Abstract
Abstract. In complex mountainous terrain the mapping efficiency is a crucial factor. Unmanned aerial vehicle (UAV) based laser scanning (ULS) has the capability for efficient mapping, as it allows realizing higher flight velocities, higher flying altitude above ground level (AGL) and larger distances between neighbouring flight strips, compared to image based techniques. However, fully utilising the efficiency of the system in mission planning (especially for complex terrain projects, where occlusions and differently inclined surfaces are present) is prone to miss the project requirements in terms of point density and strip overlap. Therefore, the numerical simulation of point densities is a helpful tool for realizing a reliable planning of scan coverage. We implemented a ray-tracing-based ULS-simulator, specifically designed for emulating the mechanism of a Riegl VUX-1LR laser scanner carried by a Riegl RiCOPTER. The simulator can consider copter and scanner motion, which makes it possible to generate synthetic scan data excluding or including the aircraft movement due to aerodynamics by using either planned trajectories from a flight planning software or recorded and post-processed trajectories from an inertial measurement unit (IMU). Laser shots are simulated by intersecting rays from the virtual scanner with a mesh-based digital surface model (DSM). The results show that the tool generates plausible synthetic laser point distributions. However, this is only the case, when aircraft aerodynamics are considered, as the effect of striping due to flight control corrections during the flight is very prominent. It can be shown that applying the presented tool for mission planning (without knowing the actual flight movements) has to consider an error margin of ±50pts/m2 in order to guarantee a compliance with the planned project requirements. Nevertheless, the consideration of terrain by a high resolution DSM, especially in complex terrain, improves the correlation between simulated and real point densities significantly.
Highlights
Unmanned aerial vehicle (UAV) based laser scanning (ULS) is a powerful technique in order to efficiently map project areas of up to a few km2
The simulation model shows good performance in recreating ULS point densities both in simple and complex terrain. This is especially true for the simulation with flown trajectories as this significantly reduces the number of unknown factors influencing the scanning mechanism
The tool is useful for post mission analysis, which is demonstrated by the correct simulation of aerodynamic effects when recorded flight trajectories of the real flights are used
Summary
Unmanned aerial vehicle (UAV) based laser scanning (ULS) is a powerful technique in order to efficiently map project areas of up to a few km. Compared to UAV based photogrammetry (i.e. structure-from-motion and dense matching approaches), a point measurement does not require at least two observations, which allows a higher flexibility in planning of overlaps. It allows realizing higher flight velocities, higher flying altitude above ground level (AGL) and larger distances between neighbouring flight strips. In complex mountainous terrain the mapping efficiency is a crucial factor and has to be optimized in order to guarantee reasonable field logistics This causes a high risk of erroneous mission planning, leading to incomplete coverage, unsatisfying point densities and strip overlaps. An adequate planning of strip configurations, flying heights and scanning parameters, including pulse repetition rate (PRR) and angular scan resolution, are required
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