Distributed Acoustic Sensing
The distributed acoustic sensor (DAS) detects ground seismo-acoustic vibrations at distances of up to several dozens of kilometers along the optical cable. A standard single-mode optical fiber (G.652) is used as a sensitive element. The optical fiber is connected to the hardware unit which is continuously monitoring vibro-acoustic events along the optical fiber line.
The system operation is based on the principle of coherent reflectometry. Optical pulses are repetitively sent into the monitored fiber, where a very small fraction of light is backscattered due to material non-uniformities. Fiber microdeformations caused by seismo-acoustic signals affects this backscattered signal. The signal changes are continuously monitored and analyzed to identify the location and specifics of the vibro-acoustic event detected by the fiber.
DAS allows to detect various types of events throughout the fiber deployment zone with an accuracy of 10 meters including approach to the guarded zone, movement along the guarded zone, or trespassing the monitored zone border. Detection accuracy increases greatly if several adjacent monitoring zones can be arranged. Once a person or vehicle approach is detected, or if ground work in progress near the protected object is registered, Dunay system immediately transmits an alarm message to the operator’s computer indicating the source location. The system permits to detect any kind of activity that is causing water or soil vibrations. Installation of the system is customized, and FPS Photonics specialists fine tune the system configuration taking into consideration the particular features of the deployment place and specific customer needs.
One of the main DAS applications is the development of early detection systems for critical infrastructure objects. Since acoustic sensor sensitivity permits to detect signals from sources located at dozens or even hundreds meters away from fiber, the system operator gets an alarm signal well before the trespassing.
DAS system is a 3U device unit to be installed in a telco rack. The unit has three slots for: receiver and transmitter board (coherent reflectometer), amplifier module, and industrial computer for data processing and transfer to a remote server. Dunay system can be operated both as a stand alone unit and as a part of an integrated security system (API and Ethernet output are available).