Statistic and coherence response of ship-based lidar observations to motion compensation

Abstract

Ship-based profiling Lidar systems experience a strong influence of rotational and translational motion on beam direction and hence the line-of-sight velocity. This motion error is inherited by the retrieved 3-dimensional wind vector and is especially visible in the velocity spectra and cross-spectra of velocities at different measurement heights (coherence). Applying motion compensation on the line-of-sight velocity observations was found to have a strong impact on the statistical properties of the retrieved wind vector and successfully improved the corresponding velocity distributions. The impact of motion correction on the spectra of the horizontal wind speed components was found to be neglectable. The Lidar measurement principle, in particular the effect of cross-contamination at higher frequencies, was found to have a larger impact in shaping the horizontal spectra than motion correction. Vertical velocity spectra were strongly affected by ship motion and the motion correction was only partly successful. Precisely, this effect was present at frequencies larger than the resonance frequency of the ship.