Study of Airborne Doppler Radar Navigation Correction using a Variational Technique

Airborne Doppler radar data needs to go through a careful navigation correction procedure before accurate dual-Doppler synthesis can be obtained, owing to the simple fact that the radar is mounted on a fast moving, sometimes very unsteady platform. Over the past two decades, separate techniques have been developed to correct navigation errors of ELDORA, an X band airborne Doppler radar developed and operated by the National Center for Atmospheric Research. The goal of this research is to develop a navigation correction algorithm, which can be used in future ELDORA field campaigns in realtime and in conjunction with the algorithm presented by Wolff et al. in these proceedings to quickly synthesize Dual Doppler data. It consolidates different techniques into one single algorithm that can be applied over all kinds of surface conditions including complex terrain and ocean. Based on a thorough literature review, a variational method originated by Georgis et al. (2000) was selected and modified to be used for the future realtime navigation correction system. This algorithm uses three constraints (the surface height, the surface velocity, and flight level winds) to derive 12 navigation correction factors of both the fore and aft radar. Testing of this algorithm using both real and synthetic ELDORA data over flat and complex terrain will be presented. Preliminary results show that the surface height and velocity constraints work well over flat and complex terrain, while the flight level wind constraint needs substantial modifications before it can be used satisfactorily.