ABSTRACT Surface roughness of sea ice is primary information for understanding sea ice dynamics and air–ice–ocean interactions. Synthetic aperture radar (SAR) is a powerful tool for investigating sea ice surface roughness owing to the high sensitivity of its signal to surface structures. In this study, we explored the surface roughness signatures of the summer Arctic snow-covered first-year sea ice in X-band dual-polarimetric SAR in terms of the root mean square (RMS) height. Two ice campaigns were conducted for the first-year sea ice with dry snow cover in the marginal ice zone of the Chukchi Sea in August 2017 and August 2018, from which high-resolution (4 cm) digital surface models (DSMs) of the sea ice were derived with the help of a terrestrial laser scanner to obtain the in situ RMS height. X-band dual-polarimetric (HH and VV) SAR data (3 m spatial resolution) were obtained for the 2017 campaign, at a high incidence angle (49.5°) of TerraSAR-X, and for the 2018 campaign, at a mid-incidence angle (36.1°) of TanDEM-X 1–2 days after the acquisition of the DSMs. The sea ice drifted during the time between the SAR and DSM acquisitions. As it is difficult to directly co-register the DSM to SAR owing to the difference in spatial resolution, the two datasets were geometrically matched using unmanned aerial vehicle (4 cm resolution) and helicopter-borne (30 cm resolution) photographs acquired as part of the ice campaigns. A total of five dual-polarimetric SAR features―backscattering coefficients at HH and VV polarizations, co-polarization ratio, co-polarization phase difference, and co-polarization correlation coefficient ―were computed from the dual-polarimetric SAR data and compared to the RMS height of the sea ice, which showed macroscale surface roughness. All the SAR features obtained at the high incidence angle were statistically weakly correlated with the RMS height of the sea ice, possibly influenced by the low backscattering close to the noise level that is attributed to the high incidence angle. The SAR features at the mid-incidence angle showed a statistically significant correlation with the RMS height of the sea ice, with Spearman’s correlation coefficient being higher than 0.7, except for the co-polarization ratio. Among the intensity-based and polarimetry-based SAR features, HH-polarized backscattering and co-polarization phase difference were analyzed to be the most sensitive to the macroscale RMS height of the sea ice. Our results show that the X-band dual-polarimetric SAR at mid-incidence angle exhibits potential for estimation of the macroscale surface roughness of the first-year sea ice with dry snow cover in summer.

中文翻译：

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X波段双极化SAR夏季北极积雪海冰表面粗糙度特征

摘要 海冰表面粗糙度是了解海冰动力学和空气-冰-海洋相互作用的主要信息。合成孔径雷达（SAR）由于其信号对表面结构的高度敏感性而成为研究海冰表面粗糙度的有力工具。在这项研究中，我们根据均方根 (RMS) 高度探索了 X 波段双极化 SAR 中夏季北极积雪第一年海冰的表面粗糙度特征。2017 年 8 月和 2018 年 8 月，针对楚科奇海边缘冰区干雪覆盖的第一年海冰开展了两次冰活动，从中获得了高分辨率（4 cm）的海洋数字表面模型（DSMs）冰是在地面激光扫描仪的帮助下获得的，以获得原位 RMS 高度。X 波段双极化（HH 和 VV）SAR 数据（3 m 空间分辨率）是在 TerraSAR-X 的高入射角（49.5°）下获得的 2017 年运动和 2018 年运动中的获得 DSM 后 1-2 天 TanDEM-X 的入射角 (36.1°)。海冰在 SAR 和 DSM 获取之间的时间内漂移。由于空间分辨率的差异，很难将 DSM 直接配准到 SAR，因此使用无人机（4 cm 分辨率）和直升机（30 cm 分辨率）照片对这两个数据集进行几何匹配，作为冰运动。共 5 个双极化 SAR 特征——HH 和 VV 极化的后向散射系数、共极化比、共极化相位差、和共极化相关系数——是根据双极化 SAR 数据计算的，并与海冰的 RMS 高度进行比较，显示了宏观表面粗糙度。在高入射角获得的所有 SAR 特征在统计上与海冰的 RMS 高度相关性较弱，这可能受到由于高入射角导致的接近噪声水平的低反向散射的影响。中入射角的 SAR 特征与海冰的 RMS 高度具有统计学上的显着相关性，Spearman 相关系数高于 0.7，除共极化比外。在基于强度和基于极化的 SAR 特征中，HH 偏振反向散射和共偏振相位差被分析为对海冰的宏观尺度 RMS 高度最敏感。我们的结果表明，中入射角的 X 波段双极化 SAR 具有估计夏季干雪覆盖的第一年海冰的宏观表面粗糙度的潜力。