Chirped-Pulse $\Phi$-OTDR and Seismic Noise Interferometry: Enhancing Distributed Optical Sensing for Seismic Applications

Urban subsurface exploration is a powerful tool for infrastructure health monitoring and terrain studies, providing essential information about geological processes and soil composition. Metropolitan areas usually present a greater challenge for traditional subsurface imaging techniques, as restrictions apply to both the deployment of large measurement devices and the generation of large seismic noise. To overcome these problems, ambient noise interferometry takes advantage of passive seismic noise such as wind, microseisms and anthropogenic activity [1]. As high-resolution ambient noise tomography requires an extensive and dense detector array, distributed acoustic sensing (DAS) results in a cost-effective solution to seismic noise measurements. Despise its advantages, DAS presents several inherent disadvantages such as non-linear measurements, non-uniform SNR and the presence of random fading points along the measured fiber. As high sensitivity is required for passive seismic noise detection, Chirped-Pulse DAS technology has been employed in this study, which overcomes the aforementioned challenges and provides a linear and quantitative measurement [2].