Spectral attenuation of ocean waves in pack ice and its application in calibrating viscoelastic wave-in-ice models

Abstract. We investigate a case of ocean waves through a pack ice cover captured by Sentinel-1A synthetic aperture radar (SAR) on 12 October 2015 in the Beaufort Sea. The study domain is 400 km by 300 km, adjacent to a marginal ice zone (MIZ). The wave spectra in this domain were reported in a previous study (Stopa et al., 2018b). In that study, the authors divided the domain into two regions delineated by the first appearance of leads (FAL) and reported a clear change of wave attenuation of the total energy between the two regions. In the present study, we use the same dataset to study the spectral attenuation in the domain. According to the quality of SAR-retrieved wave spectrum, we focus on a range of wave numbers corresponding to 9–15 s waves from the open-water dispersion relation. We first determine the apparent attenuation rates of each wave number by pairing the wave spectra from different locations. These attenuation rates slightly increase with increasing wave number before the FAL and become lower and more uniform against wave number in thicker ice after the FAL. The spectral attenuation due to the ice effect is then extracted from the measured apparent attenuation and used to calibrate two viscoelastic wave-in-ice models. For the Wang and Shen (2010b) model, the calibrated equivalent shear modulus and viscosity of the pack ice are roughly 1 order of magnitude greater than that in grease and pancake ice reported in Cheng et al. (2017). These parameters obtained for the extended Fox and Squire model are much greater, as found in Mosig et al. (2015) using data from the Antarctic MIZ. This study shows a promising way of using remote-sensing data with large spatial coverage to conduct model calibration for various types of ice cover.Highlights. Three key points: The spatial distribution of wave number and spectral attenuation in pack ice are analyzed from SAR-retrieved surface wave spectra. The spectral attenuation rate of 9–15 s waves varies around 10−5 m2 s−1, with lower values in thicker semicontinuous ice fields with leads. The calibrated viscoelastic parameters are greater than those found in pancake ice.

摘要。我们研究了2015年10月12日 Sentinel - 1A合成孔径雷达（SAR）在波弗特海拍摄到的一个穿过浮冰覆盖层的海浪案例。研究区域为400千米×300千米，毗邻边缘冰区（MIZ）。该区域的波谱在先前的一项研究（斯托帕等人，2018b）中已有报道。在那项研究中，作者根据首次出现的水道（FAL）将该区域划分为两个区域，并报告了两个区域之间总能量的波衰减有明显变化。在本研究中，我们使用相同的数据集来研究该区域内的频谱衰减。根据SAR反演波谱的质量，我们依据开阔水域频散关系，聚焦于对应9 - 15秒波的波数范围。我们首先通过将不同位置的波谱配对来确定每个波数的表观衰减率。在FAL之前，这些衰减率随波数增加而略有增加，在FAL之后，在较厚的冰层中，衰减率随波数降低且更加均匀。然后从测量到的表观衰减中提取由于冰的影响而产生的频谱衰减，并用于校准两个粘弹性冰中波模型。对于王和沈（2010b）模型，校准后的浮冰等效剪切模量和粘度大约比程等人（2017）报道的油脂状冰和饼状冰中的数值大1个数量级。为扩展的福克斯和斯夸尔模型获得的这些参数要大得多，正如莫西格等人（2015）使用南极边缘冰区的数据所发现的那样。这项研究展示了一种利用具有大空间覆盖范围的遥感数据对各种类型的冰盖进行模型校准的有前景的方法。 亮点。三个关键点：从SAR反演的表面波谱分析了浮冰中波数和频谱衰减的空间分布。9 - 15秒波的频谱衰减率在10⁻⁵平方米·秒⁻¹左右变化，在有航道的较厚半连续冰原中数值较低。校准后的粘弹性参数大于在饼状冰中发现的参数。