Fiber optic sensing technology is a new type of sensing technology that emerged in the 1970s with the development of fiber optic technology and fiber optic communication technology. It uses optical waves as sensing signals and optical fibers as transmission media to sense and detect external signals. Among them, distributed optical fiber sensing technology uses the sensitivity of optical fibers to combine information transmission and sensing into one, and only requires one light source and one detection line to detect the sensing object along the fiber transmission path, realizing large-scale and long-distance sensing measurement.
An optical time domain reflectometer is a distributed fiber optic sensor based on scattering, which can identify and locate disturbances on the fiber optic line. However, the signal obtained by the sensing system from backscattered light is very weak, and the influence of environmental noise makes it difficult to identify the disturbance point, especially at the end of the sensing fiber. The attenuation of the signal light is already large and its scattered light intensity is almost submerged in the noise. Moreover, the coherence principle of the phase optical time domain reflectometer makes it extremely sensitive to small disturbances in the environment and susceptible to noise interference. In order to improve its performance, it is necessary to reduce noise and improve the signal-to-noise ratio through signal processing methods.
The wavelet threshold filtering method of the optical time domain reflectometer can effectively reduce noise and identify disturbance information, but it needs to find a suitable wavelet basis and its decomposition level. In practical applications, a comprehensive judgment method that uses multiple wavelet bases can reduce system errors and omissions and improve the accuracy of the system.
The signal processing scheme of the optical time domain reflectometer subtracts the collected real-time backscattered signal from the stored signal without disturbance to obtain a backscattered difference signal, and then performs the tests of the above schemes separately.
Single overlay averaging method: Collect the difference signal in each cycle and overlay it multiple times before averaging it.
Wavelet threshold method: Decompose and reconstruct the difference signal at multiple levels using the selected wavelet basis.
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