越冬期树木枝干水分冻融信息传感机理与原位无损检测方法研究

The freeze-thaw information of woody stems during overwintering stage is not only the production guidance information urgently needed by agroforestry producers and ecologist, but also the object of long-term concern of plant physiologists. Based on the theory of high frequency electromagnetic field, this presented proposal will take the ice content in woody stems during overwintering in the field as the research object to propose a perceptual mechanism model about freeze-thaw information of woody stems. Meanwhile, the variation of dielectric constant during water phase transformation of woody stems under high frequency electromagnetic signal excitation (> 100 MHz) will be investigated. The dielectric properties of bark, phloem, cambium and xylem of tree stems, which has radial layered structures, will be analyzed in-depth. The measurement errors caused by non-uniform spatial distribution of measured media will be corrected. A new ice content sensor based on inner-fringe-field effect with double ring electrodes is developed, which provides an effective new technical means for nondestructive, quantitative, continuous and on-line measurement of ice content in woody stems. Based on this, the temporal and spatial variations of ice content in stems of different tree species will be monitored at various time scales during the wintering period, the migration trajectory of freeze-thaw peak with temperature during freezing process of stems will be tracked and radial transfer model of ice nuclei in stems will be proposed. According to the freezing point temperature and ice nucleus diffusion rate of stems, the index parameters of cold resistance of trees will be defined, and the evaluation system of cold resistance of trees based on freeze-thaw information detection of stems will be constructed.

越冬期树木枝干水分冻融信息不仅是农林生产者和生态维护人员迫切需要的生产指导信息，也是植物生理学家长期关注的研究对象。本申请拟以高频电磁场理论为基础，以野外环境下越冬期树木枝干含冰量为研究对象，构建树木枝干水分冻融信息感知机理模型，探究高频电磁信号激励下的树木枝干水分相变过程中介电常数的变化规律，深入解析树木枝干中树皮、韧皮部、形成层、木质部等径向分层结构的介电特征，校正被测介质非均匀空间分布带来的测量误差。研制基于内边缘场效应的双环形电极结构枝干含冰量传感器，为实现树木枝干含冰量的无损、定量、连续、在线测量提供一种有效的新型技术手段。在此基础上，监测不同树种越冬期枝干含冰量多种时间尺度上的时空变化规律，追踪枝干结冰过程中冻融峰随温度变化的迁移轨迹，建立枝干冰核径向转移模型。根据枝干冰点温度和冰核扩散速率定义树木抗寒特性指标参数，构建基于枝干水分冻融信息检测的树木抗寒特性评价体系。

中国华北区域多为温带大陆性气候和温带季风气候，冬季有较长时间的冰霜期，这些区域中有大面积的经济和生态林木每年都会面临比较严重的寒害威胁。枝干径向分层结构的介电特征解析可以获取树木各层的相对介电常数和厚度，对树木冻融研究都具有重要意义。植物冻融特性对于植物的存活及生长具有重要作用，是评价植物抗冻能力及进行植物选育的重要依据。针对上述问题本研究根据木本植物树干结构特征，根据无损原位测量的设计要求，提出内边缘场环形弹性电极设计。利用介电物理理论，将植物茎秆体积含水量映射到植物茎秆和电极组成的负载阻抗上，并从传输线理论角度分析了端口阻抗的测量原理,设计了枝干含冰量监测传感器。此外，构建了雷达信号在树干分层结构的传播模型。基于该模型提出一种树干分层介电参数解析方法，并借助软件无线电设备搭建树干分层探测雷达，实现对树干分层结构的探测，使用稀疏分解算法、K-SVD字典训练以及分层剥离算法对探测雷达接收信号进行分层介电参数的反演。试验表明在回波混叠和无混叠的情况下，该方法均能够对树干分层介质厚度和相对介电常数进行估算；无混叠时相对介电常数和厚度的反演误差分别在2.934%和3.5%以内，混叠时相对介电常数和厚度的反演误差分别在7.227%和7.538%以内。此外，根据木本植物树干生理特征，构建基于树干分层温度信息的冻融计算模型，根据枝干冰点温度定义树木抗寒特性指标参数，构建基于枝干水分冻融信息检测的树木抗寒特性评价体系。最后，将树干分层介电参数与基于树干分层温度信息的冻融计算模型，综合理解树木抗寒调控机制和全面评价树木抗寒特性。综上所述，本文所提方法能够精确实现对树干径向分层结构的介电特征进行解析；通过设计树干分层结构探测雷达对该方法进行实现；最后将树干分层介电参数与基于树干分层温度信息的冻融计算模型相结合，将该方法应用于树木冻融特性的检测。试验结果表明，树干径向分层结构的介电特征解析方法能够对植物冻融特性进行研究，可以追踪树干冻融过程中冻融峰随温度变化的迁移轨迹。