External disturbance event phase extraction method based on local space data

Abstract

The invention discloses a local space data-based external disturbance event phase extraction method, which comprises the following steps of: firstly, adjusting trigger delay of synchronous trigger pulses according to an optical fiber position concerned by a collector, and changing a starting point of optical fiber sampling, so that an acquisition end delays for a period of time after capturing each synchronous trigger pulse and then starts to acquire certain local space data; therefore, each time of synchronous triggering plays a role, the data storage space is saved, and the calculation burden of the system is reduced; the optimized phase unwrapping algorithm is adopted to carry out phase unwrapping on the local space data, the optimized phase unwrapping algorithm does not need phase information of an optical fiber injection end, the result of the optimized phase unwrapping algorithm is consistent with that of a traditional phase unwrapping algorithm under the condition that differential positions are the same, the algorithm processing process is optimized, and the data processing duration is shortened. According to the method, the local space data is combined with the optimized phase unwrapping algorithm, so that the data volume can be effectively reduced, the time required for data processing is shortened, and the real-time performance of system monitoring is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, and in particular to a method for extracting the phase of an external disturbance event based on local spatial data. Background Art

[0002] Phase-Sensitive Optical Time Domain Reflectometry Using optical fiber as a sensing medium to detect external disturbances has the characteristics of high sensitivity and wide monitoring range, and is widely used in perimeter security monitoring, seabed exploration, oil and gas pipeline monitoring and other fields. (like Figure 1 As shown in the figure, the laser emitted by the laser is divided into 90% detection light and 10% reference light by the coupler. After 90% of the detection light is modulated into pulse light by the acousto-optic modulator, it enters the sensing optical fiber through the circulator and collides with the scattering particles in the optical fiber, generating a continuous and random backward Rayleigh scattering signal (the backward Rayleigh scattering signal contains the disturbance information generated by the external disturbance event). The backward Rayleigh scattering signal is transmitted back through the circulator, coupled with the 10% reference light and split into a balanced detector, and the intermediate frequency signal is obtained after being processed by the balanced detector. The intermediate frequency signal is collected by the acquisition card and sent to the host computer. The host computer performs orthogonal (IQ) demodulation on the intermediate frequency signal and calculates the amplitude and phase of the demodulated intermediate frequency signal to realize the analysis of the external disturbance event. The pulse signal emitted by the signal generator is used as the modulation pulse of the acousto-optic modulator on the one hand, and as the synchronization trigger pulse of the acquisition card on the other hand.

[0003] current The acquisition method used is that after the acquisition card captures the first synchronous trigger pulse emitted by the signal generator, it continuously acquires all intermediate frequency signals under all subsequent modulated pulses and no longer pays attention to subsequent synchronous trigger pulses. Traditional data acquisition requires that the intermediate frequency data under all pulse periods be acquired and demodulated (demodulation obtains amplitude and phase), and the pulse period of the modulated pulse is required to be greater than the single round-trip time of light in the sensing optical fiber in the initial setting to ensure that two consecutive pulses of light do not meet in the optical fiber. This approach undoubtedly increases the "optical fiber length" actually acquired, and it is much greater than the length of the measured optical fiber. It also means that the added acquisition points behind the measured optical fiber are invalid, resulting in a large amount of data acquisition and an increased system burden during data processing. In addition, because the phase of the external disturbance event is wrapped in (-π,π) after demodulation, it cannot reflect the linear relationship with the external disturbance, so it is also necessary to perform phase unfolding on it. However, the current The traditional phase unwrapping algorithm must include four steps: spatial difference, unwinding along the spatial direction, unwinding along the temporal direction, and temporal difference. The unwinding along the spatial direction requires processing the phase of all positions on the measured optical fiber to ensure the continuity of phase unwrapping, which increases the calculation burden of the system and reduces the efficiency of obtaining phase information. For this reason, in real-time online monitoring In the process of external disturbance, amplitude information is usually used to describe external disturbance events, while the phase information of external disturbance events is more likely to be obtained by saving intermediate frequency data or IQ data and then performing offline processing. Summary of the invention

[0004] The present invention is to solve the current The traditional data acquisition method and traditional phase unwrapping method used have problems such as large data volume, great processing difficulty, long time and low timeliness. This paper provides a phase extraction method for external disturbance events based on local spatial data.

[0005] To solve the above problems, the present invention is achieved through the following technical solutions:

[0006] The method for extracting the phase of an external disturbance event based on local spatial data includes the following steps:

[0007] Step 1, determine the optical fiber segments L1-L2 that currently need attention;

[0008] Step 2: Determine the fiber segment L1 to L2 that needs attention. The local spatial position to be collected is L1-l1~L2+l2;

[0009] Step 3: According to the determined local spatial position, set The trigger delay τ of the synchronous trigger pulse and the data record length RL after the trigger delay;

[0010] The trigger delay τ is:

[0011] τ=t ′ ×(L1-l1)

[0012] The data record length RL is:

[0013] RL≥(L2-L1+l1+l2)×t ′ ×f

[0014] Step 4, collecting intermediate frequency data under n consecutive synchronous trigger pulses, that is, when the trigger edge of each synchronous trigger pulse arrives, start collecting intermediate frequency data with a length of RL after a delay of τ, thereby obtaining a local spatial intermediate frequency data matrix IF with a size of n×RL;

[0015] Step 5, perform orthogonal demodulation on the local spatial intermediate frequency data matrix IF to obtain an initial phase matrix θ;

[0016] Step 6: Use the optimized phase unwrapping algorithm to unwrap the initial phase matrix θ, restore the true value of the phase, and obtain the true phase matrix Θ; that is:

[0017] Step 6.1: Perform spatial difference operation on the initial phase matrix θ to obtain the spatial difference matrix θ 1 ;

[0018] Step 6.2: Spatial difference matrix θ 1 Perform phase unwrapping along the time direction to obtain the unwrapped phase matrix θ 2 ;

[0019] Step 6.3: The phase matrix θ after unwrapping 2 Perform time difference operation to obtain the real phase matrix Θ;

[0020] Step 7: extract the phase of the external disturbance event based on the real phase matrix Θ, that is, the phase of any position in the stable region after the end point L2 of the optical fiber segment currently in need of attention in the real phase matrix Θ;

[0021] The above L1 is the starting point of the fiber segment that needs to be paid attention to, and L2 is the end point of the fiber segment that needs to be paid attention to; l1 is the front reserved fiber length of the fiber segment that needs to be paid attention to, and l2 is the rear reserved fiber length of the fiber segment that needs to be paid attention to, l1≥SR, l2≥SR, SR is The spatial resolution of ′ is the time required for light to travel 1 meter in the optical fiber; f is The sampling frequency is τ, the trigger delay is RL, the data record length is n, and the number of pulses is n.

[0022] In the above step 1, the optical fiber segments L1 to L2 that currently require attention are determined by a manual designation method or an adaptive method.

[0023] The specific process of using the adaptive method to determine the fiber segments L1 to L2 that need attention is as follows: first, the intermediate frequency signals within a certain period of time after a trigger pulse are collected using a traditional data acquisition method; then, these intermediate frequency signals are demodulated and divided according to the sampling points under a single modulation pulse to obtain a time-space matrix containing the intermediate frequency signal amplitudes of M×N sampling points, where M is the number of data frames and N is the single modulation pulse period T pulse Finally, the differential accumulation algorithm is used to locate the fiber segment range where the disturbance roughly occurs on the spatiotemporal matrix of the intermediate frequency signal amplitude, and the located fiber segment range where the disturbance roughly occurs is taken as the fiber segment L1~L2 that needs attention.

[0024] In step 2 above, the spatial resolution SR is:

[0025]

[0026] In the formula, c is the speed of light in vacuum, w is The modulation pulse width of the acousto-optic modulator, n eff is the refractive index of the sensing fiber core.

[0027] In step 3 above, the sampling frequency f is:

[0028]

[0029] Where f0 is The frequency shift of the acousto-optic modulator is The integer part of .

[0030] Compared with the prior art, the present invention has the following characteristics:

[0031] 1. The present invention adjusts the trigger delay of the synchronous trigger pulse according to the optical fiber position of the collector, changes the starting point of the optical fiber sampling, and makes the acquisition end delay for a period of time after capturing each synchronous trigger pulse before starting to collect certain spatial data (i.e., local spatial data). This makes each synchronous trigger work, saves data storage space, and reduces the system calculation burden;

[0032] 2. The present invention adopts an optimized phase unwrapping algorithm (spatial difference, unwinding along the time direction, time difference) to perform phase unwrapping on local spatial data. The optimized phase unwrapping algorithm does not require phase information at the fiber injection end, nor does it require unwinding along the spatial direction. When the differential position is the same, the results are consistent with those of the traditional phase unwrapping algorithm. The optimized algorithm greatly reduces the data processing time.

[0033] 3. The present invention combines local spatial data with an optimized phase unwrapping algorithm, which can effectively reduce the amount of data, shorten the time required for data processing, and ensure the real-time nature of system monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 for Schematic diagram.

[0035] Figure 2 Schematic diagram of the phase extraction method of external disturbance events based on local spatial data.

[0036] Figure 3 This is the waveform phase recovery diagram of Experiment 1.

[0037] Figure 4 The waveform phase recovery diagram of Experiment 2: (a) phase change caused by disturbance 1, (b) phase change caused by all disturbances, and (c) phase change caused by disturbance 2. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific examples.

[0039] A phase extraction method for external disturbance events based on local spatial data, such as Figure 2 As shown, the specific steps include the following:

[0040] Step 1: Determine the optical fiber segments L1 to L2 that currently require attention, where L1 is the starting point of the optical fiber segment that currently requires attention, and L2 is the end point of the optical fiber segment that currently requires attention.

[0041] The optical fiber segments L1~L2 that currently need to be paid attention to can be determined manually or adaptively. When the optical fiber segments L1~L2 that need to be paid attention to are determined manually, the optical fiber segments L1~L2 are fixed values. When the optical fiber segments L1~L2 that need to be paid attention to are determined adaptively, the optical fiber segments L1~L2 are variable values. The specific process of determining the optical fiber segments L1~L2 that need to be paid attention to in an adaptive manner is: first, the traditional data acquisition method is used to collect the intermediate frequency signal within a certain period of time after a trigger pulse; then these intermediate frequency signals are demodulated and divided according to the sampling points under a single modulation pulse to obtain a time-space matrix containing the intermediate frequency signal amplitudes of M×N sampling points, where M is the number of data frames and N is the single modulation pulse period T pulse The number of sampling points under the condition is set; then the differential accumulation algorithm is used to locate the fiber segment range where the disturbance roughly occurs on the space-time matrix of the intermediate frequency signal amplitude, and the fiber segment range where the disturbance roughly occurs is taken as the fiber segment L1~L2 that needs to be paid attention to.

[0042] Step 2: Determine the fiber segment L1 to L2 that needs attention. The local spatial position to be collected is L1-l1~L2+l2, where l1 is the pre-reserved fiber length of the fiber segment currently in need of attention, l2 is the post-reserved fiber length of the fiber segment currently in need of attention, and l1≥SR, l2≥SR, SR is spatial resolution.

[0043] The spatial resolution SR is:

[0044]

[0045] Where c is the speed of light in a vacuum, w is The modulation pulse width of the acousto-optic modulator, n eff is the refractive index of the sensing fiber core.

[0046] Step 3: According to the determined local spatial position, set the trigger delay τ of the synchronous trigger pulse and the data record length RL after the trigger delay.

[0047] By setting the trigger delay τ of the synchronous trigger pulse, the starting position of the local spatial data acquisition is L1-l1. The trigger delay τ set accordingly needs to satisfy the following relationship:

[0048] τ=t ′ ×(L1-l1)

[0049] Among them, t ′ is the time required for light to travel 1 meter in the optical fiber, L1 is the starting point of the optical fiber segment that currently needs attention, and l1 is the front reserved optical fiber length of the optical fiber segment that currently needs attention.

[0050] By setting the data record length RL after the trigger delay, the data length of the local space data acquisition is equal to the number of optical fiber sampling points within the local space position L1-l1 to L2+l2. The data record length RL set accordingly needs to satisfy the following relationship:

[0051] RL≥(L2-L1+l1+l2)×t ′ ×f

[0052] Where L2 is the end point of the fiber segment that needs attention, L1 is the starting point of the fiber segment that needs attention, l1 is the front reserved fiber length of the fiber segment that needs attention, l2 is the rear reserved fiber length of the fiber segment that needs attention, t ′ is the time required for light to travel 1 meter in the optical fiber, and f is The sampling frequency f is calculated by combining the bandpass sampling theorem:

[0053]

[0054] Where f0 is The frequency shift of the acousto-optic modulator; B is the bandwidth of the intermediate frequency signal, which is related to the modulation pulse width; m is an integer, 1≤m≤j, j and k are The integer and decimal parts of .

[0055] Step 4: Collect intermediate frequency data under n consecutive synchronous trigger pulses to obtain a local spatial intermediate frequency data matrix IF of size n×RL; wherein n is the set number of pulses.

[0056] The acquisition method of the intermediate frequency data under each synchronous trigger pulse is: when the trigger edge of each synchronous trigger pulse arrives, the intermediate frequency data with a length of RL is collected after a delay of τ.

[0057] Step 5: Perform orthogonal demodulation on the local spatial intermediate frequency data matrix IF to obtain an initial phase matrix θ.

[0058] The element θ(t i , z j ) indicates that at the i-th sampling time t i The next j-th actual optical fiber sampling point z j The initial phase at (starting from the local spatial position), where t i ∈[1, n], n is the number of pulses; z j ∈[1,RL], RL is the record length.

[0059] Step 6: Use the optimized phase unwrapping algorithm to perform phase unwrapping on the initial phase matrix θ, restore the true value of the phase, and obtain the true phase matrix Θ.

[0060] The optimized phase unwrapping algorithm is inferred from the definition of phase unwrapping. Phase unwrapping is defined as: when the phase jump between two consecutive phases θ1 and θ2 is greater than |π|, k 2π are added to the next phase θ2 to make the jump less than |π|, which can be expressed as:

[0061] |θ2+2kπ-θ1|<π

[0062] Wherein, k is an integer.

[0063] According to the definition of phase unwrapping, its three properties are derived: ① The uniqueness of k: for two phases in a specific order, k exists and is unique; ② The followability of k: when the current phase θ1 increases by 2k1π, the next phase θ2 increases by 2kπ and follows the change of the previous phase θ1 by another 2k1π, where k1 is an integer; ③ The constant invariance of k: for two phases in a specific order, increasing or decreasing the constant C at the same time will not affect the jump.

[0064] Based on the three properties of phase unwrapping, the present invention can optimize the phase unwrapping algorithm. Considering that the main dispute between the optimized phase unwrapping algorithm and the traditional phase unwrapping algorithm is the necessity of two phase unwrapping, here we directly perform phase unwrapping on any random matrix along the row vector and column vector respectively to simulate the phase unwrapping of the differential phase matrix along the spatial and temporal directions, and observe the changes brought by the two phase unwrapping to the random matrix.

[0065] For a matrix θ of shape M×N:

[0066]

[0067] Perform the first phase unwinding along the row vector, that is, perform spatial unwinding along the length direction of the optical fiber, and obtain the unwinding matrix θ 1 , where the unwinding matrix θ 1 The element θ in the mth row and nth column 1 (m,n) is:

[0068]

[0069] |θ 1 (m,n)-θ 1 (m,n-1)|<π

[0070] In the formula, is an integer, is the phase change produced by the mth row and nth column of the matrix θ after unwrapping along the row vector.

[0071] Before performing phase unwrapping along the column direction, we first observe the effect of the unwrapping operation on the phase value of each position. According to the uniqueness of unwrapping, we can conclude that:

[0072] |θ(m,n)+2h mn π-θ(m,n-1)|<π

[0073] In the formula, h mn is an integer, h m1 =0,2h mn π is the phase jump between the mth row and the nth and n-1th columns in θ.

[0074] According to property ② (followability), the unwinding matrix θ 1 In To rewrite:

[0075]

[0076] It can be seen that the phase change after each row vector is unwrapped is They are all obtained by superimposing the phase jump values ​​of the first n columns of the mth row. That is, the phase unwrapping along any direction has a unique and additive effect on the phase of a certain point (for data in a fixed order, its phase jump value is unique and additive). This property has nothing to do with the direction (row / column, space / time), but only with the phase unwrapping itself. Specifically:

[0077]

[0078] in, is θ 1 The mth row of

[0079]

[0080] According to the uniqueness and superposition of phase jump values, it can be deduced that: matrix θ 1 Unwind along the column vector, for θ 1 Any point θ 1 (m,n), its phase jump value only depends on the phase of the first m rows of the nth column. At this time, the effect of row vector unwrapping on phase unwrapping only retains the first row of row vector unwrapping. For other row vectors, the phase change caused by row vector unwrapping is reset when the column vector is unwrapped due to the uniqueness of the jump; and the follow-up property determines that the phase at the nth position of each subsequent row must contain a constant value. For θ 1 Unwrapping along the column vector is specifically expressed as:

[0081]

[0082] θ 2 is the matrix θ 1 The matrix after unwrapping along the column vector, where:

[0083]

[0084] in, is θ 2 The nth column, c mn is an integer, c 1n =0,2c mn π is the phase change at adjacent moments in the same position in the random matrix θ[M,N], that is:

[0085] |θ(m,n)+2c mn π-θ(m-1,n)|<π

[0086] Observe the matrix θ after the phase unwrapping of row vectors and column vectors 2 The difference between [M,N] and the original matrix θ only retains the effects of column vector unwrapping and row vector unwrapping along the first row of matrix θ. However, in order to eliminate system noise, the overall phase unwrapping algorithm also includes time difference, that is, the phase at each spatial position is subtracted from the mean phase of that position over time. The mean contains After time difference, it is directly eliminated It can be seen that the influence of row vector unwrapping on phase unwrapping is completely eliminated after subtracting the mean. In other words, spatial phase unwrapping fails in the traditional phase unwrapping algorithm, and the optimization of the phase unwrapping algorithm can be achieved accordingly. Accordingly, the optimized phase unwrapping algorithm proposed in the present invention specifically includes the following steps:

[0087] Step 6.1: Perform spatial difference operation on the initial phase matrix θ to obtain the spatial difference matrix θ 1 . The spatial difference matrix θ 1 The element θ in the i-th row and j-th column of 1 (t i , z j )for:

[0088] θ 1 (t i , z j )=θ(t i , z j )-θ(t i , z s )

[0089] Among them, θ(t i , z j ) represents the element of the i-th row and j-th column of the initial phase matrix θ; θ(t i , z s ) represents the element of the i-th row and s-th column of the initial phase matrix θ, where s is the specified column, z s is the reference point of the initial phase, z s ∈[1,l1×t ′ ×f], l1 is the pre-reserved fiber length of the fiber segment that needs attention, t ′ is the time required for light to travel 1 meter in the optical fiber, f is the sampling frequency, z s The closer to the disturbance location, the better the suppression effect on phase noise.

[0090] Step 6.2: Spatial difference matrix θ 1 Perform phase unwrapping along the time direction to obtain the unwrapped phase matrix θ 2 .

[0091] The phase matrix θ after unwrapping 2 The element θ in the i-th row and j-th column of 2 (t i , z j )for:

[0092] θ 2 (t i , z j )=θ 1 (t i , z j )+2k ij π

[0093] Among them, θ 1 (t i , z j ) represents the spatial difference matrix θ1 The element in the i-th row and j-th column of ij π represents θ 1 (t i , z j ) and θ 2 (t i-1 , z j ), k ij The value of needs to make the phase matrix θ after unwrapping 2 The following conditions are met:

[0094] |θ 2 (t i , z j )-θ 2 (t i-1 , z j )|<π

[0095] Among them, k 1j =0, that is, θ 2 (t1, z j )=θ 1 (t1, z j ).

[0096] Step 6.3: The phase matrix θ after unwrapping 2 Perform time difference operation to obtain the real phase matrix Θ.

[0097] The element Θ(t i , z j )for:

[0098]

[0099] Among them, θ 2 (t i , z j ) represents the phase matrix θ after unwrapping 2 The element in the i-th row and j-th column of , where n is the number of pulses.

[0100] Step 7: Extract the phase of the external disturbance event based on the true phase matrix Θ.

[0101] The phase of the extracted external disturbance event is the phase of any position in the stable region after the end point L2 of the fiber segment that needs to be paid attention to in the real phase matrix Θ, that is, Θ(t i , z phi ), where z phi ∈[(L2+l2)×t ′ ×f+1,RL)].

[0102] The following uses Figure 1 The coherent detection structure shown As an experimental device, the frequency shift of the acousto-optic modulator is 80MHz, and the pulse width is adjusted to 100ns. The data acquisition system can adjust the trigger delay and the acquisition length of a single trigger, and can also adjust the sampling frequency. The schematic diagram of local space data acquisition is as follows Figure 2 As shown, the approximate location of the disturbance is determined first, and then local spatial data collection is performed. Figure 2 In the figure, the horizontal axis is the fiber length in meters (m), which can also be converted into the round-trip time of a single pulse in seconds (s); the vertical axis is the number of pulses, which is proportional to the disturbance time. Pulse period T pulse It is set according to the optical fiber length L; the trigger delay τ and the record length RL are set according to the disturbance position (L1~L2); the number of pulses n is set according to the time T of the acquisition event.

[0103] Example 1: Experiment on 1.2 km optical fiber, setting the pulse period T pulse Should be greater than the round trip time T of light in the optical fiber L = 12μs, in order to ensure that the time for collecting disturbances is long enough, the pulse period is set to T pulse = 100μs; use a piezoelectric ceramic (PZT) of about 50m as disturbance 1, assume that the range of the known disturbance is 525m to 575m, set the sampling frequency f = 200MSa / s, the local spatial position is 450m to 650m, the trigger delay τ = 450ns, and the record length RL = 400. The phase of the disturbance signal recovered by the present invention is as follows Figure 3 As shown in the figure, the horizontal axis represents the time T of the acquisition event; the vertical axis represents the phase value of the disturbance. pulse =100μs The actual sampleable fiber length is L ′ =10km, while local spatial data only needs to collect data on 200m optical fiber to successfully recover the phase of the disturbance signal. It can be seen that when collecting disturbance events of the same time T at the same sampling frequency, the amount of data collected by the traditional method is 50 times that of the local spatial data collection method, that is, k=50.

[0104] Note: Set T pulse >T L The purpose is to reduce the number of pulse acquisitions under the same disturbance time. pulse =T L In this example, k = 6. In practical applications, it is necessary to set it reasonably according to the disturbance frequency collected. pulse =100μs, the disturbance range that can be collected is [0,5k), which meets most application scenarios.

[0105] Example 2: Based on Example 1, a new PZT is added at 710m-720m as disturbance 2, and the sampling frequency f=100MSa / s is set in combination with the bandpass sampling theorem, the local spatial position is 450m-750m, the trigger delay τ=450ns is set, and the recording length RL=300. The amplitude waveforms of disturbance 1 and disturbance 2 can be represented by the waveforms of any point in 525m-575m and 710m-720m, and the phase waveform of the disturbance signal recovered by the local spatial data acquisition method combined with the bandpass sampling theorem is as follows: Figure 4 As shown in the figure, the horizontal axis represents the time T of the acquisition event; the vertical axis represents the phase value. The phase waveform of disturbance 1 can be represented by the phase of any position in the stable area 580m~700m after the end of the first disturbance (580m), as shown in Figure 4 (a); and the phase in the stable region 720m~750m after the end of disturbance 2 (720m) contains the phases of all previous disturbances, such as Figure 4 (b) shows; the phase waveform of disturbance 2 is the result of the difference between (b) and (a), as shown in Figure 4 (c) As shown. According to T pulse =100μs, the actual sampleable fiber length is 10km, while the local spatial data can successfully recover the phase of the disturbance signal by collecting data on only 300m of optical fiber. It can be seen that when collecting disturbance events of the same time T at the same sampling frequency, the amount of data collected by the traditional collection method is 33 times that of the local spatial data collection method, that is, k=33.

[0106] The results of the above two implementation cases show that the present invention can reliably restore the phase of single-point / multi-point disturbances and significantly reduce the amount of data collected. Under the same sampling frequency and data duration, the amount of data collected by the traditional acquisition method is k times that of the local space data acquisition method, where

[0107]

[0108] Wherein, L is the length of the optical fiber under test.

[0109] In summary, the present invention proposes a phase extraction method for external disturbance events based on local spatial data, which can effectively reduce the amount of data and alleviate the storage space of the system. Based on the collected local spatial data, the optimized phase unwrapping algorithm is used to perform phase unwrapping, which can reduce the time required for data processing and ensure the real-time monitoring of the system.

[0110] It should be noted that although the embodiments of the present invention described above are illustrative, they are not intended to limit the present invention, and therefore the present invention is not limited to the above specific embodiments. Without departing from the principles of the present invention, any other embodiments obtained by those skilled in the art under the guidance of the present invention are deemed to be within the protection of the present invention.

Claims

1. A method for extracting the phase of an external disturbance event based on local spatial data, characterized in that: The steps include: Step 1, determine the optical fiber segments L1-L2 that currently need attention; Step 2: Determine the fiber segment L1 to L2 that needs attention. The local spatial position to be collected is L1-l1~L2+l2; Step 3: According to the determined local spatial position, set The trigger delay τ of the synchronous trigger pulse and the data record length RL after the trigger delay; The trigger delay τ is: τ=t ′ ×(L1-l1) The data record length RL is: <h2 style=";text-align:left;direction:ltr">RL≥(L2-L1+l1+l2)×t<h2 style=";text-align:left;direction:ltr"> ′ <h2 style=";text-align:left;direction:ltr"> ×f Step 4, collecting intermediate frequency data under n consecutive synchronous trigger pulses, that is, when the trigger edge of each synchronous trigger pulse arrives, start collecting intermediate frequency data with a length of RL after a delay of τ, thereby obtaining a local spatial intermediate frequency data matrix IF with a size of n×RL; Step 5, perform orthogonal demodulation on the local spatial intermediate frequency data matrix IF to obtain an initial phase matrix θ; Step 6: Use the optimized phase unwrapping algorithm to unwrap the initial phase matrix θ, restore the true value of the phase, and obtain the true phase matrix Θ; that is: Step 6.1: Perform spatial difference operation on the initial phase matrix θ to obtain the spatial difference matrix θ 1 ; Step 6.2: Spatial difference matrix θ 1 Perform phase unwrapping along the time direction to obtain the unwrapped phase matrix θ 2 ; Step 6.3: The phase matrix θ after unwrapping 2 Perform time difference operation to obtain the real phase matrix Θ; Step 7: extract the phase of the external disturbance event based on the real phase matrix Θ, that is, the phase of any position in the stable region after the end point L2 of the optical fiber segment currently in need of attention in the real phase matrix Θ; The above L1 is the starting point of the fiber segment that needs to be paid attention to, and L2 is the end point of the fiber segment that needs to be paid attention to; l1 is the front reserved fiber length of the fiber segment that needs to be paid attention to, and l2 is the rear reserved fiber length of the fiber segment that needs to be paid attention to, l1≥SR, l2≥SR, SR is The spatial resolution of ′ is the time required for light to travel 1 meter in the optical fiber; f is The sampling frequency is τ, the trigger delay is RL, the data record length is n, and the number of pulses is n.

2. According to the method for extracting the phase of an external disturbance event based on local spatial data in claim 1, it is characterized in that the steps 1, the optical fiber segments L1-L2 that currently need to be concerned are determined by a manual designation method or an adaptive method.

3. The method for extracting the phase of an external disturbance event based on local spatial data according to claim 2 is characterized in that: The specific process of using the adaptive method to determine the optical fiber segments L1 to L2 that need attention is as follows: Firstly, the traditional data acquisition method is used to collect the intermediate frequency signal within a certain period of time after a trigger pulse; Then, these intermediate frequency signals are demodulated and divided according to the sampling points under a single modulation pulse to obtain a time-space matrix containing the intermediate frequency signal amplitudes of M×N sampling points, where M is the number of data frames and N is the single modulation pulse period T. pulse The number of sampling points under ; Finally, the differential accumulation algorithm is used to locate the fiber segment range where the disturbance roughly occurs on the spatiotemporal matrix of the intermediate frequency signal amplitude, and the located fiber segment range where the disturbance roughly occurs is taken as the fiber segment L1-L2 that needs attention.

4. According to claim 1, the method for extracting the phase of an external disturbance event based on local spatial data is characterized in that: In step 2, the spatial resolution SR is: In the formula, c is the speed of light in vacuum, w is The modulation pulse width of the acousto-optic modulator, n eff is the refractive index of the sensing fiber core.

5. The method for extracting the phase of an external disturbance event based on local spatial data according to claim 1, characterized in that: In step 3, the sampling frequency f is: Where f0 is The frequency shift of the acousto-optic modulator is The integer part of .

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