The wind profiling method is based on determining the movements of aerosol structures from subsequent CAPPI scans of the VIL. The CAPPI scans represent two-dimensional horizontal maps of the convective boundary layer aerosols at different altitudes. The mean movements of aerosol structures are determined by calculating spatial, two-dimensional cross correlation functions (CCF) between subsequent CAPPI scans at each altitude. The position of the CCF maximum peak indicates the mean wind speed and direction averaged over a 70 km VIL scanning area.
At the top of the convective boundary layer, where the backscatter signals have a good contrast between the structures and clearer air, the wind estimation can be done directly from the two-dimensional cross correlation function between two subsequent CAPPI scans. Above the top of the CBL and near the surface, however, the situation is more complicated. Above the top, lidar signal extinction on clouds causes correlations between shadowed portions of the signal. Near the surface, aerosol plumes anchored to particular locations may lead to strong zero space lag correlations. Intense structures appearing only on one CAPPI scan may cause strong random correlations. These conditions prompt a need for preprocessing the backscatter signal and CAPPI scans before calculating the cross correlation functions.