GPS Based Relative Navigation for the TanDEM-X Mission – First Flight Results

Abstract

TanDEM-X is the first Synthetic Aperture Radar (SAR) mission using close formation flying for bistatic SAR interferometry. Within three years, TanDEM-X will enable a global mapping of Earth and production of a high resolution digital elevation model (DEM). As a prerequisite for the interferometric SAR processing, the relative position, or baseline, of the two spacecraft must be determined with millimeter accuracy. In support of this task, the two spacecraft are equipped with geodetic-grade GPS receivers. Independent baseline solutions from the German Space Operations Center (DLR/GSOC) and the German Research Centre for Geosciences (GFZ) will be merged into a quality controlled combined product prior to use in the DEM generation. This paper provides an overview of the baseline determination process and discusses specific aspects such as phase pattern calibration, ambiguity resolution, and a trade-off between single- and dual-frequency solutions. First flight results from the early commissioning phase are presented.