1. Introduction . DAS technology can detect acoustic wave quantitively by demodulating phase information of coherent Rayleigh backscattering light in optical fiber with long sensing range, precise localization accuracy and high efficiency in real-time [ 1 – 4 ]. At present, DAS technology is widely deployed in seafloor detection [ 5 ], oil/gas exploration [ 6 ], border security [ 7 ], seismic surveillance [ 8 ], train speed monitoring [ 9 ], etc.In recent years, sensitivity e...