星载激光雷达波形长度提取与林业应用潜力分析

Lidar (light detection and ranging) remote sensing is a breakthrough of active remote sensing technology in recent years. It has shown enormous potential for forest parameters retrieval. Lidar remote sensing has the unique advantage of providing horizontal and vertical information at high accuracies. Especially it can be used to measure forest height directly with unprecedented accuracy. Large footprint lidar has demonstrated its great potential for accurate estimation of many forest parameters. The geoscience laser altimeter system (GLAS) instrument aboard the ice, cloud and land elevation satellite (ICEsat) has acquired a large amount of data including topography and vegetation height information. Although GLAS’ primary mission is the topographic mapping of the ice sheets of greenland and antarctica, it has potential use over land, especially for vegetation height extraction. These data provide an unprecedented vegetation height data set over large area. After a general discussion of GLAS waveform pre_processing, the waveform length extraction method has been developed. Then the waveform length from GLAS Laser 2a data in the northeast China was calculated. The waveform length map was analyzed together with land cover map from Landsat ETM+. The waveform length shows good accordant with land cover types from Landsat ETM+ data. As for forest area, the waveform length map contains much more information about forest height information, which can be used to inverse other forest parameters quantitatively together with other remote sensing data.

波形长度分形维数在结构振动诊断中的应用

在Hausdorff维数和分配维数的基础上 ,采用拓扑映射技术 ,提出了振动波形长度分形维数的定义和计算公式 ,并对其数学严密性进行了证明。结合工程实例探讨了基于振动波形长度分形维数计算的结构振动诊断技术 :模型增长法和滑动窗法。该技术对于波形异常检测表现出精度高、抗噪能力强及自动快捷等优势 ,构成了一条分形理论用于结构振动诊断的有效技术路线 ,具有良好的应用价值。

基于零序信号全波形识别的小电流接地系统故障选线方法

小电流接地系统发生单相接地故障时,故障电流微弱,暂态特征复杂,导致现有选线方法正确率偏低,可靠性较差。该文提出了一种基于零序信号全波形识别的选线方法。首先,介绍了基于故障信号全波形识别的通用方法,指出从波形的角度认识并识别信号,可以充分利用信号的全部故障信息;其次,选取母线电压和所有馈线电流波形作为待识别信号,并根据电流波形分布特征自适应捕捉信号中特征差异最明显的波形进行故障识别,提出了基于故障信号全波形识别的选线方法;然后,利用改进后的全卷积神经网络来识别不同信号波形,并基于Dice系数对识别出的故障信号波形进行可信赖性评价。最后,PSCAD仿真和真型实验测试结果表明该方法具有很高的选线正确率和可靠性。

Study on applicability of modal analysis of thin finite length cylindrical shells using wave propagation approach

Donnell’s thin shell theory and basic equations based on the wave propagation method discussed in detail here, is used to investigate the natural frequencies of thin finite length circular cylindrical shells under various boundary conditions. Mode shapes are drawn to explain the circumferential mode number n and axial mode number m, and the natural frequencies are cal-culated numerically and compared with those of FEM (finite element method) to confirm the reliability of the analytical solution. The effects of relevant parameters on natural frequencies are discussed thoroughly. It is shown that for long thin shells the method is simple, accurate and effective.

全波LiDAR反演地形参数的树高估计

针对全波激光雷达(LiDAR)数据在坡地森林高度估测中的应用,该文提出利用地形参数估测树高的方法。首先以ICESat-GLAS大光斑全波形数据为数据源,利用指数加权和形式建立全波LiDAR波形的理想数据模型,并采用最小二乘法求解该理想模型;其次,利用阈值法确定有效波形的始末位置,进而得到有效波形的波形长度,并据此估计地形起伏参数;结合光斑直径、波形长度、地形起伏参数以及地表展宽程度,建立树高估测模型。以黑龙江省大兴安岭为实验研究区,估测树高与实际测量值之间的相关系数为0.926 2。实验结果表明:针对地形坡度等外在因素影响,利用波形本身特征参数,能有效量化地形因素的影响,并能有效解决地形复杂地区树木高度估测问题。