Method for correcting das data

Abstract

The present disclosure provides a method for correcting vibration data of causing, by an information processing device, vibration which is out of vibration data acquired by a distributed acoustic sensing (DAS) device and has a displaced center of vibration to approach vibration centered at zero.

Description

DAS data correction method

[0001] The present disclosure relates to a method for correcting vibration data obtained by a DAS and transmitted to an optical fiber.

[0002] A distributed acoustic sensing (DAS) device can measure vibrations transmitted to optical fibers (see, for example, Non-Patent Document 1). Because the phase range obtained by a DAS is -π to π, the actual phase difference can be estimated in the range of -nπ to nπ (n is a natural number) by performing phase unwrapping processing.

[0003] On the other hand, there is a method for correcting vibration discontinuities due to the failure of phase unwrapping by performing bandpass filtering in the time axis direction to remove sudden changes in vibration intensity that cannot occur in the desired observation phenomenon (see, for example, Non-Patent Document 2). The method in Non-Patent Document 2 is a method that can correct vibration discontinuities regardless of the type of DAS device.

[0004] Technical information: Technical principle "Optical fiber distributed vibration sensor (DAS)", Lasac Co., Ltd., http: / / www. lazoc. jp / technical / principle / 000356. htmlT. S. Hudson, A. F. Baird, J. M. Kendall, S. K. Kufner, A. M. Brisbourne, A. M. Smith, A. Butcher, A. Chalari, A. Clarke, “Distributed Acoustic Sensing (DAS) for Natural Microseismicity Studies: A Case Study From Antarctica”, Journal of Geophysical Research: Solid Earth, Volume 126, Issue 7, (2021) https: / / agupubs. onlinelibrary. wiley. com / doi / full / 10.1029 / 2020JB021493

[0005] However, due to the influence of excessively large vibrations or noise, there is a problem in that the influence of discontinuous vibrations remains even after the bandpass filter processing of Non-Patent Document 2.

[0006] The information processing device of the present disclosure executes the vibration data correction method of the present disclosure, in which the information processing device adjusts vibrations of which the center of vibration is shifted among the vibration data acquired by the DAS device to vibrations centered around zero.

[0007] The present disclosure brings vibration data with a deviation in vibration center closer to vibration centered around zero, thereby reducing the effect of vibration discontinuities.

[0008] The information processing device may set a correction constant according to the vibration intensity of the vibration data, calculate a constant multiple shift amount by dividing all the vibration intensities of the vibration data by the correction constant, and derive the vibration intensity of the corrected vibration data by subtracting the constant multiple shift amount from the vibration intensity of the vibration data. In this embodiment, the information processing device may calculate the constant multiple shift amount by dividing all the vibration intensities of the vibration data by the correction constant and converting the obtained value into an integer value of a predetermined number of digits.

[0009] The information processing device may also create a histogram showing the number of occurrences of each vibration intensity of the vibration data, create a line graph connecting the number of occurrences of each vibration intensity in the histogram, and derive the correction constant using the vibration intensity at which the line graph peaks. In this embodiment, the information processing device may derive the correction constant by calculating an average value of differences in vibration intensity at which the line graph peaks.

[0010] The program of the present disclosure is a program that causes a computer to execute the vibration data correction method of the present disclosure. The program of the present disclosure may be recorded on a computer-readable recording medium.

[0011] The above disclosures can be combined as much as possible.

[0012] The present disclosure can bring vibration intensity, the center of which is shifted from intensity "0," closer to vibration centered at intensity "0." As a result, the present disclosure can reduce the influence of excessively large vibrations or discontinuities in vibration due to the influence of noise.

[0013] 2 shows an example of a system configuration according to the present disclosure. It is a two-dimensional map showing an example of a distance distribution and a time-varying distribution of vibration intensity ... １ 3 shows an example of the time transition of vibration intensity at a point. １ 14(b) is a diagram illustrating an example of a time transition of vibration intensity at a point; FIG. 14(c) is a diagram illustrating an example of a failure of a phase unwrapping process; FIG. 14(d) is a diagram illustrating an example of a correction of vibration intensity according to the present disclosure; FIG. 14(e) is a flow diagram illustrating an example of a method according to the present disclosure; FIG. 14(f) is an example of vibration data before correction; FIG. 14(f) is an example of a histogram; FIG. 14(f) is an example of a line graph creation; FIG. 14(f) is a diagram illustrating a method of calculating a correction constant; FIG. 14(f) is an example of vibration data after correction; FIG. 14(c) is a two-dimensional map illustrating an example of a distance distribution and a time distribution of vibration intensity. １ 10 is an example of the time progression of vibration intensity at a point.

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0015] 1 shows an example of a system configuration according to the present disclosure. The system according to the present disclosure includes a DAS device 91 and an information processing device 92. In this embodiment, the DAS device 91 includes a light source 11, an acousto-optic modulator (AOM) 12, an amplifier 13, an optical circulator 14, a balanced receiver 15, and optical couplers 16 and 17, and shows an example in which the phase of Rayleigh scattered light in an optical fiber 93 is measured using a C-OTDR (Coherent detection OTDR).

[0016] The light source 11 emits laser light, and the optical coupler 16 branches the laser light into two. One of the laser lights branched by the optical coupler 16 is pulsed by the AOM 12, amplified by the amplifier 13, and input to the optical fiber 93 via the optical circulator 14. The other laser light branched by the optical coupler 16 is input to the optical coupler 17 as reference light. The test light scattered by the optical fiber 93 is sent from the optical circulator 14 to the optical coupler 17, where it is multiplexed with the reference light. The balanced receiver 15 performs coherent detection of the multiplexed light multiplexed by the optical coupler 17. As a result, a signal corresponding to the phase difference between the test light and the reference light at each point on the optical fiber 93 is output from the DAS device 91.

[0017] The information processing device 92 uses the signal output from the balanced receiver 15 to calculate the phase difference between the test light and the reference light at a certain point on the optical fiber 93 (S01), calculates the difference between the calculated phase difference and the phase difference at a point that is the gauge length away (S02), and calculates the vibration intensity of the optical fiber 93 in the longitudinal direction of the fiber using the calculated difference (S03).

[0018] Steps S01 to S03 are performed for a time T ｍ－１ From time T ｍ By performing the measurement between the time points, it is possible to measure the change in vibration intensity over time at each point on the optical fiber 93, as shown in Fig. 2. Note that in step S02, the difference in phase difference between the two points may not be calculated, but the difference in phase difference between two different times may be calculated.

[0019] The phase difference output from the DAS device 91 is a value in the range of -π to π. Therefore, in step S01, the information processing device 92 expands the phase difference from the range of -π to π to the range of -nπ to nπ (n is a natural number) in order to calculate the actual phase difference. This processing is called phase unwrapping processing.

[0020] Examples of vibration data are shown in Figures 2 and 3. By performing band-pass filtering on the vibration data shown in Figure 2 in the time axis direction, it is possible to detect vibrations whose location moves over time, as shown by the dashed line in Figure 3. However, in the case of temporally discontinuous vibrations as shown in Figure 4, performing band-pass filtering in the time axis direction causes undulations as shown in Figure 5 due to the influence of the discontinuous vibrations, making it difficult to measure the vibration intensity accurately. To eliminate this undulation, it is necessary to narrow the passband of the band-pass filter, but this also suppresses frequency components that are the main components of the vibration to be observed, such as vehicle traffic vibrations, making it difficult to see the trajectory of vehicle traffic or even eliminating it.

[0021] (Summary of the Present Disclosure) Due to the principle of DAS measurement, discontinuous oscillations may occur in measurement data due to a failure in phase unwrapping. When the phase unwrapping process fails, the time T １ and T ２ A discontinuous time of vibration occurs, and the time before and after the discontinuous time is 0 to T １ and T ２ ~T ３ As shown in Fig. 7, the center of vibration may be shifted, resulting in a vibration waveform that oscillates between -π and π. Therefore, the vibration data correction method disclosed herein brings vibrations whose center is shifted from an intensity "0" closer to vibrations whose center is centered at intensity "0". As a result, as shown in Fig. 7, vibrations in all sections along the time axis are corrected to vibrations whose center is "0".

[0022] 8 shows an example embodiment of the vibration data correction method of the present disclosure. In the vibration data correction method of the present disclosure, an information processing device 92 executes steps S11 to S13 using the vibration intensity obtained in step S03. This will be described in detail below.

[0023] (Step S11) In step S11, a histogram is created from the vibration data, with the horizontal axis (class) representing vibration intensity and the vertical axis (frequency) representing the number of occurrences of vibration intensity. For example, in the case of vibration data as shown in FIG. 9, １ This creates a histogram at point D １A histogram as shown in FIG. 10 is obtained for

[0024] Here, the horizontal axis of the histogram is set to ascending or descending order of vibration intensity. Furthermore, in this embodiment, the vibration intensity is expressed as a numerical value for ease of understanding. This quantification depends on the granularity when the output signal from the DAS device 91 is quantized into a digital signal, and any desired form may be adopted. Furthermore, the range of vibration data to be corrected for histogramming is arbitrary, and the histogram may be the vibration intensity and the frequency of occurrence of vibration data at one point in any distance direction, or the histogram may be the vibration intensity and the frequency of occurrence of vibration data at all points in any distance direction range.

[0025] (Step S12) In step S12, the information processing device 92 derives a correction constant using the histogram created in step S11. However, if the number of convexities present in the histogram created in step S11 is one, the vibration intensity at the peak position of the convexity is used as the correction constant.

[0026] Specifically, the information processing device 92 creates a line graph connecting the number of occurrences of each vibration intensity in the histogram created in step S11 (S21), obtains the vibration intensity at which the line graph peaks (S22), calculates the difference between the obtained vibration intensities (S23), calculates the average value of the calculated differences (S24), and sets the average value of the differences as a correction constant (S25).

[0027] In step S21, in the case of the histogram shown in FIG. 11, the information processing device 92 generates a line graph G that connects the occurrence counts of vibration intensities 6428, 6430, 6432, 6434, and 6436. １ Create a line graph G １ The vibration intensity at which the peak occurs is "6432." １ This is performed for all vibration intensities of the correction target vibration data. As a result, it is possible to obtain the vibration intensity at which the line graph of the correction target vibration data reaches its peak, as shown in FIG.

[0028] In step S23, the information processing device 92 calculates the difference in vibration intensity at which the line graph reaches its peak. In this embodiment, the horizontal axis of the histogram is set to represent the vibration intensity in ascending or descending order. Therefore, as shown in Fig. 12, the distribution interval of the vibration intensity can be calculated by calculating the difference in vibration intensity between adjacent points in the histogram.

[0029] Here, in steps S22 and S23, the difference in vibration intensity is not limited to all peaks in the line graph, but may be calculated for only some of the peaks in the line graph. For example, １ , P １１ , P ２１ In this case, the information processing device 92 may calculate the difference in vibration intensity between peaks at regular intervals and thin out some of the peaks, for example, the peak P ０ and Peak P １ The difference between the peak P １０ and Peak P １１ The difference between a peak at a fixed interval and a peak adjacent to that peak is calculated, for example, the difference between the peaks at a fixed interval and the peak adjacent to that peak.

[0030] In step S25, the average value obtained in step S24 may be converted into an integer value of a predetermined number of digits and set as the correction constant. For example, if the average value obtained in step S24 is 3215.86, 3215.86 may be rounded up or down, and 3216 may be set as the correction constant.

[0031] (Step S13) In step S13, the information processing device 92 corrects the vibration data for all vibration intensities of the vibration data to be corrected using the correction constant set in step S12. However, if the correction constant is 0, the vibration data to be corrected may be output as is.

[0032] Specifically, the information processing device 92 calculates a quotient by dividing the vibration intensity of the uncorrected vibration data by a correction constant (S31), rounds off each of the quotients to an integer value (S32), calculates a constant multiple shift amount N by multiplying the integer value by the set correction constant (S34), subtracts the constant multiple shift amount N from the vibration intensity of the uncorrected vibration data, and outputs the result as the vibration intensity of the vibration data with the vibration discontinuity corrected (S35).

[0033] For example, the distance D shown in FIG. １ If the correction constant for the vibration data at each elapsed time is 3216, in step S31, the information processing device 92 calculates the distance D １ Time T at １ The information processing device 92 divides the vibration intensity "6300" by the correction constant "3216" to obtain 1.958. In step S32, the information processing device 92 rounds off 1.958 to obtain an integer value of "2" with a predetermined number of digits. In step S33, the information processing device 92 multiplies the integer value "2" by the correction constant "3216" to obtain a constant multiple shift amount N = "6432". In step S34, the information processing device 92 subtracts the constant multiple shift amount N = "6432" from the vibration intensity "6300" to obtain a vibration intensity of "-132" for the corrected vibration data.

[0034] Distance D １ The vibration intensity of the vibration data to be corrected at distance D is corrected using the correction constant "3216". １ Similarly, the vibration intensity is corrected using a correction constant at all distances. As a result, the vibration intensity of the corrected vibration data, as shown in FIG. 13, takes values ​​in the range of −1608 to 1608, and becomes a continuous vibration oscillating around 0, and vibration data in which the discontinuity of the vibration has been corrected is provided.

[0035] 14A and 14B are two-dimensional maps showing an example of the distance distribution and time distribution of vibration intensity. Fig. 14A shows a two-dimensional map obtained using uncorrected vibration data, and Fig. 14B shows a two-dimensional map obtained using corrected vibration data. It can be seen that vibrations whose location moves over time, which do not appear on the map in Fig. 14A, appear in Fig. 14B.

[0036] FIG. 15 shows the distance D １ This is an example of the time transition of vibration intensity at a point. By using the corrected vibration data, discontinuities are corrected when viewed along the time axis, and it can be seen that the vibration is centered around 0 in any time range.

[0037] When an optical fiber in an aerial or underground cable laid for optical communications was measured using a DAS device 91, vibration data was found to have discontinuous times when the vibration was discontinuous, but vibrations with no change in the center of vibration were continuous in the time range before and after the discontinuous times, and the vibration intensity in that time range was a value in the range corresponding to a phase difference of -π to π. Therefore, the present disclosure can be applied to optical fibers for communications.

[0038] The present disclosure can be applied to a vibration data set by a computer and a program, and the program can be recorded on a recording medium or provided via a network. Furthermore, any processing, including band-pass filtering in the time axis direction, can be performed on the vibration data set by the present disclosure.

[0039] Furthermore, the present disclosure can correct discontinuities in vibration information regardless of the type of DAS device, as long as the vibration data oscillates between -π and π in the time range before or after the vibration discontinuity time. Therefore, the present disclosure can provide a method for correcting vibration discontinuities regardless of the type of DAS device 91. Furthermore, the present disclosure can correct imperfections in the phase unwrapping process, thereby improving the accuracy of DAS over long distances.

[0040] 11: Light source 12: Acousto-optic modulator 13: Amplifier 14: Optical circulator 16, 17: Optical coupler 15: Balanced receiver 91: DAS device 92: Information processing device 93: Optical fiber

Claims

1. A vibration data correction method in which an information processing device adjusts vibrations having a shifted center among vibration data acquired by a distributed acoustic sensing (DAS) device to vibrations having a center center of zero.

2. The vibration data correction method according to claim 1, wherein the information processing device sets a correction constant corresponding to the vibration intensity of the vibration data, calculates a constant multiplication shift amount by dividing all vibration intensities of the vibration data by the correction constant, and derives the vibration intensity of the corrected vibration data by subtracting the constant multiplication shift amount from the vibration intensity of the vibration data.

3. The vibration data correction method according to claim 2, wherein the information processing device calculates the constant multiple shift amount by dividing all vibration intensities of the vibration data by the correction constant and converting the obtained value into an integer value of a predetermined number of digits.

4. The vibration data correction method according to claim 2, wherein the information processing device creates a histogram showing the number of occurrences of each vibration intensity of the vibration data, creates a line graph connecting the number of occurrences of each vibration intensity in the histogram, and derives the correction constant using the vibration intensity at which the line graph peaks.

5. The vibration data correction method according to claim 4, wherein the information processing device derives the correction constant by calculating an average value of the differences in vibration intensity at which the line graph reaches a peak.

6. The vibration data correction method according to claim 1, wherein the vibration data oscillates between -π and π in a time range before or after a discontinuous time of the vibration.

7. A program for causing a computer to execute a method executed by an information processing device, the program comprising: the information processing device bringing vibrations with a shifted center among vibration data acquired by a Distributed Acoustic Sensing (DAS) device closer to vibrations centered around zero.

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