Du Kai, Li Yuan, Huang Huaguo, Mao Xufeng, Xiao Xiulai, Liu Zhiqu
Qinghai Provincial Key Laboratory of Physical Geography and Environmental Process, College of Geographical Science, Qinghai Normal University, Xining 810008, China.
State Forestry and Grassland Administration Key Laboratory of Forest Resources and Environmental Management, Beijing Forestry University, Beijing 100083, China.
Sensors (Basel). 2024 Dec 25;25(1):46. doi: 10.3390/s25010046.
Using microwave remote sensing to invert forest parameters requires clear canopy scattering characteristics, which can be intuitively investigated through scattering measurements. However, there are very few ground-based measurements on forest branches, needles, and canopies. In this study, a quantitative analysis of the canopy branches, needles, and ground contribution of Masson pine scenes in C-, X-, and Ku-bands was conducted based on a microwave anechoic chamber measurement platform. Four canopy scenes with different densities by defoliation in the vertical direction were constructed, and the backscattering data for each scene were collected in the C-, X-, and Ku-bands across eight incidence angles and eight azimuth angles, respectively. The results show that in the vertical observation direction, the backscattering energy of the C- and X-bands was predominantly contributed by the ground, whereas the Ku-band signal exhibited higher sensitivity to the canopy structure. The backscattering energy of the scene was influenced by the incident angle, particularly in the cross-polarization, where backscattering energy increased with larger incident angles. The scene's backscattering energy was influenced by the scattering and extinction of canopy branches and needles, as well as by ground scattering, resulting in a complex relationship with canopy density. In addition, applying orientation correction to the polarization scattering matrix can mitigate the impact of the incident angle and reduce the decomposition energy errors in the Freeman-Durden model. In order to ensure the reliability of forest parameter inversion based on SAR data, a greater emphasis should be placed on physical models that account for signal scattering and the extinction process, rather than relying on empirical models.
利用微波遥感反演森林参数需要清晰的树冠散射特性，这可以通过散射测量直观地进行研究。然而，针对森林树枝、针叶和树冠的地面测量非常少。在本研究中，基于微波暗室测量平台，对马尾松场景在C波段、X波段和Ku波段的树冠树枝、针叶及地面贡献进行了定量分析。构建了四个在垂直方向通过落叶形成不同密度的树冠场景，并分别在C波段、X波段和Ku波段，跨越八个入射角和八个方位角收集了每个场景的后向散射数据。结果表明，在垂直观测方向上，C波段和X波段的后向散射能量主要由地面贡献，而Ku波段信号对树冠结构表现出更高的敏感性。场景的后向散射能量受入射角影响，特别是在交叉极化中，后向散射能量随入射角增大而增加。场景的后向散射能量受树冠树枝和针叶的散射和消光以及地面散射的影响，导致与树冠密度的关系复杂。此外，对极化散射矩阵进行方向校正可以减轻入射角的影响，并减少弗里曼-杜尔登模型中的分解能量误差。为确保基于合成孔径雷达（SAR）数据的森林参数反演的可靠性，应更加强调考虑信号散射和消光过程的物理模型，而不是依赖经验模型。
