I. Introduction
Distributed fiber optical acoustic sensor (DAS) based on the phase-sensitive optical time-domain reflectometry (-OTDR) technology [1], [2], provides a long distance, highly sensitive, and cost-effective continuous acoustics and vibration measurement way for our environment. With the existing underground communication optical cables as its sensing media, various vibration sources in the surrounding environment can be sensed and located by DAS with high precision, thus it has been applied in many safety monitoring applications of urban infrastructures [3]. Most of the related research was devoted to source detection [4], [5], identification [6]–[8], and localization [9]–[15]. However, complexity of the underground environment brings great challenges to the vibration detection and localization for DAS.