Thermal infrared cameras sense the temperature information of sensed scenes. With the development of UASs (Unmanned Aircraft Systems), thermal infrared cameras can now be carried on a quadcopter UAV (Unmanned Aircraft Vehicle) to appropriately collect high-resolution thermal images for volcanic geothermal monitoring in a local area. Therefore, the quadcopter UAS used to acquire thermal images for volcanic geothermal monitoring has been developed in Taiwan as part of this study to overcome the difficult terrain with highly variable topography and extreme environmental conditions. An XM6 thermal infrared camera was employed in this thermal image collection system. The Trimble BD970 GNSS (Global Navigation Satellite System) OEM (Original Equipment Manufacturer) board was also carried on the quadcopter UAV to gather dual-frequency GNSS observations in order to determine the flying trajectory data by using the Post-Processed Kinematic (PPK) technique; this will be used to establish the position and orientation of collected thermal images with less ground control points (GCPs). The digital surface model (DSM) and thermal orthoimages were then produced from collected thermal images. Tests conducted in the Hsiaoyukeng area of Taiwan’s Yangmingshan National Park show that the difference between produced DSM and airborne LIDAR (Light Detection and Ranging) data are about 37% between −1 m and 1 m, and 66% between −2 m and 2 m in the area surrounded by GCPs. As the accuracy of thermal orthoimages is about 1.78 m, it is deemed sufficient for volcanic geothermal monitoring. In addition, the thermal orthoimages show some phenomena not only more globally than do the traditional methods for volcanic geothermal monitoring, but they also show that the developed system can be further employed in Taiwan in the future.
Wetlands and other critical habitat Bock et al. (2005) Urban areas Weeks et al. (2007) Cleve et al. (2008) Durieux et al. (2008) Land use and land cover Maxwell (2010) Public health Kelly et al. (2011) Disease vector habitats Koch et al. (2007) Troyo et al. (2009) Public health infrastructure (e.g., refugee camps) Lang and Blaschke (2006) Hazard vulnerability and disaster aftermath Al-Khudhairy et al. (2005) Gusella et al. (2005)
In conducting land boundary verification surveys in digitalized cadastral areas in Taiwan, possible parcel points must be surveyed. These points are employed in the overlap analysis and map registration of possible parcel points and digitalized cadastral maps to identify the coordinates of parcel points. Based on the computed horizontal distance and angle between control points and parcel points, parcels are staked out using ground surveys. Most studies survey possible parcel points using ground surveys with, for example, total stations. Compared with ground surveys, UAV (Unmanned Aerial Vehicle) aerial photogrammetry can provide more possible parcel points. Thus, an overlap analysis of digitalized cadastral maps, combined with the collection of possible parcel points, will be more comprehensive. In this study, a high-quality-medium format camera, with a 55 mm focal length, was carried on a rotary UAV to take images, with a 3 cm ground sampling distance (GSD), flying 300 m above the ground. The images were taken with an 80% end-lap and side-lap to increase the visibility of the terrain details for stereo-mapping. According to the test conducted in this study, UAV aerial photogrammetry can accurately provide supplementary control points and assist in the boundary verification of digitalized cadastral areas in Taiwan.
Abstract:Unmanned Aircraft Systems (UASs) can collect high resolution and high quality images for local mapping. If the highly accurate GPS flying trajectory of a UAS is collected, it can support bundle adjustment aerial triangulation (AT) of UAS images and reduce the demands on ground control points (GCPs). This study installs a Trimble BD970 GNSS OEM on a fixed-wing UAS for capturing highly accurate GPS data by using a Virtual Base Station (VBS) RTK GPS technique for AT. Meanwhile, the GPS antenna-camera offset is resolved by stripwise linear drift parameters introduced in GPS observation equations, while performing bundle adjustment for AT. Additionally, self-calibration bundle adjustment is used in VBS RTK GPS-assisted AT to solve incomplete camera parameters calibrated by a close-range photogrammetric approach. The results show that the AT accuracy of fixed-wing UAS images collected with a 24 mm focal-length Canon EOS 5D Mark II camera at a flying height of 550 m above ground level is 0.21 m in planimetry and 0.22 m in height using two cross strips with two full GCPs at each corner of the block. The RMSE of check points from stereoscopic viewing can reach 0.27 m in planimetry and 0.24 m in height. The test results show that the accuracy of VBS RTK GPS-assisted bundle adjustment with self-calibration for the AT of fixed-wing UAS image can be used for updating local 1/5000 topographic maps in Taiwan. Keywords: VBS RTK GPS, Self-Calibration Bundle Adjustment, Aerial Triangulation, UAS Resumo:Imagens de alta resolução espacial e radiométrica podem ser coletadas por Sistemas de Aeronaves Não Tripuladas (UASs) para fins de mapeamento local. Se a trajetória de um UAS é coletada por antena GPS de alta confiabilidade, os dados obtidos podem ser empregados no processo de fototriangulação e ajudar a reduzir o custo do projeto em apoio de campo (GCPs). Neste trabalho foi instalada uma antena da Trimble BD970 GNSS OEM na asa de um UAS para captar dados GPS usando a técnica GPS RTK da Estação Base Virtual (VBS). O parâmetro de deslocamento linear da origem da antena GPS em relação ao sistema referencial da câmera foi solucionado por fototriangulação. Além disso, uma auto-calibração de câmeras foi usada na fototriangulação assistida por VBS RTK GPS para refinar os parâmetros de orientação interior da camera, determinados com uma calibração prévia a partir de uma abordagem a curta distância. Os resultados mostraram que a partir de uma câmera Canon EOS 5D Mark II com distância focal de 24 mm e imagens coletadas por um UAS a uma altura de voo em torno de 550 m a acurácia planimétrica é de 0.21 m e altimétrica de 0.22 m usando duas faixas
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