Influence of meter-scale wind-formed features on the variability of the microwave brightness temperature around Dome C in Antarctica
Influence of meter-scale wind-formed features on the variability of the microwave brightness temperature around Dome C in Antarctica
复制标题
米级风形成特征对南极Dome C周围微波亮温变化的影响
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
M. Fily
中科院分区：
文献类型：
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作者：
G. Picard;A. Royer;L. Arnaud;M. Fily
星载无源微波辐射计利用微波辐射对雪的特性的高度敏感性，广泛用于在多雪地区检索信息。对于南极高原，许多研究提出的检索算法或数值模拟都假设，明确或不，亚像素尺度的异质性是可以忽略不计的，检索的属性是代表整个像素。在本文中，我们调查的空间变化的亮温在几公里的范围内的圆顶C区。使用地面辐射计拖曳的车辆，我们收集了亮度温度在11，19和37 GHz的水平和垂直极化沿着断面米的分辨率。最显著的观测结果是一系列规则的信号波动，在37 GHz处的显著幅度达到10 K，准周期为30-50 m。相比之下，在较长的长度尺度的变化似乎是弱的调查区域，和平均亮温接近SSM/I和WindSat卫星观测的所有频率和偏振。为了建立雪的特性和微波发射波动之间的联系，我们收集了详细的雪颗粒大小和密度分布在两个点，观察到相反的亮度温度极值。DMRT-ML微波发射模型的数值模拟表明，在第一米的上部密度的差异解释了大部分的亮度温度变化。此外，我们发现，这些密度的变化接近表面与雪的硬度。成片的硬雪-可能是由风压实形成的-清晰可见，覆盖了多达39%的调查区域。亮温高于正常地区。这一结果意味着卫星在圆顶C上空测量的微波发射比预期的要复杂，很可能取决于两种不同类型雪的逐年面积比例。
Space-borne passive microwave radiometers are widely used to retrieve information in snowy regions by exploiting the high sensitivity of microwave emission to snow properties. For the Antarctic Plateau, many studies presenting retrieval algorithms or numerical simulations have assumed, explicitly or not, that the subpixel-scale heterogeneity is negligible and that the retrieved properties were representative of whole pixels. In this paper, we investigate the spatial variations of brightness temperature over a range of a few kilometers in the Dome C area. Using ground-based radiometers towed by a vehicle, we collected brightness temperature at 11, 19 and 37 GHz at horizontal and vertical polarizations along transects with meter resolution. The most remarkable observation was a series of regular undulations of the signal with a significant amplitude reaching 10 K at 37 GHz and a quasi-period of 30–50 m. In contrast, the variability at longer length scales seemed to be weak in the investigated area, and the mean brightness temperature was close to SSM/I and WindSat satellite observations for all the frequencies and polarizations. To establish a link between the snow characteristics and the microwave emission undulations, we collected detailed snow grain size and density profiles at two points where opposite extrema of brightness temperature were observed. Numerical simulations with the DMRT-ML microwave emission model revealed that the difference in density in the upper first meter explained most of the brightness temperature variations. In addition, we found that these variations of density near the surface were linked to snow hardness. Patches of hard snow – probably formed by wind compaction – were clearly visible and covered as much as 39% of the investigated area. Their brightness temperature was higher than in normal areas. This result implies that the microwave emission measured by satellites over Dome C is more complex than expected and very likely depends on the year-to-year areal proportion of the two different types of snow.