CN104215271B - Positioning method for disturbance position in distributed optical fiber disturbance monitoring system - Google Patents

Abstract

The invention belongs to the technical field of distributed measurement, in particular to a method for locating disturbance positions in a distributed optical fiber disturbance monitoring system. In this method, the obtained interferometric phase signal difference is firstly subjected to Fourier transform to obtain the spectrum , and then take its logarithm to obtain the logarithmic spectrum, the logarithmic spectrum of the signal is then filtered and subtracted or autocorrelated in a single step, or after the two steps of filtered subtraction and autocorrelation are combined, and finally Fourier transformed, you can get disturbance position. The advantage of this method is that the peak is obvious, the peak energy is concentrated, the positioning is accurate, and the applicable positioning range is wide. The invention is especially suitable for optical fiber distributed monitoring and positioning system.

Description

A Disturbance Location Method in Distributed Optical Fiber Disturbance Monitoring System

technical field

The invention belongs to the technical field of distributed measurement, and in particular relates to a method for locating disturbance positions in a distributed optical fiber disturbance monitoring system.

Background technique

The distributed optical fiber disturbance monitoring and positioning system is widely used in measurement, and the measurement signal is also used to analyze the characteristics of the monitoring target. For example, in oil pipelines, the distributed optical fiber disturbance monitoring and positioning system is used instead of manual patrols to detect oil theft, oil leakage, damage to pipelines and other behaviors in time, and accurately locate the location of the behavior, intelligently manage pipelines, and ensure pipeline safety. In the field of security, due to the concealment and anti-electromagnetic properties of optical fibers, the distributed optical fiber disturbance monitoring and positioning system is very suitable for real-time monitoring of various emergencies, and the monitoring success rate is higher than that of ordinary photoelectric systems.

The positioning algorithms in the traditional distributed optical fiber disturbance monitoring and positioning system mainly include notch point method and time delay method. The notch point method selects a single frequency notch point or several frequency notch points of the interference phase signal spectrum, and locates through the relationship between the position of these frequency points and the position of the disturbance point. This approach has two main disadvantages. First, the positions of these frequency points are easily shifted by other factors, resulting in low positioning accuracy; second, the multiple peak-finding algorithm is not effective and time-consuming, and the wrong sag frequency is often selected, resulting in final positioning failure. The time delay method uses the relationship between the time delay difference between the constructed two-way signals and the distance of the disturbance point for positioning, extracts the time delay through an appropriate method, and uses the corresponding relationship to convert it into a positioning distance. The main disadvantage of this method is that it uses an iterative algorithm, which leads to slow calculation, high requirements for processing equipment, and complex optical path structure.

Contents of the invention

Aiming at the distributed optical fiber disturbance detection system, the invention proposes a disturbance location positioning method in the distributed optical fiber disturbance monitoring system; the positioning accuracy is high.

The present invention is aimed at the distributed optical fiber disturbance detection system shown in Figure 5, assuming that disturbances occur at 5 places in Figure 5, the interference signal has been amplified or attenuated, and the phase difference signal ϕ(t) is obtained by the phase restoration algorithm, and has passed An FFT obtained the spectrum of the phase difference signal , which can be expressed in the following form:

The positioning distance information is contained in item, by Determined, the relationship with the positioning distance is,

According to the theory, the frequency spectrum is directly subjected to a Fourier transform again to obtain , the disturbance position can be obtained . But due to the frequency spectrum of the perturbation itself and other factors, resulting in delay times containing The features are not obvious, affecting the positioning effect. It is necessary to perform waveform conditioning before the second Fourier transform.

In the present invention, two technologies are used to adjust the disturbance position location waveform. The first is filter subtraction technology, that is, the logarithmic spectrum is low-pass filtered to obtain the envelope of the logarithmic spectrum, and the envelope is subtracted from the original spectrum. , so that the logarithmic spectrum is "lifted" to near 0, reducing the low-frequency background of another FFT transformation (that is, the strong background in the near-positioning distance area), so that the accuracy of short-distance positioning is greatly improved. The second is autocorrelation technology, which is to perform autocorrelation on the processed spectrum to make the modulation trend of the spectrum more obvious, which is beneficial to the effective energy concentration when performing FFT transformation again, so as to obtain more accurate positioning in the whole positioning range.

In the present invention, the filter subtraction technique and the autocorrelation technique can be used alone or in combination. The specific plan is introduced as follows.

The present invention provides a method for locating disturbance positions in a distributed optical fiber disturbance monitoring system, which uses filter subtraction technology alone, and the specific steps are as follows:

(1) First, the two interference signals PIN I and PIN II collected on the optical fiber are phase restored to obtain the interference phase difference signal , and then Fourier transform it to get the spectrum , then for the spectrum Take the logarithm to get the log spectrum ;

(2) Use filter subtraction technology and/or autocorrelation technology to perform disturbance position positioning waveform conditioning; wherein, the filter subtraction technology is to convert the logarithmic frequency spectrum Through a low-pass filter, the logarithmic spectrum envelope is obtained ; Then the logarithmic spectrum Subtract the log spectral envelope get ; The autocorrelation technique is the logarithmic spectrum or Carry out autocorrelation calculations;

(3) Finally, perform Fourier transform on the result of step (2) to obtain the positioning distance.

The beneficial effects of the present invention are:

(1) The present invention provides an effective method for processing disturbance location information of the distributed optical fiber disturbance location system with the structure shown in FIG. 5 .

(2) The present invention can extract the location information of the disturbance source, and can obtain the frequency spectrum characteristics of the disturbance source, which provides a solution for analyzing and judging the characteristics of the disturbance source.

(3) The filtered subtraction signal and the autocorrelation signal in the intermediate process of the present invention can be used to judge the disturbance feature, so that the positioning result is accurate.

Description of drawings

Fig. 1 is an effect diagram corresponding to different implementation steps of the invention.

Fig. 2 is a positioning error diagram of the present invention at 100km in an embodiment.

Fig. 3 is a series of positioning curve diagrams in the embodiment of the present invention.

Fig. 4 is an algorithm flow chart of an embodiment of the present invention.

Fig. 5 is the optical path adopted in the embodiment.

Numbers in the figure: 1 is a 3*3 fiber optic splitter; 2 is a 2*2 fiber optic splitter; 3 is a delay fiber, one end is connected to the 1b1 port of the fiber optic splitter 1, and the other end is connected to the fiber optic splitter 2 4 is the sensing optical cable, which is led out from the 2a port of the fiber optic splitter 2, and the end is connected to 6; 5 is the action position of the disturbance point, which is the amount to be detected; 6 is the reflection head.

detailed description

In this embodiment, the specific structure of the optical path of the optical fiber distributed disturbance location system is shown in FIG. 5 . The wide-spectrum light source with a center wavelength of 1550nm is input to the port 1a1 of the optical fiber splitter 1, and after passing through the optical fiber splitter 1, it is divided into two beams, which are respectively output from the ports 1b1 and 1b2 on the other side. The corresponding interference light path is:

A1: 1b1→3→2b1→2a→4→5→6→5→4→2a→2b2→1b2

A2: 1b2→2b2→2a→4→5→6→5→4→2a→2b1→3→1b1

In this embodiment, the 1550nm light source is a superluminescence diode (SLD) produced by the 44 Research Institute of the Electronics Group Corporation. Optical fiber splitters and wavelength division multiplexers are produced by Wuhan Institute of Posts and Telecommunications. 1 is a 3*3 fiber optic coupler, and 2 is a 2*2 fiber optic coupler. The feedback device 6 is made by coating the end of the optical fiber with a reflective film. The monitoring optical cable (optical fiber 4) is laid near the pipeline that needs to be monitored, and the optical fiber interference module needs to be placed in a soundproof device to shield external interference. The interference signal output from the fiber splitter 1a2, 1a3 is converted into an electrical signal by an InGaAs photodetector whose model is GT322C500 produced by 44. In the range of 10km to 130km, 20 disturbances are generated every 10km. The electrical signal is collected into the computer through the National Instruments data acquisition card PCI-6122 for signal processing. The data processing software is written by Labview software. The low-pass filter is a Butterworth filter with a value of 0.75 and an order of 2. Observe the disturbance localization distribution for each disturbance distance.

Figure 1 is the effect diagram corresponding to the different implementation steps of the invention, respectively enumerating the positioning results of four implementation methods without improvement measures, only filter subtraction, only autocorrelation, and filter subtraction autocorrelation. It can be found that superposition and filter subtraction are applied Works best with autocorrelation.

Fig. 2 is a positioning error diagram of the present invention at 100km in an embodiment. The positioning results are distributed in four adjacent value points, and the interval represented by each value point is about 25m. It can be seen that the positioning effect is very good.

Fig. 3 is a series of positioning graphs in the embodiment of the present invention, covering a positioning range of 10 km to 130 km, with obvious peaks and concentrated peak energy.

Claims (1)

1. a location method of disturbance position in distributed optical fiber disturbance monitoring system, it is characterized in that, concrete steps are as follows: (1) First, the two interference signals PIN I and PIN II collected on the optical fiber are phase restored to obtain the interference phase difference signal , and then Fourier transform it to get the spectrum , then for the spectrum Take the logarithm to get the log spectrum ; (2) Use filter subtraction technology and/or autocorrelation technology to adjust the disturbance position positioning waveform; wherein, the filter subtraction technology is to convert the logarithmic frequency spectrum Through a low-pass filter, the logarithmic spectrum envelope is obtained ; Then the logarithmic spectrum Subtract the log spectral envelope get ; The autocorrelation technique is the logarithmic spectrum or Carry out autocorrelation calculations; (3) Finally, perform Fourier transform on the result of step (2) to obtain the positioning distance.