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Implications of surface flooding on airborne estimates of snow depth on sea ice

机译:地表洪水对海冰雪深空估计的影响

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Snow depth observations from airborne snow radars, such as the NASA's Operation IceBridge (OIB) mission, have recently been used in altimeter-derived sea ice thickness estimates, as well as for model parameterization. A number of validation studies comparing airborne and in situ snow depth measurements have been conducted in the western Arctic Ocean, demonstrating the utility of the airborne data. However, there have been no validation studies in the Atlantic sector of the Arctic. Recent observations in this region suggest a significant and predominant shift towards a snow-ice regime caused by deep snow on thin sea ice. During the Norwegian young sea Ice, Climate and Ecosystems (ICE) expedition (N-ICE2015) in the area north of Svalbard, a validation study was conducted on 19?March?2015. This study collected ground truth data during an OIB overflight. Snow and ice thickness measurements were obtained across a two-dimensional (2-D) 400?m? × ?60?m grid. Additional snow and ice thickness measurements collected in situ from adjacent ice floes helped to place the measurements obtained at the gridded survey field site into a more regional context. Widespread negative freeboards and flooding of the snowpack were observed during the N-ICE2015 expedition due to the general situation of thick snow on relatively thin sea ice. These conditions caused brine wicking into and saturation of the basal snow layers. This causes the airborne radar signal to undergo more diffuse scattering, resulting in the location of the radar main scattering horizon being detected well above the snow–ice interface. This leads to a subsequent underestimation of snow depth; if only radar-based information is used, the average airborne snow depth was 0.16?m thinner than that measured in situ at the 2-D survey field. Regional data within 10?km of the 2-D survey field suggested however a smaller deviation between average airborne and in situ snow depth, a 0.06?m underestimate in snow depth by the airborne radar, which is close to the resolution limit of the OIB snow radar system. Our results also show a broad snow depth distribution, indicating a large spatial variability in snow across the region. Differences between the airborne snow radar and in situ measurements fell within the standard deviation of the in situ data (0.15–0.18?m). Our results suggest that seawater flooding of the snow–ice interface leads to underestimations of snow depth or overestimations of sea ice freeboard measured from radar altimetry, in turn impacting the accuracy of sea ice thickness estimates.
机译:空中雪雷达的雪深度观测,例如NASA的操作冰桥(OIB)使命,最近用于高度计衍生的海冰厚度估计,以及模型参数化。在西北海洋中进行了一些比较空中和原位雪深度测量的验证研究,展示了空中数据的效用。然而,北极地区没有验证研究。最近在该地区的观察结果表明,朝着薄海冰深雪引起的雪地政权的显着和主要的转变。在挪威年轻的海冰,气候和生态系统(ICE)探险(N-ICE2015)在斯瓦尔巴特北部的地区,验证研究于19岁?3月份进行了2015年。这项研究在OIB过天空中收集了地面真理数据。在二维(2-D)400℃下获得雪和冰厚度测量值? ×?60?M网格。额外的冰雪和冰厚度测量从相邻的冰浮炉收集,有助于将在网格调查现场获得的测量放入更大的区域背景下。由于相对薄的海冰上厚雪的一般情况,在N-ICE2015探险期间观察到广泛的阴性收割机和洪水的洪水。这些条件引起了基础雪层的盐水污渍和饱和度。这导致机载雷达信号经历更多的漫射散射,从而导致雷达主散射地平线的位置远低于冰雪界面。这导致随后低估了雪深;如果仅使用基于雷达的信息,则平均空气雪深度比在2-D测量领域的原位测量的平均空气雪雪深度为0.16Ωm。在2-D调查领域的10千米内的区域数据表明,平均空气传播和原位雪深度之间的差异较小,在空中雷达中低估了雪深度的0.06?米,接近OIB的分辨率限制雪雷达系统。我们的结果还显示出广阔的雪深度分布,表明整个地区的雪中的巨大空间变异性。空中雪雷达与原位测量之间的差异落入原位数据的标准偏差范围内(0.15-0.18米)。我们的研究结果表明,雪地冰界面的海水洪水导致从雷达高度测量的雪冰干舷减少雪地深层或高估,反过来影响海冰厚度估计的准确性。

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