Snow scattering signals in ground‐based passive microwave radiometer measurements
Snow scattering signals in ground‐based passive microwave radiometer measurements
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地面无源微波辐射计测量中的雪散射信号
DOI：
10.1029/2010jd013856
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
D. Siebler
中科院分区：
文献类型：
--
作者：
Kneifel;U. Löhnert;A. Battaglia;S. Crewell;D. Siebler
本文研究了积雪微物理参数对地基被动微波亮度温度（TB）测量增强的影响。除了20 - 150 GHz的多光谱无源微波观测外，作为2008-2009年冬季“基于最优估计的降雪表征算法”活动的一部分，在平均海平面2650米的高山环境中，部署了一台35 GHz云雷达和一台2 - D视频测距仪，用于现场测量降雪。这些观测与附近的无线电探空仪上升和地面标准气象测量相结合，重建大气状态（即温度、湿度、雪和液态水含量场），并随后用作微波辐射传输（RT）模型的输入。研究了雪形和雪粒度分布信息缺失对微波TB测量结果的敏感性，并将disrometer数据作为粗略约束。对于一个扩展的案例研究，我们发现90 GHz和150 GHz的TBs由于雪晶表面辐射的散射而显著增强，并且这种增强与雷达导出的雪水路径（SWP < 0.2 kg m−2）明显相关。RT模拟显示，云中液态水的垂直分布（液态水路径LWP < 0.1 kg m−2）对TB的影响较大，在极端情况下，可以完全遮蔽雪散射信号。同样量级的TB变化也可能是由固态硬盘参数和颗粒形状的典型变化引起的，这与太空研究获得的结果相似。地面站结合主动和被动微波观测的基础设施能力，有可能解决不同雪形、SSD和SWP对积雪检索的影响，从而支持当前和未来的卫星任务。
This paper investigates the influence of snow microphysical parameters on the enhancement of ground‐based passive microwave brightness temperature (TB) measurements. In addition to multispectral passive microwave observations between 20 and 150 GHz, a 35 GHz cloud radar and a 2‐D video disdrometer for in situ measurements of snowfall were deployed as part of the “towards an optimal estimation‐based snowfall characterization algorithm” campaign in the winter season of 2008–2009 at an Alpine environment located at 2650 m mean sea level. These observations are combined with nearby radiosonde ascents and surface standard meteorological measurements to reconstruct the atmospheric state (i.e., fields of temperature, humidity, snow, and liquid water contents) and are subsequently used as input for a microwave radiative transfer (RT) model. We investigate the sensitivity of the missing information about snow shape and snow particle size distribution (SSD) on the microwave TB measurements using the disdrometer data as a rough constraint. For an extended case study, we found that TBs at 90 and 150 GHz are significantly enhanced because of scattering of surface radiation at snow crystals and that this enhancement is clearly correlated with the radar derived snow water path (SWP < 0.2 kg m−2). RT simulations highlight the strong influence of the vertical distribution of cloud liquid water (liquid water path LWP < 0.1 kg m−2) on the TB, which in extreme cases, can fully obscure the snow scattering signal. TB variations of the same magnitude can also be caused by typical variations in SSD parameters and particle shape similar to results obtained by space‐borne studies. Ground‐based stations with their infrastructural capabilities in combining active and passive microwave observations have the potential to disentangle the influences of different snow shape, SSD, and SWP in snow retrievals, thus supporting current and future satellite missions.
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