A study on the applicability of unmanned aerial vehicles to the sounding survey of tidelands

The southwestern coast of Korea is characterized as a complex ria coast with a wide tideland. In this area, information on the minimum low water level is important for ship safety. While using aerial photographs and satellite images to measure the water depth of a tideland is expensive for smaller areas, using echo sound does not guarantee a precise measurement because it is difficult for ships to reach such areas. This study aims to verify the applicability of unmanned aerial vehicles (UAVs) to the sounding survey of a tideland by comparing the results of a UAV survey with those of a single beam survey. The study was conducted in and around Seohong-ri, Haenam-gun, and Jeollanam-do by using an unmanned fixed-wing aerial vehicle with a 24.36-megapixel camera to take pictures at an overlap rate of 60 % ~ 80 % from an altitude of 110 m ~ 150 m. Ground control points (GCPs) were installed at intervals of 500 m with three checkpoints. The GCP locations were determined using Network-RTK. In the photographs, GCPs and checkpoints were matched to create DSM and orthophotos. The root mean square error in the GCP of an orthophoto was X = 0.0085 m, Y = 0.0091 m, and Z = 0.0027 m. On comparing the overlapped parts, the water depth error was found to be 0 m ~ 0.1 m on a verage, satisfying the special grade criterion of tolerance by waterway survey depth and confirming the applicability of unmanned aerial vehicles to the sounding survey of tidelands. It was possible to draw the coastline by correcting the tide to the orthophoto and depth values. Using GSD 5 cm images obtained from the unmanned aerial vehicle, it was possible to precisely describe the coastline and confirm changes in the coastline.