Spatial-spectral joint classification of airborne multispectral LiDAR point clouds based on the multivariate GMM
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摘要: 针对传统机载多光谱激光雷达(multispectral light detection and ranging,MS-LiDAR)土地覆盖分类方法空谱信息协同利用能力不足或多类型特征联合利用时特征维数过高的缺陷,提出一种基于多元高斯混合模型(Gaussian mixture model,GMM)的机载MS-LiDAR点云空谱联合分割算法。该算法首先对原始多波段独立点云进行辐射校正、异常剔除及融合,形成同时表达空间位置及其对应多波段光谱信息的多光谱点云; 然后,提取各激光点的多光谱、高程等特征构建空谱特征矢量,并通过特征标准化及离散化消除不同类型特征间的单位和尺度差异; 再次,构建多元GMM建模目标在空谱特征空间呈现的多峰分布,获取激光点属于各类目标的响应度并按照最大响应度原则确定类属; 最后,设计3D多数投票法优化分割结果。实验基于实测的Optech Titan MS-LiDAR数据验证提出算法的有效性和可行性。实验结果表明: 联合多波段强度特征及高程特征的多元GMM的分割总体精度可达93.57%,Kappa系数可达0.912,仅联合四维特征即可实现MS-LiDAR点云的高精度分割。该项研究可为综合利用MS-LiDAR数据的多光谱及空间信息提供新途径。Abstract: Conventional land cover classification methods based on airborne multispectral light detection and ranging (MS-LiDAR) data have insufficient capability for the cooperative utilization of spatial-spectral information or too high dimensions of features in the joint utilization of various features. This study proposed a spatial-spectral joint segmentation algorithm for airborne MS-LiDAR point clouds based on the multivariate Gaussian mixture model (GMM). First, radiometric correction, anomaly removal, and data fusion were performed for the original multi-band independent point clouds, forming multispectral point clouds that presented spatial locations and their multi-band spectral information. Then, spatial-spectral feature vectors were constructed using the extracted multispectral and elevation features of laser points. Meanwhile, the unit and scale differences among different types of features were eliminated through feature normalization and discretization. Subsequently, a GMM was built to fit the multimodal distribution of objects in the spatial-spectral feature space. Accordingly, the response levels of laser points to various objects were obtained, and the classification of various objects was determined according to the principle of maximum responsiveness. Finally, a 3D majority voting method was designed to optimize the segmentation results. The effectiveness and feasibility of the proposed algorithm were verified through experiments based on surveyed Optech Titan MS-LiDAR data. The experimental results show that the multivariate GMM combined with multi-band intensity features and elevation features yielded an overall segmentation accuracy of 93.57% and a Kappa coefficient of 0.912. The results also indicate that the high-accuracy segmentation of MS-LiDAR point clouds can be achieved by only combining four-dimensional features. This study provides a new approach for comprehensively utilizing the multispectral and spatial information in MS-LiDAR data.
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