Coherent detection type phi-OTDR (Optical Time Domain Reflectometer) and standard deviation-based strain tower positioning method and system

Abstract

The invention discloses a strain tower positioning method and system based on a coherent detection type phi-OTDR and a standard deviation, and relates to the technical field of tower positioning. The method comprises the following steps: carrying out vibration monitoring on the whole OPGW optical cable by using a phi-OTDR system to obtain an optical fiber vibration signal; demodulating the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber; fourier transform is carried out on the phase disturbance signal of each spatial position to obtain corresponding spectrum distribution; synthesizing the spectrum distribution of all spatial positions into a two-dimensional spectrum image, and processing the two-dimensional spectrum image by adopting an image enhancement algorithm; for each spatial position, a sliding window is adopted to calculate the spectrum standard deviation of the enhanced two-dimensional spectrum image; and identifying a spectrum distribution abrupt change area based on the spectrum standard deviation so as to position and connect the strain tower. The method has the advantages of no need of additional sensors, no need of field measurement and high automation degree. The method is suitable for tower intelligent identification and state monitoring in various power transmission line environments.

Description

Technical Field

[0001] The present invention relates to the field of tower positioning technology, and in particular to a method based on coherent detection -OTDR and standard deviation tension tower positioning method and system. Background Art

[0002] Existing tension tower positioning technologies primarily rely on GPS, inertial navigation, or manual measurement. However, these methods have limitations: 1) GPS and inertial navigation are susceptible to environmental factors, and accuracy may decrease in complex terrain or areas with signal obstruction; 2) Manual measurement requires on-site inspection by inspectors, which is time-consuming and labor-intensive; and 3) GIS (Geographic Information System) data is subject to construction errors and terrain variations, making it difficult to accurately match the actual fiber optic installation. Therefore, a more automated, efficient, and accurate tension tower positioning method is urgently needed.

[0003] With the development of distributed optical fiber sensing technology, coherent detection type -OTDR (Phase-sensitive Optical Time Domain Reflectometry) is widely used for vibration monitoring of transmission lines due to its high sensitivity and high spatial resolution. Tension towers are important supporting structures for transmission lines, and their location is of great significance to line operation safety, fault inspection, and wind vibration monitoring. In actual operation, the fixed points of the tension towers hardly vibrate, while the optical cables will produce varying degrees of vibration under the influence of wind, icing, or changes in line load. Therefore, by analyzing the spectrum of the vibration signal of the optical fiber composite overhead ground wire (OPGW), it is possible to identify changes in vibration intensity, accurately locate the position of the tension tower, and realize automatic calibration of the transmission line. Summary of the Invention

[0004] To this end, the present invention proposes a coherent detection type -OTDR and standard deviation tension tower positioning method and system.

[0005] According to one aspect of the present invention, a coherent detection-based - A method for locating a tension tower using an OTDR and standard deviation, the method comprising:

[0006] use -The OTDR system monitors the vibration of the entire OPGW optical cable line and obtains optical fiber vibration signals;

[0007] Demodulating the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber;

[0008] Perform Fourier transform on the phase disturbance signal at each spatial position to obtain the corresponding spectrum distribution;

[0009] The spectrum distributions of all spatial positions are synthesized into a two-dimensional spectrum image, and the two-dimensional spectrum image is processed using an image enhancement algorithm;

[0010] For each spatial position, a sliding window is used to calculate the spectrum standard deviation of the enhanced two-dimensional spectrum image; based on the spectrum standard deviation, the spectrum distribution mutation area is identified, and then the connection tension tower is located.

[0011] Furthermore, the -The structure of the OTDR system includes: a narrow linewidth laser 1, a first optical coupler 2, an acousto-optic modulator 3, a first erbium-doped laser amplifier 4, a circulator 5, an arbitrary function generator 6, a second erbium-doped laser amplifier 7, a dense wavelength division multiplexer 8, a second optical coupler 9, a photoelectric balanced detector 10, a data acquisition card 11, and a computer 12; wherein, the optical signal output end of the narrow linewidth laser 1 is connected to the input end of the first optical coupler 2, and the output end of the first optical coupler 2 is connected to the input end of the acousto-optic modulator 3 and the input end of the second optical coupler 9 respectively; the output end of the acousto-optic modulator 3 is connected to the input end of the first erbium-doped laser amplifier 4, and the output end of the first erbium-doped laser amplifier 4 is connected to the first end of the circulator 5. Port 5-1 is connected, the second port 5-2 of the circulator 5 is connected to the optical fiber to be tested, the third port 5-3 of the circulator 5 is connected to the input end of the second erbium-doped laser amplifier 7, the output end of the second erbium-doped laser amplifier 7 is connected to the input end of the dense wavelength division multiplexer 8, the output end of the dense wavelength division multiplexer 8 is connected to the input end of the second optical coupler 9, the output end of the second optical coupler 9 is connected to the input end of the photoelectric balance detector 10, the output end of the photoelectric balance detector 10 is connected to the data acquisition card 11, and the data acquisition card 11 is connected to the computer 12; the output end of the arbitrary function generator 6 is connected to the acousto-optic modulator 3, which is used to generate a radio frequency pulse signal for modulating the light source, thereby controlling the acousto-optic modulator 3 to output light pulses.

[0012] Furthermore, the demodulating the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber includes:

[0013] The optical fiber vibration signal is expressed as follows:

[0014]

[0015] Where A s (t)=2A R (t)A L (t), A R (t),A L(t) represents the amplitude of the reference light and the local oscillator light corresponding to the t-th sampling point at time t, respectively; denote the phases of the reference light and the local oscillator light respectively; Δω denotes the frequency shift introduced by the acousto-optic modulator 3;

[0016] A pair of orthogonal signals I and Q are constructed in the digital domain for the above optical fiber vibration signal:

[0017] I=I out (t)·cos(Δω·t)

[0018] Q=I out (t)·sin(Δω·t)

[0019] Perform trigonometric function transformation on the orthogonal signals I and Q to obtain I' and Q' containing the double frequency and fundamental frequency terms respectively, and then pass them through a low-pass filter to obtain:

[0020]

[0021] The phase disturbance signal is obtained by taking the inverse tangent as follows:

[0022]

[0023] The obtained multiple phase disturbance signals are unwrapped to correct the phase disturbance signal value of the next sampling point.

[0024] Furthermore, the unwrapping of the obtained multiple phase disturbance signals includes: calculating the phase difference Δθ between two adjacent phase disturbance signal values, Δθ=θ t+1 -θ t , If Δθ>π or Δθ<-π, it is determined that the phase is wrapped; when Δθ>π, the phase disturbance signal value is unwound as follows: θ t+1 '=θ t+1 -2π; when Δθ<-π, the phase disturbance signal value is unwrapped as follows: θ t+1 '=θ t+1 +2π.

[0025] Furthermore, the processing of the two-dimensional spectrum image by using an image enhancement algorithm includes image contrast enhancement and gamma correction transformation processing.

[0026] Furthermore, the calculation formula of the spectrum standard deviation is:

[0027]

[0028] Among them, A enh (i, j) represents the spectrum amplitude of the enhanced image; Represents the spatial position xi The mean of the spectrum at ; N is the number of frequency points in the sliding window.

[0029] Furthermore, the method of identifying the spectrum distribution mutation area based on the spectrum standard deviation and then locating the connected tension tower includes:

[0030] The spatial position corresponding to the spectrum standard deviation being less than the preset standard deviation lower limit threshold is determined as the spectrum distribution sudden drop position;

[0031] The sudden drop position of the frequency spectrum distribution is matched with a preset comparison table of connected tension towers to obtain the corresponding tower number, thereby achieving the positioning of the tension tower.

[0032] According to another aspect of the present invention, a coherent detection-based -OTDR and standard deviation tension tower positioning system, the system includes:

[0033] A signal acquisition module configured to utilize The system monitors the vibration of the entire OPGW optical cable line and obtains optical fiber vibration signals;

[0034] a signal demodulation module configured to demodulate the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber;

[0035] a signal processing module configured to perform a Fourier transform on the phase disturbance signal at each spatial position to obtain a corresponding spectrum distribution; synthesize the spectrum distributions of all spatial positions into a two-dimensional spectrum image, and process the two-dimensional spectrum image using an image enhancement algorithm;

[0036] a standard deviation calculation module configured to calculate a spectrum standard deviation of the enhanced two-dimensional spectrum image using a sliding window for each spatial position;

[0037] The tower positioning module is configured to identify the spectrum distribution mutation area based on the spectrum standard deviation, and then locate the subsequent tension tower.

[0038] Furthermore, the signal demodulation module demodulates the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber, which includes: the optical fiber vibration signal is represented as follows:

[0039]

[0040] Where A s (t)=2A R (t)A L (t), A R (t),A L (t) represents the amplitude of the reference light and the local oscillator light corresponding to the t-th sampling point at time t, respectively; denote the phases of the reference light and the local oscillator light respectively; Δω denotes the frequency shift introduced by the acousto-optic modulator 3;

[0041] A pair of orthogonal signals I and Q are constructed in the digital domain for the above optical fiber vibration signal:

[0042] I=I out (t)·cos(Δω·t)

[0043] Q=I out (t)·sin(Δω·t)

[0044] Perform trigonometric function transformation on the orthogonal signals I and Q to obtain I' and Q' containing the double frequency and fundamental frequency terms respectively, and then pass them through a low-pass filter to obtain:

[0045]

[0046] The phase disturbance signal is obtained by taking the inverse tangent as follows:

[0047]

[0048] The obtained multiple phase disturbance signals are unwrapped to correct the phase disturbance signal value of the next sampling point.

[0049] Furthermore, the calculation formula of the spectrum standard deviation in the standard deviation calculation module is:

[0050]

[0051] Among them, A enh (i, j) represents the spectrum amplitude of the enhanced image; Represents the spatial position x i The mean of the spectrum at ; N is the number of frequency points in the sliding window.

[0052] The beneficial technical effects of the present invention are:

[0053] The present invention proposes a method based on coherent detection The method and system for locating tension towers based on OTDR and standard deviation have the advantages of no need for additional sensors, no need for on-site measurements, and a high degree of automation. Compared with traditional measurement methods, the present invention can remotely obtain the position information of tension towers and is suitable for intelligent identification and status monitoring of towers in various transmission line environments. The present invention improves the intelligent operation and maintenance level of transmission lines and provides new technical means for inspection, fault diagnosis and wind vibration monitoring of transmission lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily apparent by reading the following detailed description with reference to the accompanying drawings, in which several embodiments of the present invention are shown by way of example and not limitation, in which:

[0055] Figure 1 The coherent detection type according to the embodiment of the present invention -Flowchart of the tension tower positioning method using OTDR and standard deviation;

[0056] Figure 2 In the embodiment of the present invention -Schematic diagram of OTDR system structure;

[0057] Figure 3 1 is a comparison diagram before and after phase unwrapping in an embodiment of the present invention;

[0058] Figure 4 This is an example diagram of the results after FFT in an embodiment of the present invention;

[0059] Figure 5 This is a standard deviation result diagram in an embodiment of the present invention;

[0060] Figure 6 This is an example diagram of the positioning results of the tension tower in an embodiment of the present invention;

[0061] Figure 7 The coherent detection type according to the embodiment of the present invention -Schematic diagram of the structure of the tension tower positioning system using OTDR and standard deviation. DETAILED DESCRIPTION

[0062] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided solely to enable those skilled in the art to better understand and implement the present invention, and are not intended to limit the scope of the present invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0063] It is known to those skilled in the art that the embodiments of the present invention may be implemented as a system, apparatus, device, method, or computer program product. Therefore, the present disclosure may be specifically implemented in the following forms, namely: complete hardware, complete software (including firmware, resident software, microcode, etc.), or a combination of hardware and software. It should be understood that any number of elements in the accompanying drawings is for illustration and not limitation, and any nomenclature is for distinction only and does not have any limiting meaning.

[0064] The present invention proposes a method based on coherent detection A method and system for locating tension towers based on OTDR and standard deviation. By collecting phase change signals along the OPGW line in real time and performing Fast Fourier Transform (FFT) analysis on them, the distribution characteristics of the vibration spectrum are extracted. The optical cable structure at the tension tower is fixed and vibrations are weak, with its spectrum energy concentrated near 0 Hz. However, the overhead section of the optical cable is susceptible to disturbances such as wind loads and icing, resulting in a broad vibration spectrum distribution, with high-amplitude, broadband signals. The present invention first performs FFT on the phase demodulated signal in the time dimension to construct a two-dimensional spectrum image of the optical fiber length and frequency; in order to improve the signal-to-noise ratio and visual recognition of the spectrum image, the image is further normalized, contrast stretched, and gamma nonlinear correction are performed to enhance the spectrum characteristics of different structural areas, so that the spectrum characteristics of different structural areas are clearer; then, the standard deviation (STD) of each spatial position within the specified frequency range is calculated on the enhanced spectrum image to characterize the degree of discreteness of the vibration spectrum at that position; since the vibration of the connected tower section is stable, the STD value is significantly lower than that of the overhead section that is significantly affected by wind, so the connection position of the tension tower can be accurately identified by detecting the mutation point of the STD.

[0065] The embodiment of the present invention proposes a method based on coherent detection -OTDR and standard deviation tension tower positioning method, such as Figure 1 As shown, the method includes:

[0066] S1. Utilization -The OTDR system monitors the vibration of the entire OPGW optical cable line and obtains optical fiber vibration signals;

[0067] S2. Demodulating the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber;

[0068] S3, performing Fourier transform on the phase disturbance signal at each spatial position to obtain the corresponding spectrum distribution;

[0069] S4, synthesizing the spectrum distributions of all spatial positions into a two-dimensional spectrum image, and processing the two-dimensional spectrum image using an image enhancement algorithm;

[0070] S5. For each spatial position, a sliding window is used to calculate the spectrum standard deviation of the enhanced two-dimensional spectrum image;

[0071] S6. Identify the spectrum distribution mutation area based on the spectrum standard deviation, and then locate the connection tension tower.

[0072] The method starts from S1, in S1, using -The OTDR system monitors the vibration of the entire OPGW optical cable line and obtains optical fiber vibration signals.

[0073] According to an embodiment of the present invention, OTDR is a distributed fiber-optic sensing technology based on coherent detection. It can be used to detect phase changes caused by external disturbances along the fiber. Its basic principle is to use the coherence of Rayleigh scattered light to transmit pulsed light within the fiber. By detecting the phase changes of the echo signal, it can obtain vibration information along the fiber. -The optical path structure of the OTDR system is as follows Figure 2 As shown, the system includes: a narrow linewidth laser 1, a first optical coupler 2, an acousto-optic modulator 3, a first erbium-doped laser amplifier 4, a circulator 5, an arbitrary function generator 6, a second erbium-doped laser amplifier 7, a dense wavelength division multiplexer 8, a second optical coupler 9, a photoelectric balanced detector 10, a data acquisition card 11, and a computer 12; wherein, the optical signal output end of the narrow linewidth laser 1 is connected to the input end of the first optical coupler 2, the output end of the first optical coupler 2 is connected to the input end of the acousto-optic modulator 3 and the input end of the second optical coupler 9 respectively, the output end of the acousto-optic modulator 3 is connected to the input end of the first erbium-doped laser amplifier 4, and the output end of the first erbium-doped laser amplifier 4 is connected to the first port of the circulator 5. 5-1 is connected, the second port 5-2 of the circulator 5 is connected to the optical fiber to be tested, the third port 5-3 of the circulator 5 is connected to the input end of the second erbium-doped laser amplifier 7, the output end of the second erbium-doped laser amplifier 7 is connected to the input end of the dense wavelength division multiplexer 8, the output end of the dense wavelength division multiplexer 8 is connected to the input end of the second optical coupler 9, the output end of the second optical coupler 9 is connected to the input end of the photoelectric balance detector 10, the output end of the photoelectric balance detector 10 is connected to the data acquisition card 11, and the data acquisition card 11 is connected to the computer 12; the output end of the arbitrary function generator 6 is connected to the acousto-optic modulator 3, which is used to generate a radio frequency pulse signal for modulating the light source, thereby controlling the acousto-optic modulator 3 to output light pulses. Among them, the splitting ratio of the first optical coupler 2 is 90:10, and the splitting ratio of the second optical coupler 9 is 50:50. -OTDR system uses a series of optical devices to realize the modulation, transmission, detection and data collection of optical signals to monitor the vibration information along the optical fiber.

[0074] -The Rayleigh scattering signal of the OTDR system at a certain position z in the optical fiber can be expressed as:

[0075]

[0076] Where E0 is the amplitude of the incident light field, ω0 is the center frequency of the light source, and φ(z,t) is the phase of the fiber at position z, which is affected by external disturbances. Since the phase change of the fiber is related to the strain ε(z,t), φ(z,t) can be expressed as:

[0077]

[0078] Among them, n eff is the effective refractive index of the optical fiber, L is the length of the optical fiber segment, and λ is the wavelength of the light source.

[0079] When external disturbances (such as wind vibration and mechanical vibration) act on the optical fiber, it causes local strain changes, which makes the phase of the scattered light change periodically, so that the vibration information of the optical fiber can be monitored using the coherent detection method. In OTDRs, interferometric detection is typically used to obtain phase information of Rayleigh scattered signals. Unlike direct detection, coherent detection generally uses a photoelectric balanced detector. The signal light and local oscillator light scattered back from the fiber are injected through the two ports of a coupler. Then, through the coupler, they are input into the two ports of the photoelectric balanced detector, where each port is a photodetector.

[0080] The signal light and local oscillator light scattered back by the optical fiber can be expressed as:

[0081]

[0082] Among them A R (t),A L (t) are the amplitudes of the signal light and the local oscillator light corresponding to the t-th sampling point at time t, are the phases of the signal light and the local oscillator light, respectively; ω0 is the angular frequency of the light pulse, and Δω is the frequency shift introduced by the acousto-optic modulator 3. After passing through the second optical coupler 9, the two light pulses interfere with each other. Therefore, the light fields at the two output ends of the second optical coupler 9 are expressed as:

[0083]

[0084] Ignoring the influence of the polarization state, after passing through the photoelectric balanced detector 10, the output photocurrent signal is proportional to the power of the input optical signal. The photocurrents at the two output ports of the photoelectric balanced detector 10 are respectively expressed as:

[0085]

[0086] Where r d For the photoelectric balanced detector 10, the final photocurrent output is the subtraction of the upper and lower outputs, so the final current is expressed as:

[0087]

[0088] Let A s (t) = 2A R (t)A L (t), then the above formula can be written as follows:

[0089]

[0090] Then, S2 is executed, in which the optical fiber vibration signal is demodulated to obtain a phase disturbance signal along the length direction of the optical fiber.

[0091] According to an embodiment of the present invention, in order to extract the phase term in the final current expression, an IQ demodulation method is adopted, and the process is as follows.

[0092] First, construct a pair of orthogonal signals in the digital domain:

[0093] I=I out (t)·cos(Δω·t)

[0094] Q=I out (t)·sin(Δω·t)

[0095] Then perform trigonometric function transformation to obtain I' and Q' containing double frequency and fundamental frequency terms respectively:

[0096]

[0097] After passing it through a low-pass filter, we get:

[0098]

[0099] Finally, the inverse tangent is calculated to obtain the phase disturbance signal value:

[0100]

[0101] Since the range of the trigonometric function arctanx is (-π / 2,π / 2), which is finite, when the actual phase value exceeds this range, the calculated phase will "fold" back into its defined range, forming a phase jump. This means that the actual phase change is continuous, but due to the limitations of the measurement method, it will suddenly change, making the data appear to be "entangled." Therefore, it is necessary to unwrap the multiple phase disturbance signals obtained to correct the phase disturbance signal value at the next sampling point.

[0102] The phase unwrapping process includes:

[0103] 1) Calculate the phase difference Δθ between two adjacent phase values; let the two adjacent phase values be θ t and θ t+1 ,in Calculate the phase difference between them: Δθ = θ t+1 -θ t ;

[0104] 2) If Δθ>π or Δθ<-π, it is determined that the phase is wrapped; if Δθ>π, it means that from θ t Jump to θ t+1 , it crosses the boundary from -π to π (i.e., exceeds the range); if Δθ<-π, it means that from θ t Jump to θ t+1 , it crosses the boundary from π to -π (i.e., exceeds the range); if -π≤Δθ≤π, it means that from θ t Jump to θ t+1 When , no entanglement occurs and no untangle is required;

[0105] 3) Unwinding process: If Δθ>π, it means that the phase jump exceeds π and needs to be adjusted in θ t+1 Subtract 2π from the top, which is θ t+1 '=θ t+1 -2π to maintain phase continuity; if Δθ < -π, it means the phase jump exceeds -π, and it is necessary to adjust the phase in θ t+1 Add 2π to it, which is θ t+1 '=θ t+1 +2π to maintain phase continuity. Figure 3 A comparison before and after phase unwrapping is shown.

[0106] Then, S3 is executed. In S3, the phase disturbance signal at each spatial position is subjected to Fourier transform to obtain the corresponding spectrum distribution.

[0107] According to an embodiment of the present invention, a fast Fourier transform (FFT) is performed on the phase signal at a certain spatial position z in the time dimension to obtain its spectrum distribution:

[0108]

[0109] in, represents the frequency domain response at position z; f is the frequency. FFT reveals the frequency distribution characteristics of the vibration experienced by the optical cable at that location. In the overhead section, subject to external disturbances such as wind vibration, the spectral distribution is typically more complex and the energy is dispersed. Meanwhile, at splicing points or coiled sections, the structure is stable, vibration is weak, and the spectral energy is primarily concentrated in the low-frequency region near 0 Hz. Figure 4 The results after FFT are shown.

[0110] Then, S4 is executed, in which the frequency spectrum distributions of all spatial positions are synthesized into a two-dimensional spectrum image, and the two-dimensional spectrum image is processed using an image enhancement algorithm.

[0111] According to an embodiment of the present invention, processing the two-dimensional spectrum image includes image contrast enhancement and Gamma correction transformation processing.

[0112] 1) Image contrast enhancement processing

[0113] Assume that the original spectrum image is a two-dimensional matrix F(i,j), where i = 1, 2, ..., N represents the sampling point (spatial position) along the fiber length, j = 1, 2, ..., N represents the frequency component index (vertical axis), and F(i,j) is the spectrum amplitude at the i-th position at the j-th frequency. First, the original spectrum image is normalized and stretched to make the image pixel intensity distribution more dispersed:

[0114]

[0115] Among them, F min =min(F), F max = max(F). This normalization process compresses all pixel values to the interval [0, 1] to facilitate subsequent nonlinear enhancement operations.

[0116] 2) Gamma correction transformation

[0117] Apply Gamma correction transformation to the enhanced image to make nonlinear adjustments to the pixel values: F gamma (i,j)=F norm (i,j) γ Where 0 < γ < 1. In this embodiment, a gamma value of 0.4 is selected to enhance the grayscale value of low-intensity areas, suppress overexposure in high-intensity areas, and enhance the contrast between weak signals (such as background noise far from the tower) and strong signals (such as the frequency energy concentration area corresponding to the tower).

[0118] The final output image is: F enh (i,j)=F gamma (i, j). Compared to the original image, the enhanced image shows a more pronounced concentration of frequency energy in the tower area, and the background noise distribution is effectively suppressed. After these two steps, the high-energy areas in the spectrum image associated with the tower vibration characteristics can be enhanced visually and in standard deviation calculations. This image is then input into the standard deviation sliding window module for tower positioning, significantly improving positioning accuracy and robustness.

[0119] Then, S5 is executed. In S5, for each spatial position, a sliding window is used to calculate the spectrum standard deviation of the enhanced two-dimensional spectrum image.

[0120] According to an embodiment of the present invention, to quantitatively describe the dispersion of the vibration spectrum, the standard deviation of the frequency domain amplitude is used as a stability criterion. Standard deviation is a statistical indicator that measures the degree of data dispersion. The standard deviation is calculated for each spatial location to measure the degree to which the signal energy at that location varies with frequency.

[0121] For each spatial position x i, calculate its spectrum standard deviation within a selected sliding window (for example, the frequency range is 0-125Hz):

[0122]

[0123] Among them, A enh (i, j) is the spectrum amplitude of the enhanced image, is the frequency spectrum mean at that location, and N is the number of frequency points within the selected frequency range. A higher standard deviation indicates a wider distribution of vibration frequencies at that location, typically corresponding to areas with strong wind-induced vibration disturbances on overhead optical cables. Locations with lower standard deviations often correspond to structurally stable tension towers where downlink optical cables experience weak vibrations. Figure 5 As shown, the STD value shows a significant dip at a specific location, which corresponds well to the location of the tension tower. By traversing the STD curve of the entire length of the optical cable, the tower location can be automatically determined and the span can be divided.

[0124] Then, S6 is executed, in which a spectrum distribution mutation area is identified based on the spectrum standard deviation, and the connected tension tower is located.

[0125] According to an embodiment of the present invention, STD is introduced as a quantitative indicator of the vibration spectrum distribution characteristics. By calculating the standard deviation of the spectrum amplitude at each location, regions of sudden changes in the spectrum distribution are identified. Spatial locations where the standard deviation shows a significant drop typically correspond to the connection points of tension towers. Specifically, spatial locations where the spectrum standard deviation is less than a preset standard deviation lower limit threshold are identified as locations where the spectrum distribution suddenly drops.

[0126] By matching the drop-off location obtained through standard deviation analysis with the preset tower number and fiber length comparison table (see Table 1) and obtaining the corresponding tower number, the precise location of the tension tower can be achieved. Specifically, after using standard deviation analysis to locate the tension tower, the tension tower number can be matched one-to-one with the identified tension tower. By referring to the subsequent tension tower comparison table, the correspondence between the tension tower number and the DAS fiber length can be obtained. The tension tower position determined by standard deviation analysis (i.e., the standard deviation drop-off point) needs to be matched with the DAS fiber length in Table 1. The closest tension tower number is found to achieve tension tower positioning. The "tension section fiber length" refers to the actual fiber length of the large-side tension section measured by the DAS system. For example, the tension section numbered 4508 represents the fusion splice between tension towers 2152# and 2162#. The actual physical span covered by this fiber section is the sum of multiple straight tower sections between the two tension towers. Figure 6 The results of tension tower positioning are shown.

[0127] Table 1 Comparison table of connected tension towers

[0128]

[0129]

[0130] Another embodiment of the present invention proposes a method based on coherent detection -OTDR and standard deviation tension tower positioning system, such as Figure 7 As shown, the system includes:

[0131] The signal acquisition module 710 is configured to utilize -The OTDR system monitors the vibration of the entire OPGW optical cable line and obtains optical fiber vibration signals;

[0132] a signal demodulation module 720 configured to demodulate the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber;

[0133] a signal processing module 730 configured to perform a Fourier transform on the phase disturbance signal at each spatial position to obtain a corresponding spectrum distribution; synthesize the spectrum distributions of all spatial positions into a two-dimensional spectrum image, and process the two-dimensional spectrum image using an image enhancement algorithm;

[0134] a standard deviation calculation module 740 configured to calculate a spectrum standard deviation for the enhanced two-dimensional spectrum image using a sliding window for each spatial position;

[0135] The tower positioning module 750 is configured to identify the spectrum distribution mutation area based on the spectrum standard deviation, and then locate the subsequent tension tower.

[0136] In this embodiment, optionally, the signal demodulation module 720 demodulates the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber, including: the optical fiber vibration signal is represented as follows:

[0137]

[0138] Where A s (t)=2A R (t)A L (t), A R (t),A L (t) represents the amplitude of the reference light and the local oscillator light corresponding to the t-th sampling point at time t, respectively; denote the phases of the reference light and the local oscillator light respectively; Δω denotes the frequency shift introduced by the acousto-optic modulator 3;

[0139] A pair of orthogonal signals I and Q are constructed in the digital domain for the above optical fiber vibration signal:

[0140] I=I out (t)·cos(Δω·t)

[0141] Q=I out (t)·sin(Δω·t)

[0142] Perform trigonometric function transformation on the orthogonal signals I and Q to obtain I' and Q' containing the double frequency and fundamental frequency terms respectively, and then pass them through a low-pass filter to obtain:

[0143]

[0144] The phase disturbance signal is obtained by taking the inverse tangent as follows:

[0145]

[0146] Dewrapping the obtained multiple phase disturbance signals to correct the phase disturbance signal value of the next sampling point; including: calculating the phase difference Δθ between two adjacent phase disturbance signal values, Δθ=θ t+1 -θ t , If Δθ>π or Δθ<-π, it is determined that the phase is wrapped; when Δθ>π, the phase disturbance signal value is unwound as follows: θ t+1 '=θ t+1 -2π; when Δθ<-π, the phase disturbance signal value is unwound as follows: θ t+1 '=θ t+1 +2π.

[0147] In this embodiment, optionally, the calculation formula of the spectrum standard deviation in the standard deviation calculation module 740 is:

[0148]

[0149] Among them, A enh (i, j) represents the spectrum amplitude of the enhanced image; Represents the spatial position x i The mean of the spectrum at ; N is the number of frequency points in the sliding window.

[0150] It should be noted that the coherent detection type described in this embodiment -OTDR and standard deviation of the tension tower positioning system can be based on the aforementioned coherent detection type - Description of the tension tower positioning method using OTDR and standard deviation. For parts not described in detail in the system embodiment, please refer to the above method embodiment.

[0151] In summary, this invention, based on vibration signals acquired by the #imgpt65#-OTDR system, automatically identifies the locations of towers and poles along which optical cables pass, without relying on external markers or specialized cable structures. By extracting frequency domain features and combining image enhancement with statistical analysis, a correspondence between fiber distance and physical structure is established, effectively reflecting the differences in vibration response characteristics between aerial and spliced sections. This method improves spatial resolution and possesses non-invasive, highly adaptable engineering applications.

[0152] Compared to the traditional OTDR method that relies on the reflection or attenuation characteristics at the fusion point for positioning, the present invention completes the identification by observing the vibration spectrum distribution characteristics. Since the attenuation value of the fusion point of modern optical cables has dropped significantly to about 0.05dB, the OTDR identification accuracy has been significantly reduced. At the same time, structures such as bends and coils in the optical cable path are easily misjudged as fusion points, affecting accuracy. The method proposed in the present invention locates by identifying the difference between the area where low-frequency vibration energy is concentrated (corresponding to the pole tower connection point) and the area where high-frequency vibration is significant (corresponding to the overhead section), effectively avoiding the misjudgment problem of the OTDR method.

[0153] Some existing methods rely on differences in Brillouin frequency shifts between different types of optical fibers for positioning. However, this approach is limited in application given that the same type of fiber is commonly used in current optical cable projects. The present invention does not rely on fiber type differences, but instead identifies vibration differences between optical cable segments in actual environments, thereby improving adaptability and universality.

[0154] Overhead optical cables suspended between towers are susceptible to wind disturbances, resulting in breeze vibration and fluttering, with their frequency spectrum containing significant natural frequency components. However, at the splice tower, structural constraints such as down conductors and cable reels prevent the cables from vibrating significantly, with their frequency spectrum concentrated in low frequencies (near 0 Hz). This invention leverages this difference in vibration characteristics to achieve stable and reliable identification of splice points. This method is applicable to various overhead optical cable environments and possesses excellent engineering practicality and widespread application value.

[0155] Although the spirit and principles of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the specific embodiments disclosed, and the division into various aspects does not mean that the features of these aspects cannot be combined to benefit. Such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A tension tower positioning method based on coherent detection φ-OTDR and standard deviation, characterized in that: include: Use the φ-OTDR system to monitor the vibration of the entire OPGW optical cable line and obtain optical fiber vibration signals; Demodulating the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber; Perform Fourier transform on the phase disturbance signal at each spatial position to obtain the corresponding spectrum distribution; The spectrum distributions of all spatial positions are synthesized into a two-dimensional spectrum image, and the two-dimensional spectrum image is processed using an image enhancement algorithm; For each spatial position, a sliding window is used to calculate the spectral standard deviation of the enhanced two-dimensional spectrum image; Based on the spectrum standard deviation, the spectrum distribution mutation area is identified and the connection tension tower is located.

2. The method for positioning a tension tower based on coherent detection φ-OTDR and standard deviation according to claim 1, characterized in that: The structure of the φ-OTDR system comprises: a narrow linewidth laser (1), a first optical coupler (2), an acousto-optic modulator (3), a first erbium-doped laser amplifier (4), a circulator (5), an arbitrary function generator (6), a second erbium-doped laser amplifier (7), a dense wavelength division multiplexer (8), a second optical coupler (9), a photoelectric balance detector (10), a data acquisition card (11), and a computer (12); wherein the optical signal output end of the narrow linewidth laser (1) is connected to the input end of the first optical coupler (2), the output end of the first optical coupler (2) is connected to the input end of the acousto-optic modulator (3) and the input end of the second optical coupler (9); the output end of the acousto-optic modulator (3) is connected to the input end of the first erbium-doped laser amplifier (4), the output end of the first erbium-doped laser amplifier (4) is connected to the circulator (5). ), the second port (5-2) of the circulator (5) is connected to the optical fiber to be tested, the third port (5-3) of the circulator (5) is connected to the input end of the second erbium-doped laser amplifier (7), the output end of the second erbium-doped laser amplifier (7) is connected to the input end of the dense wavelength division multiplexer (8), the output end of the dense wavelength division multiplexer (8) is connected to the input end of the second optical coupler (9), the output end of the second optical coupler (9) is connected to the input end of the photoelectric balance detector (10), the output end of the photoelectric balance detector (10) is connected to the data acquisition card (11), and the data acquisition card (11) is connected to the computer (12); the output end of the arbitrary function generator (6) is connected to the acousto-optic modulator (3) for generating a radio frequency pulse signal for modulating the light source, thereby controlling the acousto-optic modulator (3) to output an optical pulse.

3. The method for positioning a tension tower based on coherent detection φ-OTDR and standard deviation according to claim 2, characterized in that: Demodulating the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber includes: The optical fiber vibration signal is expressed as follows: Where A s (t) = 2A R (t)A L (t), A R (t),A L (t) represents the amplitude of the reference light and the local oscillator light corresponding to the t-th sampling point at time t, respectively; denote the phases of the reference light and the local oscillator light respectively; Δω denotes the frequency shift introduced by the acousto-optic modulator (3); A pair of orthogonal signals I and Q are constructed in the digital domain for the above optical fiber vibration signal: I=I out (t)·cos(Δω·t) Q=I out (t)·sin(Dω·t) Perform trigonometric function transformation on the orthogonal signals I and Q to obtain I' and Q' containing the double frequency and fundamental frequency terms respectively, and then pass them through a low-pass filter to obtain: The phase disturbance signal is obtained by taking the inverse tangent as follows: The obtained multiple phase disturbance signals are unwrapped to correct the phase disturbance signal value of the next sampling point.

4. The method for positioning a tension tower based on coherent detection φ-OTDR and standard deviation according to claim 3, characterized in that: The unwrapping of the obtained multiple phase disturbance signals includes: calculating the phase difference Δθ between two adjacent phase disturbance signal values, Δθ=θ t+1 -θ t , If Δθ>π or Δθ<-π, it is determined that the phase is wrapped; when Δθ>π, the phase disturbance signal value is unwound as follows: θ t+1 '=θ t+1 -2π; when Δθ<-π, the phase disturbance signal value is unwrapped as follows: θ t+1 '=θ t+1 +2π.

5. The coherent detection-based method according to claim 1 and standard deviation of the tension tower positioning method, characterized in that, The process of processing the two-dimensional spectrum image by using the image enhancement algorithm includes image contrast enhancement and Gamma correction transformation processing.

6. The coherent detection-based method according to claim 1 and standard deviation of the tension tower positioning method, characterized in that, The calculation formula of the spectrum standard deviation is: Among them, A enh (i, j) represents the spectrum amplitude of the enhanced image; Represents the spatial position x i The mean of the spectrum at ; N is the number of frequency points in the sliding window.

7. The coherent detection-based method according to claim 1 and standard deviation of the tension tower positioning method, characterized in that, The method of identifying a spectrum distribution mutation area based on the spectrum standard deviation and then locating the connected tension tower includes: The spatial position corresponding to the spectrum standard deviation being less than the preset standard deviation lower limit threshold is determined as the spectrum distribution sudden drop position; The sudden drop position of the frequency spectrum distribution is matched with a preset comparison table of connected tension towers to obtain the corresponding tower number, thereby achieving the positioning of the tension tower.

8. Based on coherent detection and standard deviation of the tension tower positioning system, characterized in that, include: A signal acquisition module configured to utilize The system monitors the vibration of the entire OPGW optical cable line and obtains optical fiber vibration signals; a signal demodulation module configured to demodulate the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber; a signal processing module configured to perform a Fourier transform on the phase disturbance signal at each spatial position to obtain a corresponding spectrum distribution; synthesize the spectrum distributions of all spatial positions into a two-dimensional spectrum image, and process the two-dimensional spectrum image using an image enhancement algorithm; a standard deviation calculation module configured to calculate a spectrum standard deviation of the enhanced two-dimensional spectrum image using a sliding window for each spatial position; The tower positioning module is configured to identify the spectrum distribution mutation area based on the spectrum standard deviation, and then locate the subsequent tension tower.

9. The coherent detection-based method according to claim 8 and standard deviation of the tension tower positioning system, characterized in that, The signal demodulation module demodulates the optical fiber vibration signal to obtain a phase disturbance signal along the length direction of the optical fiber, including: the optical fiber vibration signal is represented as follows: Where A s (t) = 2A R (t)A L (t), A R (t),A L (t) represents the amplitude of the reference light and the local oscillator light corresponding to the t-th sampling point at time t, respectively; denote the phases of the reference light and the local oscillator light respectively; Δω denotes the frequency shift introduced by the acousto-optic modulator (3); A pair of orthogonal signals I and Q are constructed in the digital domain for the above optical fiber vibration signal: I=I out (t)·cos(Δω·t) Q=I out (t)·sin(Dω·t) Perform trigonometric function transformation on the orthogonal signals I and Q to obtain I' and Q' containing the double frequency and fundamental frequency terms respectively, and then pass them through a low-pass filter to obtain: The phase disturbance signal is obtained by taking the inverse tangent as follows: The obtained multiple phase disturbance signals are unwrapped to correct the phase disturbance signal value of the next sampling point.

10. The coherent detection-based method according to claim 8 and standard deviation of the tension tower positioning system, characterized in that, The calculation formula of the spectrum standard deviation in the standard deviation calculation module is: Among them, A enh (i, j) represents the spectrum amplitude of the enhanced image; Represents the spatial position x i The mean of the spectrum at ; N is the number of frequency points in the sliding window.

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