The b-factor as a function of frequency and canopy type at H-polarization
The b-factor as a function of frequency and canopy type at H-polarization
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DOI：
10.1109/tgrs.2003.821889
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发表时间：
2004-04
影响因子：
8.2
通讯作者：
A. V. D. Griend;J. Wigneron
中科院分区：
文献类型：
--
作者：
A. V. D. Griend;J. Wigneron
为了使土壤水分和海洋盐度使命中的L波段辐射计与诸如高级微波扫描辐射计（AMSR）（C波段）等高频微波辐射计预期的协同增效方法，对植被光学厚度与辐射强度之间的线性关系的频率依赖性进行了重新分析。（/spl tau//sub o/）和植被含水量（W），由/spl tau//sub o/=B/spl middot/W给出。深入了解频率依赖性的b-因子是重要的检索从双或多频微波亮温观测从空间植被覆盖的地区，使用模型反演技术的表面水分。文献中提供的b值基于不同的方法和途径。因此，直接比较并不简单，需要进行批判性分析。本文证实了当考虑大频域时，b因子与波长的功率成反比B=c/（/spl λ/）/sup x/，这与理论上的考虑是一致的。结果发现，不同的林冠类型可以分成不同的组，每组具有不同的log（c）和x值组合，其特征是线性关系log（B）=log（c）-x/spl middot/log（/spl lambda/）。比率B/sub C//B/sub L/（C和L分别表示C带和L带）的比较也导致基本相同的组。
For anticipated synergistic approaches of the L-band radiometer on the Soil Moisture and Ocean Salinity (SMOS) mission with higher frequency microwave radiometers such as the Advanced Microwave Scanning Radiometer (AMSR) (C-band), a reanalysis has been performed on the frequency dependence of the linear relationship between vegetation optical depth (/spl tau//sub o/) and vegetation water content (W), given by /spl tau//sub o/=b/spl middot/W. Insight into the frequency dependence of the b-factor is important for the retrieval of surface moisture from dual- or multifrequency microwave brightness temperature observations from space over vegetation-covered regions using model inversion techniques. The b-values presented in the literature are based on different methods and approaches. Therefore, a direct comparison is not straightforward and requires a critical analysis. This paper confirms that when a large frequency domain is considered, the b-factor is inversely proportional to the power of the wavelength b=c/(/spl lambda/)/sup x/, which is in line with theoretical considerations. It was found that different canopy types could be separated into different groups, each with a different combination of values for log(c) and x, which characterize the linearized relationship log(b)=log(c)-x/spl middot/log(/spl lambda/). A comparison of ratios b/sub C//b/sub L/ (with C and L denoting C- and L-band, respectively) also resulted in basically the same groups.