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 the next three years, TanDEM-X will enable a global mapping of the Earth to produce a high accuracy, high resolution digital elevation model (DEM) of the entire globe. 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 will be generated by expert teams at both the German Space Operations Center (DLR/GSOC) and the German Research Centre for Geosciences (GFZ). These will be merged into a quality controlled combined product prior to use in the interferometric SAR processing. The 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.