Method and apparatus of distributed acoustic sensing

A fiber optic distributed acoustic sensing (DAS) system for performing acoustic and vibration measurements, the DAS system comprising:

• a DAS acquisition device connectable toward an optical fiber link and comprising a coherent Optical Time Domain Reflectometer (OTDR) for performing repetitive DAS acquisitions, wherein each DAS acquisition is performed by propagating in the optical fiber link, a pulsed test signal and detecting corresponding return light from the optical fiber link so as to obtain a DAS trace representing backscattered and reflected light as a function of distance in the optical fiber link;
• a memory to store said DAS traces, at least one group of DAS traces at a time;
• and
• a processing unit receiving said DAS traces and configured for:
• processing said DAS traces to produce a DAS signal;
• obtaining an amplitude-normalization trace Γ(z) with respect to distance along the optical fiber link;
• and
• normalizing said DAS signal using the amplitude-normalization trace, thereby improving a linearity of the DAS signal.

A non-transitory computer-readable storage medium comprising instructions that, when executed, cause a processor to perform the steps of:

• receiving DAS acquisitions performed toward an end of an optical fiber link using a DAS acquisition device comprising a coherent Optical Time Domain Reflectometer (OTDR), wherein each DAS acquisition is performed by propagating in the optical fiber link, a pulsed test signal and detecting corresponding return light from the optical fiber link so as to obtain a DAS trace P(n,k)(z) representing backscattered and reflected light as a function of distance in the optical fiber link;
• processing said DAS traces to produce a DAS signal;
• obtaining an amplitude-normalization trace Γ(z) with respect to distance along the optical fiber link;
• normalizing said DAS signal using the amplitude-normalization trace, thereby improving a linearity of the DAS signal.