These systems detect vibrations and capture acoustic energy along the optical fiber. The fiber functions as if there were thousands of microphones installed. Classification algorithms are used to detect and locate, for example, intrusion activities, leaks or other abnormal sounds.
Various DAS / DVS technologies are used in the market, but the most common is based on Coherent Optic Time Domain Reflectometry (C-OTDR). C-OTDR utilizes Rayleigh back-scattering, allowing acoustic frequency signals to be detected over large distances. The interrogator sends a coherent laser pulse along an optical fiber (sensor cable) and scattering sites within the fiber cause the fiber to act as a distributed interferometer with a gauge length like the pulse length (e.g. 10 meters). Acoustic disturbance on a fiber generates microscopic elongation or compression of the fiber (micro-strain), which causes a change in the phase relation and/or amplitude.
