Preprints
https://doi.org/10.5194/tc-2021-71
https://doi.org/10.5194/tc-2021-71

  04 Mar 2021

04 Mar 2021

Review status: this preprint is currently under review for the journal TC.

Elastic properties of floating sea ice from air-coupled flexural waves

Rowan Romeyn1,2, Alfred Hanssen1,2, Bent Ole Ruud2,3, and Tor Arne Johansen2,3,4 Rowan Romeyn et al.
  • 1Department of Geosciences, University of Tromsø – The Arctic University of Norway, 9037 Tromsø, Norway
  • 2Research Centre for Arctic Petroleum Exploration (ARCEx)
  • 3Department of Earth Science, University of Bergen, 5007 Bergen, Norway
  • 4The University Centre in Svalbard (UNIS), 9171 Longyearbyen, Norway

Abstract. Air-coupled flexural waves appear as wave trains of constant frequency that arrive in advance of the direct air-wave from an impulsive source travelling over a floating ice sheet. The frequency of these waves varies with the flexural stiffness of the ice sheet, which is controlled by a combination of thickness and elastic properties. We develop a theoretical framework to understand these waves, utilizing modern numerical and Fourier methods to give a simpler and more accessible description than the pioneering, yet unwieldly analytical efforts of the 1950's. Our favoured dynamical model can be understood in terms of linear filter theory and is closely related to models used to describe the flexural waves produced by moving vehicles on floating plates. We find that air-coupled flexural waves are a robust feature of floating ice-sheets excited by impulsive sources over a large range of thicknesses, and we present a simple closed-form estimator for the ice thickness. Our study is focussed on first-year sea ice of ~20–80 cm thickness in Van Mijenfjorden, Svalbard, that was investigated through active source seismic experiments over four field campaigns in 2013, 2016, 2017 and 2018. The air-coupled flexural frequencies for sea-ice in this thickness range are ~60–240 Hz. While air-coupled flexural waves for thick sea-ice have received little attention, the higher frequencies associated with thin ice on fresh water lakes and rivers are well known to the ice-skating community and have been reported in popular media. Estimation of ice physical properties, following the approach we present, may allow improved surface wave modelling and wavefield subtraction in reflection seismic studies where flexural wave noise is undesirable. On the other hand, air-coupled flexural waves may also permit non-destructive continuous monitoring of ice thickness and flexural stiffness using simple, relatively inexpensive microphones located in the vicinity of the desired measurement location, either above the ice-sheet or along the shoreline. In this case, naturally forming cracks in the ice may be an appropriate impulsive source capable of exciting flexural waves in floating ice sheets in a passive monitoring context.

Rowan Romeyn et al.

Status: open (until 29 Apr 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-71', Ludovic Moreau, 10 Mar 2021 reply
    • AC1: 'Reply on RC1', Rowan Romeyn, 23 Apr 2021 reply
  • RC2: 'Comment on tc-2021-71', Anonymous Referee #2, 09 Apr 2021 reply
    • AC2: 'Reply on RC2', Rowan Romeyn, 23 Apr 2021 reply

Rowan Romeyn et al.

Rowan Romeyn et al.

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Short summary
Air-coupled flexural waves are produced by the interaction between pressure waves in air and bending waves in a floating ice sheet. The frequency of these waves is related to the physical properties of the ice sheet, specifically its thickness and rigidity. We demonstrate the usefulness of air-coupled flexural waves for estimating ice physical properties and give a theoretical description of the governing physics that highlights their similarity to related phenomena in other fields.