## 1 Introduction  
### Motivation  
Nowadays, the use of mobile mapping systems has become increasingly popular due to the rapid technological development and the resulting increase in the range of applications. As a result, these multi-sensor systems are used on mobile platforms, whether on the ground, on water or in the air, and have been adopted in a wide range of application areas. Typical fields for the use of mobile mapping systems are topographic and bathymetric surveys, road and power line inspections, mining, forestry or precision agriculture [1, 2, 3, 4, 5].  
The recent development of sensor technology for mobile mapping systems in the field of airborne laser scanning offers the possibility to operate compact profile line scanners on an Unmanned Aerial Vehicle (UAV) [6]. The advantages of using a combination of UAV and laser scanner are numerous compared to traditional airborne laser scanning, and benefit, in particular, from a higher level of detail and more flexible flight planning. In comparison to conventional Terrestrial Laser Scanners (TLS), it also offers a faster acquisition of survey objects with higher coverage. In addition, one of the major benefits of UAV-based laser scanning is the possibility of direct georeferencing, which describes the calculation of a 3D point cloud in a global reference frame [7]. The direct georeferencing relies on the UAV's trajectory estimation with positions and orientations, using the fusion of sensors such as IMU (Inertial Measurement Unit) and GNSS (Global Navigation Satellite System) receiver. Since the trajectory estimation is the most critical component in the error budget of the UAV-based laser scanning, the overall accuracy of the georeferenced point cloud is highly dependent on the quality of the UAV trajectory [7]. In the following, the error budget is used as a summary of errors included in the measurements or processing of the UAV-based laser scanning system. If direct georeferencing with a sufficient accuracy is provided, different advantages are obvious. The need for overlapping flight strips in data collection is less important, which is a great advantage for applications such as corridor mapping, also resulting in larger areas being covered in the same amount of time. Furthermore, the need for Ground Control Points (GCPs) is less important and potentially not needed anymore [8]. Finally, most of the benefits lead to time and cost savings in the execution of a project. This study aims to provide a reliable strategy for the quality assessment of the direct georeferencing of a UAV-based laser scanning system. The main aspects are the analysis of the **absolute accuracy** in the horizontal and vertical direction and the **precision** of the system considering repetitions of the same measurement and, thus, the same flight planning.  
This paper is organized as follows: Section 1 focuses on the methodology of UAV-based laser scanning, related work and the research scope. This is followed by Section 2 about materials and methods, which describes the used sensor system, the evaluation strategy and the study areas. Section 3 presents and discusses the results of all experiments conducted in this study. Section 4 concludes the paper.