Distributed acoustic sensing based acoustic wave speed scanning and mapping of civil infrastructures
Aspects of the present disclosure describe distributed fiber optic sensing (DFOS)-distributed acoustic sensing (DAS) based systems, methods, and structures that advantageously enable and/or facilitate the monitoring of civil infrastructures via acoustic wave speed measurements.
1. A method of monitoring civil infrastructure using distributed fiber optic sensing (DFOS)—distributed acoustic sensing (DAS), the method comprising:
providing a length of optical fiber, at least a portion of which is positioned in physical contact with the civil infrastructure; and
providing a distributed optical fiber sensing—distributed acoustic sensing interrogator in optical communication with the length of optical fiber;
providing at least two acoustic transducers positioned on the infrastructure and operating the transducers such that acoustic impulses/vibrations with predetermined temporal differences are generated;
generating by a first one of the acoustic transducers a first acoustic impulse at time t 1 , and at location h 1 on the infrastructure; and
detecting this impulse generated by the first one of the acoustic transducers by the DOFS-DAS system at time τ 1 ;
operating the DFOS-DAS to detect/determine strain(s) induced into the optical fiber by the acoustic impulses/vibrations; and
determining, from the detected strain(s), an average wave speed of the acoustic impulses in the infrastructure;
generating by a second one of the acoustic transducers a second acoustic impulse substantially identical to the first acoustic impulse at time t 2 =t 1 +Δt, and at location h 2 =h 1 +Δh on the infrastructure; and
detecting this impulse generated by the first one of the acoustic transducers by the DOFS-DAS system at time τ 2 =τ 1 +Δτ;
wherein the at least two acoustic transducers are spaced apart from one another by a predetermined distance.
2. The method of claim 1 further comprising determining an average wave-speed of the acoustic signal along the infrastructure according to the following:
v
=
Δ
h
Δ
τ
-
Δ
t
.
3. The method of claim 2 further comprising relocating the transducers on the infrastructure and subsequently obtaining average wave-speed information at multiple regions of the infrastructure.