Retrieval of three-dimensional particle velocity from airborne Doppler radar data

A technique has been developed for the retrieval of three-dimensional particle velocities from Doppler data obtained with an airborne radar. The 95-GHz radar was mounted on the University of Wyoming KingAir aircraft. The retrieval technique is derived from the velocity azimuth display (VAD) analysis and is termed the airborne velocity azimuth display (AVAD). Data for this analysis are taken when the radar beam is scanned by the turning of the aircraft. As in VAD analysis, a functional form for the horizontal variation of the velocity of the scatterers must be assumed. The components of the velocity field are then determined using a least squares fit to the Doppler velocities. The AVAD technique differs from VAD analysis because of the mobility of the platform and its proximity to regions of interest, and it is due to geometric considerations dictated by the turning of the aircraft. The analysis region is only a few kilometers in diameter-considerably smaller than for a ground-based VAD analysis. This reduces the required area of cloud coverage and the importance of horizontal Variations in the wind field. However, the reduced analysis area also limits the accuracy with which higher-order characteristics of the wind field, such as divergence, can be resolved. This paper presents the AVAD technique and describes the data processing required. Results from multiple AVAD analyses from flights on two days are presented and are shown to be in generally good agreement with winds measured by sensors on board the KingAir.