Measurement of Winds Flowing toward an Urban Area using Coherent Doppler Lidar

A coherent Doppler lidar was deployed by Arizona State University as part of an urban dispersion experiment in Oklahoma city in July of 2003 (Joint Urban Dispersion Experiment – JU2003). A major goal of the experiment was to help characterize the inflow boundary conditions for winds upstream of a central business district (CBD) where a tracer gas was released. A variety of scanning techniques were used to probe the inflow region which consisted of a three-dimensional sector with a radial depth of approximately 4 kilometers. Sequences of PPI scans show patchy or streaky regions of the radial velocity field advecting toward the CBD. Several techniques will be presented which attempt to retrieve velocity vectors from the radial velocity fields. One approach is to track inhomogeneities in the radial or aerosol backscatter fields. Another is to use a sector-VAD algorithm which can provide estimates of velocity vectors while sacrificing resolution. A unique aspect of the JU2003 experiment was the deployment of another, matched coherent Doppler lidar deployed by the Army Research Laboratory. Overlapping scans originating from different locations provide the opportunity to retrieve velocity vectors using simple geometrical considerations. RHI scans show depth of the boundary layer and rough size of the larger turbulent structures. The vertical extent of both daytime convective conditions and nocturnal conditions can be discerned from the lidar data. Stare scans through the CBD and over a profiler site will be discussed. A unique attempt to use two lidars executing intersecting RHI scans to create "virtual towers" will be evaluated.