Inspection Standards for Applying Unmanned Aerial Vehicle Photogrammetry to River Topographic Surveys

Abstract

The Ministry of Land, Infrastructure, and Transport of Korea has established a basic river plan to be implemented every 10 years for the systematic reorganization and management of rivers. However, the conventional river topographic survey method requires considerable time and cost. To overcome this problem, work regulations have been established and applied to efficiently conduct river topographic surveys using unmanned aerial vehicles (UAVs). However, in these work regulations, there are no inspection standards for the mosaic orthophotos and digital elevation models (DEMs) acquired from UAVs. In addition, when conducting river topographic surveys using UAVs, ground control point (GCP) surveys are often not performed, which decreases the accuracy of the results. Rivers have topographic elements, such as banks, crests, and berms, with elevation differences. Therefore, it is necessary to perform a GCP survey of the field when river topographic surveys are conducted using UAVs. To determine the necessity of GCP surveying, in this study, we evaluated the accuracy of mosaic orthophotos and DEMs acquired using UAVs with and without GCP surveying. Without GCP surveying, the root mean square error (RMSE) of the mosaic orthophotos was +/- 19.110 m and that of the DEMs was +/- 6.950 m. However, with GCP surveying, the RMSE of the mosaic orthophotos was +/- 0.057 m and that of the DEMs was +/- 0.024 m. Therefore, it is concluded that a GCP survey is necessary in river topographic surveys with UAV photogrammetry. On the basis of the study results, the inspection criteria for applying UAV photogrammetry to river topographic surveys were divided into aerial triangulation accuracy criteria, orthophoto inspection criteria, and DEM inspection criteria, and presented as numerical values.