基于三角位移法姿态矫正的激光线扫描海底地形三维测绘

3D mapping of submarine topography by laser line scanning based on pose correction by triangular displacement method

作为一种三维成像技术,激光线扫描技术在海底目标探测和地形地貌测绘中获得了广泛应用。本文搭建了一套水下激光线扫描实验装置,对经过标定的激光线扫描装置获得的图像进行激光光条提取、特征提取匹配等图像处理后进行三维重建。在光条提取算法方面,针对水下散射粒子等干扰,结合单通道阈值法和灰度重心法提高了光条提取的精度,较其他光条中心提取算法有更强的鲁棒性;在特征提取匹配方面,提出了一种基于图像的三角位移估计法用于系统定位和位姿矫正,该方法利用线结构光三角测量原理估计场景深度,结合特征点匹配计算系统位移,然后融合点云数据完成姿态矫正。利用自研的线扫描系统在实验室进行了标准球精度测试,在800 mm~2500 mm的工作距离内误差可以控制在1 mm以下。2019年和2020年该设备搭载遥控无人潜水器进行了深海海底地形三维成像试验,在海底沙坡区域对本文提出的三角位移法姿态校正方法成功进行了验证,并进一步对不同条件的海底地形进行测试,结果表明校正后的激光线扫描成像装置能够快速准确地成像,具有较高的形貌还原度。

As a three-dimensional(3D)imaging technology,laser line scanning has been widely used in underwater target detection and topographic mapping.In this study,a set of underwater laser line scanning experimental equipment is constructed,and images obtained using a calibrated laser line scanning device are processed via laser strip extraction,feature extraction,and matching;subsequently,3D reconstruction is performed.To mitigate the interference of underwater scattering particles,the light strip extraction algo⁃rithm is used,where the single channel threshold and gray center methods are combined to improve the ac⁃curacy of light strip extraction.Consequently,a higher robustness is achieved compared with that afforded by other light strip center extraction algorithms.In terms of feature extraction and matching,an image-based triangular displacement estimation method for system positioning and pose correction is proposed herein.This method applies the principle of line-structured light triangulation to estimate the scene depth,matches feature points to estimate system displacement,and fuses point cloud data to complete pose cor⁃rection.We performed a standard ball accuracy test in a laboratory using a self-developed line scanning sys⁃tem,and the error can be controlled below 1 mm within a distance of 800–2500 mm.In 2019 and 2020,we performed 3D imaging tests of deep-sea seabed terrains with an ROV using the abovementioned sys⁃tem.The tests successfully validated the pose correction method of the proposed triangular displacement method in a sloped seabed sand area,and further tests were performed on the seabed terrain under different conditions.The results demonstrate that the corrected laser line scanning imaging device can perform im⁃aging rapidly and accurately with a high degree of morphology reduction.