森林树高的反演,一直是极化干涉SAR(Polari metric SAR Interferometry)研究领域中的热点。介绍了近年来分别基于相干优化算法和高分辨率波达算法(ESPRIT)的树高反演方法,并尝试了ESPRIT算法和三阶段反演算法的结合。最后利用德国宇航局(DLR)的全极化干涉L波段ESAR数据及其相应的林地平均树高实测数据,对所述方法进行了验证与分析。结果表明:三阶段算法和三阶段Sinc算法相对于其它算法而言具有较好的结果,但同其它基于散射模型的树高反演算法一样,存在着一定程度的高估;而ESPRIT相位差值算法则严重地低估了平均树高;尽管ES-PRIT算法与三阶段算法、三阶段Sinc算法相结合的尝试可在一定程度上提高计算效率,但其树高反演结果并没有得到明显改善。
It is difficult to make an inventory of vertical profiles of forest structure parameters in field measurements.However,analysis and understanding of forest backscattering characteristics contribute to estimation and detection of forest vertical structure because of the close relationships between backscattering characteristics and structure parameters.The vertical structure function in the complex interferometric coherence definition,which represents the vertical variation of microwave scattering with the penetration depth at a point in the 2-D radar image and can be used to analyze the forest backscattering characteristics,can be reconstructed from polarization coherence tomography(PCT).Based on PCT,the paper analyzes the forest backscattering characteristics and explores the inherent relationship between the result of PCT and the forest structure parameters from numerical simulation of Random Volume over Ground model(RVoG),Polarimetric SAR interferometry(PolInSAR)simulation of forest scene and PolInSAR data at L-band of the test site Traunstein.Firstly,the effects of the extinction coefficient and surface-to-volume scattering ratio in RVoG model on vertical backscattering characteristics are analyzed by means of numerical simulation.Secondly,by applying PCT to L-band POLInSAR simulations of forest scene,different variations of vertical backscattering due to different extinction coefficients and the ratios of surface-to-volume scattering resulting from different polarizations,forest types and densities are displayed and analyzed.Then a concept of relative average backscattering intensity is presented,and the factors which affect its vertical distribution are also discussed.Preliminary results show that there is high sensitivity of the vertical distribution of forest relative average backscattering intensity to the polarization,forest type and density.Finally,based on repeat pass DLR E-SAR L-band airborne POLInSAR data,the capability of PCT technology for detection of forest layer,type and density is discussed.
LUO HuanMin 1,LI XiaoWen 1,2,CHEN ErXue 3,CHENG Jian 4 & CAO ChunXiang 21 Institute of Geo-Spatial Information Science and Technology,University of Electronic Science and Technology of China,Chengdu 610054,China
