Algorithmic Implementation And Response Characteristics Analysis Of Φ-OTDR Vibration Sensing System

The Φ-OTDR vibration sensing system has the advantages of simple structure,stable operation,accurate positioning and simultaneous detection of multi-point disturbance events,which has become a new focus in distributed optical fiber sensing system.Moving average-moving difference signal recognition algorithm is simple and convenient,which is widely used in Φ-OTDR vibration sensing.In this dissertation,the optimization of moving average-moving difference algorithm and some factors affecting the response characteristics of the Φ-OTDR vibration sensing system are studied.Firstly,the interchangeability of moving average window width and moving difference interval and the optimal moving difference interval for moving average-moving difference algorithm are found and proved from both mathematical and measured vibration data processing.These two important mathematical relations reveal the intrinsic relationship between the moving average and the moving difference operations,which will play an important role in understanding the moving average-moving difference signal recognition algorithm and its practical application.In Φ-OTDR vibration sensing,optimization according to these two relations can not only obtain the maximum signal-to-noise ratio for vibration measurement of different vibration frequencies,but also significantly improve the search efficiency of vibration signals and avoid missing vibration signals.Then,an optical waveguide ring resonator is used to self-injection lock the DFB semiconductor laser,and the vibration sensing are carried out as using it as the light source of the Φ-OTDR system.The experimental results show that the sensing system has good sensing performance in remote sensing,simultaneous measurement of two vibration sources and minimum measurable vibration frequency.These show that the DFB semiconductor laser self-injection locked with an optical waveguide ring resonator has the potential to be used as the light source of the Φ-OTDR vibration sensing system.Finally,we analyze the influence of moving average-moving difference algorithm on the signal-to-noise ratio and frequency response characteristics of Φ-OTDR vibration sensing system.We reveal that the frequency response of the moving average-moving difference algorithm has periodicity,different from the transfer function of the moving averaging algorithm.Identifying the vibrational signal spectrum using the trajectory set after the moving average-movement difference works better than using the original trajectory set,and it can also compensate for the loss of spectrum amplitude caused by the moving averaging algorithm.