Inversion of residual motion error in Airborne Single and Repeat Pass interferometry under the presence of squint and large topography variations

Abstract

The potential and necessity of the estimation and compensation of motion errors beyond the accuracy of up-to-date navigation systems has been demonstrated and proved in several studies during the last years. This paper presents an improved method to invert the estimated residual phase error to navigation errors of the airplane using an accurate model of the airplane and scene geometry in Single and Repeat Pass SAR mode. The performance of current estimation algorithms is limited because of the inseperability between topography induced and residual motion errors. The proposed method tries to extract the residual phase caused by motion errors by introducing a model of the imaging geometry including the scene topography using a backgeocoded elevation model. This leads, in cooperation with the precise topography and aperture dependend motion compensation, to precise interferograms and finally to a refined accuracy of the derived elevation model. The method has been extensively tested and finally implemented into E-SAR’s processing chain. It is fully operational for single pass interferometric processing by first estimating the residual motion error, converting the residual motion error into residual platform motion and then processing the second interferometric channel by comprising not only platform but also residual platform motion. In order to reach the required accuracy, the second channel must be processed iteratively no more than 2-3 times. The quality improvement caused by the algorithm is investigated by evaluating the accuracy of the resulting digital elevation models on a dataset with more than 1000 meters of height variation.