An Intelligent Detection Method for Different Types of Outliers in Multibeam Bathymetric Point Cloud

Bathymetric multibeam echo sounder systems (MBESs) are the most effective and reliable way to survey the Earth’s seafloor. However, multibeam bathymetric data inevitably contain different types of outliers due to measurement characteristics and complex underwater environments. The traditional automatic approach to eliminate outliers may lead to more than one of the questions of reliability, limitation, and efficiency. This article offers an algorithm aiming to detect different types of outliers by considering their characteristic of distribution and distance of them rapidly. First, a coding octree based on the Morton code is built to guarantee perfect efficiency and space division. Second, coarse outlier removal is performed by the octree-based voxelized representation of the bathymetric data, and outliers far away from the seafloor will be detected and eliminated by connected component labeling. Third, fine outlier removal is employed to delete outliers connected closely to the seafloor by the improved morphological method based on the combination of the k-D tree and octree. Experimental results show that the proposed algorithm can achieve promising results. The percent of outliers that are detected by the hand-edit method that is regarded as a reference result is 5.06%; 4.70% of points in a total number of 3 645 541 points are detected in our method. Compared with other classical filtering methods, the intelligent method for detecting different types of outliers from coarse to fine attains favorable performance in a reasonable time, avoiding overfiltering, and demonstrates high reliability for multibeam bathymetric point cloud.