CN103954349B - A kind of lateral register method of distributed optical fiber vibration sensing system - Google Patents

Abstract

The invention discloses a lateral positioning method that can be used in a distributed optical fiber sensing system. Step 1: search for the point with the highest vibration amplitude in the optical fiber, and define this point as the first sensor point S1; Step 2: define and The point at a distance d from the first sensor point S1 is the second sensor point S2; Step 3: Obtain the time difference Δt between the vibration signal of the vibration source reaching the first sensor point S1 and the second sensor point S2; Step 4: Calculate and obtain The lateral distance from the vibration source to the vibration sensing fiber where v is the propagation velocity of the vibration signal in the soil. The positioning method of the invention can accurately measure the lateral distance between the vibration source and the optical fiber, and can be realized only by using the existing distributed optical fiber sensing system.

Description

A Lateral Positioning Method of Distributed Optical Fiber Vibration Sensing System

technical field

The invention relates to a lateral positioning method of a distributed optical fiber vibration sensing system.

Background technique

Distributed optical fiber vibration sensor has become a research hotspot at home and abroad in recent years because of its simple structure, long detection distance, and immunity to electromagnetic interference. Distributed optical fiber vibration sensor is an urgently needed technology in the fields of national defense, oil pipelines, and electric power. Protection of national property and life safety. The distributed fiber optic vibration sensor is mainly based on two principles: one is a distributed fiber optic vibration sensor based on the principle of optical fiber white light interference; the other is a distributed fiber optic vibration sensor based on the principle of Rayleigh backscattering spectral interference.

The structure of the distributed optical fiber vibration sensor is shown in Figure 1. The laser emits a continuous optical signal with a line width of 5 kHz, a center wavelength of 1550 nm, and a power of 10 mW. After being modulated by an acousto-optic modulator (AOM), the pulse width is 10 ns and the repetition frequency is 1kHz pulse signal. The narrow pulse signal is amplified by the fiber amplifier (EDFA1) and injected into the sensing fiber through the isolator (Isolator) and the circulator (Circulator) to generate back Rayleigh scattered light in the fiber. After the backscattered light is amplified by the fiber amplifier (EDFA1), it is converted into an electrical signal by the detector (Detector) after passing through the optical filter (Filter). After the electrical signal is amplified, electrically filtered and sampled, it is sent to the computer for data processing to obtain distributed vibration curve data.

The continuous narrow-linewidth optical signal emitted by the fiber laser is modulated into a pulsed light with a certain width by the acousto-optic modulator. The modulated pulsed light is injected into the sensing fiber through the circulator. The pulsed light interacts with the fiber material in the sensing fiber to generate a backscattering spectrum. The backscattering spectrum generates self-interference during backward transmission. After the scattered spectrum passes through the circulator, it is filtered by an optical filter and then converted into an electrical signal by a photodetector. The electrical signal is amplified by the amplifier, filtered by the electric filter, converted into a digital signal by the acquisition card, and finally enters the data processing system for data processing and analysis. The signal generator in the system is used to drive the acousto-optic modulator to generate a pulse signal, and simultaneously send the pulse synchronization signal to the acquisition card. The above-mentioned distributed optical fiber vibration sensor has only longitudinal positioning function, but no lateral positioning function, which limits the practical application of distributed optical fiber vibration sensor.

Contents of the invention

The technical problem to be solved by the invention is to realize a lateral positioning method that can be used in a distributed optical fiber sensing system.

In order to achieve the above object, the technical scheme adopted in the present invention is:

Step 1. Search for the point with the highest vibration amplitude in the entire optical fiber, and define this point as the first sensor point S1;

Step 2, defining a point that is at a distance d from the first sensor point S1 as the second sensor point S2;

Step 3. By analyzing the vibration waveforms of points S1 and S2, the time difference Δt between the vibration signal of the vibration source reaching the first sensor point S1 and the second sensor point S2 is obtained;

Step 4: Calculate the lateral distance from the vibration source to the vibration sensing fiber where v is the propagation velocity of the vibration signal in the soil.

The invention has the advantage that it can accurately measure the lateral distance between the vibration source and the optical fiber, and it can be realized only by using the existing distributed optical fiber sensing vibration system.

Description of drawings

The following is a brief description of the content expressed in each drawing in the description of the present invention and the marks in the figure:

Figure 1 is a structural diagram of a distributed optical fiber vibration sensing system;

Fig. 2 is the flowchart of positioning method;

Figure 3 is a schematic diagram of positioning;

Fig. 4 is a schematic diagram of the time difference between t1 and t2;

The marks in the above figures are: 1. processor; 2. acquisition card; 3. signal generator; 4. driver; 5. acousto-optic modulator; 6. laser; 7. first optical fiber amplifier; 8. isolator 9. Circulator; 10. Electric filter; 11. Signal amplifier; 12. Photodetector; 13. Optical filter; 14. Second optical fiber amplifier; 15. Sensing optical fiber.

detailed description

Referring to Figure 2, it can be seen that the lateral positioning method of the distributed optical fiber vibration sensing system is as follows:

Step 1: rearrange the data collected by the acquisition card 2 into vibration data arranged according to the time axis, search for the position point with the highest vibration amplitude in the optical fiber, and define this point as the first sensor point S1;

Step 2: Define the point at a distance d from the first sensor point S1 as the second sensor point S2, and the distance d is a custom value, for example, it can be defined as 5 meters;

Step 3: The point with the largest vibration amplitude is the point on the fiber closest to the vibration source, and the line connecting these two points (see Figure 3, point S1 and point S of the vibration source) will be perpendicular to the sensing fiber. The lateral vertical distance between the vibration source and the optical fiber can be calculated by adding the time difference Δt of the vibration signal from the vibration source to these two points (S1 and S2) and the propagation speed of the vibration in the soil. The principle of obtaining the time difference Δt is shown in Figure 4. ;

Step 4: Calculate the lateral distance from the vibration source to the vibration sensing fiber where v is the propagation velocity of the vibration signal in the soil.

In addition, the system needs to correct the v value before performing step 4 calculation for the first time.

The principle of calculating the lateral distance y is shown in Figure 3. Two points S1 (x1, y1) and S2 (x2, y1) are selected from the optical fiber as two sensing points for positioning. S(x,y) is the location of the vibration signal source to be located, where S1 is the point with the largest vibration amplitude. The lateral distance between S and the optical fiber can be calculated by the time difference of the vibration signal S arriving at S1 and S2, and the propagation speed of the vibration signal in the soil, then

(V.t1) ² +d ² ＝(V.t2) ²

v is the propagation velocity of the vibration signal in the soil, transformed into:

d ² =(v·Δt) ² +2·Δt·t1·V ²

but $\mathrm{the\; y}=\frac{d^2-{(v.\mathrm{\Δt})}^2}{2.v.\mathrm{\Δt}}.$

Claims (1)

1. the lateral register method of a distributed optical fiber vibration sensing system, it is characterised in that:

Step 1, the location point that the Oscillation Amplitude searched in whole piece optical fiber is the highest, and this point is defined as first sensor points S1；

Step 2, definition and the point that first sensor points S1 distance is d are second sensor points S2；

Step 3, acquisition vibration source vibration signal arrive first sensor points S1 and the time difference Δ of second sensor points S2 t；

Step 4: calculate the lateral distance obtaining vibration source distance vibrating sensing optical fiberWherein v It it is the spread speed of vibration signal；

System, before carrying out step 4 and calculating, needs to correct v value.