多特征参数约束的星载激光高程控制点提取

Elevation control points extraction of spaceborne lasers with multifeature parameter constraints

星载激光点位高程精度是其辅助光学立体影像复合测绘的基础。针对光学影像立体测绘对激光高程控制点精度的需求,提出了一种基于多特征参数约束的星载激光高程控制点提取方法。该方法利用全波形数据包含的目标地物垂直结构信息,分析高精度激光高程控制点特征,基于数据的有效性、波形的峰值个数、回波特征参数实现逐级约束筛选。选取信噪比、峰度和偏度作为评价指标,通过全波形数据回波特征参数的计算、统计与分析,确定其信噪比、峰度和偏度阈值,最终高效提取出可用于星载激光高程控制点的有效波形数据。以我国高分七号数据为试验对象,选取草地、戈壁、道路、水体、沙地、耕地六种典型地物样本,确定适用于提取高分七号高程控制点的信噪比、峰度与偏度的阈值。以江苏地区机载LiDAR点云数据为参考,验证分析高程控制点提取和阈值设定的准确性,试验结果表明:基于多特征参数约束算法,利用设定的适用于GF-7卫星的参数阈值,可以高效、准确地从原始波形数据中提取出有效波形用于高精度高程控制点生产。以与参考数据高程差0.32 m为高程精度要求,提取准确性平均为90.34%,所提取的激光高程平均测量精度优于0.5 m。

The point elevation accuracy of spaceborne laser is the basis of its auxiliary optical stereoscopic image composite surveying and mapping. This study proposes a method for extracting elevation control points of spaceborne lasers based on multi-feature parameters constraints in response to the requirements for the accuracy of laser elevation control points in optical image stereo mapping. This method utilizes the vertical structure information of the target objects contained in the full-waveform data to analyze the characteristics of the highprecision laser elevation control points, and realizes the constraint screening step-by-step based on the validity of data, the number of waveform peaks and echo characteristic parameters. The signal-to-noise ratio, kurtosis and skewness are selected as evaluation indexes. Through the calculation, statistics and analysis of the echo characteristic parameters, the thresholds are determined, and finally the valid waveform data that can be used for spaceborne laser elevation control points can be extracted efficiently. Taking the laser data of GF-7 as an example, such six typical feature samples as grassland, gobi, road, water body, sandy, and cultivated land are selected to determine the suitable thresholds of echo characteristic parameters for GF-7. Taking the airborne LiDAR point cloud data in Jiangsu area as a reference to verify and analyze the extraction accuracy, the experiment results show: based on the multi-feature parameters constraint algorithm, using the set parameter thresholds suitable for the GF-7, the valid waveform can be extracted from the original waveform data efficiently and accurately for the production of high-precision elevation control points. Taking the elevation difference of0.32 m from the parameter data as the elevation accuracy requirement, the average extraction accuracy is 90.34%,and the average measurement accuracy of the extracted laser elevation is better than 0.5 m.