Uncertainties in retrieved ice thickness from freeboard measurements due to surface melting
Uncertainties in retrieved ice thickness from freeboard measurements due to surface melting
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DOI：
10.3189/2014aog66a188
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发表时间：
2014
影响因子：
2.9
通讯作者：
P. Lu;Zhijun Li
中科院分区：
文献类型：
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作者：
P. Lu;Zhijun Li
摘要 机载和星载冰干舷遥感为反演极地海洋冰厚度提供了良好的方法。然而，其准确性受到改变浮冰流体静力学平衡的因素的高度限制，例如积雪和融化的池塘会改变冰体积的表面载荷。与对雪荷载的大量研究相反，人们很少关注融雪池的作用，部分原因是融雪季节干舷测量的困难。为了帮助填补这一空白，并为未来能够获取具有融化表面的冰干舷的可能仪器和算法提供基础，开发了一个理论模型来研究由于表面融化而导致的冰厚度反演的不确定性。首先，将冰厚与干舷、积雪深度、融池大小以及雪、冰和水的密度相关，然后进行敏感性分析，研究融池形态的影响。结果表明，融化的冰的平均厚度比没有融化表面的冰低得多，尽管干舷相同，因为融化导致浮冰重量损失。在池塘演化过程中，当池塘在垂直尺度上加深时，浮冰的重量会增加，但当池塘在水平尺度上扩大时，浮冰的重量会减轻，导致平均冰厚度随着池塘深度和分数的减小而增加。研究发现，干舷是第一年冰（FYI）反演厚度不确定性的主要来源，而多年冰（MYI）的情况则是冰密度。 FYI 的冰吃水与干舷的比率范围为 3.0 至 6.2，MYI 的冰吃水与干舷的比率范围为 2.0 至 4.1，与融化季节的现场观察结果一致。
Abstract Airborne and spaceborne remote sensing of ice freeboard offers a good method of retrieving ice thickness in the polar oceans. However, its accuracy is highly limited by the factors altering the hydrostatic equilibrium of ice floes, such as snow cover and melt ponds which change the surface loading on the ice volume. In contrast to the abundant studies on snow loads, little attention has been paid to the role of melt ponds, partly owing to the difficulties of freeboard measurements during the melt season. To help fill this gap and provide a basis for possible instruments and algorithms being able to access ice freeboard with melting surface in future, a theoretical model was developed to investigate the uncertainty in ice thickness retrieval due to surface melting. First, the ice thickness was related to the freeboard, snow depth, melt pond size and densities of snow, ice and water, and then a sensitivity analysis was carried out to study the influence of melt pond morphology. The results show that melting ice has a much lower mean thickness than ice without a melting surface, although with the same freeboard because of a loss of floe weight due to melting. During pond evolution, a floe gains weight when ponds deepen on the vertical scale, but loses weight when they widen on the horizontal scale, resulting in increasing mean ice thickness with decreasing pond depth and fraction. Freeboard is found to be the major source of uncertainty in the retrieved thickness of first-year ice (FYI), while it is ice density in the case of multi-year ice (MYI). The ratio of ice draft to freeboard ranges from 3.0 to 6.2 for FYI and 2.0 to 4.1 for MYI, agreeing with field observations during melting seasons.