A Three-Step Dealiasing Method for Doppler Velocity Data Quality Control

A three-step method is developed for Doppler radar velocity dealiasing. First, the modified velocity azimuth display (VAD) method of Tabary et al. is adopted and applied to raw (aliased) velocity data to estimate horizontal vector velocities averaged on selected circles of radar scans. These velocities are used as preliminary references to detect and pre-dealiase or flag (if not correctable) possible alias errors. Then, the traditional VAD method is applied to the pre-dealiased velocity data to produce refined reference velocities to further detect and dealiase or flag alias errors in the second step. After these two steps, flagged data points are confined in small areas (often associated with strong shear and/or convergence flows), so the dealiased velocities along the boundary of each small area provide reliable starting points for the continuity check in the third step. The two-dimensional continuity check can start from any and every boundary point and proceed inward until all the flagged data are checked within each small area. The method is tested with Doppler radar data collected during the 3 May 1999 Oklahoma tornado outbreak—a difficult case for dealiasing. The results show that the method is efficient and effective even in the areas of mesocyclones.