A Comparison of VHF Radar Vertical-Velocity Measurements by a Direct Vertical-Beam Method and by a VAD Technique

Abstract

Vertical-velocity measurements made by a direct vertical-beam method are compared to vertical velocities derived from VAD (velocity-azimuth display) measurements over a 27-h period. The results indicate that the two types of measurements in regions where the scatter is isotropic agree well. The largest discrepancies occur in the regions characterized by strong stratification and anisotropic or aspect-sensitive scatter. Although there are various assumptions inherent in the VAD calculations of the vertical velocities, indications are that the source of error is the aspect sensitivity, which produces effective off-vertical pointing angles in the vertical beam when the reflectivity layers are tilted out of the horizontal plane. However, other additional sources of bias or error cannot be excluded.