An Improved Procedure to Correct Airborne Doppler Radar Data for Navigation Errors Using a Variational Method

Uncertainties in aircraft Inertial Navigation System and errors in radar-pointing angles can have a large impact on airborne dual-Doppler analyses. Testud et al. (1995, referred as THL method), has been routinely applied to data collected by the National Center for Atmospheric Research Electra Doppler Radar (ELDORA), but assumptions in the algorithm require flat, non-moving terrain as a constraint. The navigation correction method proposed in Georgis et al. (2000, referred as GRH method herein) is similar to the THL method but employs a variational approach to deduce navigation errors by minimizing three cost functions related to radar-derived surface height, surface velocity and single Doppler velocity near the aircraft at flight level. The GRH method has the advantage of being applicable over complex terrain and moving ocean surfaces. An improved version of GRH method is presented in this paper which differs from the previous version by 1) adding tilt corrections for both fore and aft radar, which were omitted in the previous formulation; and 2) differentiating rotation angle errors of fore and aft radar, which were treated the same in the previous version. The weights of each term in the cost function were also re-examined. The revised GRH method is tested extensively using synthetic airborne Doppler radar data with known navigation errors as well as published data sets from previous field campaigns. Both tests show the improved GRH method was able to correct the navigation errors associated with airborne Doppler radar data with adequate accuracy.