CN-121994347-A - Interference fading point compensation method for coherent phi-OTDR

CN121994347ACN 121994347 ACN121994347 ACN 121994347ACN-121994347-A

Abstract

The invention discloses an interference attenuation point compensation method for coherent phi-OTDR, which is based on complex envelope characteristics obtained by coherent reception and I/Q demodulation, and comprises the steps of identifying interference attenuation points, carrying out interpolation reconstruction on echo vectors of the attenuation points by using neighbor non-attenuation points on a complex plane, and further recalculating phases and differential phases so as to inhibit phase demodulation failure and differential phase artifacts caused by fading. On the premise of not increasing hardware transformation, the method reduces differential phase artifacts and abnormal stripes caused by phase demodulation failure at the attenuation point, improves the stability of differential phase results and the event identifiability, and keeps lower calculation complexity so as to adapt to offline or quasi-real-time processing.

Inventors

MAO YUAN
ZHU DAHONG

Assignees

杭州旸谷智能科技有限公司

Dates

Publication Date: 20260508
Application Date: 20260212

Claims (7)

1. The interference fading point compensation method for coherent phi-OTDR is characterized by comprising the steps of identifying interference fading points based on complex envelope characteristics obtained by coherent reception and I/Q demodulation, carrying out interpolation reconstruction on fading point echo vectors by using neighbor non-fading points on a complex plane, and further recalculating phases and differential phases to inhibit phase demodulation failure and differential phase artifacts caused by fading.
2. The interference fading point compensation method for coherent phi-OTDR according to claim 1 is characterized by the following specific steps: Step S1, acquiring an I/Q discrete sampling sequence of a coherent phi-OTDR echo, and representing the I/Q discrete sampling sequence as complex signals S (z, t) =I (z, t) +jQ (z, t) on each distance sampling point z and slow time sampling point t; S2, the interference attenuation points are expressed as local depressions in amplitude distribution, the amplitude A (z, t) = |s (z, t) | is calculated, and a local base line A_base (z, t) is constructed on a distance axis and used for representing the slow-variation attenuation and average level of a distance dimension; Step S3, calculating a normalized amplitude ratio R (z, t) =A (z, t)/A_base (z, t), and marking the corresponding distance position as an interference attenuation point when R (z, t) is lower than a preset threshold gamma to form an attenuation point set F; Step S4, searching nearest non-fading points z L and z R to the left and right on a distance axis for each fading point z f , or searching a plurality of nearest non-fading points to form a neighborhood set for providing phase constraint and interpolation reconstruction basis; S5, reconstructing complex signals of the attenuation points based on the neighborhood non-attenuation points on each slow time sample t; And S6, performing phase calculation phi (z, t) =arg (S c (z, t)) on the compensated complex signal S c (z, t), completing phase unwrapping and differential phase calculation according to the existing flow, and outputting a differential phase waterfall diagram or a time sequence result for event identification and positioning.
3. The method for compensating interference fading point for coherent phi-OTDR according to claim 2 wherein the local baseline A_base (z, t) is obtained by local statistics in step S2.
4. The method for compensating for interference fading point of coherent phi-OTDR according to claim 2, wherein the preset threshold gamma in step S3 is an adaptive threshold gamma (z) or gamma (t), which can be determined by the statistics of the amplitude ratio R (z, t) in the range sliding window.
5. The method for compensating for interference fading point of coherent phi-OTDR according to claim 4 wherein the statistics of the amplitude ratio R (z, t) within the range sliding window are quantile, mean plus-minus standard deviation or robust statistics.
6. The method of claim 1, wherein the complex signal reconstruction in step S5 uses complex plane linear interpolation ：ŝ(z f ,t)=s(z L ,t)+((z f −z L )/(z R −z L ))·(s(z R ,t)−s(z L ,t)), and replaces the original S(z f , t) with ŝ (z f , t) to obtain a compensated complex signal sequence S c (z, t).
7. The method for compensating interference fading point for coherent phi-OTDR according to claim 6, wherein in step S5, the complex signal reconstruction is implemented by weighted interpolation, spline interpolation or multi-point least squares fitting, and the neighboring points can be expanded to K nearest non-fading points at two sides of the axis, and weighted according to magnitude, coherence or noise estimation.

Description

Interference fading point compensation method for coherent phi-OTDR Technical Field The invention belongs to the technical field of acoustic sensing, and particularly relates to an interference fading point compensation method for coherent phi-OTDR. Background The distributed acoustic sensing system uses the optical fiber as a distributed sensing medium, and can realize the positioning and waveform recovery of the vibration disturbance along the line. The coherent phi-OTDR obtains the I/Q component of the Rayleigh backscattering signal through coherent reception, and performs phase demodulation and differential phase calculation at a data processing end so as to realize quantitative measurement of external disturbance. In a practical system, due to the randomness of superposition of multiple scatterer vectors in a resolution unit, a phenomenon that the amplitude of an echo is obviously reduced due to destructive interference occurs in part of positions, and the positions can be called interference attenuation points. The signal amplitude at the interference attenuation point is close to the noise bottom, so that the phase estimation is highly sensitive to noise, the demodulation phase is easy to be dominated by noise, thereby generating abnormal stripes or background artifacts in the differential phase waterfall diagram, influencing the event readability and introducing false alarm. In the prior art, in order to alleviate the fading influence, common ideas include multi-frequency detection or frequency division multiplexing, polarization diversity, introduction of additional hardware structures to improve echo stability, compensation methods based on machine learning models, and the like. However, these methods often bring about an increase in system complexity and cost, or put higher demands on real-time performance and engineering deployment. Disadvantages of the prior art: when the schemes such as multi-frequency/diversity are relied on, the frequency planning of the light source, channel synthesis and synchronous control are required to be increased, and the complexity and cost of the system are increased. The partial hardware modification scheme has high requirements on the stability of the optical path, the consistency of devices and the field maintenance, and is not beneficial to rapid deployment. Machine learning methods typically require a large amount of training data and computational support, with robustness and interpretability being uncertainties in engineering scenarios. Under the condition of no additional processing, the phase demodulation failure caused by the fading point can be represented as fixed position artifact or abnormal stripe in the differential phase result, so that the event identification reliability is reduced and the false alarm risk is increased. Disclosure of Invention In order to solve the defects and shortcomings pointed out in the prior art, the invention provides an interference fading point compensation method for coherent phi-OTDR, which reduces differential phase artifacts and abnormal fringes caused by phase demodulation failure at a fading point on the premise of not increasing hardware transformation, improves the stability and event identifiability of a differential phase result, and keeps lower calculation complexity so as to adapt to offline or near real-time processing. In order to achieve the above purpose, the invention provides a technical scheme that an interference attenuation point compensation method for coherent phi-OTDR is based on complex envelope characteristics obtained by coherent reception and I/Q demodulation, the interference attenuation point is identified, interpolation reconstruction is carried out on echo vectors of the attenuation point by using neighbor non-attenuation points on a complex plane, and then phase and differential phase are recalculated, so that phase demodulation failure and differential phase artifact caused by fading are restrained. A compensating method for interference fading point of coherent phi-OTDR comprises the following specific steps: Step S1, acquiring an I/Q discrete sampling sequence of a coherent phi-OTDR echo, and representing the I/Q discrete sampling sequence as complex signals S (z, t) =I (z, t) +jQ (z, t) on each distance sampling point z and slow time sampling point t; S2, the interference attenuation points are expressed as local depressions in amplitude distribution, the amplitude A (z, t) = |s (z, t) | is calculated, and a local base line A_base (z, t) is constructed on a distance axis and used for representing the slow-variation attenuation and average level of a distance dimension; Step S3, calculating a normalized amplitude ratio R (z, t) =A (z, t)/A_base (z, t), and marking the corresponding distance position as an interference attenuation point when R (z, t) is lower than a preset threshold gamma to form an attenuation point set F; Step S4, searching nearest non-fading points z L and z R to the