Lateral positioning of vibration source for underground pipeline monitoring based on ultra-weak fiber Bragg grating sensing array

Abstract

Monitoring the underground pipeline to prevent the illegal intrusion is a quite important work for civil infrastructure security management. The distributed fiber optic sensing technology nowadays has been widely used in the monitoring. Meanwhile, it also suffers from a relatively high false alarm rate. To tackle the difficult problem of false alarms, the paper develops a short range lateral positioning method of vibration source based on ultra-weak fiber Bragg grating vibration sensing array. Two parallel fiber optic cables are required to be deployed at the both sides of the pipeline. The positioning algorithm establishes a least square misfit function between the predicted and observed travel time difference based on the double-cable data. By systematically searching through the possible lateral distance in a selected range, an optimal distance can be identified according to the minimal misfit value. The tests on synthetic and field data validate the effectiveness of the proposed method.