Polar firn properties in Greenland and Antarctica and related effects on microwave brightness temperatures
Polar firn properties in Greenland and Antarctica and related effects on microwave brightness temperatures
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格陵兰岛和南极洲的极地雪特性及其对微波亮温的相关影响
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发表时间：
2023
期刊：
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通讯作者：
L. Kaleschke
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作者：
Haokui;Xu;Brooke;Medley;Leung;Tsang;Joel;T.;Johnson;Kenneth;C.;Jezek;Macro Brogioni;L. Kaleschke
抽象的。在研究极地冰盖的质量平衡时，地表附近积雪密度的波动是一个主要的不确定因素。在本文中，我们探讨这些变化的位置上的格陵兰冰盖和南极洲的圆顶C位置。钻孔原位测量，雪雷达回波，微波亮度温度，并从社区Firn模型（CFM）的建模结果。结果表明，积雪密度剖面可以用三个过程来表示：“长尺度”和“短尺度”的密度变化和“再冻结层”。2017年在格陵兰岛进行的测量中，在机载0.5-2 GHz亮温和雪雷达回波峰值的动态范围内观察到了与这一描述一致的情况。基于这些见解，一个新的分析部分相干模型来解释微波亮度温度使用的三尺度描述的积雪。短期和长期规模的积雪过程建模为一个三维连续随机介质与有限的垂直和水平相关长度，而不是过去的一维随机分层介质的描述。再冻层被描述为具有平面界面的确定性片材，再冻层界面的数量由雷达观测确定。雪密度和相关长度参数用于正演模拟，以匹配测量的0.5-2 GHz的亮度温度在格陵兰岛的CFM预测与类似的参数的一致性。模型预测也是在良好的协议与多角度1.4千兆赫垂直和水平极化的亮度温度测量的土壤水分和海洋盐度（SMOS）卫星在圆顶C，南极洲。这项工作表明，共同定位的主动和被动微波测量可以用来推断极地积雪的属性，可以与CFM的预测。特别是，0.5-2 GHz的亮度温度测量被证明是敏感的长期规模的积雪密度波动的密度标准偏差在0.01-0.06 g cm−3和垂直相关长度的范围为6-20 cm。
Abstract. In studying the mass balance of polar ice sheets, fluctuations in firn density near the surface is a major uncertainty. In this paper, we explore these variations at locations on the Greenland Ice Sheet and at the Dome C location in Antarctica. Borehole in situ measurements, snow radar echoes, microwave brightness temperatures, and modeling results from the Community Firn Model (CFM) are used. It is shown that firn density profiles can be represented using three processes: “long-scale” and “short-scale” density variations and “refrozen layers”. Consistency with this description is observed in the dynamic range of airborne 0.5–2 GHz brightness temperatures and snow radar echo peaks in measurements performed in Greenland in 2017. Based on these insights, a new analytical partially coherent model is implemented to explain the microwave brightness temperatures using the three-scale description of the firn. Short- and long-scale firn processes are modeled as a 3D continuous random medium with finite vertical and horizontal correlation lengths as opposed to past 1D randomly layered medium descriptions. Refrozen layers are described as deterministic sheets with planar interfaces, with the number of refrozen-layer interfaces determined by radar observations. Firn density and correlation length parameters used in forward modeling to match measured 0.5–2 GHz brightness temperatures in Greenland show consistency with similar parameters in CFM predictions. Model predictions also are in good agreement with multi-angle 1.4 GHz vertically and horizontally polarized brightness temperature measured by the Soil Moisture and Ocean Salinity (SMOS) satellite at Dome C, Antarctica. This work shows that co-located active and passive microwave measurements can be used to infer polar firn properties that can be compared with predictions of the CFM. In particular, 0.5–2 GHz brightness temperature measurements are shown to be sensitive to long-scale firn density fluctuations with density standard deviations in the range of 0.01–0.06 g cm−3 and vertical correlation lengths of 6–20 cm.