Node-instrument-ground coupling frequency estimation method and system based on micro-box wave

Abstract

The embodiment of the application provides a node instrument-ground coupling frequency estimation method and system based on a micro box wave, and belongs to the technical field of geophysical exploration. The method comprises the following steps: setting a micro box wave explosion source, exciting a high main frequency seismic signal under preset energy and main frequency parameters, and taking the high main frequency seismic signal as an external excitation source for node instrument-ground coupling frequency determination; arranging a reference detector A and a measured node instrument B in a radiation range of the source, collecting seismic signals received by the reference detector A and the measured node instrument B; extracting first arrival segment signals of the reference detector A and the measured node instrument B from preprocessed signals, performing Fourier transform on the first arrival segment signals respectively to obtain amplitude spectra AmpA and AmpB, and calculating a ratio of the amplitude spectra to obtain an amplitude difference curve Ampr; performing smoothing processing on the amplitude difference curve Ampr, and taking a frequency corresponding to a first peak value in the amplitude difference curve Ampr as a ground coupling frequency of the measured node instrument B. The scheme significantly improves the resolution and stability of node instrument-ground coupling frequency determination.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration technology, specifically to a nodal instrument-earth coupling frequency estimation method based on micro-box waves and a nodal instrument-earth coupling frequency estimation system based on micro-box waves. Background Technology

[0002] In seismic exploration and geophysical observation, nodal geophones (NGMs) have been widely used in high-density seismic data acquisition due to their advantages such as flexible deployment, high degree of automation, and large data storage capacity. However, the detection accuracy of NGMs largely depends on their coupling performance with the Earth's surface medium. Insufficient coupling between the NGM and the Earth can lead to attenuation of high-frequency components of the seismic signal, phase distortion, and differences in signal response between different measuring points, thus directly affecting the signal-to-noise ratio, resolution, and reliability of the inversion results of the seismic data. Therefore, accurately assessing the coupling status between the NGM and the ground under field conditions has always been one of the key technical issues in the field of seismic acquisition.

[0003] Existing geophone coupling testing methods primarily rely on "coupling geophone" structures used in laboratory or semi-field conditions. These devices measure the vibration frequency response of the geophone-ground system by placing a mechanical excitation source inside the geophone. While this method can obtain relatively complete coupling characteristics, it depends on specially designed excitation components, making it difficult to implement in actual geophone deployment sites. Furthermore, this method is significantly dependent on the measurement results of a single geophone, failing to reflect the actual response characteristics of the geophone under real ground conditions.

[0004] On the other hand, conventional seismic coupling assessments rely on indirect judgments based on energy distribution or spectral ratios in seismic data. However, due to the limited frequency range of excitation signals and significant differences in propagation paths between different measurement points, these methods often fail to distinguish frequency changes caused by both stratigraphic characteristics and coupling states, resulting in significant uncertainty in the assessment results.

[0005] In summary, existing technologies for determining the geocoupled performance of nodal instruments mainly suffer from two problems: first, there is a lack of feasible methods to directly measure the coupling characteristics of nodal instruments under actual field deployment conditions; second, existing spectral analysis methods cannot effectively eliminate interference from differences in seismic sources and paths, making it difficult to obtain quantitative frequency indicators related to the coupling state of the nodal instrument itself. These problems keep the geocoupled performance assessment of nodal instruments at the qualitative judgment stage, limiting the further development of high-precision seismic observation and instrument quality control. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for estimating the coupling frequency of a nodal instrument based on micro-box waves, so as to at least solve the problem that the coupling characteristics of nodal instruments are difficult to accurately quantify under field conditions.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for estimating the nodal instrument-earth coupling frequency based on micro-box waves. The method includes: setting up a micro-box wave explosion source and exciting a high-frequency seismic signal under preset energy and dominant frequency parameters as an external excitation source for nodal instrument-earth coupling frequency determination; deploying a reference geophone A and a nodal instrument B under test within the radiation range of the source, acquiring the seismic signals received by the reference geophone A and the nodal instrument B under test, and performing preprocessing; extracting the first arrival segments of the reference geophone A and the nodal instrument B under test from the preprocessed signals, performing Fourier transforms on them respectively to obtain amplitude spectra AmpA and AmpB, and calculating their ratio to obtain an amplitude difference curve Ampr; smoothing the amplitude difference curve Ampr, and taking the frequency corresponding to the first peak value as the earth coupling frequency of the nodal instrument B under test.

[0008] Optionally, a miniature box wave explosion source is set up and a high-frequency seismic signal is excited under preset energy and dominant frequency parameters as an external excitation source for nodal instrument-earth coupling frequency determination. This includes: setting a preset source deployment location in the target surface area, and determining the burial depth of the miniature box wave explosion source based on the stratum cover thickness and medium density; setting ignition parameters and charge ratio to control the explosion energy and signal dominant frequency so that the excitation signal dominant frequency is within a preset high-frequency range, and the signal envelope maintains a single-peak structure in the time domain and meets the requirements for continuous energy distribution; collecting vibration signals near the surface during the excitation process to confirm the energy stability and dominant frequency consistency of the miniature box wave; and using the miniature box wave signal that has been confirmed to meet the energy and dominant frequency requirements as an external excitation source for nodal instrument-earth coupling frequency estimation.

[0009] Optionally, a pre-defined location for the seismic source is set in the target surface area, and the burial depth of the micro-box wave explosion source is determined based on the stratum cover thickness and medium density. This includes: acquiring stratum cover thickness data and shallow medium density parameters of the target surface area, and establishing a corresponding stratum acoustic wave propagation model; calculating the energy transfer coefficient and surface energy attenuation rate at different burial depths based on the stratum acoustic wave propagation model; determining the optimal burial depth of the micro-box wave explosion source under the condition of balancing the energy transfer coefficient and surface energy attenuation rate; and marking the source location corresponding to the optimal burial depth as the excitation point.

[0010] Optionally, a reference geophone A and a measured nodal instrument B are deployed within the radiation range of the seismic source. The seismic signals received by the reference geophone A and the measured nodal instrument B are acquired and preprocessed, including: selecting a deployment area within the radiation range of the seismic source; deploying the reference geophone A and the measured nodal instrument B at a preset interval in the same propagation direction; detecting the contact state of each deployment point using an accelerometer or level, and adjusting the contact angle and clamping force between the reference geophone A and the measured nodal instrument B and the ground to stabilize the coupling state; synchronously activating the acquisition channels of the reference geophone A and the measured nodal instrument B to record the seismic signals under the same excitation event; and preprocessing the acquired seismic signals to obtain the preprocessed signals.

[0011] Optionally, the acquired seismic signals are preprocessed to obtain preprocessed signals, including: performing DC offset removal and bandpass filtering on the acquired raw seismic signals to eliminate low-frequency drift and high-frequency noise interference; performing time window truncation on the filtered signals to retain effective bands containing the excitation wave and its main reflection components; performing amplitude normalization calibration based on the sensitivity coefficients and amplification factors of the reference geophone A and the measured node instrument B to unify the signal amplitude units; and performing sampling rate renormalization and phase alignment on the normalized signals to form the preprocessed signals.

[0012] Optionally, the first-arrival signals of the reference detector A and the device under test B are extracted from the preprocessed signal, and Fourier transforms are performed to obtain amplitude spectra AmpA and AmpB, respectively. The ratio of these spectra is then calculated to obtain the amplitude difference curve Ampr. This includes: determining the first-arrival time windows of the reference detector A and the device under test B based on the excitation time markers, and extracting the waveforms of the corresponding time periods as the first-arrival signals; performing multiple superposition averaging processes on the extracted first-arrival signals to reduce the impact of environmental random noise on the spectrum calculation; performing Fast Fourier Transforms on the averaged first-arrival signals to obtain the amplitude spectra AmpA and AmpB corresponding to the reference detector A and the device under test B, respectively; and calculating the amplitude ratio of AmpB to AmpA under a uniform frequency resolution to obtain the amplitude difference curve Ampr reflecting the difference in the frequency response of the two detectors.

[0013] Optionally, based on the averaged first-arrival signals, perform Fast Fourier Transform (FFT) to obtain the amplitude spectra AmpA and AmpB corresponding to the reference detector A and the tested node instrument B, respectively. This includes: applying the same type of window function to the averaged first-arrival signals of the reference detector A and the tested node instrument B to suppress spectral leakage; setting a uniform frequency resolution and number of sampling points, inputting the windowed time-domain signal into the FFT algorithm to obtain the corresponding complex frequency domain spectrum data; extracting the amplitude component from the complex frequency domain spectrum data and performing normalization processing to form the amplitude spectrum AmpA of the reference detector A and the amplitude spectrum AmpB of the tested node instrument B.

[0014] Optionally, the amplitude difference curve Ampr is smoothed, and the frequency corresponding to the first peak is taken as the earth coupling frequency of the measured node instrument B. This includes: applying a preset smoothing algorithm to the amplitude difference curve Ampr to suppress noise and obtain a smoothed difference curve Amprs; detecting local extreme points in Amprs and sorting them from low to high frequency; determining the frequency position of the first effective peak under the condition that the peak amplitude is higher than the average amplitude of the adjacent frequency band by a preset multiple; and recording the frequency value corresponding to the frequency position of the first effective peak as the earth coupling frequency output parameter of the measured node instrument B under the current surface medium conditions.

[0015] Optionally, the method further includes: repeatedly performing nodal instrument-ground coupling frequency estimation based on multiple micro-box wave excitation events to obtain multiple ground coupling frequency results of the nodal instrument B under each excitation; performing statistical analysis on the multiple ground coupling frequency results to calculate the frequency mean and standard deviation; when the standard deviation is lower than a preset stability threshold, determining that the ground coupling frequency measurement result of the nodal instrument B is valid, and using the mean as the final output parameter; when the standard deviation is higher than the stability threshold, identifying and removing abnormal excitation samples based on the frequency discrete distribution characteristics, recalculating the mean of the remaining results, and outputting the ground coupling frequency of the nodal instrument B after stability correction.

[0016] A second aspect of the present invention provides a nodal instrument-earth coupling frequency estimation system based on micro-box waves. The system is used in the aforementioned nodal instrument-earth coupling frequency estimation method based on micro-box waves. The system includes: an initialization unit, used to set up a micro-box wave explosion source and excite a high-frequency seismic signal under preset energy and dominant frequency parameters as an external excitation source for nodal instrument-earth coupling frequency determination; an acquisition unit, used to deploy a reference geophone A and a nodal instrument B under test within the radiation range of the source, acquire the seismic signals received by the reference geophone A and the nodal instrument B under test, and perform preprocessing; a processing unit, used to extract the first arrival segments of the reference geophone A and the nodal instrument B under test from the preprocessed signals, perform Fourier transforms to obtain amplitude spectra AmpA and AmpB respectively, and calculate their ratio to obtain an amplitude difference curve Ampr; and an output unit, used to smooth the amplitude difference curve Ampr and take the frequency corresponding to the first peak value as the earth coupling frequency of the nodal instrument B under test.

[0017] Through the above technical solution, this invention achieves quantitative determination of nodal instrument coupling performance under real surface conditions. Utilizing a micro-box wave explosion source to provide a high-frequency, stable external excitation signal significantly amplifies the coupling difference between the nodal instrument and the ground. Synchronous acquisition and normalization processing of the reference detector and the nodal instrument eliminates the influence of source characteristics and path differences. Based on the amplitude spectrum ratio, a difference curve is constructed and the peak frequency is extracted, achieving direct frequency domain quantization of the nodal instrument coupling state. This method can quickly and repeatedly obtain the ground coupling frequency of the nodal instrument under different surface conditions, providing a reliable basis for nodal instrument deployment quality assessment and performance testing, and significantly improving the accuracy and objectivity of coupling feature identification.

[0018] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the steps of a nodal instrument-ground coupling frequency estimation method based on micro-box wave provided by one embodiment of the present invention; Figure 2 This is a schematic diagram of the arrangement of a micro-box wave according to one embodiment of the present invention; Figure 3 This is a schematic diagram of the initial time-domain waveform provided in one embodiment of the present invention; Figure 4 This is a schematic diagram of the amplitude spectrum under different coupling conditions provided in one embodiment of the present invention; Figure 5 This is a schematic diagram of the amplitude spectrum difference curve provided in one embodiment of the present invention; Figure 6 This is a system structure diagram of a nodal instrument-earth coupling frequency estimation system based on micro-box wave provided by one embodiment of the present invention. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] Figure 1 This is a flowchart of a nodal instrument-ground coupling frequency estimation method based on micro-box wave provided by one embodiment of the present invention. Figure 1As shown, this invention provides a nodal instrument-ground coupling frequency estimation method based on micro-box wave, the method comprising: Step S10: Set up a miniature box wave explosion source and excite a high-frequency seismic signal under preset energy and dominant frequency parameters as an external excitation source for nodal instrument-earth coupling frequency determination.

[0022] Specifically, the location of the seismic source is predetermined in the target surface area, and the burial depth of the micro-box wave explosion seismic source is determined based on the thickness of the stratum cover and the density of the medium. Ignition parameters and charge ratio are set to control the explosion energy and the dominant frequency of the signal, so that the dominant frequency of the excitation signal is within the predetermined high-frequency range, and the signal envelope maintains a single-peak structure in the time domain and meets the requirements of continuous energy distribution. Vibration signals near the ground surface are collected during the excitation process to confirm the energy stability and dominant frequency consistency of the micro-box wave. The micro-box wave signal that has been confirmed to meet the energy and dominant frequency requirements is used as the external excitation source for nodal instrument-earth coupling frequency estimation.

[0023] Furthermore, the location of the seismic source is pre-set in the target surface area, and the burial depth of the micro-box wave explosion source is determined based on the stratum cover thickness and medium density. This includes: acquiring stratum cover thickness data and shallow medium density parameters of the target surface area, and establishing a corresponding stratum acoustic wave propagation model; calculating the energy transfer coefficient and surface energy attenuation rate at different burial depths based on the stratum acoustic wave propagation model; determining the optimal burial depth of the micro-box wave explosion source under the condition of balancing the energy transfer coefficient and surface energy attenuation rate; and marking the source location corresponding to the optimal burial depth as the excitation point.

[0024] In this embodiment of the invention, it is necessary to plan the deployment location of the micro-box wave explosion source in the target surface area. Typically, areas with minimal surface undulation and relatively simple geological structures are selected to reduce interference from topography and shallow heterogeneity on the wave field. Parameters such as overburden thickness, medium density, and shallow wave velocity are obtained through on-site shallow geological surveys or existing geological profile data; these data form the basis for determining the source burial depth and energy parameters. Subsequently, a simplified ground-based acoustic wave propagation model is established, and the balance point between energy transfer and attenuation is obtained by calculating the energy transfer coefficient and surface energy attenuation rate at different burial depths.

[0025] Generally, the optimal burial depth in shallow sandy soil areas is about 0.6 to 1.2 meters. If the surface is cohesive soil or contains a layer of gravel, the burial depth needs to be appropriately increased to avoid energy loss. Through this method of calculation and test blast correction, the optimal burial depth of the micro-box wave explosion source can be determined, and the excitation point can be accurately marked on the surface, providing stable and controllable excitation conditions for subsequent nodal instrument testing.

[0026] In terms of energy parameter settings, strict control is required over the trigger delay of the ignition device, the charge ratio, and the sealing structure. The charge quantity should be determined based on the density of the formation and the sensitivity of the nodal instrument. Generally, a charge quantity capable of generating a signal with a dominant frequency range of 30-250Hz is selected, ensuring that the signal has sufficient high-frequency energy without waveform oversaturation in the near-field region. The ignition delay is controlled within the millisecond range to ensure that the dominant frequency of the excitation signal is concentrated and the waveform envelope maintains a single-peak structure. To avoid double-peak interference or frequency drift, paraffin wax or bentonite can be used to fill the orifice to form a stable energy reflection interface, thereby ensuring that the excitation wave exhibits continuous energy distribution characteristics in the time domain.

[0027] After excitation, reference vibration signals are collected by monitoring and detection points deployed near the ground surface. The energy spectrum and dominant frequency position are compared and analyzed to determine if the excitation signal reaches the designed frequency range. If the dominant frequency of the detected signal deviates from the target frequency band by more than 5%, the propellant dosage or ignition parameters need to be readjusted until a frequency-stable and amplitude-continuous excitation waveform is obtained. The validated miniature box wave signal exhibits a clear dominant frequency distribution, concentrated energy, and a smooth time-domain envelope, capable of significantly exciting minute coupling differences between the nodal instrument and the ground at high frequencies.

[0028] Through the above process, a stable external high-frequency excitation source can be constructed without the need for large-scale excitation equipment. This excitation signal exhibits good anisotropic spatial distribution and high energy concentration in its temporal structure, thus providing reliable excitation conditions for the accurate determination of the nodal instrument-earth coupling frequency.

[0029] The present invention achieves optimal propagation of the excitation signal within the target surface medium by rationally controlling the burial depth and energy parameters, thus ensuring that high-frequency components are fully preserved; it also ensures that the excitation signal has high repeatability and stable spectral characteristics, allowing direct comparison of the responses of different nodal instruments under the same excitation field, thereby eliminating measurement errors caused by differences in seismic sources.

[0030] In another possible implementation, the excitation of the micro-box wave explosion source does not employ the conventional method of burying explosive charges. Instead, it achieves surface-oriented excitation through a "semi-coupled shallow-buried gas explosion cavity" structure. Specifically, a shallow hole approximately 0.3-0.5 meters deep is drilled in the target area. A small amount of high-energy gas mixture is placed at the bottom of the hole, and the hole opening is covered with a controllable thickness of soil or rubber membrane to form a semi-closed cavity. At the moment of ignition, the gas explosion generates a short-duration high-pressure pulse. The micro-shock wave formed by the gas pressure expansion is reflected and superimposed by the cavity wall before propagating vertically to the ground surface, exciting a near-single-cycle high-frequency seismic wave. By adjusting the cavity volume and the thickness of the sealing material, the dominant frequency and energy distribution of the excitation wave can be precisely controlled, stabilizing the dominant frequency within the 50-300Hz range. This structure avoids the problem of excessive energy dissipation of explosives in deeply buried media. Furthermore, because the explosion cavity is semi-coupled, the excitation directionality is stronger, and the wave field is concentrated in the vertical direction, making it suitable for local nodal array testing.

[0031] To ensure consistent repeated excitation, an electric spark ignition device is used in conjunction with a gas mixing and metering valve to control the gas ratio and triggering time. After each excitation, the residual gas in the cavity is released through the exhaust port before the next filling.

[0032] Step S20: Deploy reference geophone A and the measured nodal instrument B within the radiation range of the seismic source, collect the seismic signals received by reference geophone A and measured nodal instrument B, and perform preprocessing.

[0033] Specifically, within the radiation range of the seismic source, a deployment area is selected, and the reference geophone A and the measured nodal instrument B are deployed at a preset interval along the same propagation direction. The contact state of each deployment point is detected by an accelerometer or level, and the contact angle and clamping force between the reference geophone A and the measured nodal instrument B and the ground are adjusted to ensure stable coupling. The acquisition channels of the reference geophone A and the measured nodal instrument B are simultaneously activated to record the seismic signals under the same excitation event. The acquired seismic signals are preprocessed to obtain the preprocessed signals.

[0034] Furthermore, the acquired seismic signals are preprocessed to obtain preprocessed signals, including: performing DC offset removal and bandpass filtering on the acquired raw seismic signals to eliminate low-frequency drift and high-frequency noise interference; performing time window truncation on the filtered signals to retain effective bands containing excitation waves and their main reflection components; performing amplitude normalization calibration based on the sensitivity coefficients and amplification factors of the reference geophone A and the measured node instrument B to unify the signal amplitude units; and performing sampling rate renormalization and phase alignment on the normalized signals to form the preprocessed signals.

[0035] In this embodiment of the invention, it is necessary to rationally plan the deployment area of ​​the reference geophone A and the measured nodal instrument B within the radiation range of the seismic source. Generally, areas with minimal surface undulation and relatively uniform soil density are selected to avoid signal distortion caused by local topographic or medium differences. The reference geophone A and the measured nodal instrument B are typically arranged along a propagation path consistent with the direction of arrival of the seismic source, maintaining approximately consistent wavefront incident angles. The spacing between the two types of sensors can be determined based on the length of the measurement line and the wavelength range, typically ranging from 10cm to 30cm, to ensure sufficient spatial sampling points are covered without waveform aliasing between adjacent sensors. After deployment, a level or miniature accelerometer is used to check the tilt angle and contact state of each deployment point. If necessary, the supports are lightly pressed or adjusted to ensure close contact between the geophone housing and the ground surface, with a flat contact surface and no air gaps, thereby ensuring stable coupling and sufficient signal energy transfer.

[0036] like Figure 2 In one possible implementation, a reference geophone A and a nodal instrument B array are deployed within approximately 100 meters of the micro-box wave explosion source. The reference geophone A is arranged in a 5×4 matrix on the left side of the array, and the nodal instrument B is arranged in a 5×4 matrix with the same spacing on the right side, with a 20cm distance between the two sets of devices. All geophones and nodal instruments are buried in the same direction and in close contact with the ground surface to ensure consistent incident conditions when the seismic waves arrive. During the excitation process, a high-frequency seismic signal is generated by the micro-box wave explosion source. The energy propagates in the surface medium and is simultaneously received by both sets of sensors. The acquired signals are normalized and Fourier transformed to calculate the amplitude spectrum ratio between the reference geophone A and the nodal instrument B, and a difference curve is plotted. Based on the frequency corresponding to the first peak of the difference curve, the earth coupling frequency of each nodal instrument B under the current surface medium conditions is determined, achieving a quantitative determination of the nodal instrument coupling performance.

[0037] After deployment, the reference geophone A and the measured nodal sensor B need to be synchronized to ensure that the sampling frequency, gain parameters, and trigger timing of the two acquisition channels are completely consistent. An external unified trigger line or wireless synchronization signal can be used to align the acquisition start times of the two sets of sensors, avoiding time drift during later signal comparison. It is particularly important to keep the nodal sensor's clock drift within ±1ms; otherwise, it will cause phase shifts in the high-frequency band. After the seismic source is excited, the two types of sensors synchronously acquire seismic signals, and each excitation data is stored as a waveform file for subsequent unified preprocessing.

[0038] The acquired raw signals often contain various interference components, requiring preprocessing to improve signal comparability. First, a DC offset removal operation is performed on the waveform to eliminate low-frequency bias caused by circuit zero drift and ground potential difference. Then, a bandpass filter is applied to limit the frequency range, typically using a passband parameter of 10Hz to 300Hz. Long-period interference below 10Hz and electrical noise above 300Hz are suppressed. The filtered waveform is then truncated into a time window, selecting an effective band containing the main excitation wave and the main reflection components. The length of this time window is usually calculated based on the distance between the seismic source and the receiving point and the ground wave velocity. For example, when the seismic source is 100m from the detection array, the time window can be 0.2s to 0.5s to cover the first wave while avoiding subsequent reflection overlap.

[0039] Amplitude normalization is a crucial step in ensuring direct comparison of data from reference detector A and node instrument B. Since the sensitivity coefficients and amplification factors of the two types of equipment differ, failure to calibrate will result in distorted spectral amplitudes. Specifically, the sensitivity calibration constants of each device are read, their corresponding output voltages or digital quantities are converted to velocity units (m / s), and then the waveforms of each channel are scaled according to the same amplitude standard, ensuring that the two sets of signals are physically identical. After normalization, sampling rate renormalization and phase alignment are also required. If the sampling rates are different, interpolation or resampling algorithms are used to unify them to the same frequency resolution; if there is a trigger time deviation, the phase difference is corrected using cross-correlation methods to align the two types of signals in the time domain.

[0040] After preprocessing, the obtained signals have a good basis for comparison, eliminating instrument differences and external noise while retaining spectral information reflecting the nodal instrument-ground coupling state. Reference detector A serves as a high-coupling benchmark, its waveform representing the actual surface vibration; the waveform of nodal instrument B includes ground coupling loss characteristics. The difference between the two under the same source excitation can be directly used for subsequent spectral ratio and coupling frequency analysis.

[0041] This setup and preprocessing method, through standardized setup and coupling state adjustment, ensures that each node instrument operates under the same wave field conditions, reducing errors caused by spatial inhomogeneity. Synchronous acquisition and normalization calibration guarantee the comparability of data from the reference detector and node instruments, ensuring that spectral differences fully reflect the instrument's coupling performance. Bandpass filtering, time window truncation, and phase alignment effectively improve the signal-to-noise ratio, providing high-quality input data for subsequent amplitude spectrum calculation and coupling frequency extraction.

[0042] Step S30: Extract the first arrival signals of the reference detector A and the measured node instrument B from the preprocessed signal, perform Fourier transform to obtain the amplitude spectra AmpA and AmpB respectively, and calculate their ratio to obtain the amplitude difference curve Ampr.

[0043] Specifically, the first arrival time windows of the reference detector A and the measured node instrument B are determined based on the excitation time marker, and the waveforms of the corresponding time periods are extracted as the first arrival segment signals. The extracted first arrival segment signals are subjected to multiple superposition and averaging processes to reduce the impact of environmental random noise on the spectrum calculation. Based on the averaged first arrival segment signals, fast Fourier transforms are performed to obtain the amplitude spectra AmpA and AmpB corresponding to the reference detector A and the measured node instrument B, respectively. The amplitude ratio of AmpB to AmpA is calculated under a uniform frequency resolution to obtain the amplitude difference curve Ampr, which reflects the difference in frequency response between the two detectors.

[0044] Furthermore, based on the averaged first-arrival signals, Fast Fourier Transform (FFT) is performed to obtain the amplitude spectra AmpA and AmpB corresponding to the reference detector A and the tested node instrument B, respectively. This includes: applying the same type of window function to the averaged first-arrival signals of the reference detector A and the tested node instrument B to suppress spectral leakage; setting a uniform frequency resolution and number of sampling points, and inputting the windowed time-domain signal into the FFT algorithm to obtain the corresponding complex frequency domain spectrum data; extracting the amplitude component from the complex frequency domain spectrum data and performing normalization processing to form the amplitude spectrum AmpA of the reference detector A and the amplitude spectrum AmpB of the tested node instrument B.

[0045] In this embodiment of the invention, after the preprocessing stage is completed, it is necessary to accurately extract the first-arrival segment data from the signal that represents the actual coupling state between the geophone and the ground. The first-arrival segment is the short waveform segment when the first wave of energy generated by the seismic source arrives. It usually carries the most direct surface response characteristics and is also the most sensitive part for judging the coupling performance between the geophone and the ground. The accuracy of its selection directly affects the reliability of subsequent spectrum calculations.

[0046] The method involves locating the arrival time of the first wave based on the time stamp triggered by the seismic source. The start and end points of the time window are determined by calculating the propagation delay between the source and the receiver, plus a safety margin. Typically, the first-arrival time window length is 0.05–0.2 seconds, adjusted based on the formation wave velocity and sampling frequency, ensuring the window fully covers the main energy envelope without introducing interference from subsequent reflected waves. The extracted waveform represents the first-arrival signal, corresponding to the first-wave responses of the reference geophone A and the measured nodal instrument B, respectively.

[0047] Due to unavoidable factors such as wind noise, mechanical vibration, and geoelectric interference in the field environment, signals from a single excitation often exhibit random fluctuations. To improve the stability of subsequent spectral analysis, multiple superposition and averaging processes are required for the first-arrival signal. Typically, the excitation is repeated 3-5 times, and the first-arrival signals obtained each time are aligned along the time axis and averaged point-by-point. Superposition and averaging effectively cancels out random noise while preserving the true seismic signal components with phase consistency. After averaging, the resulting waveform signal is smoother in the time domain, with a significantly improved signal-to-noise ratio, making it suitable for direct use in spectral calculations.

[0048] like Figure 3 In one possible implementation, the blue curve represents the first-arrival average waveform of the reference detector A, and the red curve represents the first-arrival average waveform of the tested nodal device B. Both maintain good synchronization in the time domain, with the main amplitude position and phase of the waveforms essentially consistent, indicating that the source signals received by the two types of sensors propagate along the same path and are excited synchronously. It can be seen that nodal device B experiences slight energy attenuation at the peak of the main amplitude, and the oscillation amplitude in the high-frequency portion is slightly smaller, reflecting that its coupling stiffness with the ground is slightly lower than that of the reference detector A. Obtaining this average first-arrival waveform effectively improves the signal-to-noise ratio, laying a data foundation for subsequent Fourier transform and amplitude spectrum ratio calculations.

[0049] During the spectrum analysis phase, to prevent energy leakage during the Fourier transform, a window function needs to be applied to the averaged time-domain signal. Commonly used window functions include the Hanning window or the Blackman window, both of which can effectively suppress sidelobes without weakening the main lobe energy. The reference detector A and the nodal device B must use the same window function to maintain computational comparability. Then, a uniform number of sampling points and frequency resolution are set, for example, 1024 or 2048-point FFT, to ensure that the two spectra are on the same frequency grid. The windowed signal is then input into a Fast Fourier Transform algorithm to obtain complex frequency domain spectrum data. The complex spectrum contains real and imaginary parts; by calculating its magnitude, the amplitude spectrum can be obtained, and then amplitude normalization is performed to eliminate residual differences in the gains of different sensors. This forms the amplitude spectrum AmpA of the reference detector A and the amplitude spectrum AmpB of the nodal device B under test, which can be directly compared in the frequency domain.

[0050] After obtaining AmpA and AmpB, the amplitude ratio AmpB / AmpA is calculated point-by-point at a uniform frequency resolution, yielding the amplitude difference curve Ampr. This ratio physically reflects the difference in response between the nodal instrument B and the reference detector A at various frequencies. If the nodal instrument has good coupling performance, the difference curve should be relatively stable in the low-frequency range, gradually showing energy attenuation as the frequency increases; if the coupling is poor, the decrease in the high-frequency range is more pronounced. By calculating this ratio, the influence of external factors such as changes in source energy and differences in propagation paths can be effectively eliminated, allowing the analysis to focus on the contact state between the nodal instrument and the ground.

[0051] In practice, the difference curve can be smoothed or interpolated to make it more continuous and facilitate subsequent peak identification. Typical smoothing algorithms include moving average or Savitzky-Golay polynomial fitting, with the window length selectable according to the frequency resolution. The smoothed Ampr curve can more clearly show the fluctuations in the frequency response, where the first obvious peak frequency often corresponds to the coupling resonance point of the nodal instrument-earth system, that is, its earth coupling frequency.

[0052] Step S40: Smooth the amplitude difference curve Ampr and take the frequency corresponding to the first peak as the ground coupling frequency of the measured node instrument B.

[0053] Specifically, a preset smoothing algorithm is used to suppress noise on the amplitude difference curve Ampr to obtain a smoothed difference curve Amprs; local extreme points are detected in Amprs and sorted by frequency from low to high; under the condition that the peak amplitude is higher than the average amplitude of the adjacent frequency band by a preset multiple, the frequency position of the first effective peak is determined; the frequency value corresponding to the frequency position of the first effective peak is recorded as the geodetic coupling frequency output parameter of the measured node instrument B under the current surface medium conditions.

[0054] In this embodiment of the invention, after obtaining the amplitude difference curve Ampr, it needs to be further smoothed to reduce high-frequency fluctuations caused by finite sampling, noise interference, and discrete Fourier transform in the spectrum calculation. A moving average or Savitzky-Golay polynomial smoothing algorithm is typically used. By setting a fixed window on the frequency axis, the curve is locally fitted, preserving the main peak shape while filtering out random oscillation components. The choice of window width depends on the frequency resolution, generally 5 to 10 times the frequency sampling interval. Too wide a window will cause peak blurring, while too narrow a window will not effectively suppress noise. After smoothing, the difference curve Amprs has a smoother and more continuous trend line, and the main peak position is clearly distinguishable.

[0055] Extremum detection was then performed on the Amprs. A scan along the frequency direction was performed to identify all local maxima, which were then numbered sequentially from low to high frequency. To prevent noise points from being misidentified as peaks, a peak validity criterion needed to be set, such as the amplitude needing to be higher than 1.2 times the average of neighboring frequency bands or higher than a preset multiple of the full-spectrum average. The first local peak meeting the criteria was defined as the valid peak. This peak frequency is typically located in the resonance region of the nodal instrument-ground interface, representing the first energy response inflection point of the nodal instrument-earth coupling system at the high-frequency end.

[0056] Once the location of the first valid peak value is determined, its corresponding frequency value can be extracted and marked as the geodetic coupling frequency of the nodal instrument. This frequency has a clear physical meaning: it reflects the overall stiffness and damping characteristics of the interface between the nodal instrument and the ground surface. The higher the frequency, the tighter the coupling between the nodal instrument and the ground, and the more efficient the signal transmission; if the frequency is too low, it indicates a loose contact or the presence of an air gap layer, resulting in weak coupling performance.

[0057] In practice, to improve the stability of the results, the Ampr curves obtained from multiple excitations can be smoothed and averaged before peak detection is performed to reduce random bias from a single excitation. If necessary, the standard deviation of the peak frequency can be calculated; if it is below a preset threshold (e.g., 5%), the measurement results are considered reliable. This frequency parameter is ultimately output as a quantitative characterization of the nodal instrument's ground coupling performance, which can be directly used for comparing different nodal instruments or evaluating the quality of field deployment.

[0058] Preferably, the method further includes: repeatedly performing nodal instrument-ground coupling frequency estimation based on multiple micro-box wave excitation events to obtain multiple ground coupling frequency results of the nodal instrument B under each excitation; performing statistical analysis on the multiple ground coupling frequency results to calculate the frequency mean and standard deviation; when the standard deviation is lower than a preset stability threshold, determining that the ground coupling frequency measurement result of the nodal instrument B is valid, and using the mean as the final output parameter; when the standard deviation is higher than the stability threshold, identifying and removing abnormal excitation samples based on the frequency discrete distribution characteristics, recalculating the mean of the remaining results, and outputting the ground coupling frequency of the nodal instrument B after stability correction.

[0059] In this embodiment of the invention, to further improve the reliability of the nodal instrument coupling frequency measurement results, multiple miniature box wave excitations can be performed under the same deployment conditions. The source energy of each excitation remains consistent, and the excitation interval is generally controlled between 30 seconds and 1 minute to avoid interference from surface stress release and residual wave field superposition. After each excitation, the response signals of the reference detector A and the nodal instrument B under test are re-recorded, and the aforementioned signal preprocessing, Fourier transform, difference spectrum construction, and peak extraction processes are repeated to obtain multiple sets of independent ground coupling frequency results.

[0060] After obtaining these frequency data, statistical analysis is performed. First, the mean μ and standard deviation σ of each measurement frequency are calculated to determine the stability of the results. When σ is below a preset threshold (usually within 5% of the mean), it indicates that the nodal instrument's response is consistent under repeated excitation, the coupling state is stable, and the mean of the measurement results can be directly used as the final earth coupling frequency output parameter. If the standard deviation exceeds the threshold, it means that individual excitation events are affected by external interference, such as fluctuations in the source charge, changes in shallow moisture, or slight changes in the instrument's contact state. In this case, based on the discrete characteristics of the frequency distribution, abnormal samples with large deviations from the mean are identified and removed. Then, the mean is recalculated for the remaining valid samples to obtain the coupling frequency results corrected for stability.

[0061] By employing this method of repeated excitation and statistical correction, the influence of random factors in a single experiment can be effectively offset, resulting in higher repeatability and representativeness of the measured ground coupling frequencies. This method can serve as a verification procedure for nodal instrument factory testing and can also be applied to the quality assessment of field deployment. Through repeated measurements and discrete analysis, a stability criterion framework is established, ensuring that the output coupling frequency data not only accurately reflects the physical contact state of the nodal instrument but also quantifies the reliability of the results, thereby significantly improving the overall accuracy and engineering applicability of the test.

[0062] In one possible implementation, the difference curve Ampr is obtained by comparing the amplitude spectra of the reference detector A and the nodal instrument under test B, and the coupling frequency of the nodal instrument is extracted from this curve. Figure 4 The figures illustrate the amplitude spectrum variations under different coupling conditions. The left figure shows the theoretical model results, and the right figure shows the actual measured spectrum distribution. It can be seen that in the theoretical simulation, the reference detector (red dashed line) exhibits a significant main peak at approximately 130Hz, while the nodal instrument (blue solid line) shows a lower amplitude and a slightly shifted peak position in this frequency band. This high-frequency energy attenuation reflects the contact damping effect between the nodal instrument and the ground. In the corresponding measured results, the spectral variation trends of both are consistent with the theory. The nodal instrument exhibits energy reduction at high frequencies, and its overall amplitude level is lower than that of the reference detector, verifying the model's rationality.

[0063] Based on this, the amplitude spectrum AmpB of the nodal instrument is compared with the amplitude spectrum AmpA of the reference detector to obtain the amplitude difference curve Ampr, as shown below. Figure 5 As shown in the figure, the left figure presents the theoretical calculation results, clearly showing the first significant peak at approximately 60Hz, which is the dominant coupling frequency of the nodal instrument-earth system. The right figure shows the actual measurement data; the smoothed curve shows a corresponding peak at approximately 55Hz, which highly matches the theoretical prediction. This peak represents the resonant response range between the nodal instrument and the Earth's surface interface, a key indicator characterizing coupling stiffness and energy transfer capability.

[0064] The results show that the difference curves between the theoretical and measured values ​​are consistent, both exhibiting characteristics of low-frequency stability and high-frequency attenuation. This method can quickly identify the coupling frequency of nodal instruments in specific surface media, avoiding errors caused by path effects and source energy differences, and enabling a quantitative assessment of the coupling performance of nodal instruments. The final results demonstrate that this frequency domain ratio analysis method can stably extract the coupling characteristic frequencies of nodal instruments under field conditions, providing a reliable technical means for nodal instrument deployment quality inspection and equipment consistency verification.

[0065] Figure 6 This is a system structure diagram of a nodal instrument-ground coupling frequency estimation system based on micro-box wave provided by one embodiment of the present invention. Figure 6 As shown, this invention provides a nodal instrument-earth coupling frequency estimation system based on micro-box wave. The system includes: an initialization unit, used to set up a micro-box wave explosion source and excite a high-frequency seismic signal under preset energy and dominant frequency parameters as an external excitation source for nodal instrument-earth coupling frequency determination; an acquisition unit, used to deploy a reference geophone A and a nodal instrument B under test within the radiation range of the source, acquire the seismic signals received by the reference geophone A and the nodal instrument B under test, and perform preprocessing; a processing unit, used to extract the first arrival segments of the reference geophone A and the nodal instrument B under test from the preprocessed signals, perform Fourier transforms to obtain amplitude spectra AmpA and AmpB respectively, and calculate their ratio to obtain the amplitude difference curve Ampr; and an output unit, used to smooth the amplitude difference curve Ampr and take the frequency corresponding to the first peak as the earth coupling frequency of the nodal instrument B under test.

[0066] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0067] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe the various possible combinations.

[0068] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the embodiments of the present invention, they should also be regarded as the content disclosed by the embodiments of the present invention.

Claims

1. A nodal-to-ground coupling frequency estimation method based on micro-box wave, characterized in that, The method includes: A miniature box wave explosion source was set up and a high-frequency seismic signal was excited under preset energy and dominant frequency parameters, which served as the external excitation source for nodal instrument-earth coupling frequency determination; Within the radiation range of the seismic source, a reference geophone A and a measured nodal instrument B are deployed to collect the seismic signals received by the reference geophone A and the measured nodal instrument B and perform preprocessing. The first arrival signals of the reference detector A and the measured node instrument B are extracted from the preprocessed signal. Fourier transforms are performed to obtain the amplitude spectra AmpA and AmpB, respectively, and their ratio is calculated to obtain the amplitude difference curve Ampr. The amplitude difference curve Ampr is smoothed, and the frequency corresponding to the first peak value is taken as the earth coupling frequency of the measured node instrument B.

2. The method according to claim 1, characterized in that, A miniature box-wave explosion source is set up to excite a high-frequency seismic signal under preset energy and dominant frequency parameters, serving as the external excitation source for nodal instrument-earth coupling frequency determination, including: The location of the seismic source is pre-set in the target surface area, and the burial depth of the micro-box wave explosion seismic source is determined based on the thickness of the stratum cover and the density of the medium. The ignition parameters and charge ratio are set to control the explosion energy and signal frequency, so that the excitation signal frequency is in a preset high frequency range, and the signal envelope maintains a single-peak structure in the time domain and meets the requirements of continuous energy distribution. Vibration signals near the Earth's surface were collected during the excitation process to confirm the energy stability and frequency consistency of the micro-box wave. The miniature box wave signal, which has been confirmed to meet the energy and main frequency requirements, is used as the external excitation source for the nodal instrument-ground coupling frequency estimation.

3. The method according to claim 2, characterized in that, Pre-determine the location of the seismic source in the target surface area, and determine the burial depth of the micro-box wave explosion source based on the thickness of the overburden and the density of the medium, including: Obtain the stratigraphic cover thickness data and shallow medium density parameters of the target surface area, and establish the corresponding stratigraphic acoustic wave propagation model; Based on the aforementioned stratum acoustic wave propagation model, the energy transfer coefficient and surface energy attenuation rate at different burial depths were calculated. Determine the optimal burial depth of the micro-box wave explosion source under the condition of balancing the energy transfer coefficient and the surface energy attenuation rate; The location of the seismic source corresponding to the optimal burial depth is marked as the excitation point.

4. The method according to claim 1, characterized in that, A reference geophone A and a measured nodal instrument B are deployed within the radiation range of the seismic source. The seismic signals received by the reference geophone A and the measured nodal instrument B are acquired and preprocessed, including: Within the radiation range of the seismic source, select a deployment area and deploy the reference geophone A and the measured node instrument B at a preset interval in the same propagation direction. The contact state of each deployment point is detected by accelerometer or level, and the contact angle and clamping force between the reference detector A and the measured node instrument B and the ground are adjusted to stabilize the coupling state. The acquisition channels of reference geophone A and the measured node instrument B are started simultaneously to record the seismic signal under the same excitation event; The acquired seismic signals are preprocessed to obtain preprocessed signals.

5. The method according to claim 4, characterized in that, The acquired seismic signals are preprocessed to obtain preprocessed signals, including: The acquired raw seismic signals were processed by DC offset removal and bandpass filtering to eliminate low-frequency drift and high-frequency noise interference. The filtered signal is subjected to time window truncation to retain the effective band containing the excitation wave and its main reflection components; Amplitude normalization calibration is performed based on the sensitivity coefficients and amplification factors of the reference detector A and the measured node instrument B to unify the signal amplitude unit; The normalized signal is subjected to sampling rate reshaping and phase alignment to form a preprocessed signal.

6. The method according to claim 1, characterized in that, The first arrival signals of the reference detector A and the measured node instrument B are extracted from the preprocessed signal. Fourier transforms are performed on them to obtain the amplitude spectra AmpA and AmpB, respectively, and their ratio is calculated to obtain the amplitude difference curve Ampr, including: The first arrival time window of the signals from the reference detector A and the measured node instrument B is determined based on the excitation time mark, and the waveform of the corresponding time period is extracted as the first arrival segment signal. Multiple superposition and averaging processes are performed on the captured initial arrival segment signal to reduce the impact of environmental random noise on spectrum calculation; Based on the averaged first-arrival segment signal, perform fast Fourier transform to obtain the amplitude spectra AmpA and AmpB corresponding to the reference detector A and the measured node instrument B; The amplitude ratio of AmpB to AmpA is calculated under a uniform frequency resolution, resulting in the amplitude difference curve Ampr, which reflects the difference in the frequency response of the two detectors.

7. The method according to claim 6, characterized in that, Based on the averaged first-arrival signals, Fast Fourier Transforms are performed to obtain the amplitude spectra AmpA and AmpB corresponding to the reference detector A and the measured node instrument B, respectively, including: The first arrival signals of the reference detector A and the measured node instrument B after averaging are respectively loaded with the same type of window function to suppress spectral leakage; By setting a uniform frequency resolution and number of sampling points, the windowed time-domain signal is input into the fast Fourier transform algorithm to obtain the corresponding complex frequency domain spectrum data. The amplitude components are extracted from the complex frequency domain spectrum data and normalized to form the amplitude spectrum AmpA of the reference detector A and the amplitude spectrum AmpB of the measured node instrument B.

8. The method according to claim 1, characterized in that, The amplitude difference curve Ampr is smoothed, and the frequency corresponding to the first peak value is taken as the ground coupling frequency of the measured node instrument B, including: The amplitude difference curve Ampr is subjected to noise suppression using a preset smoothing algorithm to obtain the smoothed difference curve Amprs; Detect local extrema in AMPRS and sort them by frequency from low to high; Determine the frequency position of the first effective peak value if the peak amplitude is higher than the average amplitude of the adjacent frequency band by a preset multiple. Record the frequency value corresponding to the frequency position of the first effective peak as the geodetic coupling frequency output parameter of the measured node instrument B under the current surface medium conditions.

9. The method according to claim 8, characterized in that, The method further includes: Based on repeated execution of nodal instrument-ground coupling frequency estimation based on multiple micro-box wave excitation events, multiple ground coupling frequency results of the tested nodal instrument B under each excitation are obtained. Perform statistical analysis on the multiple ground coupling frequency results to calculate the frequency mean and standard deviation; When the standard deviation is lower than the preset stability threshold, the earth coupling frequency measurement result of node instrument B is determined to be valid, and the mean value is used as the final output parameter. When the standard deviation is higher than the stability threshold, abnormal excitation samples are identified and removed based on the frequency discrete distribution characteristics. The mean of the remaining results is recalculated, and the stability-corrected geodetic coupling frequency of node instrument B is output.

10. A nodal-to-ground coupling frequency estimation system based on micro-box wave, characterized in that, The system is used to execute the nodal-to-ground coupling frequency estimation method based on micro-box wave as described in any one of claims 1-9, and the system comprises: The initial unit is used to set up a micro-box wave explosion source and excite a high-frequency seismic signal under preset energy and dominant frequency parameters, serving as an external excitation source for nodal instrument-earth coupling frequency determination; The acquisition unit is used to deploy reference geophone A and measured node instrument B within the radiation range of the seismic source, acquire the seismic signals received by reference geophone A and measured node instrument B, and perform preprocessing. The processing unit is used to extract the first arrival signals of the reference detector A and the measured node instrument B from the preprocessed signal, perform Fourier transform to obtain the amplitude spectra AmpA and AmpB respectively, and calculate their ratio to obtain the amplitude difference curve Ampr. The output unit is used to smooth the amplitude difference curve Ampr and take the frequency corresponding to the first peak as the earth coupling frequency of the measured node instrument B.

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