Roughness length estimation along road transects using airborne LIDAR data

Roughness length (Z₀) is traditionally used as the primary measure of the aerodynamic roughness of a surface, but is notoriously difficult to estimate. This study takes a new approach to the estimation of Z₀, using high resolution LIDAR data coupled with spatial processing techniques to provide estimates of effective roughness length (Z₀ ^eff) based upon the prevailing wind direction and the height of the surface elements (e.g. buildings, trees) within a defined area of upwind fetch. The range of roughness values obtained using this new technique is consistent with published values obtained from detailed boundary layer experiments, and is shown to distinguish between a variety of landuse categories, ranging from high density urban areas to rural farmland. Indeed, comparisons in Z₀ ^eff values between different landuse classes using a detailed land-cover dataset have revealed significant differences in surface roughness between landuse classes, giving confidence not only in the technique itself but also to the validity of the land-cover dataset used in the study.