Method for identifying the location of utility poles from vibration distribution waveforms
The vibration analysis apparatus and method utilize high-pass filtering and envelope detection to automate the identification of utility pole positions in optical fiber cables, improving measurement accuracy and efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- NIPPON TELEGRAPH & TELEPHONE CORP
- Filing Date
- 2022-09-15
- Publication Date
- 2026-06-18
Smart Images
Figure 0007875484000001 
Figure 0007875484000002 
Figure 0007875484000003
Abstract
Description
Technical Field
[0001] The present disclosure relates to vibration distribution sensing technology.
Background Art
[0002] Distributed vibration sensing (DVS) has been proposed to obtain and analyze the vibration distribution of an aerial optical fiber cable using OTDR (Optical Time Domain Reflectometry), OFDR (Optical Frequency Domain Reflectometry), etc. (see, for example, Non-Patent Document 1). When the measurement performance of the obtained vibration distribution is higher than the frequencies of time and space, which are the vibration characteristics of the aerial optical fiber cable, the Nyquist theorem is satisfied, and the vibration of the aerial optical fiber cable can be faithfully measured.
[0003] The vibration distribution of an aerial optical fiber cable can be regarded as an independent vibration system for each span. The continuous section of vibration propagation represents the aerial optical fiber cable, and the discontinuous part represents the boundary point with the adjacent vibration system, that is, the utility pole. However, since there is no algorithm for automatically identifying the utility pole position, the discontinuous parts of the vibration distribution waveform are identified visually.
Prior Art Documents
Non-Patent Documents
[0004]
Non-Patent Document 1
[0005] Depending on the vibration distribution waveform, it may not be clear that the vibration system is discontinuous. Therefore, this disclosure aims to enable the identification of utility pole locations from the vibration distribution waveform of overhead optical fiber cables without relying on visual inspection. [Means for solving the problem]
[0006] The vibration analysis apparatus and vibration analysis method disclosed herein are: The vibration distribution waveform, which shows the time evolution of the longitudinal spatial distribution of vibrations in an overhead optical fiber cable, is filtered using a high-pass filter with a cutoff frequency higher than the spatial frequency of the vibration. The location of the utility pole is identified by performing envelope detection on the filtered waveform obtained by the above filtering process.
[0007] The aforementioned cutoff frequency can be any frequency higher than the spatial frequency of the vibration.
[0008] The vibration analysis apparatus and vibration analysis method of this disclosure may extract only the traveling wave component or the backward wave component in the longitudinal direction of the vibration from the vibration distribution waveform, and perform the filtering on the extracted traveling wave component or backward wave component.
[0009] Furthermore, the above disclosures can be combined as much as possible. [Effects of the Invention]
[0010] This disclosure makes it possible to determine the location of a utility pole from the vibration distribution waveform of an overhead optical fiber cable without relying on visual inspection. [Brief explanation of the drawing]
[0011] [Figure 1] An example of the vibration distribution waveform F0 is shown. [Figure 2]An example of the position of a utility pole in a vibration distribution waveform is shown. [Figure 3] An example of the system configuration described herein is shown. [Figure 4] An example of a vibration analysis method is shown in this disclosure. [Figure 5] An example of the spectrum S1 for each spatial frequency k and time frequency w is shown. [Figure 6] An example of a unidirectional spectrum S2 is shown. [Figure 7] An example of a unidirectional vibration distribution waveform F1 is shown. [Figure 8] An example of a high-pass filtered waveform F2 is shown. [Figure 9] An example of the high-pass filtered waveform F3 after envelope detection is shown. [Modes for carrying out the invention]
[0012] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.
[0013] Figure 1 shows an example of a vibration distribution waveform. This disclosure uses the vibration distribution waveform of an aerial optical fiber cable. By measuring the strain at each point along the longitudinal direction of the optical fiber using an OTDR or OFDR, the vibration distribution waveform in the longitudinal direction of the optical fiber can be obtained. The vibration distribution waveform includes two distributions: the spatial distribution in the longitudinal direction of the aerial optical fiber cable and the temporal distribution, i.e., the change over time. The figure shows an example of a two-dimensional distribution of distance (m) and time (s) in the longitudinal direction of the aerial optical fiber cable.
[0014] Vibrations propagating along an aerial optical fiber cable exhibit continuous behavior over one span between utility poles, as indicated by the arrows in FIG. 2. Since the propagation of vibrations in the aerial optical fiber cable 91 is interrupted by the utility poles 92, the vibration distribution waveform becomes discontinuous at the distances D1, D2, D3, and D4 of the utility pole positions. The vibration analysis device of the present disclosure identifies the distances at which the utility poles are located by executing the vibration analysis method of the present disclosure.
[0015] FIG. 3 shows a configuration example of the vibration analysis device of the present disclosure. The vibration analysis device 10 of the present disclosure includes a signal processing unit 11 and a memory 12. In the memory 12, a vibration distribution waveform in the longitudinal direction of the aerial optical fiber cable is stored. Note that the vibration distribution waveform may be calculated from measurement results such as OTDR or OFDR in the signal processing unit 11.
[0016] FIG. 4 shows an example of the vibration analysis method of the present disclosure. The vibration analysis method of the present disclosure is such that the signal processing unit 11 sequentially executes the following steps. Step S11: Obtain the vibration distribution waveform F0 from the memory 12. Step S15: Apply a high-pass filter in the spatial direction to the vibration distribution waveform F0. Step S16: Calculate the square of the high-pass filtered waveform F2 after high-pass filtering. Step S17: Perform envelope detection on the high-pass filtered waveform F2. Step S18: Output (display) the utility pole positions using the detection result.
[0017] Between step S11 and S15, the following steps may be sequentially provided. Step S12: Perform a two-dimensional Fourier transform on the vibration distribution waveform F0 to obtain a spectrum S1 of the spatial frequency. Step S13: Extract only the components of the traveling wave or the backward wave from the spectrum S1 to obtain a one-directional spectrum S2. Step S14: Perform an inverse two-dimensional Fourier transform on the components of the traveling wave or the backward wave to obtain a one-directional vibration distribution waveform F1. In this case, in step S15, a high-pass filter in the spatial direction is applied to the vibration distribution waveform F1. The following explains each step in detail.
[0018] In step S11, a vibration distribution waveform as shown in Figure 1 is obtained. When step S12 is executed, spectra S1(dB) for each spatial frequency k and time frequency w are obtained as shown in Figure 5.
[0019] In this spectrum S1, the vibration is divided into a traveling wave component (region k / w < 0) and a backward wave component (region k / w > 0) at the time frequency w = 0. Therefore, step S13 is performed to set both the traveling wave and backward wave components of the vibration to zero, and the vibration components in the forward direction (traveling wave) or backward direction (backward wave) along the longitudinal direction of the overhead optical fiber cable are extracted, as shown in spectrum S2 in Figure 6. By extracting components in one direction in this way, the discontinuity location in the vibration in the spatial direction can be highlighted.
[0020] Step S14 is performed, and the extracted spectrum S2 is subjected to an inverse 2D Fourier transform. This yields a vibration distribution waveform F1 that emphasizes the vibration discontinuity, as shown in Figure 7. In this vibration distribution waveform F1, the amplitude is larger in region A1 from around 275m to around 310m and in region A2 from around 420m to around 450m.
[0021] Since the vibration becomes discontinuous at the distance of the utility pole, step S15 is executed, and a high-pass filter in the spatial direction is applied to the vibration distribution waveform F1 with a cutoff frequency higher than the spatial frequency of the vibration. For example, in the example shown in Figure 5, a cutoff frequency of 0.5 or higher is used. This makes it possible to obtain a high-pass filtered waveform F2 in which the vibration amplitude due to the discontinuation of vibration in regions A1 and A2 is extracted, as shown in Figure 8.
[0022] In the two-dimensional spectrum of the vibration distribution waveform, the (k,w) points scattered along the straight line passing through (spatial frequency k=0, time frequency w=0) represent the vibration spectrum. For example, in Figure 5, the straight line connecting (k=0,w=0), (k=0.3,w=10), and (k=0.3,w=-10) represents the spectrum of vibration. The largest k on this straight line is... max Since this represents the spatial frequency of vibration, in the example shown in Figure 5, k max This becomes 0.5.
[0023] Envelope detection is performed on the high-pass filtered waveform F2 to highlight discontinuities in the high-pass filtered waveform F2. Envelope detection is performed, for example, by applying a low-pass filter in the time direction. In this case, the low-pass filter may be applied after squaring the high-pass filtered waveform.
[0024] Figure 9 shows an example of the high-pass filtered waveform F3 after envelope detection. The signal processing unit 11 may graph the amplitude of the high-pass filtered waveform F3 after envelope detection on a logarithmic scale. This allows for further emphasis on discontinuities in the high-pass filtered waveform F2.
[0025] The signal processing unit 11 detects the amplified distance and outputs the detected distance as the utility pole position. For example, it detects the distance where the amplitude exceeds a predetermined value. Alternatively, it may be the distance where the amplitude exceeds a predetermined value over a predetermined period of time. Here, the predetermined period may be continuous or the sum of intermittent periods of time. In the example of this embodiment, since each distance D1 to D8 is amplified, the signal processing unit 11 outputs each distance D1 to D8 as the utility pole position.
[0026] (Effects of this disclosure) As explained above, this disclosure makes it possible to extract the position of a utility pole from the vibration distribution waveform of an overhead optical fiber cable using signal processing, without relying on visual inspection.
[0027] The discontinuity of vibration at the location of a utility pole has statistical properties, and it is easier to observe the discontinuity by measuring over a longer period of time. Although each span of an overhead fiber optic cable is an independent vibration system, their frequency characteristics are almost the same. For example, the discontinuity point (phase synchronization shift) between a section vibrating at 1 Hz and a section vibrating at 10 Hz can be detected in a short measurement time because the frequencies are significantly different, but a long measurement time is required to detect the discontinuity point between a 1 Hz section and a 1.1 Hz section.
[0028] Therefore, in step S11, the signal processing unit 11 may acquire the vibration distribution waveform such that the time axis is equal to or greater than a predetermined time. For example, the frequency difference between 1 Hz and 1.1 Hz is 0.1 Hz, and a measurement time with a minimum frequency resolution of 0.1 Hz is required to distinguish between these two vibrations. Since the length of the measurement time and the frequency resolution are inversely related, a measurement time of 10 seconds or more is sufficient for the vibration distribution waveform.
[0029] In this disclosure, the vibration distribution can be accurately measured by performing measurements that satisfy the Nyquist theorem in spatial and temporal sampling. Furthermore, to detect discontinuities in vibration, the time scale (length of measurement time) may be made longer than the vibration period. The vibration period depends on the overhead cable installation conditions, but it is at most a few seconds, so a time scale of about one minute is sufficient. Additionally, the distance scale (length in the distance direction) can be made significantly larger than the width of the utility pole. Since the width of a utility pole is about 1 meter, a distance scale of about 5 meters is sufficient.
[0030] The apparatus described herein can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided over a network. The program described herein is a program for realizing a computer as each functional unit of the apparatus described herein, and is a program for causing the computer to execute each step of the method performed by the apparatus described herein. [Explanation of symbols]
[0031] 10: Vibration analysis device 11: Signal Processing Unit 12: Memory 91: Overhead fiber optic cable 92: Utility pole
Claims
1. The vibration distribution waveform, which shows the time evolution of the longitudinal spatial distribution of vibrations in an overhead optical fiber cable, is filtered using a high-pass filter with a cutoff frequency higher than the spatial frequency of the vibration. By performing envelope detection on the filtered waveform obtained by the above filtering, the location of the utility pole can be identified. Vibration analysis equipment.
2. From the aforementioned vibration distribution waveform, only the traveling wave component or the backward wave component in the longitudinal direction of the vibration is extracted. The filtering described above is performed on the extracted forward wave component or backward wave component. The vibration analysis apparatus according to claim 1.
3. The vibration distribution waveform, which shows the time evolution of the longitudinal spatial distribution of vibrations in an overhead optical fiber cable, is filtered using a high-pass filter with a cutoff frequency higher than the spatial frequency of the vibration. By performing envelope detection on the filtered waveform obtained by the above filtering, the location of the utility pole can be identified. Vibration analysis method.