Simultaneous Retrieval of Surface Roughness Parameters for Bare Soils From Combined Active–Passive Microwave SMAP Observations
Simultaneous Retrieval of Surface Roughness Parameters for Bare Soils From Combined Active–Passive Microwave SMAP Observations
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DOI：
10.1109/tgrs.2020.3035204
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发表时间：
2021-10
影响因子：
8.2
通讯作者：
Anke Fluhrer;T. Jagdhuber;R. Akbar;P. O’neill;D. Entekhabi
中科院分区：
文献类型：
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作者：
Anke Fluhrer;T. Jagdhuber;R. Akbar;P. O’neill;D. Entekhabi
提出了一种同时确定裸地土壤表面粗糙度参数[垂直均方根（RMS）高度（${s}$）和水平相关长度（${l}$）]的主-被动微波检索算法。该算法基于主-被动微波共变，包括改进的积分方程法（I2EM），并利用全球土壤湿度主-被动（SMAP）观测数据进行了验证。${s}$和${l}$的估计检索结果与文献值总体一致，表明本文算法的有效性。灵敏度分析表明，所开发的粗糙度检索算法与${\varepsilon}_{s} > 10$[-]的介电常数无关。此外，该方法的物理模型基础（I2EM）允许应用不同的自相关函数（ACF），如高斯和指数ACF。全球粗糙度检索结果证实了撒哈拉或戈壁等沙漠的光秃秃的区域。然而，在粗糙度参数估计中使用的ACF类型很重要。高斯ACF的检索结果比指数ACF的检索结果描述了一个更粗糙的表面。粗糙度结果与降水量或土壤质地之间没有相关性，这可能是由于SMAP数据的空间分辨率较粗。计划将这种方法扩展到植被土壤中，作为一项附加研究。
An active–passive microwave retrieval algorithm for simultaneous determination of soil surface roughness parameters [vertical root-mean-square (RMS) height ( ${s}$ ) and horizontal correlation length ( ${l}$ )] is presented for bare soils. The algorithm is based on active–passive microwave covariation, including the improved Integral Equation Method (I2EM), and is tested with global soil moisture active passive (SMAP) observations. The estimated retrieval results for ${s}$ and ${l}$ are overall consistent with values in the literature, indicating the validity of the proposed algorithm. Sensitivity analyses showed that the developed roughness retrieval algorithm is independent of permittivity for ${\varepsilon }_{s} > 10$ [-]. Furthermore, the physical model basis of this approach (I2EM) allows the application of different autocorrelation functions (ACF), such as Gaussian and exponential ACFs. Global roughness retrieval results confirm bare areas in deserts such as Sahara or Gobi. However, the type of ACF used within roughness parameter estimation is important. Retrieval results for the Gaussian ACF describe a rougher surface than retrieval results for the exponential ACF. No correlations were found between roughness results and the amount of precipitation or the soil texture, which could be due to the coarse spatial resolution of the SMAP data. The extension of this approach to vegetated soils is planned as an add-on study.