Monitoring ice thickness and elastic properties from the measurement of leaky guided waves: A laboratory experiment

Abstract

The decline of Arctic sea ice extent is one of the most spectacular signatures of global warming, and studies converge to show that this decline has been accelerating over the last four decades, with a rate that is not reproduced by climate models. To improve these models, relying on comprehensive and accurate field data is essential. While sea ice extent and concentration are accurately monitored from microwave imagery, an accurate measure of its thickness is still lacking. Moreover, measuring observables related to the mechanical behavior of the ice (such as Young's modulus, Poisson's ratio, etc.) could provide better insights in the understanding of sea ice decline, by completing current knowledge so far acquired mostly from radar and sonar data. This paper aims at demonstrating on the laboratory scale that these can all be estimated simultaneously by measuring seismic waves guided in the ice layer. The experiment consisted of leaving a water tank in a cold room in order to grow an ice layer at its surface. While its thickness was increasing, ultrasonic guided waves were generated with a piezoelectric source, and measurements were subsequently inverted to infer the thickness and mechanical properties of the ice with very good accuracy.

Micro‐Seismic Monitoring of a Shear Fault Within a Floating Ice Plate

“…In a previous experimental work on wave propagation modes, using the very same set‐up and accelerometers, we demonstrated that QS0 and QA0 modes are found as expected, on top of a slower Stoneley (or quasi‐Scholte) mode propagating along the ice‐water surface (Moreau et al, ). The SH mode was absent likely because we recorded the vertical acceleration only.…”

“…In addition to the work done by Moreau et al (), new experiments were conducted to characterize the propagation velocities and the attenuation of these modes for the specific needs of the present study. Accelerometers were linearly arranged and spaced by 5cm away from each other.…”

Sea Ice Thickness and Elastic Properties From the Analysis of Multimodal Guided Wave Propagation Measured With a Passive Seismic Array

“…The present paper follows up on our work initiated at the laboratory scale to infer the thickness and mechanical properties of the ice from the observation of guided wave modes (Moreau, Lachaud et al, ). In a layer of ice floating on water, the wavefield is composed of modes that are of the same nature as those that propagate in a stress‐free plate, that is, the Lamb wave modes and the guided shear‐horizontal (SH) wave modes.…”

“…For higher values, the approximation no longer holds, and the dispersion branch of the QS mode starts to deviate from that of the flexural wave (Figure b). If frequency‐thickness is increased further, the energy on the vertical component of the displacement becomes progressively dominated by the QA 0 mode, the QS 0 mode becomes dispersive, and higher‐order modes become propagative (Moreau, Lachaud et al, ).…”

Wave‐Equation Dispersion Inversion of Guided P Waves in a Waveguide of Arbitrary Geometry

“…The general characteristics of guided P waves are similar to surface waves where the propagating waves are dispersive and their geometrical spreading behaves as O(r −1∕2 ). There are many applications of guided waves in seismology such as imaging low-velocity faulted-zone layers (Y. G. Li et al, 1999Li et al, , 2000, nondestructive evaluation and medical imaging with ultrasonic waves (Bochud et al, 2018;Moreau et al, 2017). The much slower arrivals in Figure 1a are the Rayleigh surface waves denoted as SW and propagate according to the S velocity of the associated layers.…”