EGU2020-21483
https://doi.org/10.5194/egusphere-egu2020-21483
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

An Experimental Study of the Systematic Underestimation of Wave Crests Measured by Lagrangian Buoys, and a Retrospective Correction Method

Mark McAllister and Ton van den Bremer
Mark McAllister and Ton van den Bremer
  • University of Oxford, Department of Engineering Science, Oxford, United Kingdom of Great Britain and Northern Ireland (mark.mcallister@eng.ox.ac.uk)

Wave-following buoys are used to provide measurements of free surface elevation across the oceans. The measurements they produce are widely used to derive wave-averaged parameters such as significant wave height and peak period, alongside wave-by-wave statistics such as crest height distributions. Particularly concerning the measurement of extreme wave crests, these measurements are often perceived to be less accurate. We directly assess this through a side-by-side laboratory comparison of measurements made using Eulerian wave gauges and model wave-following buoys for directionally spread waves representative of extreme conditions on deep water. Our experimental measurements are compared to exact (Herbers and Janssen 2016, J. Phys. Oceanogr, 46, 1009-1021) and new approximate expression for Lagrangian second-order theory derived herein. We derive simple closed-form expressions for the second-order contribution to crest height representative of extreme ocean waves. Our experiments confirm that the motion a wave-following buoy should not significantly affect the measurements of wave crests or spectral parameters, and that discrepancies observed for in-situ buoy data are most likely a result of filtering. This filtering occurs when accelerations that are measured by the sensors within a buoy are converted to displacements. We present an approximate means of correcting the resulting measured crest height distributions, which is shown to be effective using our experimental data.

How to cite: McAllister, M. and van den Bremer, T.: An Experimental Study of the Systematic Underestimation of Wave Crests Measured by Lagrangian Buoys, and a Retrospective Correction Method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21483, https://doi.org/10.5194/egusphere-egu2020-21483, 2020.

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