sweep signal

[0033] Calculate the square of the modulus of SW(ω) and obtain the power spectrum of the scanning signal |SW(ω)| 2 , to prepare for subsequent frequency response calculations;

[0034] |SW(ω)| 2 =|SW(ω)|·|SW(ω)|

[0035] Step 4.2: Calculate the frequency domain form of the ground response

[0036] The frequency domain form of the earth response E(ω) is calculated according to the formula:

[0037]

[0038] Step 4.3: Calculate the phase of the frequency response;

[0039] Calculate the phase of the frequency response S(ω) To ensure that the correlated frequency response has the same phase as the ground response;

[0040]

[0041] Step 4.4: Calculate the modulus of the frequency response;

[0042] Compute the modulus |S(ω)| of the frequency response S(ω):

[0043] |S(ω)|=|SW(ω)| 2 |E(ω)|

[0044] Step 4.5: Calculate the frequency response;

[0045] The frequency response Z(ω) after correlation is calculated according to the formula, the influence of the scanning signal is eliminated, and the seismic signal is extracted.

[0046]

[0047] Through the above steps, the frequency domain response calculation can be realized, the influence of the scanning signal can be eliminated, and the correlated seismic signal can be extracted.

[0048] Further technical solution, said step 5 includes the following specific steps:

[0049] Step 5.1: Perform RIFFT

[0050] The correlated frequency response Z(ω) is converted back to the time domain using RIFFT to obtain the final seismic trace time domain data z(t).

[0051]

[0052] Step 5.2: Calculate time domain data;

[0053] According to the RIFFT formula, the final seismic trace time domain data z(t) is calculated.

[0054]

[0055] Through the above steps, the conversion from frequency domain to time domain can be achieved to obtain the final seismic trace time domain data z(t), eliminate the influence of the scanning signal, and extract the correlated seismic signal; and the correctness and integrity of the time domain data z(t) can be ensured by checking whether the time domain data z(t) has eliminated the influence of the scanning signal.

[0056] The embodiment of the present invention provides a method for processing marine vibroseis seismic data based on frequency domain cross-correlation, which has the following beneficial effects:

[0057] (1) High efficiency: The Walsh fast real number forward and inverse Fourier transform technology and cosine function tabulation method are used to significantly improve the computational efficiency.

[0058] (2) Accuracy: The frequency domain correlation algorithm can accurately extract seismic signals and eliminate the interference of scanning signals.

[0059] (3) Practicality: Compared with the time domain correlation algorithm, the frequency domain correlation algorithm has an execution efficiency dozens of times higher and has higher practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 A block diagram of an implementation method for processing marine vibroseis seismic data based on frequency domain cross-correlation provided by an embodiment of the present invention;

[0061] Figure 2 It is the vibrator scanning signal;

[0062] Figure 3 For the related pre-record of vibroseis earthquakes;

[0063] Figure 4 It is the post-correlation record of vibroseis earthquake. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0065] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0066] like Figure 1 As shown, a method for processing marine vibroseis seismic data based on frequency domain cross-correlation is provided in accordance with an embodiment of the present invention, comprising the following steps:

[0067] Step 1: Data preprocessing;

[0068] The geophone receiving signal u(t) and the scanning signal sw(t) are obtained, and the geophone receiving signal u(t) and the scanning signal sw(t) are preprocessed by filtering, denoising and other preprocessing operations to remove environmental noise and irrelevant interference.

[0069] In seismic exploration, the signal u(t) received by a geophone contains a mixture of seismic waves and sweep signals, while the sweep signal sw(t) is a known signal emitted by a controllable vibrator. These two signals serve as the basis for subsequent processing.

[0070] Step 2: Convert from time domain to frequency domain;

[0071] The fast Fourier transform (RFFT) is used to convert u(t) and sw(t) into the frequency domain to obtain frequency domain signals U(ω) and SW(ω). The specific steps include:

[0072] Step 2.1: Calculate the discrete Fourier transform of the signal;

[0073] RFFT is used to convert the seismic detector received signal u(t) and the scanning signal sw(t) into frequency domain signals U(ω) and SW(ω), respectively. The formulas are as follows:

[0074] U(ω)=RFFT[u(t)]

[0075] SW(ω)=RFFT[sw(t)]

[0076] Step 2.2: Calculate the magnitude and phase of the signal;

[0077] Calculate the magnitude and phase of U(ω) and SW(ω) to prepare for subsequent frequency response calculations:

[0078]

[0079] Where Im represents the real part; Re represents the imaginary part; ω is the angular frequency, in rad / s; for, is the phase angle;

[0080] Through the above steps, the calculation of time domain to frequency domain can be realized, providing basic data for subsequent frequency domain related calculations.

[0081] Step 3: Frequency domain correlation calculation;

[0082] Step 3.1: Calculate the conjugate of SW(ω) conj[SW(ω)], which is calculated as follows:

[0083]

[0084] Where, e is the base of natural logarithm, j is the imaginary unit;

[0085] Step 3.2: Calculate the conjugate product;

[0086] Calculate the conjugate product S(ω) of U(ω) and SW(ω) to eliminate the influence of the scanning signal and extract the seismic signal

[0087] S(ω)=U(ω)·conj[SW(ω)]

[0088] Step 4: Frequency domain response calculation;

[0089] Step 4.1: Calculate the power spectrum of the sweep signal

[0090] Calculate the square of the modulus of SW(ω) and obtain the power spectrum of the scanning signal |SW(ω)| 2 , in preparation for subsequent frequency response calculations.

[0091] |SW(ω)| 2 =|SW(ω)|·|SW(ω)|

[0092] Step 4.2: Calculate the frequency domain form of the ground response

[0093] The frequency domain form of the earth response E(ω) is calculated according to the formula:

[0094]

[0095] Step 4.3: Calculate the phase of the frequency response;

[0096] Calculate the phase of the frequency response S(ω) This ensures that the correlated frequency response has the same phase as the earth response.

[0097]

[0098] Step 4.4: Calculate the modulus of the frequency response;

[0099] Compute the modulus |S(ω)| of the frequency response S(ω).

[0100] |S(ω)|=|SW(ω)| 2 |E(ω)|

[0101] Step 4.5: Calculate the frequency response;

[0102] The frequency response Z(ω) after correlation is calculated according to the formula, the influence of the scanning signal is eliminated, and the seismic signal is extracted.

[0103]

[0104] Through the above steps, the frequency domain response calculation can be realized, the influence of the scanning signal can be eliminated, and the correlated seismic signal can be extracted.

[0105] Step 5: Frequency domain to time domain conversion

[0106] Use RIFFT to convert Z(ω) back to the time domain to obtain the final seismic trace time domain data z(t).

[0107] The inverse fast Fourier transform (RIFFT) is an efficient algorithm used to convert frequency-domain signals into time-domain signals. Using the RIFFT, the correlated frequency response Z(ω) can be converted back into the time domain, yielding the final seismic trace time-domain data z(t). This step converts the frequency-domain processing results into time-domain data, facilitating subsequent seismic data interpretation and analysis.

[0108] Step 5.1: Perform RIFFT

[0109] The correlated frequency response Z(ω) is converted back to the time domain using RIFFT to obtain the final seismic trace time domain data z(t).

[0110]

[0111] Step 5.2: Calculate time domain data;

[0112] According to the RIFFT formula, the final seismic trace time domain data z(t) is calculated.

[0113]

[0114] Through the above steps, we can achieve frequency-domain to time-domain conversion, obtain the final seismic trace time-domain data z(t), eliminate the influence of the sweep signal, and extract the correlated seismic signal. We can also verify the accuracy and integrity of the time-domain data z(t) by checking whether the sweep signal has been eliminated.

[0115] Step 6: Output the results;

[0116] Output the processed seismic data z(t), eliminate the influence of the scanning signal, and extract the correlated seismic data.

[0117] After these processing steps, the final output seismic data z(t) has eliminated the influence of the scanning signal and extracted the correlated seismic signal. This data can be used for subsequent seismic data interpretation and analysis, providing important information support for seismic exploration.

[0118] Figure 2 is the scanning signal sw(t) of the marine vibrator. The overall signal shows a typical attenuated oscillation structure. Figure 3 is the record u(t) before the cross-correlation of the marine vibroseis. It can be seen that there are a lot of high-frequency signals and background noise in the gather profile, the signal is weak, and the interface is fuzzy. The cross-correlation processing of the present invention is performed on the two to obtain the following Figure 4 As a result, from Figure 4 From the gather profile, we can see that the effective part of the source wavelet correlation is enhanced, the signal-to-noise ratio is significantly improved, and the reflection interface is clearly visible.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for processing marine vibroseis seismic data based on frequency domain cross-correlation, characterized in that: The following steps are involved: Step 1: Obtain the geophone received signal u(t) and the sweep signal sw(t), and perform preprocessing operations on the geophone received signal u(t) and the sweep signal sw(t) to remove environmental noise and irrelevant interference; Step 2: Use RFFT to convert u(t) and sw(t) to the frequency domain to obtain frequency domain signals U(ω) and SW(ω); Step 3: Calculate the conjugate product S(ω) of U(ω) and SW(ω); Step 4: Calculate the power spectrum of the sweep signal |SW(ω)| 2 , and correct S(ω) to get Z(ω); Step 5: Use RIFFT to convert Z(ω) back to the time domain to obtain the final seismic trace time domain data z(t); Step 6: Output the results.

2. The method for processing marine vibroseis seismic data based on frequency domain cross-correlation according to claim 1, characterized in that: The step 2 includes the following specific steps: Step 2.1: Calculate the discrete Fourier transform of the signal; RFFT is used to convert the seismic detector received signal u(t) and the scanning signal sw(t) into frequency domain signals U(ω) and SW(ω), respectively. The formulas are as follows: U(ω)=RFFT[u(t)] SW(ω)=RFFT[sw(t)] Step 2.2: Calculate the magnitude and phase of the signal; Calculate the magnitude and phase of U(ω) and SW(ω) to prepare for subsequent frequency response calculations: Where Im represents the real part; Re represents the imaginary part; ω is the angular frequency, in rad / s; is the phase angle.

3. The method for processing marine vibroseis seismic data based on frequency domain cross-correlation according to claim 2, characterized in that: The step 3 includes the following specific steps: Step 3.1: Calculate the conjugate of SW(ω) conj[SW(ω)], which is calculated as follows: Where, e is the base of natural logarithm, j is the imaginary unit; Step 3.2: Calculate the conjugate product; Calculate the conjugate product S(ω) of U(ω) and SW(ω): S(ω)=U(ω)·conj[SW(ω)].

4. The method for processing marine vibroseis seismic data based on frequency domain cross-correlation according to claim 2, characterized in that: The step 4 includes the following specific steps: Step 4.1: Calculate the power spectrum of the sweep signal Calculate the square of the modulus of SW(ω) and obtain the power spectrum of the scanning signal |SW(ω)| 2 , to prepare for subsequent frequency response calculations; |SW(ω)| 2 =|SW(ω)|·|SW(ω)| Step 4.2: Calculate the frequency domain form of the ground response The frequency domain form of the earth response E(ω) is calculated according to the formula: Step 4.3: Calculate the phase of the frequency response; Calculate the phase of the frequency response S(ω) To ensure that the correlated frequency response has the same phase as the ground response; Step 4.4: Calculate the modulus of the frequency response; Compute the modulus |S(ω)| of the frequency response S(ω): |S(ω)|=|SW(ω)| 2 |E(ω)| Step 4.5: Calculate the frequency response; Calculate the frequency response Z(ω) after correlation according to the formula, eliminate the influence of the scanning signal, and extract the seismic signal; 5. The method for processing marine vibroseis seismic data based on frequency domain cross-correlation according to claim 2, characterized in that: The step 5 includes the following specific steps: Step 5.1: Perform RIFFT Use RIFFT to convert the correlated frequency response Z(ω) back to the time domain to obtain the final seismic trace time domain data z(t): Step 5.2: Calculate time domain data; According to the RIFFT formula, calculate the final seismic trace time domain data z(t): The above steps realize the conversion from frequency domain to time domain, obtain the final seismic trace time domain data z(t), eliminate the influence of the scanning signal, and extract the correlated seismic signal; and check whether the time domain data z(t) has eliminated the influence of the scanning signal to ensure the correctness and integrity of the time domain data z(t).

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