- 1Norwegian University of Science and Technology, Information Technology and Electrical Engineering, Electronic Systems, Norway (robin.a.rorstadbotnen@ntnu.no)
- 2Norwegian University of Science and Technology, Information Technology and Electrical Engineering, Electronic Systems, Norway (martin.landro@ntnu.no)
Distributed fiber-optic sensing is becoming increasingly topical because of its potential for recording a wide range of frequencies, at a high spatial sampling and over long distances. Distributed Acoustic Sensing (DAS) is one example of such an emerging technology. The lowest frequencies observed on marine DAS data are complex temperature signals at tidal periods (Ide et al, 2021). This presentation shows tidal period signals recorded on four DAS interrogators connecting Ny-Ålesund and Longyearbyen, Norway.
DAS records the phase changes in Rayleigh backscattered light from inherent impurities along the fiber to detect changes in the optical cable length. DAS data contain contributions from both temperature variation and elastic deformation. Interrogators normally record this as time-differentiated phase-change data which is linearly related to strain rate. At high frequencies (> 0.01 Hz, Sladen et al., 2019) the strain rate is dominated by elastic deformation, while at tidal frequencies (< 0.01 Hz) it is believed to primarily be generated from slow temperature variation, e.g., from internal tides (Williams et al., 2023). However, there are examples of strain measurements of tides (Roeloffs, 2010) and DAS signals that are proportional to the barotropic tidal pressure (Williams et al., 2023). Therefore, interplay between temperature and strain effects generated by tidal waves is not yet fully understood and remains a challenge.
During a field test in the summer of 2022 four interrogator units were installed in Svalbard, two in Ny-Ålesund and two in Longyearbyen. These recorded DAS data simultaneously for almost one month and covered two 260 km long fiber cables (see Rørstadbotnen et al., 2023, for more information). After the conclusion of the four-interrogator experiment, one of the interrogators was left recording in Ny-Ålesund. From this data, we have studied tidal period signals at selected channels over longer time periods (>14 days) and along the fibers for shorter periods (~4 days).
The results of the analyses will be presented, and we will demonstrate how the tidal signal varies along, and between, the two fiber cables. Additionally, the long-term signals will be compared to the water level data from Ny-Ålesund to validate the long-term trend in the data.
References:
Ide, S., Araki, E., Matsumoto, H., 2021, Very broadband strain-rate measurements along a submarine fiber-optic cable off Cape Muroto, Nankai subduction zone, Japan, Earth, Planets and Space, DOI: https://doi.org/10.1186/s40623-021-01385-5
Sladen, A., et al., 2019, Distributed sensing of earthquakes and ocean-solid Earth interactions on seafloor telecom cables, Nature Communications, https://doi.org/10.1038/s41467-019-13793-z
Williams, E. F., et al., 2023, Fiber-optic observations of internal waves and tides, Journal of Geophysical Research: Oceans, https://doi.org/10.1029/2023JC019980
Roeloffs, E., 2010, Tidal calibration of Plate Boundary Observatory borehole strainmeters: Roles of vertical and shear coupling. Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/2009JB006407
Rørstadbotnen, R. A., et al., 2023. Simultaneous tracking of multiple whales using two fiber-optic cables in the arctic, Frontiers in Marine Science, https://doi.org/10.3389/fmars.2023.1130898
How to cite: Rørstadbotnen, R. A. and Landrø, M.: Tidal period signals observed on DAS data from two 260 km fiber cables in Svalbard, Norway, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8409, https://doi.org/10.5194/egusphere-egu25-8409, 2025.
