Improved Procedure to Correct Airborne Doppler Radar Data

The navigation correction method proposed in Testud et al. (1995) (referred as the THL method) systematically identifies uncertainties in the aircraft Inertial Navigation System and errors in the radar pointing angles by analyzing the radar returns from a flat and stationary earth surface. This paper extends Testud et al. (1995) study and presents two new procedures to address: 1) the sensitivity of the dual-Doppler analyses to errors in individual parameters, 2) further improvement of the accuracy of the airborne Doppler radar data to all flight legs from the correction factors obtained during the °¥calibration leg°¦, and 3) identifying drift, ground speed and tilt errors over a flat and non-stationary earth surface. The results show that the errors in each of the parameters affect the dual-Doppler wind analyses and the first order derivatives in different manners. Tilt error is the most difficult parameter to determine and has the greatest impact on the dual-Doppler analysis. The extended THL method can further reduce the drift, ground speed and tilt errors in all flight legs over land by analyzing the residual velocities of the earth surface using the corrections obtained in the calibration legs. When reliable dual-Doppler winds can be deduced at flight level, the Bosart-Lee-Wakimoto method can identify all 8 errors by satisfying three criteria: 1) the flight-level dual-Doppler winds near the aircraft statistically agree with the in situ winds, 2) the flight-level dual-Doppler winds are continuous across the flight track, and 3) the surface velocities of the left (right) fore radar have the same magnitude but opposite sign as their counterparts of right (left) aft radar. This procedure is able to correct airborne Doppler radar data when the surface is moving and has been evaluated using FASTEX and VORTEX datasets. Consistent calibration factors are obtained in multiple legs. The dual-Doppler analyses using the corrected data are statistically superior to those using uncorrected data.