活立木内部结构特性雷达波成像与全波反演表征

The living Tree Trunk internal structure is divided into three main parts: heartwood, sapwood and bark, which make the wooden medium highly anisotropic and heterogeneous. Furthermore, the properties of the wood are not only specie-dependent but also depend on genetic and environment conditions. The main subject of this research is the observation of the inner part of living tree trunk using Radar wave imaging and Full-wave Inversion. Radar uses the principle of the scattering of the electromagnetic waves that are radiated from a transmitting antenna. Then the waves propagate through the medium and are reflected from object and they are received by a receiving antenna. The velocity of the scattered signal is determined primarily by the permittivity of the material. The optimal functionality of the radar wave was investigated using the numerical simulation based on a Finite-Difference Time-Domain (FDTD) numerical model. Subsequently, the Radar functionality was tested using the laboratory controlled models of a decayed tree trunk and filed testing. The comparison between the numerical simulations, simplified tree trunk model and real data from field testing was presented. The results of this research can provide an efficient, non-destructive and non-intuitive detection method for forest trees healthy talent assessment, urban trees disaster prevention, and maintaining ancient trees.

活立木内部结构的复杂性，躯干主要结构（心材，边材和树皮）及异常（结疤，开裂，腐朽和中空），纹理特征，各向异性，含水率及生长环境导致的个体差异性提高了树木躯干内部无损检测的难度。针对这一问题，本申请拟从雷达波在木质体内部及其异常媒介中传播的路径，振幅，波速变化以及反射、透射等传输特性出发，研究木质体内部结构的电学特性（介电常数，电导率）与物理特性（含水率，密度）的相关性和对应分布曲线，采用雷达波正演数值模拟，控制实验以及现场实际测试的方法，使用全波反演技术对树木内部结构及异常的电学特性和物理特性进行表征。根据不同电学、物理特性的分布特征研究实现树木内部状况的成像，定位和识别，进而提高雷达波活立木无损检测的准确性和测试精度。研究结果可以为林区与林场树木健康成材评估、城区树木灾害防护和古树的健康维护提供高效，无损和直观的检测方法和分析手段。本研究也可扩展应用于基于木质体结构的古建筑的无损检测。

自然环境下生长的树木易受外界侵害，影响树木的健康和稳固，从而造成经济损失和人员伤亡。活立木由于生长环境和树种的差异导致树木内部结构介电常数个体化差异较大，给树木健康监测和维护带来很大的困难性。本项目采用雷达波树木实地无损检测与树干样本采集测量结合的方式，在北京颐和园，北京八宝山革命公墓，北京鹫峰国家森林公园与河北北戴河中直疗养院等地对松、柏、柳和银杏等典型树木展开了实地观测和测量数据分析，检验了雷达波对于不同树种，不同立地环境下的树干内部结构缺陷的雷达波反演特征识别与成像能力，开发了雷达波活立木不规则轮廓躯干内部缺陷无损检测成像方法和分析软件，建立了雷达波树木内部物理结构与电学特性参数的估测模型，研究分析了活立木内部结构特征参数的雷达波传输影响规律和特征曲线。本研究有助于林区、林场树木健康成材评估，城市行间道活立木稳固性评估以及古树健康维护，同时也对木质体的古建筑健康稳固性评估具有重要意义。