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森林垂直结构参数反演是进行森林资源管理、森林蓄积量估算及全球碳循环研究的基础。层析合成孔径雷达TomoSAR(Tomography Synthetic Aperture Radar)是随着InSAR/Pol-InSAR技术的日益发展而产生的,更适用于森林垂直结构参数反演。本文首先介绍了TomoSAR的概念与实现方式:PCT(Polarization Coherence Tomography)、多基线干涉层析SAR MB-InTomoSAR(Multi-baseline Interferometric Tomographic SAR)、多基线极化层析SAR MB-PolTomoSAR(Multi-baseline Polarization Tomographic SAR);概括了目前应用TomoSAR技术反演森林垂直结构参数的技术方法与信号模型等;论述了应用TomoSAR技术提取森林垂直结构参数的现状,最后分析了应用TomoSAR技术提取森林垂直结构参数可能的发展方向。
The inversion of the forest vertical structural parameters is the basis of forest resource management, forest volume estimation, and global carbon cycle studies. However, very limited research has been conducted regarding forestry applications. With the increasing development of Interferometric Synthetic Aperture Radar (InSAR)/Polarimetric Interferometric Synthetic Aperture Radar (Pol-InSAR) techniques, Tomographic Synthetic Aperture Radar (TomoSAR) has been widely considered suitable for the inversion of the forest vertical structural parameters. TomoSAR is a new technique introduced to remote sensing applications, particularly for the remote sensing of land covers with complex three-dimensional structures, such as forests and urban areas. This study mainly aimed to summarize the new developments and applications of TomoSAR in extracting information regarding vertical forest structures. Three approaches can be used to extract information regarding vertical forest structures: Polarization Coherence Tomography (PCT), Multi-baseline Interferometric TomoSAR (MB-InTomoSAR), and multi-baseline polarimetric TomoSAR (MB-PolTomoSAR). In PCT, forest vertical profile is obtained using Fourier-Legendre expansion series with a priori knowledge, such as forest height and topographic phase estimated with polarimetric interferometric information or Lidar. With this approach, the profile of vertical forests with two tracks in a repeat-path mode can also be extracted. In MB-InTomoSAR technique, information regarding forest vertical structures can be obtained by multi-baseline interferometric SAR images in a repeat-path mode with low temporal and spatial decoherence. MB-InTomoSAR can be used to estimate the vertical parameters of forests in a physical model. Along with spectral analysis method, MB-InTomoSAR can also be used to extract vertical forest information. In MB-PolTomoSAR technique, the vertical structural parameters of forests are determined using multi-baseline polarimetric interferometric SAR images in a repeat-path mode. MB-PolTomoSAR can be used to obtain not only forest height, forest aboveground biomass, and other forest vertical structural parameters but also variation in scattering mechanisms in vertical forests. In this study, the principles and methodologies of these three TomoSAR techniques were described. The application status and developments of TomoSAR technique were summarized. TomoSAR was used to extract the vertical structural parameters of forests. Afterward, this technique was evaluated. This study also described further advances in TomoSAR applications for the vertical structural parameters of forests. TomoSAR was applied to extract information regarding forest vertical structures. Our results indicated that TomoSAR could be a suitable technique in studying forests with large slopes or complex topographic characteristics.