Frequency response calibration method and system for fiber optic accelerometer arrays used in microseismic monitoring

Abstract

This invention discloses a method and system for frequency response calibration of a fiber optic accelerometer array for microseismic monitoring, belonging to the field of fiber optic sensing and microseismic monitoring technology. This method obtains the precise frequency response function of each probe in the array and generates a corresponding frequency response compensation filter to eliminate the negative impact of hardware manufacturing parameter dispersion and improve the source interpretation accuracy of microseismic monitoring. Unlike traditional calibrations that only normalize the amplitude, this invention designs an inverse filter in the complex domain to correct both amplitude and phase distortion. This invention uses cross-power spectral density to calculate the transfer function, effectively suppressing interference from environmental noise on frequency response evaluation. This invention allows for relaxed hardware manufacturing tolerances for fiber optic sensors and achieves high-consistency digital compensation through a back-end digital compensation filter matrix, directly improving the accuracy of waveform cross-correlation and source localization.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing and microseismic monitoring technology, specifically, it relates to a method and system for calibrating the frequency response of a fiber optic accelerometer array for microseismic monitoring. Background Technology

[0002] Fiber optic accelerometer arrays are widely used in microseismic monitoring fields such as mine rockburst and oil and gas fracturing due to their advantages such as resistance to electromagnetic interference and ease of large-scale multiplexing. In microseismic monitoring, information such as the arrival time difference and waveform amplitude of microseismic waves received by the array is typically used to calculate the source location and assess the source energy.

[0003] However, during the manufacturing process of fiber optic accelerometer probes, due to limitations in machining tolerances, fiber optic packaging stress, and minute variations in material properties, the frequency response (including amplitude and phase characteristics) of each sensor unit in the array inevitably exhibits dispersion. This dispersion leads to varying degrees of waveform distortion in amplitude and phase even when facing the same microseismic signal. Waveform distortion severely affects the accuracy of cross-correlation analysis of microseismic signals, resulting in poor accuracy in calculated source location, energy, and other indicators, often failing to meet the practical application requirements of high-precision microseismic monitoring. To address these problems, this invention provides the following technical solution. Summary of the Invention

[0004] The purpose of this invention is to provide a frequency response calibration method and system for fiber optic accelerometer arrays used for microseismic monitoring. The aim is to obtain the accurate frequency response function of each probe in the array and generate a corresponding frequency response compensation filter to eliminate the negative impact of hardware manufacturing parameter dispersion and improve the source interpretation accuracy of microseismic monitoring.

[0005] The objective of this invention can be achieved through the following technical solutions: A frequency response calibration system for a fiber optic accelerometer array used for microseismic monitoring includes: The excitation subsystem includes a standard vibration table, a signal generator, and a power amplifier; The signal generator produces a broadband excitation signal covering the microseismic monitoring frequency band, which is then used to drive a standard vibration table to vibrate via a power amplifier. The oscillator system includes a high-precision standard accelerometer with flat frequency response characteristics and a fiber optic accelerometer under test. The vibration sensing subsystem is used to sense excitation signals and output corresponding electrical and optical signals; The fiber optic demodulation module is used to connect to the fiber optic accelerometer array to be calibrated, demodulate the optical phase change in real time, and output the acceleration signal to be measured. The charge amplification / conditioning module is connected to a high-precision standard accelerometer and is used to condition the output signal of the high-precision standard accelerometer. The clock synchronization module is used to provide a high-precision external synchronization clock signal to the charge amplification / conditioning module and the fiber optic demodulation module; The data acquisition card is used to convert the analog signals output by the charge amplification / conditioning module and the fiber optic demodulation module into digital signals; The data processing and compensation control terminal receives the synchronous data from the data acquisition card, calculates the calibration parameters, and generates a digital compensation filter.

[0006] This invention also discloses a method for calibrating the frequency response of an optical fiber accelerometer array, comprising the following steps: Step S1: Rigidly coaxially connect the high-precision standard accelerometer and the fiber optic accelerometer to be calibrated on a standard vibration table; Step S2: Start the clock synchronization module to enable the charge amplification / conditioning module and the fiber demodulation module to operate under the same time reference; Step S3: The control signal generator generates a wideband excitation signal covering the microseismic monitoring frequency band, which drives the standard vibration table to vibrate through a power amplifier; Step S4: Synchronously acquire the time-domain reference signal output by the standard accelerometer. and the time-domain measurement signal output by the fiber optic probe to be calibrated ,right and Perform windowing truncation and fast Fourier transform; Step S5: In the data processing terminal, calculate... and self-power spectral density function and cross-power spectral density function ; Step S6: Calculate the transfer function of the fiber optic probe to be calibrated according to the following formula. We obtain its amplitude frequency response and phase frequency response:

[0007] Step S7: Based on the calculated A digital compensation filter implemented in the time domain is designed using digital filtering algorithms to improve its frequency response. satisfy or:

[0008] in The frequency response of the preset ideal target system; Step S8: Store the generated digital compensation filter coefficients for real-time waveform compensation in the subsequent micro-vibration demodulation system.

[0009] The specific algorithm for designing the digital compensation filter is as follows: (a) Determine the target response characteristics: Select the frequency response of the probe with the flattest passband in the array. As an ideal target response ; (b) Calculate the frequency response of the inverse filter: Within the effective microseismic monitoring frequency band, calculate... Outside the frequency band The amplitude is set to 0; (c) Frequency domain smoothing and regularization: Introducing regularization parameters during computation. ,satisfy:

[0010] in, Let be the conjugate complex number of the frequency response of the probe under test. It is a very small positive number, to prevent The calculation result tends to infinity; (d) Temporal transformation: For the regularized... Perform an inverse fast Fourier transform to obtain the initial time-domain impulse response. ; (e) Windowing truncation: Windowing truncation is performed to generate a fixed-length finite impulse response filter coefficient matrix.

[0011] The beneficial effects of this invention are: The core of this invention lies in the specific algorithm implementation of the digital compensation filter. Unlike traditional calibration that only normalizes the amplitude, this invention specifically corrects both amplitude and phase distortion by designing an inverse filter in the complex domain. This invention uses cross-power spectral density to calculate the transfer function, which can effectively suppress the interference of environmental noise on frequency response evaluation. This invention introduces a hardware-level clock synchronization module, which ensures the absolute reference consistency between the reference electrical signal and the optical demodulation signal during phase calculation, and solves the phase calibration error caused by system delay. This invention allows for relaxed hardware manufacturing tolerances for fiber optic sensors and achieves highly consistent data compensation through a back-end digital compensation filter matrix, directly improving the accuracy of waveform cross-correlation and source localization. Attached Figure Description

[0012] The invention will now be further described with reference to the accompanying drawings.

[0013] Figure 1This is a structural block diagram of the fiber optic accelerometer array frequency response calibration system of the present invention; Figure 2 This is a schematic flowchart of the fiber optic accelerometer array frequency response calibration method of the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Frequency response calibration system for fiber optic accelerometer arrays used in microseismic monitoring, such as Figure 1 As shown, it includes: The excitation subsystem includes a standard vibration table, a signal generator, and a power amplifier; The signal generator produces a broadband excitation signal covering the microseismic monitoring frequency band, which is then used to drive a standard vibration table to vibrate via a power amplifier. The wideband excitation signal can be a swept-frequency sine wave or white noise covering the target frequency band; The oscillator system includes a high-precision standard accelerometer with flat frequency response characteristics and a fiber optic accelerometer under test. The vibration sensing subsystem is used to sense excitation signals and output corresponding electrical and optical signals; Fiber demodulation module: used to connect to the fiber optic accelerometer array to be calibrated, demodulate the optical phase change in real time, and output the acceleration signal to be measured; The charge amplification / conditioning module is connected to a high-precision standard accelerometer and is used to condition the output signal of the high-precision standard accelerometer. Clock synchronization module: Used to provide a high-precision external synchronization clock signal to the charge amplification / conditioning module and the fiber demodulation module to ensure strict synchronization of the corresponding electrical and optical signals.

[0016] The data acquisition card is used to convert the analog signals output from the charge amplification / conditioning module and the fiber optic demodulation module into digital signals; Data processing and compensation control terminal: Receives synchronous data from the data acquisition card, calculates calibration parameters, and generates a digital compensation filter.

[0017] The frequency response calibration method for fiber optic accelerometer arrays used for microseismic monitoring employs the aforementioned frequency response calibration system, such as... Figure 2 As shown, it includes the following steps: Step S1: Rigidly coaxially connect the high-precision standard accelerometer and the fiber optic accelerometer to be calibrated on the standard vibration table, ensuring that their axes are aligned. Specifically, the high-precision standard accelerometer and the fiber optic accelerometer to be calibrated are connected in series on the same axis and rigidly fixed in series along the axial direction of the vibration table by fastening bolts to ensure that the central axis of the two is completely coincident with the excitation direction of the vibration table; Step S2: Start the clock synchronization module to enable the charge amplification / conditioning module and the fiber demodulation module to operate under the same time reference; Step S3: The control signal generator generates a wideband excitation signal covering the microseismic monitoring frequency band, which drives the standard vibration table to vibrate through a power amplifier; Step S4: Synchronously acquire the time-domain reference signal output by the standard accelerometer. and the time-domain measurement signal output by the fiber optic probe to be calibrated ,right and Perform windowing truncation and fast Fourier transform; Step S5: In the data processing terminal, calculate... and self-power spectral density function and cross-power spectral density function ; Step S6: Calculate the transfer function of the fiber optic probe to be calibrated according to the following formula. We obtain its amplitude frequency response and phase frequency response:

[0018] Step S7: Based on the calculated A digital compensation filter implemented in the time domain is designed using digital filtering algorithms to improve its frequency response. satisfy or:

[0019] in The frequency response of the preset ideal target system; The specific algorithm for designing the digital compensation filter is as follows: (a) Determine the target response characteristics: Select the frequency response of the probe with the flattest passband in the array. As an ideal target response ; Considering that forcibly compensating each probe's frequency response to a "completely flat" straight line might introduce significant gain at specific frequencies, thus amplifying noise, this embodiment selects the probe in the array whose production parameters are closest to the design values ​​and whose passband is the flattest as the benchmark. Its measured... This serves as the ideal target response for all other probes. This effectively eliminates frequency response dispersion between probes.

[0020] (b) Calculate the frequency response of the inverse filter: Within the effective microseismic monitoring frequency band, calculate... Outside the frequency band The amplitude is set to 0; (c) Frequency domain smoothing and regularization: to prevent... The existence of a minimum value leads to If the amplitude is too large, a regularization parameter is introduced during the calculation. ,satisfy:

[0021] in, Let be the conjugate complex number of the frequency response of the probe under test. It is a very small positive number (e.g.) () is used as a regularization parameter. Its function is to... When the amplitude is close to 0, prevent The calculation result tends to infinity, thus ensuring the numerical stability of the filter.

[0022] (d) Time-domain transformation: for the regularized... Perform an inverse fast Fourier transform to obtain the initial time-domain impulse response. ; (e) Windowing truncation: Windowing truncation is performed to generate a fixed-length finite impulse response (FIR) filter coefficient matrix; Due to the initial It is infinitely long and non-causal; this embodiment uses the Kaiser Window for... Windowing and truncation are performed. The truncation generates fixed-length FIR filter coefficients. The final generated impulse response coefficient is the dedicated digital compensation filter for this probe; Step S8: Store the generated digital compensation filter coefficients for real-time waveform compensation in the subsequent micro-vibration demodulation system.

[0023] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A frequency response calibration system for a fiber optic accelerometer array used for microseismic monitoring, characterized in that, include: The excitation subsystem includes a standard vibration table, a signal generator, and a power amplifier; The signal generator produces a broadband excitation signal covering the microseismic monitoring frequency band, which is then used to drive a standard vibration table to vibrate via a power amplifier. The oscillator system includes a high-precision standard accelerometer with flat frequency response characteristics and a fiber optic accelerometer under test. The vibration sensing subsystem is used to sense excitation signals and output corresponding electrical and optical signals; The fiber optic demodulation module is used to connect to the fiber optic accelerometer array to be calibrated, demodulate the optical phase change in real time, and output the acceleration signal to be measured. The charge amplification / conditioning module is connected to a high-precision standard accelerometer and is used to condition the output signal of the high-precision standard accelerometer. The clock synchronization module is used to provide a high-precision external synchronization clock signal to the charge amplification / conditioning module and the fiber optic demodulation module; The data acquisition card is used to convert the analog signals output by the charge amplification / conditioning module and the fiber optic demodulation module into digital signals; The data processing and compensation control terminal receives the synchronous data from the data acquisition card, calculates the calibration parameters, and generates a digital compensation filter.

2. The frequency response calibration system for fiber optic accelerometer array for microseismic monitoring according to claim 1, characterized in that, The wideband excitation signal output by the signal generator is a swept-frequency sine wave or white noise.

3. The frequency response calibration system for fiber optic accelerometer arrays for microseismic monitoring according to claim 1, characterized in that, The high-precision standard accelerometer and the fiber optic accelerometer to be calibrated are connected in series on the same axis and rigidly fixed in series along the axial direction of the vibration table by fastening bolts, so as to ensure that the central axis of the two is completely coincident with the excitation direction of the vibration table.

4. A method for calibrating the frequency response of a fiber optic accelerometer array based on the system described in any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1: Secure the high-precision standard accelerometer and the fiber optic accelerometer to be calibrated in series on the standard vibration table using bolts. Step S2: Start the clock synchronization module to enable the charge amplification / conditioning module and the fiber demodulation module to operate under the same time reference; Step S3: The control signal generator generates a wideband excitation signal covering the microseismic monitoring frequency band, which drives the standard vibration table to vibrate through a power amplifier; Step S4: Synchronously acquire the time-domain reference signal output by the standard accelerometer. and the time-domain measurement signal output by the fiber optic probe to be calibrated ,right and Perform windowing truncation and fast Fourier transform; Step S5: In the data processing terminal, calculate... and self-power spectral density function and cross-power spectral density function ; Step S6: Calculate the transfer function of the fiber optic probe to be calibrated according to the following formula. We obtain its amplitude frequency response and phase frequency response: Step S7: Based on the calculated A digital compensation filter implemented in the time domain is designed using digital filtering algorithms to improve its frequency response. satisfy or: in The frequency response of the preset ideal target system; Step S8: Store the generated digital compensation filter coefficients for real-time waveform compensation in the subsequent micro-vibration demodulation system.

5. The fiber optic accelerometer array frequency response calibration method according to claim 4, characterized in that, The specific algorithm for designing a digital compensation filter is as follows: (a) Determine the target response characteristics: Select the frequency response of the probe with the flattest passband in the array. As an ideal target response ; (b) Calculate the frequency response of the inverse filter: Within the effective microseismic monitoring frequency band, calculate... Outside the frequency band The amplitude is set to 0; (c) Frequency domain smoothing and regularization: Introducing regularization parameters during computation. ,satisfy: in, Let be the conjugate complex number of the frequency response of the probe under test. It is a very small positive number, to prevent The calculation result tends to infinity; (d) Temporal transformation: For the regularized... Perform an inverse fast Fourier transform to obtain the initial time-domain impulse response. ; (e) Windowing truncation: Windowing truncation is performed to generate a fixed-length finite impulse response filter coefficient matrix.

6. The fiber optic accelerometer array frequency response calibration method according to claim 5, characterized in that, The windowing truncation uses a Kaiser window to process the initial time-domain impulse response c(t).

7. The fiber optic accelerometer array frequency response calibration method according to claim 5, characterized in that, The regularization parameter λ is set to 10. -6 .

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