Spaced-antenna measurements of cross-beam velocity in severe storms

To study the dynamics and kinematics of convective storms, it is necessary to map the three-dimensional wind field. For years, retrieval of the wind field has been accomplished using dual or pseudo-dual Doppler analysis. These techniques require either that the storm lie within a restricted area with respect to stationary radars, or that a moving (e.g. airborne) radar move by the storm. In either case, the time between volume scans is relatively long. To overcome these limitations, a spaced-antenna technique is considered for which only one stationary radar is required.

Observations of tangential and radial velocities in obtained in supercell and smaller storms are presented. These measurements employ a dual-polarized, overlapped-aperture, spaced-antenna attached to a mobile X-band Doppler radar. Tangential (cross-beam) velocities are inferred from estimates of the spatial cross-correlation function of the backscattered field measured by two orthogonally polarized antennas. The use of orthogonal polarizations eases the implementation of a compact spaced-antenna aperture. Radial velocities are obtained through standard Doppler signal processing.

The fidelity of the tangential velocity estimate depends upon the precision of the cross-correlation estimate, which, in turn, depends upon the number of independent samples available assuming use of covariance-based estimator. For scanning antennas, this impacts the scan rate, and hence defines the overall tradeoff between spatial resolution and tangential velocity precision. Case studies from storms observed in the plains of the U.S. during Spring 2005 illustrate the utility of the technique.