| The runup of waves on offshore structures is an important parameter.Moreover,it plays a significant role in related research fields such as seawall constructions and coastal erosion prediction.The traditional research methods of wave runup are mainly based on physical experiments,which will consume time,workforce,and material resources.The development of UAV systems and computer technology have recently brought great convenience to field measurement and computer numerical simulation,which has become a research hotspot.In conclusion,it is of great significance to research wave runup based on airborne LIDAR systems and computer numerical simulations.This thesis researches wave runup from three perspectives: image edge detection,radon transform,and computer numerical simulation.Specifically,the detection idea of image edge detection and image radon transform is mainly based on detecting instantaneous water lines to deduce wave runup.The main research contents of this thesis are as follows:(1)The preprocessing of point cloud data and image data obtained by the airborne LIDAR system is completed.Specifically,Normal filtering of the laser point cloud data is used to achieve the effect of smoothing the point cloud,which lays a foundation for the subsequent terrain fitting of the coastal zone;the ground control points are used to construct a reprojection error model to obtain the extrinsic parameters corresponding to each frame of the airborne camera;the extrinsic parameters are used to rectify the images and obtain the orthophotos and time stack images.(2)Since current algorithms for extracting instantaneous waterline from the perspective of image edge detection are sensitive to changes in light conditions and water color,and the results often need manual correction,this thesis proposes and implements an algorithm to detect the instantaneous waterline and wave runup based on time stack images,which includes image binarization,morphological processing,canny edge detection,and piecewise linear regression.(3)Since instantaneous waterline is extracted from image space only from the perspective of edge detection and not based on wave motion form,this thesis proposes and implements an algorithm that uses radon transform and inverse radon transform to process sharpened and enhanced time stack images to separate wave components in two propagation directions and get instantaneous waterline and wave runup.(4)To expand the application value of the airborne LIDAR system in nearshore measurement,the SWASH model is used to simulate the wave runup on the terrain obtained by the airborne LIDAR system and unmanned ship.In addition,the SWASH model’s necessary derivation and feasibility were carried out before it was used. |
