Abstract
Abstract. Unmanned Aerial Vehicle (UAV) is one of the geoinformation data acquisition technologies that popularly used for slope mapping. UAV is capable to produce high resolution imageries in a short period. In order to obtained suitable results in slope mapping, specific UAV mapping factors have to be followed and the selection of the optimum Ground Control Point (GCP) and the UAV flying altitude become the most important factors. This paper presents the production of high resolution slope map using UAV technology. The research involved with the following steps, (i) preparation of field work (i.e. determination of the number of GCPs and flying altitude) and the flight mission; (ii) processing and evaluating of UAV images, and (iii) production of slope map. The research was successfully conducted at Kulim, Kedah, Malaysia as the condition of slope in that area is prone to the landslide incidences. A micro rotary wing UAV system known as DJI Phantom 4 was used for collecting the high resolution images with various flying altitudes. Due to the un-accessibility of the slope area, all the GCPs are measured from the point cloud data that was acquired from the Pheonix AL-32 LiDAR system. The analysis shows that the coordinates (X, Y and Z) accuracy is influenced by the flying altitude. As the flying altitude increases, the coordinate’s accuracy also increased. Furthermore, the results also show that the coverage slope area and number of tie point increases when the flying altitude increases. This practical study contributed to the slope work activities where the specific requirements for flying altitudes have been clearly stated.
Highlights
1.1 BackgroundA slope area is associated with the height of an area as it becomes higher the steeper is the gradient
There are several technologies that have been used in monitoring and mapping of slope area such as satellite imagery (Bagnardi et al, 2016), Light Ranging and Radar (LiDAR) (Dunham et al, 2017), Terrestrial Laser Scanner (TLS) (Francioni et al, 2014; Tahar, 2015), manned aircraft, Total Station, Mobile Laser Scanner (MLS) (Michoud et al, 2015), Global Positioning System (GPS) and Unmanned Aerial Vehicle (UAV)
This study has successfully evaluates the orthophoto and DEM accuracy based on different flying altitudes using UAV technology to produced slope map
Summary
A slope area is associated with the height of an area as it becomes higher the steeper is the gradient. There are several factors that causes landslides such as: (a) gravity acts on the slope (Reis et al, 2016) ; (b) erosion by rivers, glaciers, or sea waves which produce steep slopes (Blyth and de Freitas, 2017); (c) sloping rock or land slopes due to saturation by heavy rain; (d) an earthquake that produces tensions causing weak slopes to collapse; (e) volcanic eruptions produce ash, heavy rain, and trash flow; (f) tremors from machines, traffic, explosives, even thunder may trigger tremendous collapse; (g) extreme weight resulting from the accumulation of rain or snow, stacks of rocks or ores, from garbage dumps, or man-made structures that put pressure on weak to heavy cracks and other structures; (h) Groundwater pressure acts to make the slope unstable on shallow soils, deeprooted plantings that bind colluvium to base stones These factors can affect a slope condition in a long-term if not monitored regularly. According to Tahar (2013), number of ground control points and flying altitudes are the most important aspect need to be consider during data acquisitions These two aspects can influence the accuracy of the produced map. Technology where it can fly with low flying altitude and under cloud cover
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