Using a Discrete Scattering Model to Constrain Water Cloud Model for Simulating Ground-Based Scatterometer Measurements and Retrieving Soil Moisture
Using a Discrete Scattering Model to Constrain Water Cloud Model for Simulating Ground-Based Scatterometer Measurements and Retrieving Soil Moisture
复制标题
使用离散散射模型约束水云模型来模拟地基散射计测量并反演土壤湿度
DOI：
10.1109/jstars.2021.3111606
复制
发表时间：
2021
影响因子：
5.5
通讯作者：
van der Velde Rogier
中科院分区：
文献类型：
--
作者：
Bai Xiaojing;Zheng Donghai;Wen Jun;Wang Xin;van der Velde Rogier
用基于物理的散射模型模拟来约束半经验模型的潜力早已被认识到。这项研究通过评估后向散射系数(σo)模拟和在冻土和融化土壤条件下使用离散散射模型(即Tor Vergata)约束的水云模型来反演土壤水分。WCM分别与OH(以下简称WCM+OH)和Dubois(WCM+Dubois)表面散射模型耦合。利用四相介质混合模型得到了土壤的介电常数。部署在季节性冻结的西藏草甸生态系统中的地面散射计收集了一年的C波段共振σo观测数据。结果表明：经校正的Tor Vergata(以下简称“TVG”)模式较好地模拟了散射计测量的季节动态和量级，模拟的散射分量和植被透射率与季节植被动态一致；约束Tor Vergata模式模拟的总散射与散射计测量结果具有较好的一致性，模拟的土壤和植被散射分量与TVG模拟结果一致；基于约束WCMS的土壤水分反演值较好地反映了现场观测的季节变化。实验结果表明，校正后的WCMS与校正后的TVG模型和约束条件下的WCMS在总σo和土壤水分的反演结果上具有可比性。然而，WCMS的直接定标导致了对单个土壤和植被散射贡献的不切实际的描述，其中最显著的是低估了VV极化下的植被贡献。
Potential of constraining semiempirical model with physically based scatter model simulations has long been recognized. This study contributes to this topic through the assessment of backscattering coefficient (σo) simulations and soil moisture retrieval using the water cloud model (WCM) constrained by a discrete scattering model (i.e., Tor Vergata) under both frozen and thawed soil conditions. The WCM is coupled with Oh (hereafter “WCM+Oh”) and Dubois (WCM+Dubois) surface scattering models, respectively. The soil permittivity is obtained using the four-phase dielectric mixing model. One year of C-band copolarized σo observations are collected by a ground-based scatterometer deployed in the seasonally frozen Tibetan meadow ecosystem. It is found that: the calibrated Tor Vergata (hereafter “TVG”) model simulates well the seasonal dynamics and magnitudes of scatterometer measurements, and the simulated scattering components and vegetation transmissivity agree well with the seasonal vegetation dynamics; the total scattering simulated by the TVG constrained WCMs shows a good consistency with the scatterometer measurements, and the simulated soil and vegetation scattering components are in line with the TVG simulations; and the retrieved soil moisture based on the constrained WCMs captures well the seasonal variability noted in the in situ measurements. An additional experiment is performed to calibrate the WCMs directly, and the results show that the calibrated WCMs achieve comparable results with the calibrated TVG model and the constrained WCMs in terms of the total σo and soil moisture retrieved. However, the direct calibration of the WCMs leads to unrealistic characterization of individual soil and vegetation scattering contributions, of which an underestimation of the vegetation contribution at VV polarization is most notable.