Accuracy Verification of UAV-SfM Survey of Terrace Paddy Fields in a Hilly and Mountainous Area

Abstract

In order to facilitate environmental restoration and reconstruction following natural disasters, accumulation of detailed topography and land use information before the disaster is essential. Recently, the Geospatial Information Authority of Japan announced a survey manual using Unmanned Aerial Vehicles (UAV). The UAV-Structure from Motion (SfM) system has accumulated a great deal of accuracy verification information from the topographic survey, and it is expected that in the future UAV surveying and mapping will be expanded in scope. However, many research cases were performed in flat areas, and UAV surveying and mapping in hilly and mountainous areas are few. With the progress of depopulation and ageing, there is concern that regional disaster prevention capabilities will decline because of the devastation of agricultural land and the disappearance of communities in hilly and mountainous areas. It is necessary to clarify the method for UAV surveying and mapping with high accuracy even in the complex geographical conditions of hilly and mountainous areas. In the present paper, we attempted to create a Digital Elevation Model with UAV in the terrace paddy field of Shizuoka prefecture, Japan. We investigated the influence of flight conditions and the number and location pattern of Ground Control Positions (GCPs) on surveying accuracy by UAV. UAV surveying results are compared with the accuracy of the digital topographic map with scale in Japan specified by the public survey work regulations. We also surveyed the GCPs by RTK-GPS at 15 locations in the terrace paddy field. Comparing the results of UAV surveying without GCPs and RTK-GCP, the standard deviation in the horizontal direction and elevation was 2.44 m ± 1.59 m (SD) and 39.36 m ± 45.30 m (SD), respectively, and corresponds to the digital topographic map with scale in Japan 1:1,000 and 1:5,000, respectively. From these results, it is verified that correction by GCPs is necessary for UAV-SfM surveying in order to ensure high accuracy.