# An Inter-Comparison Study of Multi- and DBS Lidar Measurements in Complex Terrain
## Materials and Methods
### Experimental Setup: The Kassel 2014 Experiment  
The data presented in this paper was collected during the _Kassel 2014 Experiment_ at Rodeser Berg--a hill in central Germany close to Kassel--during summer 2014 (3 July-17 August 2014). Five long-range WindScanners (scanning lidars based on the Windcube WLS200s) were set up around the hill (EE, SE, SW, WW, NN in Figure 2). A sixth scanner (MA) was placed on the ridge of the hill directly next to a 200 m high meteorological mast. An additional Windcube v2 (DBS lidar) was operated at a few meters' distance from the mast. The measurements from a sonic anemometer mounted on the mast serve as a reference in this study. The reference mast is erected on a small clearance within a forest which, depending on direction, stretches from 0.4 to 2.5 km around the mast. The wider surroundings are characterised by a patchy landscape of mainly agricultural land use, villages and forested hills (Figure 2). The height of the hill above the surrounding terrain is approx. 100-200 m depending on direction. More details about the measurement site can be found in [6]. During the deployment of the WindScanners the procedures for calibration of the home position, levelling, and sensing range as outlined in [15] were applied. For the purpose of these procedures around each WindScanner, with the exception of the MA WindScanner, at distances of approx. 100 m, three 2 cm thick surveying stakes were installed, separated by 120\({}^{\circ}\) in azimuth. The absolute positions of the WindScanners, stakes, and reference mast top were surveyed using a differential GPS and a theodolite. These positions were acquired with cm accuracy. The stakes were then mapped using the CNR-Mapper [15]. After the calibration, the reference mast top was mapped by each WindScanner to validate the setup procedure, and the static laser beam pointing accuracy and the sensing range accuracy were estimated to be 0.05\({}^{\circ}\) and 1 m, respectively. Due to the terrain configuration, reference mast structure and surrounding vegetation, the deployment steps, which are described above, could not be applied completely to the MA WindScanner. Hence, a single surveying stake and the branch of a tree nearby were used for the CNR mapping. Both hard targets were located about 50 m from the WindScanner and separated by 180\({}^{\circ}\) in azimuth. However, since the MA system was located directly next to the reference mast, the static pointing accuracy and sensing range accuracy could not be validated by mapping the  
Figure 2: Instrumental setup during the measurement campaign. Left: aerial photograph (data source: published with kind permission of ©Hessische Verwaltung für Bodenmanagement und Geoinformation (HVBG)) with circles indicating the locations of the lidar and the met mast; the locations which are used in this study are indicated in black. Right: terrain (data source: Shuttle Radar Topography Mission [31] version 2.1) and trajectories of the intersecting lidar beams for the ML measurement. The windcube v2 (WC) is also located at the MA position. must top. The WindScanners were coordinated and synchronized by a remote master computer [15], which communicated with the WindScanners using a 3G network [32]. This paper analyses data from measurements when all WindScanners were staring at a single point close to a Gill HS50 sonic anemometer mounted on the reference mast at a height of 188 m (agl). The reference anemometer is mounted on a foldable boom with a length of 5.4 m to minimise the effects of the mast structure. The wind sector 100\({}^{\circ}\)-160\({}^{\circ}\) is excluded from the analysis to remove data which is affected by the mast shadow. According to [2], the influence of the mast structure is estimated to be less than 0.5%. In a wind tunnel test the directional deviation of the Gill HS50 is well below \(\pm\)1%. The inclinometer accuracy is given as \(\pm\)0.15\({}^{\circ}\). The direction-dependent error of the measurement of the horizontal wind speed is thus estimated to be below \(\pm\)1%.