A method and system for nonlinear scanning signal with controllable time-frequency slope

Abstract

The present invention provides a method and system for a nonlinear scanning signal with controllable time-frequency slope, belonging to the field of geophysical exploration. The method first obtains a nonlinear scanning signal with controllable time-frequency slope, and then generates the frequency of the scanning signal by controlling the falling frequency of the weight of the controllable vibrator vehicle under the same initial frequency, end frequency and scanning duration, and generates the amplitude of the scanning signal by controlling the energy generated by the impact of the weight of the controllable vibrator vehicle with the ground surface, thereby generating a nonlinear scanning signal with controllable time-frequency slope. The present invention solves the problem that the nonlinear scanning signal is limited by the start and end frequencies, the duration of the scanning signal, and the like, and the change trend of the slope of the time-frequency curve cannot be freely controlled. The present invention can generate scanning signals with different time-frequency slopes according to different geological conditions, thereby more flexibly highlighting the advantageous frequency band of the formation or compensating for high-frequency information than conventional nonlinear scanning signals, and achieving the effect of optimizing conventional nonlinear scanning signals.

Description

Technical Field

[0001] The present invention belongs to the field of geophysical exploration, and in particular relates to a method and system for nonlinear scanning signals with controllable time-frequency slope, which can be applied to the wavelet design of scanning signals in controllable vibroseis seismic exploration. Background Art

[0002] Vibroseis is not only a safe and environmentally friendly artificial excitation source, but also has good controllability. Its wavelet frequency and amplitude can be manually designed to improve the quality of seismic data acquisition. With the development of acquisition technologies such as flip-flop sweep, slip-sweep, independent simultaneous sweep (ISS), and high fidelity sweep (HFVS), the acquisition efficiency of vibroseis seismic exploration has become higher.

[0003] Unlike the short-duration narrow pulse signals emitted by other artificially excited seismic sources such as explosives and air guns, the signals emitted by controllable seismic sources are scanning signals with frequencies that continuously change over time. The duration of the scanning signal is very long, usually greater than 20 seconds, so as to ensure that the energy intensity of the deep signal can meet the exploration requirements; the initial vibration record received will be cross-correlated with the scanning signal excited by the source, and the long initial vibration record can be compressed into a short seismic record similar to the explosive source. The compression process is equivalent to the convolution of the Klauder wavelet produced by the autocorrelation of the scanning signal and the formation reflection coefficient. Therefore, the resolution of the scanning signal can be evaluated by analyzing its autocorrelation Klauder wavelet. The larger the main-sidelobe ratio of the autocorrelation wavelet, the higher the resolution of the corresponding scanning signal.

[0004] Scanning signals can be divided into linear scanning signals and nonlinear scanning signals through the design of different time-frequency curves. Nonlinear scanning signals can be further divided into pseudo-random scanning, anti-linear scanning, square scanning, square root scanning, exponential scanning, etc. (Baeten G, Ziolkowski A. The vibroseis source [M]. Elsevier Science Limted, 1990). The instantaneous frequency of the linear scanning signal increases linearly with time, and the appearance time of each frequency band is the same. It is simple in design, not difficult to operate, and easy to implement.

[0005] At present, most of the domestic vibroseis seismic exploration projects use linear scanning signals (Wang Hongti, Zhuang Cantao, Xue Bing, et al. Precision active earthquake monitoring [J]. Geophysical exploration equipment, 2001, 11 (1): 9-15; Liu Xigeng, Cui Rensheng, Wang Hongti. Detection of precision vibroseis signals using Wigner-Hough transform [J]. Earthquake, 2013), 33 (3): 33-42). However, due to the single frequency change of linear scanning signals, the energy of all frequency bands is the same, resulting in that its frequency components cannot freely adapt to complex geological environments, especially it is difficult to meet the requirements for low-frequency energy in actual exploration, thus affecting the exploration depth and the resolution of the autocorrelation Kluader. Therefore, it is necessary to introduce nonlinear scanning signals to highlight the energy of a certain dominant frequency band that meets the seismic geological conditions and improve the resolution of the strata; for special work areas with severe high-frequency attenuation and a great impact on the signal-to-noise ratio, the high-frequency compensation effect can be achieved by enhancing the high-frequency components.

[0006] However, for conventional nonlinear scanning signals, once the initial frequency, end frequency, scanning duration and other parameters are determined, the slope of the time-frequency curve at different times is also determined, and the energy distribution intensity of its different frequency components is also determined. Currently, there is no technology that can solve the problem of keeping the slope of the time-frequency curve of a nonlinear scanning signal unchanged. Summary of the invention

[0007] The purpose of the present invention is to solve the difficulties existing in the above-mentioned prior art, and to provide a method and system for a nonlinear scanning signal with controllable time-frequency slope, so as to solve the problem of the unchanged slope of the time-frequency curve of the nonlinear scanning signal, and to control the change of the time-frequency slope, and to freely allocate the energy of different frequency bands of the scanning signal, so as to flexibly adapt to the requirements of different geological conditions for the frequency components of the seismic wave field.

[0008] The present invention is achieved through the following technical solutions:

[0009] The first aspect of the present invention provides a method for a nonlinear scanning signal with a controllable time-frequency slope. The method first obtains a nonlinear scanning signal with a controllable time-frequency slope, and then generates the frequency of the scanning signal by controlling the falling frequency of the weight of a controllable seismic source vehicle under the same initial frequency, end frequency, and scanning duration, and generates the amplitude of the scanning signal by controlling the energy generated by the impact of the weight of the controllable seismic source vehicle with the ground, thereby generating a nonlinear scanning signal with a controllable time-frequency slope.

[0010] A further improvement of the present invention is that the method comprises:

[0011] (1) Design square time-frequency function;

[0012] (2) adding a phase control factor and a first-order term to the square time-frequency function to obtain a nonlinear time-frequency function with controllable slope;

[0013] (3) Obtain the instantaneous phase;

[0014] (4) Design the sweep signal ramp duration and its corresponding amplitude envelope function;

[0015] (5) generating a nonlinear vibroseis scanning signal with controllable time-frequency slope;

[0016] (6) The frequency component of the nonlinear scanning signal is adjusted by changing the value of the phase control factor.

[0017] A further improvement of the present invention is that the operation of step (1) comprises:

[0018] The squared time-frequency function is as follows:

[0019]

[0020] Among them, f max is the maximum frequency, that is, the maximum number of times the weight falls per unit time, f min is the minimum frequency, that is, the minimum number of times the weight falls per unit time, t max is the time that the heavy hammer continues to hit the ground, and t is the time variable.

[0021] A further improvement of the present invention is that f in step (1) min The value range is 3-10HZ;

[0022] f max The value range is 80-120HZ;

[0023] t max The value range is 15s-30s.

[0024] A further improvement of the present invention is that the nonlinear time-frequency function with controllable slope obtained in step (2) is as follows:

[0025]

[0026] a is the phase control factor, and the value range of a is between -1 and 1.

[0027] A further improvement of the present invention is that the operation of step (3) comprises:

[0028] The instantaneous phase Φ(t) is obtained using the following formula:

[0029]

[0030] A further improvement of the present invention is that the operation of step (4) comprises:

[0031] The amplitude envelope function A(t) is obtained using the following formula:

[0032]

[0033] Among them, t l is the sweep signal ramp duration.

[0034] A further improvement of the present invention is that the operation of step (5) comprises:

[0035] The nonlinear vibroseis scanning signal W(t) with controllable time-frequency slope is calculated using the following formula:

[0036] W(t)=A(t)*sin(φ(t)).

[0037] A further improvement of the present invention is that the operation of step (6) comprises:

[0038] When a=0, the energy of each frequency component in the obtained nonlinear scanning signal is the same;

[0039] When a increases from -1 to 0, the energy ratio of the low-frequency component in the obtained nonlinear scanning signal will gradually increase. When a deeper exploration depth is required, the value of a is controlled between -1 and 0.

[0040] When a increases from 0 to 1, the energy ratio of the high-frequency component in the obtained nonlinear scanning signal will gradually increase. When a more precise exploration resolution is required, the value of a is controlled between 0 and 1.

[0041] In a second aspect of the present invention, a system for a nonlinear scanning signal with controllable time-frequency slope is provided, the system comprising: a memory, a processor, and a computer program stored in the memory, wherein the computer program executes the following steps when executed by the processor:

[0042] (1) Design square time-frequency function;

[0043] (2) adding a phase control factor and a first-order term to the square time-frequency function to obtain a nonlinear time-frequency function with controllable slope;

[0044] (3) Obtain the instantaneous phase;

[0045] (4) Design the sweep signal ramp duration and its corresponding amplitude envelope function;

[0046] (5) generating a nonlinear vibroseis scanning signal with controllable time-frequency slope;

[0047] (6) The frequency component of the nonlinear scanning signal is adjusted by changing the value of the phase control factor.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention solves the problem that the nonlinear scanning signal is restricted by the start and end frequencies, the duration of the scanning signal and other factors, and the changing trend of the slope of the time-frequency curve cannot be freely controlled. The present invention can generate scanning signals with different time-frequency slopes according to different geological conditions, thereby more flexibly highlighting the advantageous frequency band of the formation or compensating for high-frequency information than conventional nonlinear scanning signals, thereby achieving the effect of optimizing conventional nonlinear scanning signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1-1 It is a conventional linear scanning signal;

[0051] Figure 1-2 is the time-frequency function of a conventional linear sweep signal;

[0052] Figure 1-3 is the frequency domain amplitude spectrum of the conventional linear scanning signal;

[0053] Figure 1-4 is the autocorrelation Klauder wavelet of the conventional linear scan signal;

[0054] Figure 2 Six nonlinear time-frequency curves with different slopes are generated by selecting different frequency control factors a for the present invention;

[0055] Figure 3-1 When the time-frequency control factor a=0.3, the time-frequency slope can be controlled nonlinear scanning signal;

[0056] Figure 3-2 is the time-frequency function of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=0.3;

[0057] Figure 3-3 The frequency domain amplitude spectrum of the time-frequency slope controllable nonlinear scanning signal when the time-frequency control factor a=0.33;

[0058] Figure 3-4 The autocorrelation Klauder wavelet of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=0.3;

[0059] Figure 4-1 When the time-frequency control factor a=0.5, the time-frequency slope can be controlled nonlinear scanning signal;

[0060] Figure 4-2 is the time-frequency function of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=0.5;

[0061] Figure 4-3 is the frequency domain amplitude spectrum of the time-frequency slope controllable nonlinear scanning signal when the time-frequency control factor a=0.5;

[0062] Figure 4-4 The autocorrelation Klauder wavelet of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=0.5;

[0063] Figure 5-1 When the time-frequency control factor a=0.8, the time-frequency slope can be controlled nonlinear scanning signal;

[0064] Figure 5-2 is the time-frequency function of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=0.8;

[0065] Figure 5-3 is the frequency domain amplitude spectrum of the time-frequency slope controllable nonlinear scanning signal when the time-frequency control factor a=0.8;

[0066] Figure 5-4 The autocorrelation Klauder wavelet of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=0.8;

[0067] Figure 6-1 When the time-frequency control factor a=-0.3, the time-frequency slope can be controlled nonlinear scanning signal;

[0068] Figure 6-2 is the time-frequency function of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=-0.3;

[0069] Figure 6-3 The frequency domain amplitude spectrum of the time-frequency slope controllable nonlinear scanning signal when the time-frequency control factor a=-0.3;

[0070] Figure 6-4 The autocorrelation Klauder wavelet of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=-0.3;

[0071] Figure 7-1 When the time-frequency control factor a=-0.5, the time-frequency slope can be controlled nonlinear scanning signal;

[0072] Figure 7-2 is the time-frequency function of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=-0.5;

[0073] Figure 7-3 The frequency domain amplitude spectrum of the time-frequency slope controllable nonlinear scanning signal when the time-frequency control factor a=-0.5;

[0074] Figure 7-4 The autocorrelation Klauder wavelet of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=-0.5;

[0075] Figure 8-1When the time-frequency control factor a=-0.8, the time-frequency slope can be controlled nonlinear scanning signal;

[0076] Figure 8-2 is the time-frequency function of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=-0.8;

[0077] Figure 8-3 is the frequency domain amplitude spectrum of the time-frequency slope controllable nonlinear scanning signal when the time-frequency control factor a=-0.8;

[0078] Figure 8-4 The autocorrelation Klauder wavelet of the nonlinear scanning signal with controllable time-frequency slope when the time-frequency control factor a=-0.8;

[0079] Fig. 9 Comparison of amplitude spectra obtained by spectrum analysis of nonlinear scanning signals with controllable time-frequency slopes for different frequency control factors a=0.3, a=0.5, a=0.8, a=-0.3, a=-0.5, a=-0.8;

[0080] Fig.10 A flowchart of the steps of the method of the present invention. DETAILED DESCRIPTION

[0081] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0082] The present invention uses a nonlinear scanning signal with controllable time-frequency slope (i.e., a nonlinear controllable seismic source scanning signal W(t) with controllable time-frequency slope obtained in the following step (5)), and flexibly generates time-frequency curves of different forms under the same parameters such as initial frequency, termination frequency, and scanning duration (a time-frequency curve refers to a frequency variation trend at different times, and its function expression before improvement is f(t) in the following step (1), and an improved time-frequency curve F(t) with controllable slope is obtained by adding a phase control factor a; F(t) is substituted into Φ(t) to obtain an instantaneous phase; and the instantaneous phase Φ(t) is substituted into the formula of the following step (5) to obtain a "nonlinear scanning signal with controllable time-frequency slope" W(t)), so that its time-frequency curve is controllable, thereby flexibly controlling the frequency component of the scanning signal.

[0083] The specific implementation method is as follows: design the maximum frequency, minimum frequency, scanning duration and square time-frequency function f(t); add the slope control factor a and the first-order term to the square time-frequency function f(t) to obtain the nonlinear time-frequency function F(t) with controllable slope; integrate the nonlinear time-frequency function F(t) with controllable slope to obtain the instantaneous phase Φ(t); design the ramp time and its corresponding amplitude envelope function A(t); combine the instantaneous phase function and the amplitude envelope function with the sine function to generate a nonlinear controllable seismic source scanning signal with controllable time-frequency slope.

[0084] like Fig.10 As shown, the method of the present invention comprises:

[0085] (1) Design the maximum frequency, minimum frequency, sweep duration, and the square of the instantaneous frequency increasing with time, f(t), as follows:

[0086]

[0087] Among them, f max is the maximum frequency, f min is the minimum frequency, t max is the scanning duration, and t is the time variable.

[0088] The method of the present invention mainly generates the frequency of the scanning signal by controlling the falling frequency of the weight of the controllable vibrator vehicle, and generates the amplitude of the scanning signal by the energy generated by the impact with the ground surface. The scanning signal is the wave field signal generated by the impact of the weight.

[0089] In actual seismic exploration, the scanning signal is generated by continuously hitting the ground with a heavy hammer from a vibrator vehicle to obtain a series of vibration wave fields. The actual vibrator excitation is often a process in which a heavy hammer continuously hits the ground. The time taken for this process can be expressed as t max It means that the speed of the hammer falling gradually increases or decreases during this process; the number of times the hammer hits the ground in a unit time is the frequency f(t) described in this formula, and the maximum number of times the hammer falls in a unit time is the maximum frequency f max , the weight falls the least number of times per unit time, that is, the minimum frequency f min ; The difference between the maximum frequency and the minimum frequency is the frequency band of the vibroseis wave field excited by the weight. Theoretically, the smaller the minimum frequency and the higher the maximum frequency, the wider the frequency band, and the higher the accuracy of the corresponding seismic exploration. However, in actual exploration, due to the constraints of physical factors such as the weight and underground medium, the minimum frequency is usually selected in the range of 3-10HZ and the maximum frequency is selected in the range of 80-120HZ. Similarly, the longer the duration, the stronger the wave field energy obtained by the vibroseis source. However, due to the influence of the actual seismic exploration acquisition efficiency, the duration t max It is usually selected between 15s-30s.

[0090] (2) Adding the phase control factor a and the first-order term to the square time-frequency function f(t) yields a nonlinear time-frequency function F(t) with controllable slope, as shown in the following formula:

[0091]

[0092] Among them, when the maximum frequency and the minimum frequency remain unchanged, the phase control factor a is the key to controlling the change of the slope of the time-frequency curve, and is also the key point of the method of the present invention.

[0093] (3) Integrate the slope-controllable nonlinear time-frequency function F(t) to obtain the instantaneous phase Φ(t). The instantaneous phase calculation formula is as follows:

[0094]

[0095] (4) Design the sweep signal ramp duration and its corresponding amplitude envelope function A(t), the formula is as follows:

[0096]

[0097] Among them, t l is the duration of the scanning signal slope. Since the scanning signal that appears suddenly or ends suddenly has mutation, it will cause oscillations at both ends of the signal spectrum. This oscillation is the Gibbs effect. In actual seismic exploration, at the beginning of the excitation, the amplitude is gradually increased to the most expected amplitude, and at the end of the excitation, the expected amplitude is gradually weakened to 0. The time of gradual increase to obtain the gradual weakening is the duration of the scanning signal slope, which weakens the mutation of the scanning signal at the beginning and end, and thus the Gibbs effect. In actual work, t is usually determined comprehensively based on the actual seismic acquisition efficiency and the attenuation effect of the Gibbs effect. l The value of the parameter.

[0098] The purpose of the amplitude envelope function is to reduce the Gibbs effect caused by the sudden change of frequency energy. Through the setting of this function, the amplitude ramp phenomenon of the same duration appears at both ends of the scanning signal.

[0099] (5) The instantaneous phase function and the amplitude envelope function are combined with the sine function to generate a nonlinear vibroseis scanning signal W(t) with controllable time-frequency slope. The formula is as follows:

[0100] W(t)=A(t)*sin(φ(t))

[0101] (6) The frequency component of the nonlinear scanning signal is adjusted by changing the value of the phase control factor a.

[0102] After the nonlinear vibroseis scanning signal W(t) is obtained, the wave field signal required for seismic exploration is generated by the hammer of the vibroseis vehicle. Therefore, through the invention, the value of parameter a can be changed to adjust the frequency component of the vibroseis exploration wave field signal, while the starting frequency and scanning time of the scanning signal are not changed, and the efficiency of vibroseis acquisition is not changed, as follows:

[0103] The value range of a is between -1 and 1; when a=0, the energy of each frequency component in the obtained wavefield signal (i.e., nonlinear scanning signal) is the same; when the parameter a increases from -1 to 0, the energy ratio of the low-frequency component in the obtained wavefield signal will gradually increase. When a deeper exploration depth is required, the value of parameter a can be controlled in this range; when the parameter a increases from 0 to 1, the energy ratio of the high-frequency component in the obtained wavefield signal will gradually increase. When a more precise exploration resolution is required, the value of parameter a can be controlled in this range.

[0104] Figure 1-1 to Figure 1-4 is a conventional linear scanning signal and its related properties diagram, where Figure 1-1 It is a conventional linear scanning signal; Figure 1-2 As its time-frequency function, the frequency increases linearly with time; Figure 1-3 This is its frequency domain amplitude spectrum, and it can be seen that each frequency component has the same energy; Figure 1-4 For its autocorrelation Klauder wavelet, the main-sidelobe ratio of the wavelet can reflect the resolution of the original scanning signal in the time domain.

[0105] The embodiments of the present invention are as follows:

[0106] [Example 1]

[0107] First, the maximum frequency is designed to be 84 Hz, the minimum frequency is 5 Hz, the slope duration at both ends is 1 s, and the sampling interval is 1 ms; then 6 different time-frequency slope control factors a are added, and the generated scanning signal is subjected to time-frequency analysis and autocorrelation analysis, thereby verifying that the present invention can flexibly control the frequency component of the scanning signal and the slope of the time-frequency curve. Specific achievements are as follows Figure 2 As shown, Figure 2 The figure shows the time-frequency curve comparison diagram obtained by selecting different frequency control factors a=0.3, a=0.5, a=0.8, a=-0.3, a=-0.5, a=-0.8 in the present invention. Figure 2 It can be seen that different slopes of the time-frequency curves will affect the frequency components of the corresponding scanning signals, which will be explained in detail in the subsequent figures. Figure 2 It is also verified that the present invention has the advantage of controlling the slope of the time-frequency curve, and a nonlinear time-frequency curve with different time-frequency slopes can be obtained by simply changing the time-frequency control factor a.

[0108] [Example 2]

[0109] Figure 3-1 to Figure 3-4 When the time-frequency control factor a=0.3, the time-frequency slope can be controlled nonlinear scanning signal and its related properties, where Figure 3-1 It is a nonlinear scanning signal with controllable time-frequency slope; Figure 3-2 As its time-frequency function, the frequency increases nonlinearly with time, the growth rate of low frequency is smaller than that of high frequency, and the curvature is smaller; Figure 3-3 The frequency domain amplitude spectrum obtained by spectrum analysis of the generated scanning signal shows that the energy of low-frequency components is stronger than that of high-frequency components. Figure 3-4 The autocorrelation Klauder wavelet is obtained by autocorrelating the swept frequency signal, and the main-sidelobe ratio of the wavelet is greater than that of the Klauder wavelet of the linear signal.

[0110] [Example 3]

[0111] Figure 4-1 to Figure 4-4 When the time-frequency control factor a=0.5, the time-frequency slope can be controlled nonlinear scanning signal and its related properties, where Figure 4-1 It is a nonlinear scanning signal with controllable time-frequency slope; Figure 4-2 As its time-frequency function, the frequency increases nonlinearly with time, the growth rate of low frequency is smaller than that of high frequency, and the curvature is greater than Figure 3-2 The curvature of the mid-scan signal; Figure 4-3 The frequency domain amplitude spectrum obtained by spectrum analysis of the generated scanning signal shows that the low-frequency component has stronger energy than the high-frequency component, and the ratio of low frequency to the full frequency band is greater than Figure 3-3 ; Figure 4-4 The autocorrelation Klauder wavelet is obtained by autocorrelating the frequency sweep signal, and the main-sidelobe ratio of the wavelet is greater than the Klauder wavelet of the sweep signal in FIG. 3 .

[0112] [Example 4]

[0113] Figure 5-1 to Figure 5-4 When the time-frequency control factor a=0.8, the time-frequency slope can be controlled nonlinear scanning signal and its related properties, where Figure 5-1 It is a nonlinear scanning signal with controllable time-frequency slope; Figure 5-2 As its time-frequency function, the frequency increases nonlinearly with time, the growth rate of low frequency is smaller than that of high frequency, and the curvature is greater than Figure 4-2 The curvature of the mid-scan signal; Figure 5-3 The frequency domain amplitude spectrum obtained by spectrum analysis of the generated scanning signal shows that the low-frequency component has stronger energy than the high-frequency component, and the ratio of low frequency to the full frequency band is greater than Figure 4-3 ; Figure 5-4 The autocorrelation Klauder wavelet is obtained by autocorrelating the swept frequency signal. The main lobe to side lobe ratio of the wavelet is greater than Figure 4-4 Klauder wavelet of the scanned signal.

[0114] [Example 5]

[0115] Figure 6-1 to Figure 6-4 When the time-frequency control factor a = -0.3, the time-frequency slope can be controlled nonlinear scanning signal and its related properties, where Figure 6-1 It is a nonlinear scanning signal with controllable time-frequency slope; Figure 6-2 As its time-frequency function, the frequency increases nonlinearly with time, the growth rate of low frequency is stronger than that of high frequency, the growth rate of low frequency is greater than that of high frequency, and the curvature is small; Figure 6-3 The frequency domain amplitude spectrum obtained by spectrum analysis of the generated scanning signal shows that the energy of low-frequency components is weaker than that of high-frequency components. Figure 6-4 The autocorrelation Klauder wavelet is obtained by autocorrelating the swept frequency signal. The main lobe ratio of the wavelet is less than Figure 1-4 Klauder wavelet of a linear scan signal.

[0116] [Example 6]

[0117] Figure 7-1 to Figure 7-4 When the time-frequency control factor a=-0.5, the time-frequency slope can be controlled nonlinear scanning signal and its related properties, where Figure 7-1 It is a nonlinear scanning signal with controllable time-frequency slope; Figure 7-2 As its time-frequency function, the frequency increases nonlinearly with time, the low-frequency growth rate is stronger than the high-frequency growth rate, the low-frequency growth rate is greater than the high-frequency growth rate, and the curvature is greater than Figure 6-2 The curvature of the medium time-frequency curve; Figure 7-3 The frequency domain amplitude spectrum obtained by spectrum analysis of the generated scanning signal shows that the energy of low-frequency components is weaker than that of high-frequency components. Figure 7-4 The autocorrelation Klauder wavelet is obtained by autocorrelating the swept frequency signal. The main lobe ratio of the wavelet is less than Figure 6-4 Klauder wavelet of the scanned signal.

[0118] [Example 7]

[0119] Figure 8-1 to Figure 8-4 When the time-frequency control factor a=-0.8, the time-frequency slope can be controlled nonlinear scanning signal and its related properties, where Figure 8-1 It is a nonlinear scanning signal with controllable time-frequency slope; Figure 8-2 As its time-frequency function, the frequency increases nonlinearly with time, the low-frequency growth rate is stronger than the high-frequency growth rate, the low-frequency growth rate is greater than the high-frequency growth rate, and the curvature is greater than Figure 7-2 The curvature of the medium time-frequency curve; Figure 8-3 The frequency domain amplitude spectrum obtained by spectrum analysis of the generated scanning signal shows that the energy of low-frequency components is weaker than that of high-frequency components. Figure 8-4 The autocorrelation Klauder wavelet is obtained by autocorrelating the swept frequency signal. The main lobe ratio of the wavelet is less than Figure 7-4 Klauder wavelet of the scanned signal.

[0120] The spectrum analysis of the nonlinear scanning signal with controllable time-frequency slope generated by selecting different frequency control factors a=0.3, a=0.5, a=0.8, a=-0.3, a=-0.5, a=-0.8 is performed, and the amplitude spectrum comparison diagram obtained is as follows: Fig. 9 shown.

[0121] The spectrum of the nonlinear scanning signal with variable time-frequency slope designed by the present invention is: Fig. 9 This demonstrates the flexibility of the method of the present invention in controlling frequency components.

[0122] Through the results obtained from the above examples, it can be easily seen that the present invention is very flexible in controlling the slope and frequency component of the time-frequency curve. When other parameters remain unchanged, it is only necessary to change the value of the slope control factor a to obtain nonlinear scanning signals with different frequency components. This can achieve the degree of controlling the proportion of high and low frequency bands, highlighting the advantageous frequency bands, and meeting the different requirements of complex geological structures for controllable source frequencies in seismic exploration.

[0123] Finally, it should be explained that the above technical solution is only one implementation method of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and it is not limited to the method described in the above specific implementation method of the present invention. Therefore, the method described above is only preferred and does not have a restrictive meaning.

Claims

1. A method for nonlinear scanning signal with controllable time-frequency slope, characterized in that: The method first obtains a nonlinear scanning signal with controllable time-frequency slope, and then generates the frequency of the scanning signal by controlling the falling frequency of the weight of the controllable vibrator vehicle under the condition that the initial frequency, the end frequency and the scanning duration are the same, and generates the amplitude of the scanning signal by controlling the energy generated by the impact of the weight of the controllable vibrator vehicle with the ground surface, thereby generating a nonlinear scanning signal with controllable time-frequency slope; The method comprises: (1) Design square time-frequency function; (2) adding a phase control factor and a first-order term to the square time-frequency function to obtain a nonlinear time-frequency function with controllable slope; (3) Obtain the instantaneous phase; (4) Design the sweep signal ramp duration and its corresponding amplitude envelope function; (5) generating a nonlinear vibroseis scanning signal with controllable time-frequency slope; (6) adjusting the frequency component of the nonlinear scanning signal by changing the value of the phase control factor; The operation of step (4) includes: The amplitude envelope function A(t) is obtained using the following formula: Among them, t l is the sweep signal ramp duration, t is the time variable, t max The time that the heavy hammer continues to hit the ground.

2. The method for nonlinear scanning signal with controllable time-frequency slope according to claim 1, characterized in that: The operation of step (1) includes: The squared time-frequency function is as follows: Among them, f max is the maximum frequency, that is, the maximum number of times the weight falls per unit time, f min is the minimum frequency, that is, the minimum number of times the weight falls per unit time, t max is the time that the heavy hammer continues to hit the ground, and t is the time variable.

3. The method for nonlinear scanning signal with controllable time-frequency slope according to claim 2, characterized in that: In step (1), f min The value range is 3-10HZ; f max The value range is 80-120HZ; t max The value range is 15s-30s.

4. The method for nonlinear scanning signal with controllable time-frequency slope according to claim 3, characterized in that: The nonlinear time-frequency function with controllable slope obtained in step (2) is as follows: a is the phase control factor, and the value range of a is between -1 and 1.

5. The method for nonlinear scanning signal with controllable time-frequency slope according to claim 4, characterized in that: The operation of step (3) includes: The instantaneous phase Φ(t) is obtained using the following formula:

6. The method for nonlinear scanning signal with controllable time-frequency slope according to claim 5, characterized in that: The operation of step (5) includes: The nonlinear vibroseis scanning signal W(t) with controllable time-frequency slope is calculated using the following formula: W(t)=A(t)*sin(φ(t)).

7. The method for nonlinear scanning signal with controllable time-frequency slope according to claim 6, characterized in that: The operation of step (6) includes: When a=0, the energy of each frequency component in the obtained nonlinear scanning signal is the same; When a increases from -1 to 0, the energy ratio of the low-frequency component in the obtained nonlinear scanning signal will gradually increase. When a deeper exploration depth is required, the value of a is controlled between -1 and 0. When a increases from 0 to 1, the energy ratio of the high-frequency component in the obtained nonlinear scanning signal will gradually increase. When a more precise exploration resolution is required, the value of a is controlled between 0 and 1.

8. A system for nonlinear scanning signals with controllable time-frequency slope, characterized in that: The system comprises: a memory, a processor, and a computer program stored in the memory, wherein the computer program executes the following steps when executed by the processor: (1) Design square time-frequency function; (2) adding a phase control factor and a first-order term to the square time-frequency function to obtain a nonlinear time-frequency function with controllable slope; (3) Obtain the instantaneous phase; (4) Design the sweep signal ramp duration and its corresponding amplitude envelope function; (5) generating a nonlinear vibroseis scanning signal with controllable time-frequency slope; (6) adjusting the frequency component of the nonlinear scanning signal by changing the value of the phase control factor; The operation of step (4) includes: The amplitude envelope function A(t) is obtained using the following formula: Among them, t l is the sweep signal ramp duration, t is the time variable, t max The time that the heavy hammer continues to hit the ground.

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