Strategies for Circulation Evaluation of Aircraft Wake Vortices Measured by Lidar

Abstract

An assessment of different methods for circulation evaluation from lidar measurement data of aircraft wake vortices is performed. The surface integral of vorticity serves as baseline case that is compared to a method that evaluates the lidar line-of-sight velocity midway between the vortices and to another method that calculates radii averages of circulations derived from tangential velocities. Systematic deviations from nominal circulation are discussed based on analytical vortices. High-resolution numerical simulation data are applied to perform virtual lidar measurements that reproduce, explain, and quantify (i) the frequently observed initial overestimation of circulation and (ii) the scatter of circulation data caused by the genuine variability of wake vortices in the atmospheric boundary layer. The theoretically derived characteristics of the different evaluation methods are verified against lidar data recorded by several lidar teams during the Wake Vortex Forecasting and Measuring Campaign at Oberpfaffenhofen (WakeOP), performed in spring 2001 at Fairchild Dornier Airport in Oberpfaffenhofen, Germany.