Sea-ice thickness measurement based on the dispersion of ice swell

Abstract

The dispersion of flexural waves propagating in the Arctic sea ice cover is exploited in order to locally measure the ice thickness. The observed dispersion, for waves filtered in the 4-20 s period interval, at up to 4 broad-band seismometers deployed in Spring 2007 near the North Pole, is compared to a parameterized model that accounts for a complex wavefield made of a superposition of independent plane waves with different amplitudes and back-azimuth angles. The parameterization, that includes finding the best modeled ice thickness, is performed by using the cross-correlation functions between the seismometers. The ice thickness is estimated to 2.5 ± 0.2 m for the ~1 km-large floe the seismic stations were deployed on, which is coherent with other, independent measurements at this site. This study thus demonstrates the feasibility of using broad-band seismometers deployed on the sea-ice in order to passively measure the ice thickness, without requiring active sources nor human intervention.

Observations of wave dispersion and attenuation in landfast ice

“…In the absence of high resolution space and time observations to directly calculate the wavenumber and frequency, the dispersion relation can be inferred from correlating signals between adjacent sensors [ Fox and Haskell , ; Marsan et al ., ] or by a single wave buoy measurement by comparing the PSD from the heave with the PSDs from the pitch and roll [ Longuet‐Higgins et al ., ; Long , ; Kuik et al ., ], where and S r ( f ) are the PSDs from the heave, pitch and roll respectively. In practice, (3) is not an ideal method for measuring the dispersion relation as the precise response of the measuring system, which includes the coupling of the measuring device with the media as well as the temporal response of the heave, pitch and roll sensors, must be accurately known [ Longuet‐Higgins et al ., ].…”

“…The difference can easily be spotted with a continuous spectrum from the slope in , but if discrete frequencies were analyzed, such as in Marsan et al . [], care must be taken to avoid ambiguities which could arise.…”

“…The discrepancy between the measured ice thickness and that inferred from wave propagation was assumed to arise from an omnidirectional swell spectrum and Marsan et al . [] obtained a more consistent estimate of the ice thickness using an inversion technique with a variable wave direction. Since ocean swell was the dominant source for wave motion there were large errors and low correlations in the high frequency band, especially for the 0.14 and 0.25 Hz frequencies.…”

Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

“…Seismometers installed on sea ice have allowed high-frequency monitoring of sea ice fracturing and faulting. The propagation speed of seismic waves has been found to depend on ice thickness, allowing a novel method to estimate the latter on a regional scale (Marsan et al, 2012). Seismic observations also allow for complementing satellite measurements by providing a much more detailed temporal sampling and therefore a better characterization of sea ice fracturing processes.…”

Under-ice ambient noise in Eastern Beaufort Sea, Canadian Arctic, and its relation to environmental forcing

“…The Arctic Ocean is entirely covered with ice of variable thickness and age during winter (Marsan et al, 2004;Maslanik et al, 2011;Marsan et al, 2012;Stroeve et al, 2012). The seasonal extent and the ice thickness of this polar ice cap is changing rapidly in response to global warming (Polyak et al, 2010;Stroeve et al, 2012;Wadhams, 2012).…”