By attaching a DAS integrator unit, in the example above a Silixa iDAS that is part of the AuScope ANSIR equipment pool, to a fibre optic cable, the entire cable becomes a sensing element. As a seismic wave disturbs the ground, the cable is stretched and compressed. The iDAS instrument measures the response of the cable to the external forces applied to it by sending a pulsed coherent optical laser signal to accurately measure the phase and amplitude of vibrations by detecting changes in Rayleigh scattering induced by extensional strain. The iDAS sends laser signal pulses along the cable and continuously monitors the phase and amplitude of the Rayleigh scattering from the backscattered light (Figure 1).
This is a companion discussion topic for the original entry at https://www.geo-down-under.org.au/lighting-up-dark-fibre-for-seismic-imaging/