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.