Sensing Shallow Structure and Traffic Noise with Fiber-optic Internet Cables in an Urban Area

Abstract

Distributed acoustic sensing (DAS) is a novel seismic observation system developed in recent years that can realize ultrahigh density observations and has attracted extensive attention in the field of seismology. DAS uses fiber-optic cables as sensing units, which are easy to incorporate with urban telecommunication fiber-optic cables for seismological observations. Compared with seismometers, DAS has the advantages of being rapidly deployed and recyclable, being able to acquire dense observations at low cost, and convenient data collection. In this study, a 5.2 km long telecom fiber-optic internet cable was utilized as a DAS array in an urban area to record ambient noise, and the noise cross-correlation function (NCF) was calculated. There are two different distribution types of ambient noise sources along the cable, regular along-road trucks (Taihe Road) and complex ambient noise, including human activities and traffic sources along and across the Jinniu road. In the first case, we constructed a 2D S-wave velocity model down to 100 m depth and a low-velocity zone was revealed. The S-wave model well explained the traffic signal along the Taihe road and the low-velocity zone is also consistent with the results obtained from co-located geophone arrays. In the second case, due to the complexity of the traffic noise distribution, empirical Green's functions were barely achieved. Therefore, we performed a synthetic test obtaining different NCFs with different source distributions, and two specific cases that dominate the NCF results were matched. Finally, we obtained the traffic noise distribution along the road, which is consistent with the power spectra density of the ambient noise. In conclusion, by combining DAS and urban fiber-optic internet cables with urban traffic noise, we can effectively reveal the traffic activities and image shallow structures with high resolution, which could offer a reference for urban construction and disaster prevention. Keywords Distributed acoustic sensing • Urban area • Ambient noise tomography • Ambient noise source distribution Article Highlights• DAS turns the urban fiber-optic internet cables into ultra-dense permanent seismic observation arrays • We revealed a high-resolution shallow structure using urban fiber-optic internet cables • We obtained the distribution of traffic activities along the road

Railway traffic monitoring with trackside fiber-optic cable by distributed acoustic sensing Technology

“…In actual situations, the length and coupling of the cable make the recorded DAS data impacted by different level of noise (Song et al, 2021). Therefore, we test the performance of our method on two typical train-event signals (Figure 8) with different noise levels.…”

“…With the use of the dense array features, DAS records high-fidelity seismic wavefields and can be applied in event monitoring, such as aftershock detection Lv et al, 2022), icequake detection (Walter et al, 2020;Hudson et al, 2021), and urban traffic monitoring (Lindsey et al, 2020). Another advantage of DAS is in its convenient mode of deployment, whereby, widespread existing telecommunication cables can be utilized as dense array sensors, especially in highlybuilt cities (Lindsey et al, 2020;Song et al, 2021). It is worth noting that urban-scale DAS applications are not limited to vehicle traffic monitoring (Chambers, 2020;van den Ende et al, 2021) and interferometry studies (Dou et al, 2017;Song et al, 2021), but other moving sources like subways (Ferguson et al, 2020) and railway trains (Cedilnik et al, 2018;Wiesmeyr et al, 2020).…”

“…Another advantage of DAS is in its convenient mode of deployment, whereby, widespread existing telecommunication cables can be utilized as dense array sensors, especially in highlybuilt cities (Lindsey et al, 2020;Song et al, 2021). It is worth noting that urban-scale DAS applications are not limited to vehicle traffic monitoring (Chambers, 2020;van den Ende et al, 2021) and interferometry studies (Dou et al, 2017;Song et al, 2021), but other moving sources like subways (Ferguson et al, 2020) and railway trains (Cedilnik et al, 2018;Wiesmeyr et al, 2020). The trackside cables connected to an interrogator can provide researchers with the opportunity to record traininduced signals, and monitor the location and speed of trains, towards enhancing the train control system.…”

Near-surface characterization using urban traffic noise recorded by fiber-optic distributed acoustic sensing

“…On the other hand, the kinematic information of the velocity and strain wavefield are similar. Therefore, the dispersion curves extracted from the two wavefields may reveal similar near-surface velocity (Martin, et al, 2015;Song, et al, 2021b). The dispersion curve inversion method for geophone data is applicable to DAS data.…”

“…They picked travel times from virtual source gathers on each day and estimated the velocities by least-squares linear regression. Song et al (2021b) analyzed the traffic noise distribution using the ambient noise from an urban city. The data were recorded by urban telecommunication fiber-optic cables.…”