Monitoring tidal water-column changes in ports using distributed acoustic sensing

Abstract

We show results of of using distributed acoustic sensing (DAS) for continuous relative water-column changes monitoring by relating the oscillating frequencies to measurements of a nearby tidal-station. The oscillations have a great qualitative agreement with the tidal-station, having a period of 12 hours and 25 minutes. No calibration is required to measure the tides and the relative difference in water height, though calibration would allow measuring the absolute water height at any location. Because we used two poles with different exposure lengths to air, at different depths and only 38 m apart, we can interpret he spectral oscillations are a result of constructive interference in our poles, likely generated by the wind. DAS could be a very attractive alternative for tidal monitoring in shallow marine environments, ports and waterways. DAS could potentially resolve spatial resolution problems with tidal monitoring, which is currently cost-prohibited, at a relatively low expense by wrapping a fibre around a pre-existing structure such as a docking pole. Furthermore, DAS can be used remotely and continuously, allowing for better model calibrations or local tidal fluctuation monitoring. This monitoring system could help determine if ships have enough water clearance to dock and, in turn, increase the occupation rate.