Signal processing method and signal processing apparatus

Abstract

The signal processing device (19) performs: a phase connection processing step of performing phase connection processing on phase values for each of a plurality of time instants and positions within a space; a first correction step of performing, for a prescribed time instant of the plurality of time instants, a correction of a deviation value of the phase value for each position within the space in a prescribed direction of the space, on the basis of a result of the phase connection processing; and a second correction step of performing a correction of the phase value for time instants other than the prescribed time instant for each of positions within the space that are correction targets of the first correction step.

Description

Technical Field

[0001] This invention relates to signal processing methods and signal processing apparatus. Background Technology

[0002] Previously, as a means of measuring the physical vibrations applied to an optical fiber in a distributed manner along the length of the optical fiber, a method known as DAS (Distributed Acoustic Sensing) is known, which involves incident pulsed test light onto the optical fiber under test and detecting backscattered light based on Rayleigh scattering (see, for example, Non-Patent Document 1).

[0003] In DAS (Digital Optical Array), changes in the optical path length of the optical fiber caused by physical vibrations applied to it are sensed. By detecting vibrations, it is possible to detect the movement of objects around the fiber being measured.

[0004] As a method for detecting backscattered light in DAS, there is a method that measures the intensity of scattered light from various points in the fiber being measured and observes the time change of the scattered light intensity, which is called DAS-I (DAS-intensity). DAS-I has the feature of simplifying the device structure, but it cannot quantitatively calculate the change in the optical path length of the fiber caused by vibration based on the scattered light intensity, so it is a qualitative measurement method (for example, see Non-Patent Literature 2).

[0005] On the other hand, DAS-P (DAS-phase: DAS phase) is also being researched and developed as a method for measuring the phase of scattered light from various locations in the fiber under test and observing the time change of the phase. In DAS-P, the device structure and signal processing are more complex than DAS-I, but the phase changes linearly with respect to the change in the optical path length of the fiber caused by vibration, and the rate of change is also the same in the direction of the fiber length. Therefore, it is possible to perform quantitative measurement of vibration and faithfully reproduce the vibration applied to the fiber under test (for example, see Non-Patent Literature 2).

[0006] In DAS-P measurements, an optical pulse is incident on the fiber under test, and the phase of the scattered light at the time t of the incident pulse is measured distributed along the length of the fiber. That is, the distance from the incident end of the fiber is set to l, and the phase θ(l, t) of the scattered light is measured. By repeatedly incidenting optical pulses on the fiber under test at time intervals T, and assuming n is an integer, the time change θ(l, nT) of the scattered light at time t = nT is measured at each point along the length of the fiber under test.

[0007] However, in reality, the time at the location measured at a distance l is delayed only during the time it takes for the light pulse to travel from the incident end to a distance l. Furthermore, note that the time delay of the time measured by the measuring instrument is the time required for the scattered light to return to the incident end. It is known that the magnitude of the physical vibration applied to the interval from a distance l to a distance l+δl at each time nT is proportional to the difference δθ(l,nT) between the phase θ(l+δl,nT) at a distance l+δl and the phase θ(l,nT) at a distance l. That is, if time zero is taken as the reference, then equation (1) is satisfied.

[0008] [Formula 1]

[0009]

[0010] As for the device structure for detecting the phase of scattered light, there are direct detection structures that directly use photodiodes or the like to detect the backscattered light from the optical fiber being measured, and coherent detection structures that use a combined wave with a separately prepared reference light to perform detection (for example, see Non-Patent Document 1).

[0011] The mechanism for performing coherent detection and calculating phase is further divided into two types: one that uses the Hilbert transform in a software-based manner and the other that uses a 90-degree optical mixer in a hardware-based manner. However, in either method, the in-phase component I(l, nT) and the quadrature component Q(l, nT) of the scattered light are obtained, and the phase is calculated by equation (2).

[0012] [Formula 2]

[0013]

[0014] However, the output value of the 4-quadrant arctangent operator Arctan, in radians, lies in the range (-π, π). Let m be any integer, 2mπ + θ cal (l, nT) all become the same vector direction in the xy plane, therefore, in the above-calculated θ cal There is an uncertainty of 2mπ in (l, nT), therefore, according to the phase θ at a distance l+δl... cal (l+δl, nT) and the phase θ at a distance l cal The difference δθ calculated from (l, nT) cal The effects of the aforementioned uncertainty are also evident in (l, nT).

[0015] Therefore, as a more accurate evaluation method for δθ(l, nT), further signal processing such as phase unwrapping is performed. Furthermore, let the actual phase change of the measured object be δθ(l, nT), and let the measured value of the phase change calculated from the measurement results be δθ. cal (l, nT), to distinguish between the two.

[0016] In general phase unwrapping, the unwrapped phase is set as δθ. cal unwrap (l, nT), denoted as δθ cal unwrap (l, 0) = δθ cal Based on (l, 0), the calculations are performed successively in ascending order of n as follows. For any integer p, in |θ cal (l,(p+1)T)-δθ cal unwrap When (l, pT)| is greater than π radians, choose to make |δθ cal (l,(p+1)T)+2πq-δθ cal unwrap (l, pT)| becomes an appropriate integer q less than π radians, and the unwrapped phase δθ is calculated as in equation (3). cal unwrap (l,(p+1)T). The superscript unwrap indicates the phase after unwrapping.

[0017] [Formula 3]

[0018]

[0019] Regarding the unwrapped phase δθ obtained through equation (3) cal unwrap (l, nT), only when the absolute value of the phase change between adjacent moments of δθ at any time and place is less than π radians, and when δθ cal Only under ideal conditions where there is no noise in (l, nT) can δθ(l, nT) be accurately calculated.

[0020] When measuring vibrations with high frequency or large amplitude, for any location l, it is possible that |δθ(l, (p+1)T)-δθ(l, pT)| exists at a time when pT = p, which is originally larger than π radians. s T, but at such moments p s T also performs phase unwrapping, so the integer q in equation (3) is incorrectly chosen. Due to the failure of this phase unwrapping process, δθ cal unwrap(l, nT) is inconsistent with δθ(l, nt), so δθ(l, nT) cannot be accurately calculated.

[0021] Regarding this problem, countermeasures can be taken to make |δθ(l,(p+1)T)-δθ(l,pT)| less than π radians by increasing the spatial resolution, i.e., reducing δl, or by increasing the temporal sampling rate, i.e., reducing T. For example, regarding methods to increase the temporal sampling rate, a method for optical frequency multiplexing of a structure with pulses of different optical frequencies incident at different times has been proposed (see, for example, Non-Patent Literature 3).

[0022] In actual measurements, due to δθ cal (l, nT) is accompanied by noise, which can also lead to failure of phase unwrapping. In actual measurements, there is noise from the measuring instrument, such as thermal noise from the PD used to detect light, noise in the subsequent electrical stage, and shot noise caused by light. Therefore, noise is present in the in-phase component I(l, nT) and the quadrature component Q(l, nT) of equation (2), and at θ cal Noise is also added to (l, nT), resulting in δθ cal Noise also accompanies (l, nT). This is because in δθ cal (l, nT) generates noise, thus creating the probability of incorrectly choosing the appropriate integer q.

[0023] Regarding this problem, by minimizing δθ as much as possible cal The noise generated by (l, nT) can be countermeasured to reduce the probability of incorrect selection of integer q. For example, an optical frequency multiplexing method has been proposed, in which pulses with different optical frequencies are incident with a sufficiently short time interval relative to the state changes caused by the vibration of the optical fiber, and the signals obtained from the pulses of different optical frequencies are averaged (see, for example, Patent Document 1).

[0024] Existing technical documents

[0025] Patent documents

[0026] Patent Document 1: Japanese Patent Application Publication No. 2020-169904

[0027] Non-patent document 1: A. Masoudi, TP Newson, "Contributed Review: Distributed optical fiber dynamic strain sensing," Review of Scientific Instruments, vol.87, p.011501 (2016)

[0028] Non-patent literature 2: Nishiguchi Kenichi, Lee Tetsu-hyun, Sugaru Yokoyama, Mitsuru Yokoyama, Masuda Yoshimasu, "Mitsubishi Distribution" "Signal Processing of Type Sonic Wave Trial", Journal of Information Science and Technology, 115(202), pp.29-34(2015)

[0029] Non-patent document 3: Y. Wakisaka, D. Iida, H, Oshida, "Distortion-suppressedsampling rate enhancement in phase-OTDR vibration sensing with newly designed FDM pulse sequence for correctly monitoring various waveforms," ​​OFC 2020, OSATechnical Digest, paper Th3F.5 (2020) Summary of the Invention

[0030] The problem that the invention aims to solve

[0031] However, in previous technologies, there is a problem that sometimes the phase measurement data obtained over a long period of time may be falsely detected as large apparent vibrations that accompany the failure of phase unwrapping.

[0032] For example, in the method described in Patent Document 1, it is theoretically impossible to set the probability of incorrectly selecting the integer q due to noise to zero, thus causing phase unwrapping failures in long-term measurement data. If phase unwrapping failures occur, at the location where the failure occurred, it can lead to false detections of an apparent large vibration.

[0033] Methods for solving problems

[0034] To address the aforementioned issues and achieve the objectives, a signal processing method is provided, executed by a signal processing device, characterized by comprising: a phase connection processing step, performing phase connection processing on the position in space and the phase value at each of a plurality of times; a first correction step, based on the result of the phase connection processing, correcting the deviation of the phase value at each position in the space along a predetermined direction in the space for a predetermined time among the plurality of times; and a second correction step, correcting the phase value at times other than the predetermined time for each position in the space that is the object of correction in the first correction step.

[0035] Invention Effects

[0036] According to the present invention, in phase measurement data measured over a long period of time, it is possible to reduce false detections of apparent large vibrations that accompany the failure of phase unwrapping processing. Attached Figure Description

[0037] Figure 1 This is a diagram illustrating a structural example of the signal processing system according to the first embodiment.

[0038] Figure 2 This is a flowchart illustrating the processing flow of the signal processing system according to the first embodiment.

[0039] Figure 3 This is a diagram showing an example of the calculated phase before correction.

[0040] Figure 4 This is a diagram showing an example of the calculated results for the corrected phase.

[0041] Figure 5 This is a diagram illustrating an example of a computer executing signal processing procedures. Detailed Implementation

[0042] Hereinafter, embodiments of the signal processing method and signal processing apparatus of this application will be described in detail with reference to the accompanying drawings. However, this invention is not limited to the embodiments described below.

[0043] Figure 1 This is a diagram illustrating a structural example of the signal processing system according to the first embodiment. Figure 1 The signal processing system 1 implements DAS-P through coherent detection, which uses a hardware-based processing mechanism employing a 90-degree optical mixer in the receiving system. The signal processing system 1 functions as a phase OTDR (Optical Time Domain Reflectometer).

[0044] However, the signal processing method in the first embodiment is different from the conventional DAS-P, which reduces false detections of seemingly large vibrations accompanying the failure of phase unwrapping processing. Furthermore, the same signal processing method as in the first embodiment can also be implemented in software using the Hilbert transform.

[0045] like Figure 1 As shown, it includes a light source 11, a coupler 12, an optical modulator 13, a 90-degree optical mixer 14, a circulator 15, a fiber optic cable under test 16, a balance detector 17, a balance detector 18, and a signal processing device 19.

[0046] Light source 11 emits continuous light of a single wavelength at a frequency of f0. For example, light source 11 is a CW (Continuous Wave) light source. Furthermore, coupler 12 branches the continuous light emitted by light source 11 into a reference light and a probe light.

[0047] The optical modulator 13 generates an optical pulse with a pulse width of W from the probe light branched from the coupler 12. The pulse width W is a value corresponding to the spatial resolution measured along the length of the optical fiber. Furthermore, the optical frequency of the optical pulse is set to a value obtained by offsetting the frequency f0 by an offset frequency.

[0048] Furthermore, the optical pulses generated by the optical modulator 13 can be any method for ultimately measuring phase changes, and do not have to be single-frequency pulses; they can be frequency scanned, frequency reused, or otherwise encoded.

[0049] For example, when the optical modulator 13 uses the frequency multiplexing method described in Patent Document 1, the generated optical pulse is a frequency of f0+f i A light pulse is formed by arranging pulses of width W (where i is an integer) in the order i = 1, 2, ..., N (where N is an integer). At this time, for f... i The method of selection is based on the degree to which the intensity of scattered light at each time and place is sufficiently separated to different i that can be considered unrelated to each other.

[0050] The type of optical modulator 13 can be any type that generates the aforementioned optical pulses, and there can be multiple modulators. For example, the optical modulator 13 can be an SSB (single sideband) modulator or a frequency-variable AO (acousto-optic) modulator. In addition, in order to increase the extinction ratio in pulsed pulses, the optical modulator 13 can also perform intensity modulation based on SOA (Semiconductor Optical Amplifier) ​​or the like.

[0051] The light pulse generated by the optical modulator 13 is used as probe light and is incident on the fiber 16 to be measured via the circulator 15.

[0052] Here, the light scattered at various points along the length of the measured fiber 16 returns to the circulator 15 as backscattered light and is incident on one input of the 90-degree optical mixer 14. On the other hand, the reference light branched by the coupler 12 is incident on the other input of the 90-degree optical mixer 14.

[0053] like Figure 1 As shown, the 90-degree optical mixer 14 includes coupler 141, coupler 142, shifter 143, coupler 144 and coupler 145.

[0054] First, the backscattered light from the fiber 16 being measured is incident on the input of the coupler 141 with a 50:50 branch ratio. Furthermore, the scattered light branched from the coupler 141 enters the inputs of the couplers 145 and 144 with a 50:50 branch ratio.

[0055] On the other hand, the reference light from coupler 12 is incident on the input of coupler 142 with a 50:50 branch ratio. Furthermore, one branch of the reference light from coupler 142 is directly incident on the input of coupler 144.

[0056] Shifter 143 shifts the phase of another reference light branched from coupler 142 by π / 2. Then, the phase-shifted reference light is incident on the input of coupler 145.

[0057] Here, the balance detector 17 detects the two outputs of the coupler 144 and obtains the simulated in-phase component I. analog The electrical signal is 171.

[0058] Additionally, the balanced detector 18 detects the two outputs of the coupler 145 to obtain the simulated quadrature component Q. analog The electrical signal is 181.

[0059] Electrical signals 171 and 181 are sent to signal processing device 19. For example... Figure 1 As shown, the signal processing device 19 includes an AD conversion functional element 191, an AD conversion functional element 192, a phase calculation unit 193, and a post-processing unit 194.

[0060] AD conversion element 191 converts the analog in-phase component I... analog Digitalization, to obtain I digital The AD conversion function element 192 converts the analog quadrature component Q... analog Digitalization, to obtain Q digital .

[0061] Phase calculation unit 193 uses the digitized in-phase component I output from AD conversion function element 191 digital and the quadrature component Q output from the AD conversion function element 192 digital To perform phase calculations.

[0062] For example, when the light pulse generated by the light modulator 13 has a single frequency, the phase calculation unit 193 can calculate the phase using equation (2).

[0063] Furthermore, the phase calculation unit 193 can also perform appropriate preprocessing. For example, the phase calculation unit 193 can also preprocess the in-phase component I by passing it through a digital bandpass filter having a signal bandwidth centered on the shift frequency during the modulation of the light pulse. digital and orthogonal components Q digital After filtering the signal, the phase is calculated using equation (2).

[0064] Furthermore, when performing frequency scanning, frequency multiplexing, or other encoding on the optical pulse, the phase calculation unit 193 can also perform appropriate preprocessing to calculate the phase. For example, when the optical modulator 13 performs frequency multiplexing as described in Patent Document 1, the phase calculation unit 193 separates the signal based on the scattered light, which is based on the frequencies f0+f that constitute the optical pulse. i Pulses of (i = 1, 2, ..., N). That is, the phase calculation unit 193 calculates the phase by processing I... digital and Q digital Perform signal processing to separate the signals at each frequency f0+f i The in-phase component I obtained when the pulse of the component is incident alone. i measure and orthogonal components Q i measure I digital It is the superposition of the in-phase components of all i, Q digital It is the superposition of the orthogonal components of all i.

[0065] At this time, the phase calculation unit 193 can use the ability to calculate from I digital and Q digital Accurately separate I i measure and Q i measure Any method. For example, the phase calculation unit 193 makes I digital With Q digital Passing through the center frequency f respectively i Furthermore, by ensuring the phase delay while maintaining a digital bandpass filter with a passband of 2 / W, I can be calculated. i measure With Q i measure .

[0066] In addition, the phase calculation unit 193 can be based on I i measure and Q i measure The phase is calculated by, for example, averaging of different optical frequency multiplexed signals as described in Patent Document 1.

[0067] Based on the phase calculated by the phase calculation unit 193, false detections of apparent large vibrations sometimes occur, which are associated with failures in the phase unwrapping process. Therefore, the post-processing unit 194 performs processing to reduce such false detections of apparent large vibrations.

[0068] Here, use Figure 2 Explain the processing flow of the post-processing unit 194. Figure 2 This is a flowchart illustrating the processing flow of the signal processing system according to the first embodiment.

[0069] Here, the post-processing unit 194 performs the following steps: a phase connection processing step, which performs phase connection processing on the position in space and the phase value of each time among multiple times; a first correction step, which, based on the result of the phase connection processing, corrects the deviation of the phase value along a specified direction in space for each position in space for a specified time among multiple times; and a second correction step, which corrects the phase value for each position in space that is the correction object of the first correction step for times other than the specified time.

[0070] The phase connection processing steps are equivalent to steps S101 and S102. As described above, the untangling process is an example of the phase connection processing. Furthermore, the first correction step is equivalent to step S104. Furthermore, the second correction step is equivalent to step S105.

[0071] like Figure 2 As shown, the post-processing unit 194 calculates the phase change applied to the interval with a spatial resolution for each point on the measured optical fiber 16 at a distance rΔl from the incident end, as in Equation (4) (step S101).

[0072] [Formula 4]

[0073]

[0074] Step S101 will be described in detail. First, the post-processing unit 194 sets the phase of the time nT, which is the distance l obtained as the output of the phase calculation unit 193, to θ. cal (l, nT), calculate δθ cal (l, nT) represents the phase θ at a distance l+δl. cal (l+δl,nT) and the phase θ at a distance l cal The difference between (l, nT). Here, the value of δl is set as the value of the spatial resolution.

[0075] In addition, the signal processing system 1 enables the AD conversion function elements 191 and 192 to operate at a high sampling rate so that the sampling period in the long distance direction, which is determined by the scale of distance l, i.e., the reciprocal of the sampling rate in the long distance direction, can be set to a value less than δl.

[0076] For example, when a measurement is performed with a spatial resolution of 5m, the light pulse width is 50ns. Therefore, from the point of view of spatial resolution, a sampling rate of 20MHz is sufficient. However, the signal processing system 1 makes the AD conversion function elements 191 and 192 operate at a sampling rate greater than 20MHz.

[0077] For example, in the case of frequency multiplexing, as described above, this operating condition is met in order to separate each frequency component based on the digital bandpass filter. For example, when the optical pulse width of each frequency is set to 50 ns and the optical frequency multiplexing number is set to 5, since the signals of each optical frequency occupy a 40 MHz bandwidth, the signal processing system 1 causes the AD conversion function elements 191 and 192 to operate at a sampling rate of 400 MHz or higher according to the Nyquist theorem. 400 MHz is greater than 20 MHz.

[0078] To describe it more clearly, if we denote the distance l as Δl, and let l = rΔl (where r is a non-negative integer), then it can be written as θ. cal (l, nT) = θ cal (rΔl,nT). Where r=0 corresponds to the incident end.

[0079] Furthermore, when the integer D is selected such that DΔl represents the spatial resolution level, the integer D becomes a value greater than 2 because the AD conversion elements 191 and 192 operate at a higher sampling rate. For example, when the optical pulse width is 50 ns, the spatial resolution is 5 m, but when the sampling rate is 400 MHz, the distance l is 25 cm, so the integer D can be set to 20.

[0080] Furthermore, according to the post-processing unit 194, the phase obtained by the phase calculation unit 193 is processed by decimation to reduce the number of sampling points. As long as the scale of the processed distance l is within a range smaller than the spatial resolution, the above-mentioned integer D can be calculated after processing.

[0081] Furthermore, the post-processing unit 194 calculates the phase change applied to an interval with a width equal to the spatial resolution of a distance rΔl, using time zero as a reference, as in equation (4). In this way, the post-processing unit 194 can use the phase value of the position based on the spatial resolution range as the calculation object.

[0082] Next, the post-processing unit 194 processes δθ in the time direction for each location on the fiber being measured at a distance rΔl from the incident end. cal (rΔl, nT) undergoes phase unwrapping processing to calculate δθ cal unwrap (rΔl, nT)(Step S102).

[0083] Step S102 will be described in detail. The post-processing unit 194 processes the δθ obtained in step S101. cal (rΔl, nT) undergoes the usual phase unwrapping process based on equation (3) to obtain δθ cal unwrap (rΔl, nT). However, the phase unwrapping process is performed independently for each distance rΔl, starting from n=1 and proceeding in the direction of increasing n.

[0084] In δθ cal unwrap In (rΔl, nT), a false detection of apparent large vibrations is generated due to the failure of phase unwrapping caused by noise in the measuring instrument. However, since the magnitude of the noise varies randomly, the false detection of apparent large vibrations is also generated randomly.

[0085] Such false detections occur as follows: Figure 3 As shown. Figure 3 This is a diagram showing an example of the calculated phase before correction. Figure 3 In the diagram, the vertical axis represents time nT, and the horizontal axis represents distance l. Additionally, the color gradient is represented by δθ. cal unwrap The value of (rΔl, nT).

[0086] exist Figure 3 In the example, false detections of large, visually apparent vibrations occurred at locations such as those indicated by reference numerals 301 and 302.

[0087] In addition, Figure 3 In such a two-dimensional diagram, the locations where phase untangling fails occur randomly, but the main reason for this is that it becomes δθ. cal The basis for calculating (rΔl, nT) is θ cal ((r+D)Δl,nT)orθ cal Significant noise occurred in one of (rΔl, nT). For example, note that at θ cal When large noise is generated in (rΔl, nT), not only in θ cal In (rΔl, nT), at θ cal In ((rD)Δl,nT), the probability of false detection of apparent large vibrations at the same time also increases.

[0088] Additionally, it is noted that due to θ cal The magnitude of the noise applied by (rΔl, nT) is affected by fading, so the ease with which a false detection of a seemingly large vibration occurs varies at each fiber length.

[0089] Here, as Figure 3 As shown, n increases sequentially from 1 to n... last (Steps 103, S106, S107) Post-processing unit 194 processes δθ for each n. cal unwrap (rΔl, nT) Perform steps S104 and S105.

[0090] In step S104, the post-processing unit 194 processes the phase change δθ in the length direction at time nT. cal unwrap (rΔl, nT) performs the correction of deviation values ​​(e.g., using the Hampel identifier).

[0091] Step S104 will be described in detail. The post-processing unit 194 processes the phase change δθ in the length direction at time nT. cal unwrap (rΔl, nT) performs the correction of deviation values. As mentioned above, the location of phase unwrapping failure is random, so by detecting and correcting the deviation value in the length direction, the phase unwrapping failure at time nT can be corrected.

[0092] As a method for handling deviations, one could use the Hampel identifier, for example. When using the Hampel identifier, if the phase δθ in the length direction rΔl is to be determined... cal unwrap If (rΔl, nT) is a deviation value, and the number of references to the left and right is set to k, then the value of k can be considered based on the above D.

[0093] When k / D is sufficiently small, it can be considered as an observation of δθ. cal unwrap The fiber interval [rΔl, (r+D)Δl] of (rΔl, nT) and the observed δθ cal unwrap The fiber intervals [(r±k)Δl, (r±k+D)Δl] of ((r±k)Δl, nT) are approximately the same. Therefore, the phase value δθ is considered to be... cal unwrap The phase unwrapping failure can be corrected by slowly varying between (rk)Δl and rΔl and between rΔl and (r+k)Δl, thus by detecting the deviation within the range of (rk)Δl to (r+k)Δl.

[0094] As a specific condition for considering k / D to be sufficiently small, we can set k ≤ D / 2. This is because δθ is observed. cal unwrap The fiber interval [(r±k)Δl, (r±k+D)Δl] of ((r±k)Δl, nT) and the observed δθ cal unwrap The fiber intervals [rΔl, (r+D)Δl] of (rΔl, nT) overlap with (rk)Δl. When k≤D / 2, the value of (rk)Δl is longer than half the value of its respective interval length DΔl. Therefore, as a statistical average, it helps to δθ cal unwrap The scatterer of ((r±k)Δl,nT) and the scatterer that contributes to δθ cal unwrap More than half of the scatterers of (rΔl, nT) are common.

[0095] In the Hampel identifier, it is the standard deviation evaluated based on the median value and median absolute deviation of the phase values ​​within the range (rk)Δl to (r+k)Δl of the object, in δθ. cal unwrap When the value of (rΔl, nT) increases by a factor of C from the median value, the median value is used as a replacement. However, the standard value of C, C = 3, can be used as the value of C. Nevertheless, this value can be optimized to an optimal value depending on the object being measured, etc.

[0096] Additionally, in step S105, the post-processing unit 194 performs correction on all r values ​​that need to be corrected. h The following processing is implemented: the location identified as having a deviation value (at a distance r from the incident end) is... h The phase value δθ before correction of Δl) cal unwrap (r h Δl, nT) and the corrected phase value δθ cal unwrap,h (r h The difference δθ of Δl, nT) cal unwrap,h (r h Δl,nT)-δθ cal unwrap (r h Δl, nT) and all δθ satisfying p≥n+1 cal unwrap Add (rΔl, pT) together to form the new δθ cal unwrap The value of (rΔl, pT) is used to update the value.

[0097] Step S105 will be described in detail. Let r be the distance from the incident end to the location that actually needs correction in step S104. h Δl, the corrected value is set as δθ cal unwrap,h (r h Δl, nT). At this time, δθ cal unwrap,h (r h Δl,nT)-δθ cal unwrap (r h Δl, nT) can be considered as correction values ​​used to correct the failure of phase unwrapping processing, therefore for location r h At time (n+1)T at Δl and all phase values ​​after that time (n+1)T, plus δθ cal unwrap,h (r h Δl、nT)-δθ cal unwrap (r h Δl、nT).

[0098] Furthermore, the reason for performing steps S104 and S105 sequentially from n=1 in ascending order is that, since phase unwrapping is performed sequentially from n=1 in step S102, if there are any remaining phase unwrapping failures up to time (n-1)T when the phase unwrapping failure is corrected based on deviation detection at time nT, then the phase values ​​δθ from (rk)Δl to rΔl and from rΔl to (r+k)Δl in step S104 cannot be used. cal unwrap The assumption is that things change slowly.

[0099] Figure 4 An example of calculating the final phase obtained by repeating the above steps S104 and S105 is shown. Figure 4 This is a graph showing an example of the calculated results for the corrected phase. Figure 4 In the example, correction was made in Figure 3 The large vibrations seen in the appearance were falsely detected.

[0100] Additionally, in step S101, the last point n of the measured time series nT (n = 1, 2, ...) is used. last Using T as a reference, calculate δθ cal (rΔl, nT), in step S102, it can also be derived from n last Phase unwrapping is performed in the direction where T decreases towards n. In this case, steps S104 and S105 also change from (n) last-1) Starting from T, the steps are performed in descending order of n. However, the direction of adding the correction value in step S105 also needs to be reversed, adding δθ to all points before time (n-1)T. cal unwrap.h (r h Δl,nT)-δθ cal unwrap (r h Δl, nT).

[0101] More generally, the post-processing unit 194 can also calculate δθ in step S101 using time n′T as the reference time. cal (rΔl,nT), in step S102, phase unwrapping is performed on both the direction in which n decreases and the direction in which n increases, starting from n′.

[0102] In this case, the post-processing unit 194 also performs step S104 in two directions when viewed from the time axis, in the order in which n increases from (n′-1)T and in the order in which n decreases from (n′+1)T.

[0103] In this way, the post-processing unit 194 can perform phase value correction by adding a correction value for the first time that is earlier than the reference time, and perform phase value correction by adding a correction value sequentially for each time that is earlier than the first time, starting from the later one.

[0104] In addition, the post-processing unit 194 can perform phase value correction by adding a correction value for a second time later than the reference time. In the second correction step, for each time later than the second time, the phase value correction by adding a correction value is performed sequentially from the earliest one.

[0105] As shown in the first embodiment, the AD conversion functional elements 191 and 192 sample at a higher speed than the constraints determined by spatial resolution, enabling deviation correction and reducing false detections of apparent large vibrations caused by phase unwrapping failures. Furthermore, such sampling conditions are naturally satisfied when frequency reuse is performed, so the first embodiment can be implemented without changing the conventional device structure.

[0106] Furthermore, in cases where the change in vibration of the object being measured is more gradual than the spatial resolution, it is sometimes not necessary for AD conversion elements 191 and 192 to sample at a higher speed than constrained by the spatial resolution.

[0107] When the change in vibration of the object being measured is more gradual than the spatial resolution, deviation correction can be performed on the data points contained in the spatial range where the vibration of the object is considered to be unchanged in step S104. Therefore, even if the sampling is slower than the constraint determined by the spatial resolution, it is sometimes possible to obtain enough data points for deviation correction.

[0108] That is, when the change in vibration of the object being measured is more gradual than the spatial resolution, the first embodiment can be implemented by sampling at a higher speed than the change in vibration of the object being measured.

[0109] [System architecture, etc.]

[0110] Furthermore, the constituent elements of the devices illustrated are functional concepts and do not necessarily need to be physically configured as shown. That is, the specific methods of distributing and integrating the devices are not limited to those illustrated; they can be functionally or physically distributed or integrated in any unit, depending on various loads, usage conditions, etc. Moreover, all or any part of the processing functions performed by each device can be implemented by a CPU (Central Processing Unit) and the program executed by that CPU, or as hardware based on wiring logic. Furthermore, the program can be executed not only by the CPU but also by other processors such as a GPU.

[0111] Furthermore, all or part of the processes described in this embodiment that are performed automatically can be performed manually, or all or part of the processes described that are performed manually can be performed automatically using known methods. In addition, the processing steps, control steps, specific names, and information including various data and parameters shown in the above documents and figures can be arbitrarily changed, unless specifically stated otherwise.

[0112] [program]

[0113] As one implementation, the signal processing device 19 can be installed as a packaged software or online software on a desired computer by installing the signal processing program that performs the above-described signal processing. For example, by having the information processing device execute the above-described signal processing program, the information processing device can function as the signal processing device 19. The information processing device mentioned here includes desktop or laptop personal computers. In addition, information processing devices also include smartphones, mobile phones, mobile communication terminals such as PHS (Personal Handyphone System), and tablet terminals such as PDA (Personal Digital Assistant).

[0114] Alternatively, the signal processing apparatus 19 can also be installed as a signal processing server device that takes a user's terminal device as a client and provides the aforementioned signal processing-related services to that client. For example, the signal processing server device can be installed as a server device that provides signal processing services that take the output from the balance detector as input and the result of phase calculation as output. In this case, the signal processing server device can be installed as a web server or as a cloud that provides the aforementioned signal processing-related services through outsourcing.

[0115] Figure 5 This diagram illustrates an example of a computer executing a signal processing program. The computer 1000, for example, includes a memory 1010 and a CPU 1020. Additionally, the computer 1000 has a hard disk drive interface 1030, a disk drive interface 1040, a serial port interface 1050, a video adapter 1060, and a network interface 1070. These components are connected via a bus 1080.

[0116] Memory 1010 includes read-only memory (ROM) 1011 and random access memory (RAM) 1012. ROM 1011 stores a boot program, such as a basic input / output system (BIOS). Hard disk interface 1030 is connected to hard disk drive 1090. Disk drive interface 1040 is connected to disk drive 1100. Removable storage media, such as hard disks or optical disks, are inserted into disk drive 1100. Serial port interface 1050 is connected, for example, to mouse 1110 and keyboard 1120. Video adapter 1060 is connected, for example, to monitor 1130.

[0117] The hard disk drive 1090 stores, for example, an OS 1091, an application program 1092, a program module 1093, and program data 1094. That is, programs defining each process of the signal processing device 19 are installed as program modules 1093 containing code executable by a computer. The program module 1093 is stored, for example, in the hard disk drive 1090. For example, a program module 1093 for performing processes with the same functional structure as those in the signal processing device 19 is stored in the hard disk drive 1090. Alternatively, the hard disk drive 1090 can be replaced by an SSD (Solid State Drive).

[0118] Furthermore, the setting data used in the processing of the above-described embodiment is stored as program data 1094 in, for example, memory 1010 or hard disk drive 1090. Then, CPU 1020 reads the program module 1093 and program data 1094 stored in memory 1010 and hard disk drive 1090 into RAM 1012 as needed, and executes the processing of the above-described embodiment.

[0119] Furthermore, program module 1093 and program data 1094 are not limited to being stored in hard disk drive 1090; for example, they can also be stored in removable storage media and read by CPU 1020 via disk drive 1100, etc. Alternatively, program module 1093 and program data 1094 can also be stored in other computers connected via a network (LAN (Local Area Network), WAN (Wide Area Network), etc.). Program module 1093 and program data 1094 can be read by CPU 1020 from another computer via network interface 1070.

[0120] Label Explanation

[0121] 1. Signal Processing System

[0122] 11 Light Source

[0123] Couplers 12, 141, 142, 144, and 145

[0124] 13 optical modulators

[0125] 14 90-degree light mixer

[0126] 15 Circulators

[0127] 16 Fiber Optic Under Measurement

[0128] 17 and 18 balance detectors

[0129] 19. Signal processing device

[0130] 143 Shifter

[0131] 171, 181 electrical signals

[0132] 191, 192 AD conversion function elements

[0133] 193 Phase Calculation Unit

[0134] 194 Post-processing Department

Claims

1. A signal processing method, executed by a signal processing device, characterized in that, The signal processing method includes: The phase connection processing step performs phase connection processing on the position in space and the phase value at each time point in multiple time points; The first correction step, based on the result of the phase connection processing, corrects the phase value deviation at each position in the space along a predetermined direction of the space for a specified time among the plurality of times; and The second correction step involves, for each position within the space that is the object of correction in the first correction step, and for each object time other than the specified time and located in a first time direction relative to the specified time, performing phase value correction by comparing all times located more in the first time direction with the object time in the order of the first time direction, wherein the first time direction is a forward time direction or a backward time direction.

2. The signal processing method according to claim 1, characterized in that, In the first correction step, for a time earlier than the reference time, a correction value is added to the phase value. In the second correction step, for each of the object times earlier than the first time, the phase values ​​of all times whose phase values ​​were measured earlier than the object time are corrected by adding the correction value, in order from late to early.

3. The signal processing method according to claim 1, characterized in that, In the first correction step, for the second time point that is later than the reference time, a correction value is added to the phase value. In the second correction step, for each of the object times later than the second time, the phase values ​​of all times whose phase values ​​were measured later than the object time are corrected by adding the correction value, in order from early to late.

4. The signal processing method according to any one of claims 1 to 3, characterized in that, In the first correction step, correction is performed using the Hampel identifier.

5. The signal processing method according to any one of claims 1 to 3, characterized in that, This signal processing method is executed by a signal processing device. In the phase connection processing step, phase connection processing is performed for the following positions on the optical fiber and the phase value at each of multiple times, where the position is the position obtained by incident a light pulse on the optical fiber, and the position is based on a range of spatial resolution. In the first correction step, based on the result of the phase connection processing, for a specified time among the plurality of times, the phase value deviation is corrected for each position on the optical fiber along its length. In the second correction step, for each position on the optical fiber that becomes the correction object of the first correction step, for each object time other than the specified time and located in the first time direction relative to the specified time, the phase value is corrected according to the order of the first time direction, comparing all times that are more located in the first time direction than the object time.

6. A signal processing apparatus, characterized in that, The signal processing device has: The phase connection processing unit performs phase connection processing on the position in space and the phase value at each of multiple times. The first correction unit, based on the result of the phase connection processing, corrects the deviation of the phase value for each position in the space along a predetermined direction of the space for a predetermined time among the plurality of times; as well as The second correction unit, for each position in the space that is the correction target of the first correction unit, and for each object time other than the specified time and located in a first time direction relative to the specified time, performs phase value correction on all times that are more located in the first time direction than the object time, in the order of the first time direction, where the first time direction is a forward time direction or a backward time direction.

Images