Modeling time series of microwave brightness temperature in Antarctica
Modeling time series of microwave brightness temperature in Antarctica
复制标题
南极洲微波亮温时间序列建模
DOI：
10.3189/002214309788816678
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发表时间：
2009
影响因子：
3.4
通讯作者：
G. Krinner
中科院分区：
文献类型：
--
作者：
G. Picard;L. Brucker;M. Fily;H. Gallee;G. Krinner
本文旨在解释微波亮温的时间变化（在19和37 GHz和垂直和水平极化）在南极洲使用物理为基础的雪动力学和发射模式（SDEM）。SDEM根据广泛可用的地面气象数据（ERA-40再分析）预测大气层顶亮温的时间序列。为此，它依次计算进入积雪的热通量、雪的温度分布、雪发射的微波，最后计算微波通过大气层到达卫星的传播。由于该模型包含多个参数，其值在整个大陆上是可变的和不确定的，因此对每个50 km × 50 km像素的参数值进行优化。模拟结果表明，该模型是不够的，在融化区（其中表面融化发生在每年至少有几天），因为积雪结构及其时间变化太复杂。相比之下，精度是相当不错的，在干燥区和2和4 K之间的变化取决于频率和极化的观测和位置。在南极尺度上，风通常更强的地方误差更大，这表明气象数据在多风地区不太准确，或者一些被忽视的过程（例如风泵，表面冲刷）很重要。在Dome C，在平静的条件下，详细的分析表明，大部分的误差是由于ERA-40的空气温度的不准确性（0.22 K）。最后，本文讨论了优化参数的值及其在整个南极的空间变化。
This paper aims to interpret the temporal variations of microwave brightness temperature (at 19 and 37 GHz and at vertical and horizontal polarizations) in Antarctica using a physically based snow dynamic and emission model (SDEM). SDEM predicts time series of top-of-atmosphere brightness temperature from widely available surface meteorological data (ERA-40 re-analysis). To do so, it successively computes the heat flux incoming the snowpack, the snow temperature profile, the microwaves emitted by the snow and, finally, the propagation of the microwaves through the atmosphere up to the satellite. Since the model contains several parameters whose value is variable and uncertain across the continent, the parameter values are optimized for every 50 km × 50 km pixel. Simulation results show that the model is inadequate in the melt zone (where surface melting occurs on at least a few days a year) because the snowpack structure and its temporal variations are too complex. In contrast, the accuracy is reasonably good in the dry zone and varies between 2 and 4 K depending on the frequency and polarization of observations and on the location. At the Antarctic scale, the error is larger where wind is usually stronger, suggesting either that meteorological data are less accurate in windy regions or that some neglected processes (e.g. windpumping, surface scouring) are important. At Dome C, in calm conditions, a detailed analysis shows that most of the error is due to inaccuracy of the ERA-40 air temperature (∼2 K). Finally, the paper discusses the values of the optimized parameters and their spatial variations across the Antarctic.