Snow grain-size profiles deduced from microwave snow emissivities in Antarctica
Snow grain-size profiles deduced from microwave snow emissivities in Antarctica
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DOI：
10.3189/002214310792447806
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发表时间：
2010-08
影响因子：
3.4
通讯作者：
L. Brucker;G. Picard;M. Fily
中科院分区：
文献类型：
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作者：
L. Brucker;G. Picard;M. Fily
摘要星载微波辐射计是观测南极气候的一种有吸引力的工具，因为它们的测量与雪温有关。然而，从微波发射到雪温度的转换并不简单，并且强烈依赖于雪的发射率特性。在预测南极条件下的雪的特性概况方面的困难是从微波辐射计中检索准确气候信息的主要瓶颈。我们试图解释在19.3和37 GHz的垂直偏振发射率来自特殊传感器微波/成像仪（SSM/I）获得的亮度温度和物理温度从ERA-40再分析。在南极洲，雪在19.3和37千兆赫的发射率几乎相等，但随着频率的下降，预计。为了解释这一点，我们考虑各种配置文件的雪颗粒的大小和密度，并预测其发射率使用稠密介质辐射传输（DMRT）模型。结果表明，发射率不能用恒定的晶粒尺寸和密度分布来解释。需要考虑异质积雪。我们首先测试雪密度和颗粒半径随深度的随机变化，然后在雪粒半径的单调和连续的变化。在这两种情况下，我们表明，整体增加的雪粒半径与深度相匹配，在南极洲观测到的发射率。此外，两个参数表征雪粒剖面检索和比较（1）在南极洲东部不同地点的粒度现场测量，（2）粒度估计使用可见光星载辐射计和（3）颗粒生长的半经验关系。
Abstract Spaceborne microwave radiometers are an attractive tool for observing Antarctic climate because their measurements are related to the snow temperature. However, the conversion from microwave emission to snow temperature is not simple and strongly depends on the emissivity through snow properties. This difficulty in predicting the snow property profile for Antarctic conditions is the main bottleneck in the retrieval of accurate climate information from microwave radiometers. We attempt to explain the vertically polarized emissivity at 19.3 and 37 GHz derived from brightness temperatures acquired by the Special Sensor Microwave/Imager (SSM/I) and physical temperature from the ERA-40 re-analysis. In Antarctica the snow emissivities at 19.3 and 37 GHz are nearly equal, although a decrease with frequency is expected. To explain this, we consider various profiles of snow grain size and density and predict their emissivity using a dense-medium radiative transfer (DMRT) model. The results show that the emissivities cannot be explained by constant profiles of grain size and density. Heterogeneous snowpacks need to be considered. We first test random variations of snow density and grain radius with depth and then monotonic and continuous variations in the snow grain radius. In both cases, we show that an overall increase of the snow grain radius with depth is required to match the observed emissivity in Antarctica. In addition, two parameters characterizing the snow grain profiles are retrieved and compared with (1) in situ measurements of grain size at various locations in East Antarctica, (2) grain size estimated using visible spaceborne radiometers and (3) a semi-empirical relationship for grain growth.