This work validates a numerical model of the Fraunhofer IWES LiDAR-Buoy by using open sea measurements. Such floating LiDAR systems (FLS) have been deployed for almost twenty years, aiming at exploring the offshore wind resource with lower cost. However, the uncertainty of wind measurements from a moving LiDAR are not clear, particularly due to the wave- and current-induced motion of the buoy. Therefore a numerical model with state-of-the-art approaches in conventional oil and gas industry was developed to quantify uncertainty and understand the effect of environmental conditions on the buoy. The model was validated against data from a measurement campaign at the offshore research platform FINO 3. The results show the challenges and limitations when transferring the experience from the oil and gas industry directly because of the different geometries and the much smaller buoys used for FLS. It has been found that the position of the LiDAR is dominated by the current, which is however commonly simplified in the state-of-the-art approach; the rotational motions are significantly influenced by the wave and can be reproduced up to a certain limit.