Distributed acoustic wave sensing demodulation method and system based on chirp

Abstract

The application relates to the technical field of signal processing, and discloses a distributed acoustic wave sensing demodulation method and system based on a linear frequency modulation pulse, which comprises the following steps: generating a continuous light signal, modulating and processing the continuous light signal to obtain a first light signal, pre-processing the first light signal to obtain a binary interference pattern, performing multi-sliding amount registration on a test frame based on window data of corresponding spatial positions intercepted in the reference frame and the test frame, calculating a Hamming distance between a reference window and a test window, determining a sliding amount corresponding to the minimum Hamming distance in the Hamming distance as a time delay estimation value, and converting the time delay into measured strain or vibration data based on the time delay estimation value, a linear frequency modulation slope, a light speed and a fiber strain coefficient. The binary sequence in the binary interference pattern is used to calculate the time delay estimation value, analog waveform recovery is not needed, time delay information in the bit flip structure is reserved, and the quantization noise has strong resistance.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology, and specifically to a distributed acoustic wave sensing demodulation method and system based on linear frequency modulated pulses. Background Technology

[0002] Distributed acoustic sensing systems can continuously acquire external vibration or strain information along the entire sensing fiber, and have significant application value in scenarios such as geophysical exploration, perimeter security, pipeline monitoring, and traffic monitoring. Existing systems typically require continuous acquisition of backscattered interferometric signals along the path at a high sampling rate, which brings huge pressure on data throughput, storage, and post-processing.

[0003] Existing low-bit quantization schemes are mainly aimed at phase-sensitive optical time-domain reflectometry systems. They often exhibit significant demodulation performance degradation when the quantization bit depth is low. Furthermore, they typically require the compressed sequence to be restored to an approximate analog waveform before subsequent calculations can be performed, making it impossible to balance data compression with implementation efficiency. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a distributed acoustic wave sensing demodulation method and system based on linear frequency modulated pulses.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a distributed acoustic wave sensing demodulation method based on linear frequency modulated pulses, comprising:

[0007] A continuous optical signal is generated, and the continuous optical signal is modulated to obtain a first optical signal;

[0008] The first optical signal is preprocessed to obtain a binary interference pattern;

[0009] Based on the window data of corresponding spatial positions extracted from the reference frame and the test frame, multi-slide registration is performed on the test frame to calculate the Hamming distance between the reference window and the test window. The reference frame and the test frame are obtained according to the binary interferogram. The reference window is the window data of corresponding spatial positions extracted from the reference frame, and the test window is the window data of corresponding spatial positions extracted from the test frame.

[0010] The slip value corresponding to the minimum Hamming distance among the Hamming distances is determined as the time delay estimate;

[0011] Based on the estimated time delay, linear frequency modulation slope, speed of light, and fiber strain coefficient, the time delay is converted into the measured strain or vibration data.

[0012] In this invention, preferably, the step of generating a continuous optical signal and modulating the continuous optical signal to obtain a first optical signal includes:

[0013] The continuous optical signal is divided into a probe optical signal and a local oscillator optical signal;

[0014] The probe optical signal is modulated into a linear frequency modulated pulse and then injected into the sensing optical fiber;

[0015] Receive the backscattered Rayleigh signal returned by the sensing fiber;

[0016] The backscattered Rayleigh signal and the local oscillator signal are coherently detected to obtain the first optical signal.

[0017] In this invention, preferably, the preprocessing of the first optical signal to obtain the binary interference pattern includes:

[0018] The first optical signal is subjected to bandpass filtering, envelope detection, and DC blocking to obtain an interference pattern.

[0019] The interference pattern is subjected to zero-crossing detection and converted into a binary interference pattern.

[0020] In this invention, preferably, the step of performing zero-crossing detection on the interference pattern and converting it into a binary interference pattern includes:

[0021] When the interference pattern h(t) is greater than or equal to zero, the binary interference pattern q(t) = 1;

[0022] When the interference pattern h(t) is less than zero, the binary interference pattern q(t) = 0.

[0023] In this invention, preferably, the slip amount corresponding to the minimum Hamming distance in the Hamming distance is determined as the time delay estimate, and the corresponding time delay estimate is Δt = Δn / SR, where Δn is the optimal slip amount and SR is the sampling rate.

[0024] In this invention, preferably, the measured strain or vibration data is:

[0025] ε = -(μ·Δt) / (c·K),

[0026] Wherein, ε is the measured strain or vibration data, μ is the linear frequency modulation slope, c is the speed of light, and K is the fiber strain coefficient.

[0027] In this invention, preferably, the Hamming distance is obtained by performing an XOR operation on the bits corresponding to the reference window and the test window and summing them.

[0028] In this invention, preferably, the time delay estimate is obtained by performing triangular fitting or equivalent local fitting on discrete points near the minimum Hamming distance.

[0029] Secondly, the present invention also provides a distributed acoustic wave sensing demodulation system based on linear frequency modulated pulses, the system comprising:

[0030] An optical signal generation module is used to generate a continuous optical signal and modulate the continuous optical signal to obtain a first optical signal.

[0031] An interference pattern generation module is used to preprocess the first optical signal to obtain a binary interference pattern;

[0032] The demodulation processing module is used to perform multi-slide registration on the test frame based on window data of corresponding spatial positions extracted from the reference frame and the test frame, and calculate the Hamming distance between the reference window and the test window. The reference frame and the test frame are obtained according to the binary interferogram. The reference window is the window data of corresponding spatial positions extracted from the reference frame, and the test window is the window data of corresponding spatial positions extracted from the test frame.

[0033] The demodulation processing module is further configured to determine the slip value corresponding to the minimum Hamming distance in the Hamming distance as the time delay estimate, and convert the time delay into the measured strain or vibration data based on the time delay estimate, the linear frequency modulation slope, the speed of light and the fiber strain coefficient.

[0034] In this invention, preferably, the optical signal generation module includes a narrow linewidth laser, a first coupler, a dual parallel Mach zenith modulator, a waveform generator, a modulator bias controller, a second coupler, an erbium-doped fiber amplifier, a circulator, a sensing fiber, a third coupler, and a balanced photodetector. The narrow linewidth laser, the first coupler, the dual parallel Mach zenith modulator, the second coupler, the erbium-doped fiber amplifier, and the circulator are connected in sequence. The waveform generator is connected to the dual parallel Mach zenith modulator. The modulator bias controller is connected to both the dual parallel Mach zenith modulator and the second coupler. The first coupler and the circulator are both connected to the third coupler. The third coupler is connected to the balanced photodetector. The other end of the balanced photodetector is connected to the interference pattern generation module.

[0035] The interferogram generation module includes a bandpass filter, an envelope detector, a DC blocker, and a zero-crossing detector connected in sequence.

[0036] The demodulation processing module is also connected to a storage module.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] The method of this invention directly converts interferometric patterns into binary interferometric patterns and replaces traditional analog correlation calculations with Hamming distance, achieving end-to-end data compression from data acquisition and storage to demodulation calculation, thus reducing data processing and storage pressure. Simultaneously, it directly utilizes the binary sequence in the binary interferometric pattern to calculate the time delay estimate, eliminating the need for analog waveform recovery, making it suitable for high-speed, low-power implementation using FPGAs, ASICs, or other logic circuits. Furthermore, the binary sequence in the binary interferometric pattern retains the time delay information in the bit-flipping structure, exhibiting strong resistance to quantization noise. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating the distributed acoustic wave sensing demodulation method based on linear frequency modulated pulses described in this invention.

[0040] Figure 2 This is a schematic diagram illustrating the principle of binary interference pattern generation described in this invention.

[0041] Figure 3 This is a schematic diagram illustrating the time delay estimation process described in this invention.

[0042] Figure 4 This is a schematic diagram of the distributed acoustic wave sensing and demodulation system based on linear frequency modulated pulses according to the present invention.

[0043] Figure 5 This diagram illustrates the comparison between the method of this invention and the traditional method in terms of interference signal demodulation and system performance.

[0044] Figure 5 (a) shows the conventional demodulation result obtained using the original interferogram; (b) shows the demodulation result obtained using the method of the present invention; (c) shows the waveform recovery result of the original interferogram; (d) shows the waveform recovery result of the method of the present invention; (e) shows the noise floor level of the conventional DAS system based on the amplitude spectral density; and (f) shows the noise floor level of the DAS system of the present invention based on the amplitude spectral density. Detailed Implementation

[0045] 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.

[0046] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or may have a component in between. When a component is described as "connected to" another component, it can be directly connected to the other component or may have a component in between. When a component is described as "set on" another component, it can be directly set on the other component or may have a component in between. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0048] Please see Figure 1 A preferred embodiment of this invention provides a distributed acoustic wave sensing demodulation method based on linear frequency modulated pulses. This method primarily addresses the problems of high data volume, decreased demodulation accuracy after low-bit quantization, and reliance on analog reconstruction in existing technologies. By directly converting the interferogram into a binary sequence of interferograms and utilizing the minimum Hamming distance to estimate time delay, the method achieves end-to-end data compression and digital demodulation while maintaining a low noise floor increase. The method includes:

[0049] S1. Generate a continuous optical signal, and modulate the continuous optical signal to obtain a first optical signal;

[0050] S2. Preprocess the first optical signal to obtain a binary interference pattern;

[0051] S3. Based on the window data of corresponding spatial positions extracted from the reference frame and the test frame, perform multi-slide registration on the test frame to calculate the Hamming distance between the reference window and the test window. The reference frame and the test frame are obtained according to the binary interferogram. The reference window is the window data of corresponding spatial positions extracted from the reference frame, and the test window is the window data of corresponding spatial positions extracted from the test frame.

[0052] S4. Determine the sliding amount corresponding to the minimum Hamming distance in the Hamming distances as the time delay estimate;

[0053] S5. Based on the estimated time delay, linear frequency modulation slope, light speed and fiber strain coefficient, the time delay is converted into the measured strain or vibration data.

[0054] Specifically, in step S1, the continuous optical signal can be a continuous optical wave signal with stable amplitude and frequency output from a narrow-linewidth laser, used to provide a stable light source to ensure the coherence and signal-to-noise ratio of coherent detection. Modulation processing of the continuous optical signal can include inputting the continuous optical signal into the sensing fiber after beam splitting and frequency modulation pulse modulation, and generating a scattered signal from the sensing fiber to obtain a first optical signal, which carries external strain and vibration information.

[0055] In step S2, the first optical signal can be sequentially filtered, amplitude extracted, and DC removed to obtain an interference waveform that fluctuates around a zero level. The interference waveform is then converted into a binary interference pattern containing only 0 and 1 states using a threshold comparison method. The filtering process can include at least one of analog bandpass filtering and digital bandpass filtering; the amplitude extraction process can include at least one of envelope detection, quadrature demodulation, and amplitude calculation; and the threshold comparison method can include at least one of zero-crossing detection, phase threshold comparison, and differential threshold comparison.

[0056] In step S3, a reference frame and a test frame are first selected based on the binary interferogram. The reference frame is a baseline binary data frame without external strain or vibration, and the test frame is a binary data frame at the same spatial position with external disturbance. At the same fiber optic spatial position in both frames, reference and test windows of equal length are extracted. At least one of the following methods—global sliding, adaptive step-size sliding, block sliding, interpolation sliding, or cyclic sliding—is used to perform multi-sliding registration on the test window, i.e., the test window is translated point-by-point within a preset sliding range. The Hamming distance between the reference window and the test window under each sliding amount is obtained through at least one of the following methods: bitwise XOR summation, block distance fusion, correlation equivalence calculation, or cumulative distance statistics. The Hamming distance characterizes the degree of difference between two binary sequences; the smaller the distance, the more similar the two sequences are and the higher the signal alignment.

[0057] In step S4, after calculating the Hamming distance for the full slip range, the slip range corresponding to the smallest Hamming distance is determined as the time delay estimate. All Hamming distances are traversed within a preset slip range, and the smallest Hamming distance is obtained using at least one of the following methods: global search, adaptive step-size search, and local fine search. The discrete slip range corresponding to the smallest Hamming distance is directly used as the time delay estimate, or at least one of the following processing methods—triangular fitting, local fitting, weighted fitting, and Gaussian fitting—is applied to the neighborhood points of the smallest Hamming distance to obtain the time delay estimate. This overcomes the resolution limitations caused by discrete sampling and improves the overall demodulation accuracy of the system.

[0058] In step S5, after obtaining the estimated time delay, the time delay is converted into the measured strain or vibration data based on the estimated time delay, the linear frequency modulation slope, the speed of light, and the fiber strain coefficient. Specifically, at least one of the following methods can be used: direct strain calculation, high-precision strain calculation using subsampling fitting to correct the time delay, piecewise adaptive strain coefficient correction calculation, extraction of dynamic vibration data from the strain time series using differential filtering, multi-parameter compensation conversion using the temperature coupling coefficient, interpolation conversion based on a pre-calibrated mapping table, and multi-frame time-domain smoothing and noise reduction conversion. For example, the high-precision strain calculation method using subsampling fitting to correct the time delay first obtains the subsampling high-precision time delay through minimum Hamming distance neighborhood trigonometric fitting or parabolic fitting. Then, the high-precision Δt after fitting correction is used to replace the number of discrete points to convert the time delay. Next, the strain is solved by combining the linear frequency modulation slope, the speed of light, and the strain coefficient. Finally, sampling discrete errors are suppressed, improving the accuracy of weak vibration detection.

[0059] By replacing traditional analog correlation calculations with Hamming distance, the above scheme achieves end-to-end compression from data acquisition and storage to demodulation calculation, significantly reducing data processing and storage pressure. Delay estimation is calculated directly from the binary sequence in the binary interferogram, eliminating the need for analog waveform recovery, making it suitable for high-speed, low-power implementation using FPGAs, ASICs, or other logic circuits. Simultaneously, it fully utilizes the delay information retained in the bit-flip structure after binary quantization, exhibiting strong resistance to quantization noise. Under 20 km sensing conditions, an 8x compression ratio can be achieved while keeping the noise floor increase within a small range.

[0060] In this embodiment, step S1, generating a continuous optical signal and modulating the continuous optical signal to obtain a first optical signal, further includes:

[0061] S11. Divide the continuous optical signal into a probe optical signal and a local oscillator optical signal;

[0062] S12. The probe optical signal is modulated into a linear frequency modulated pulse and then injected into the sensing optical fiber;

[0063] S13. Receive the backscattered Rayleigh signal returned by the sensing fiber;

[0064] S14. Perform coherent detection between the backscattered Rayleigh signal and the local oscillator signal to obtain the first optical signal.

[0065] Specifically, a stable, highly coherent continuous optical signal is first generated by a narrow-linewidth laser. This continuous optical signal is then split into a probe optical signal and a local oscillator optical signal via an optical coupler. A dual-parallel Mach-Zehnder modulator is used to modulate the probe light into a linearly frequency-modulated pulse optical signal, forming an optical signal that can be injected into the sensing fiber. This optical signal is then amplified and fed into the sensing fiber through a circulator. Backscattered Rayleigh signals are generated at various locations within the fiber. These backscattered Rayleigh signals return and coherently probe the local oscillator light, yielding the first optical signal carrying interference information, i.e., the beat frequency optical signal. This completes the optical signal generation and detection process.

[0066] In this embodiment, step S2 involves preprocessing the first optical signal to obtain a binary interference pattern, including:

[0067] S21. Bandpass filtering, envelope detection, and DC blocking are performed on the first optical signal to obtain an interference pattern;

[0068] S22. Perform zero-crossing detection on the interference pattern and convert it into a binary interference pattern.

[0069] Specifically, firstly, out-of-band noise and spurious interference in the first optical signal are filtered out using a bandpass filter. Then, the envelope waveform of the interference signal in the first optical signal is extracted using an envelope detector. Subsequently, DC blocking is performed to remove the DC component, causing the waveform to fluctuate around a zero level. Finally, zero-crossing detection is performed on the processed analog interference signal. When the interference pattern h(t) is greater than or equal to zero, the binary interference pattern q(t) = 1; when the interference pattern h(t) is less than zero, the binary interference pattern q(t) = 0. This converts the analog waveform into a binary interference pattern consisting only of 0s and 1s, achieving signal binarization and compression. Figure 2 As shown.

[0070] In this embodiment, the Hamming distance is obtained by performing an XOR operation on the corresponding bits of the reference window and the test window and then summing them.

[0071] Specifically, firstly, a reference frame and a test frame are selected based on the binary interferogram. The reference frame is a baseline binary data frame without external strain or vibration, and the test frame is a binary data frame at the same spatial position with external disturbance. At the same fiber spatial position in both frames, reference and test windows of equal length are extracted. A global sliding method is used to perform multi-slide registration on the test window, i.e., the test window is translated point-by-point within a preset sliding range to complete multi-slide registration. Under each slide amount, an XOR operation is performed on the corresponding bits of the reference and test windows, and the XOR results are summed. The summation result is used as the Hamming distance under that slide amount, thus completing multi-slide registration and Hamming distance calculation. Figure 3As shown, the binary interferogram q(t) is directly used in the Hamming distance calculation without having to reconstruct the original analog interferogram, thus achieving end-to-end compression from data storage to terminal demodulation.

[0072] In this embodiment, the time delay estimate is obtained by performing triangular fitting or equivalent local fitting on discrete points near the minimum Hamming distance.

[0073] Specifically, after obtaining the Hamming distances corresponding to each slip amount, the Hamming distance values ​​for all slip amounts are iterated through, and the Hamming distance with the smallest value is determined. The slip amount corresponding to this smallest Hamming distance is taken as the optimal slip amount, and this optimal slip amount is determined as the discrete time delay estimate. Trigonometric fitting or equivalent local fitting can be performed on the smallest Hamming distance and its nearby discrete points. By fitting, a time delay estimate with sub-sampling accuracy is obtained, thereby improving the resolution and accuracy of the time delay estimate, and finally obtaining the time delay estimate used for subsequent strain conversion.

[0074] In this embodiment, the slip value corresponding to the minimum Hamming distance among the Hamming distances is determined as the time delay estimate, and the corresponding time delay estimate is Δt = Δn / SR, where Δn is the optimal slip value and SR is the sampling rate. The sampling rate is set according to the quantization noise aliasing constraint, so that the proportion of quantization noise aliasing power outside the Nyquist frequency to the total quantization noise power is lower than a preset threshold.

[0075] In this embodiment, the measured strain or vibration data is:

[0076] ε = -(μ·Δt) / (c·K),

[0077] Wherein, ε is the measured strain or vibration data, μ is the linear frequency modulation slope, c is the speed of light, and K is the fiber strain coefficient.

[0078] Specifically, after obtaining the time delay estimate, based on the time delay estimate, the linear frequency modulation slope, the speed of light, and the fiber strain coefficient, the time delay is converted into the measured strain or vibration data. Specifically, first, based on the optimal slip Δn and the system sampling rate SR, according to the formula:

[0079] Δt = Δn / SR

[0080] Convert the number of sliding points into a time delay estimate Δt; then, based on the frequency modulation slope μ of the linear frequency modulated pulse, the speed of light c in vacuum, and the fiber strain coefficient K, use the formula:

[0081] ε = -(μ·Δt) / (c·K)

[0082] The time delay is converted into the measured strain or vibration data ε of the optical fiber, and the final output is strain data or vibration waveform that can directly characterize the magnitude of external vibration, sound wave or deformation, thus completing the entire binary quantitative unmodulation.

[0083] Please see Figure 4 Another preferred embodiment of the present invention provides a distributed acoustic wave sensing demodulation system based on linear frequency modulated pulses. The system includes an optical signal generation module 1, an interferogram generation module 2, and a demodulation processing module 3 connected in sequence. The optical signal generation module 1 generates a continuous optical signal and modulates the continuous optical signal to obtain a first optical signal. The interferogram generation module 2 preprocesses the first optical signal to obtain a binary interferogram. The demodulation processing module 3 performs multi-sliding registration on the test frame based on window data of corresponding spatial positions extracted from the reference frame and the test frame, and calculates the Hamming distance between the reference window and the test window. The reference frame and the test frame are obtained according to the binary interferogram, where the reference window is window data of corresponding spatial positions extracted from the reference frame, and the test window is window data of corresponding spatial positions extracted from the test frame. The demodulation processing module 3 is also used to determine the slip value corresponding to the minimum Hamming distance in the Hamming distance as the time delay estimate, and convert the time delay into the measured strain or vibration data based on the time delay estimate, the linear frequency modulation slope, the speed of light and the fiber strain coefficient.

[0084] In this embodiment, the optical signal generation module 1 includes a narrow linewidth laser 11, a first coupler 12, a dual parallel Mach zenith modulator 13, a waveform generator 14, a modulator bias controller 15, a second coupler 16, an erbium-doped fiber amplifier 17, a circulator 18, a sensing fiber 19, a third coupler 110, and a balanced photodetector 111. The narrow linewidth laser 11, the first coupler 12, the dual parallel Mach zenith modulator 13, the second coupler 16, the erbium-doped fiber amplifier 17, and the circulator 18 are connected sequentially. The waveform generator 14 is connected to the dual parallel Mach zenith modulator 13, and the modulator bias controller 15 is connected to both the dual parallel Mach zenith modulator 13 and the second coupler 16. The first coupler 12 and the circulator 18 are both connected to the third coupler 110, and the third coupler 110 is connected to the balanced photodetector 111. The other end of the balanced photodetector 111 is connected to the interference pattern generation module 2. The interferogram generation module 2 includes a bandpass filter 21, an envelope detector 22, a DC blocker 23, and a zero-crossing detector 24 connected in sequence. The demodulation processing module 3 is also connected to a storage module 4.

[0085] Specifically, a stable, highly coherent continuous optical signal is first generated by a narrow-linewidth laser 11. This continuous optical signal is then split into a probe optical signal and a local oscillator optical signal by a first coupler 12. The probe optical signal is modulated into a linearly frequency-modulated pulse optical signal using a dual parallel Mach zenith modulator 13, forming an optical signal that can be injected into the sensing fiber. This optical signal is then amplified by a second coupler 16 and an erbium-doped fiber amplifier 17, and then fed into the sensing fiber 19 through a circulator 18. Backscattered Rayleigh signals are generated at various locations within the sensing fiber 19. These backscattered Rayleigh signals return and coherently detect with the local oscillator light through a third coupler 110, yielding a first optical signal carrying interference information. This first optical signal is then acquired by a balanced photodetector 111 and input into the interference pattern generation module 2.

[0086] The interferogram generation module 2 includes a bandpass filter 21, an envelope detector 22, a DC blocker 23, and a zero-crossing detector 24 connected in sequence. The bandpass filter 21 is used to filter out out-of-band noise and spurious interference in the first optical signal. The envelope detector 22 extracts the envelope waveform of the interference signal in the first optical signal, and then the DC component is blocked by the DC blocker 23 to remove the DC component, making the waveform fluctuate around zero level. Finally, the zero-crossing detector 24 performs zero-crossing detection to construct the binary interferogram q(t). Figure 2 As shown, the backscattering interferogram h(t) undergoes a time shift under external strain. By performing zero-crossing detection on the DC-blocked interferogram, a binary interferogram q(t) can be constructed. Although quantization noise n_q(t) = q(t) - h(t) is introduced during quantization, this quantization noise still carries time shift information consistent with the original pattern, and therefore can be effectively utilized in subsequent time delay estimation processes.

[0087] In demodulation module 3, the binary interferogram q(t) is input to the demodulation processing module. A reference frame window and a test frame window are selected, and a sliding search is performed on the test frame. For each sliding amount, the Hamming distance is obtained by bitwise XOR and summation, and the sliding amount corresponding to the minimum value is taken as the time delay estimate. The corresponding time delay estimate is:

[0088] Δt = Δn / SR,

[0089] Where Δn is the optimal slip amount and SR is the sampling rate. Trigonometric fitting or equivalent local fitting can be performed on the minimum Hamming distance and its nearby discrete points. Sub-sampling level precision time delay estimation results are obtained through fitting calculations, thereby improving the resolution and accuracy of time delay estimation, and ultimately obtaining the time delay estimate for subsequent strain conversion. The slip amount corresponding to the minimum Hamming distance is determined as the time delay estimate, and the corresponding time delay estimate is Δt = Δn / SR, where Δn is the optimal slip amount and SR is the sampling rate. The sampling rate is set according to the quantization noise aliasing constraint, ensuring that the proportion of quantization noise aliasing power outside the Nyquist frequency to the total quantization noise power is lower than a preset threshold.

[0090] Convert the number of sliding points into a time delay estimate Δt; then, based on the frequency modulation slope μ of the linear frequency modulated pulse, the speed of light c in vacuum, and the fiber strain coefficient K, use the formula:

[0091] ε = -(μ·Δt) / (c·K)

[0092] The time delay is converted into the measured strain or vibration data ε of the optical fiber, and the final output is strain data or vibration waveform that can directly characterize the magnitude of external vibration, sound wave or deformation, thus completing the entire binary quantitative unmodulation.

[0093] Please see Figure 5 In one specific embodiment, a laser with a center wavelength of approximately 1550.12 nm and a linewidth of approximately 3 kHz was used as the light source to modulate linear frequency-modulated pulses ranging from 100 MHz to 220 MHz, with a pulse width of approximately 100 ns and a pulse repetition frequency of approximately 2 kHz. The sensing fiber was 20 km long, and a dynamic strain of 10 Hz and on the order of 31 nε was applied to a 21 m section of the fiber at its end. The results show that, at a sampling rate of 1 GSa / s, the binary interferogram constructed from 8-bit raw data can achieve an 8x compression ratio, and the demodulation noise floor only increases slightly, verifying the effectiveness of the present invention.

[0094] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A distributed acoustic wave sensing demodulation method based on chirp pulses, characterized in that, The method includes: A continuous optical signal is generated, and the continuous optical signal is modulated to obtain a first optical signal; The first optical signal is preprocessed to obtain a binary interference pattern; Based on the window data of corresponding spatial positions extracted from the reference frame and the test frame, multi-slide registration is performed on the test frame to calculate the Hamming distance between the reference window and the test window. The reference frame and the test frame are obtained according to the binary interferogram. The reference window is the window data of corresponding spatial positions extracted from the reference frame, and the test window is the window data of corresponding spatial positions extracted from the test frame. The slip value corresponding to the minimum Hamming distance among the Hamming distances is determined as the time delay estimate; Based on the estimated time delay, linear frequency modulation slope, speed of light, and fiber strain coefficient, the time delay is converted into the measured strain or vibration data.

2. The distributed acoustic wave sensing demodulation method based on linear frequency modulated pulses according to claim 1, characterized in that, The process of generating a continuous optical signal and modulating the continuous optical signal to obtain a first optical signal includes: The continuous optical signal is divided into a probe optical signal and a local oscillator optical signal; The probe optical signal is modulated into a linear frequency modulated pulse and then injected into the sensing optical fiber; Receive the backscattered Rayleigh signal returned by the sensing fiber; The backscattered Rayleigh signal and the local oscillator signal are coherently detected to obtain the first optical signal.

3. The chirp-based distributed acoustic wave sensor demodulation method of claim 2, wherein, The preprocessing of the first optical signal to obtain a binary interference pattern includes: The first optical signal is subjected to bandpass filtering, envelope detection, and DC blocking to obtain an interference pattern. The interference pattern is subjected to zero-crossing detection and converted into a binary interference pattern.

4. The chirp-based distributed acoustic wave sensor demodulation method of claim 3, wherein, The step of performing zero-crossing detection on the interferogram and converting it into a binary interferogram includes: When the interference pattern h(t) is greater than or equal to zero, the binary interference pattern q(t) = 1; When the interference pattern h(t) is less than zero, the binary interference pattern q(t) = 0.

5. The chirp-based distributed acoustic wave sensor demodulation method of claim 1, wherein, The slip value corresponding to the minimum Hamming distance in the Hamming distance is determined as the time delay estimate, and the corresponding time delay estimate is Δt = Δn / SR, where Δn is the optimal slip value and SR is the sampling rate.

6. The chirp-based distributed acoustic wave sensor demodulation method of claim 1, wherein, The measured strain or vibration data is: ε = -(μ·Δt) / (c·K), Wherein, ε is the measured strain or vibration data, μ is the linear frequency modulation slope, c is the speed of light, and K is the fiber strain coefficient.

7. The distributed acoustic wave sensing demodulation method based on linear frequency modulated pulses according to claim 1, characterized in that, The Hamming distance is obtained by performing an XOR operation on the corresponding bits of the reference window and the test window and then summing them.

8. The chirp-based distributed acoustic wave sensor demodulation method of claim 1, wherein, The time delay estimate is obtained by performing triangular fitting or equivalent local fitting on discrete points near the minimum Hamming distance.

9. A distributed acoustic wave sensing demodulation system based on chirp pulses, characterized in that, The system includes: The optical signal generation module (1) is used to generate a continuous optical signal and modulate the continuous optical signal to obtain a first optical signal. Interference pattern generation module (2) is used to preprocess the first optical signal to obtain a binary interference pattern; The demodulation processing module (3) is used to perform multi-slide registration on the test frame based on the window data of the corresponding spatial positions extracted from the reference frame and the test frame, and calculate the Hamming distance between the reference window and the test window. The reference frame and the test frame are obtained according to the binary interferogram. The reference window is the window data of the corresponding spatial position extracted from the reference frame, and the test window is the window data of the corresponding spatial position extracted from the test frame. The demodulation processing module (3) is also used to determine the slip value corresponding to the minimum Hamming distance in the Hamming distance as the time delay estimate, and convert the time delay into the measured strain or vibration data based on the time delay estimate, the linear frequency modulation slope, the speed of light and the fiber strain coefficient.

10. The chirp-based distributed acoustic wave sensing demodulation system of claim 9, wherein, The optical signal generation module (1) includes a narrow linewidth laser (11), a first coupler (12), a dual parallel Mach zenger modulator (13), a waveform generator (14), a modulator bias controller (15), a second coupler (16), an erbium-doped fiber amplifier (17), a circulator (18), a sensing fiber (19), a third coupler (110), and a balanced photodetector (111). The waveform generator (14) is connected to the dual parallel Mach zende modulator (13), the modulator bias controller (15) is connected to the dual parallel Mach zende modulator (13) and the second coupler (16) respectively, the first coupler (12) and the circulator (18) are both connected to the third coupler (110), the third coupler (110) is connected to the balanced photodetector (111), and the other end of the balanced photodetector (111) is connected to the interference pattern generation module (2). The interferogram generation module (2) includes a bandpass filter (21), an envelope detector (22), a DC blocker (23), and a zero-crossing detector (24) connected in sequence. The demodulation processing module (3) is also connected to a storage module (4).

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