Impact of TDX-1 Roll Steering on SAR Performance during TDM Science Phase

Abstract

This technical note summarizes the effect of the TanDEM-X Science Phase formations on the roll steering mechanism. The analyses became necessary since unique formations of the free flying TanDEM-X interferometer different from the ones flown up to now for the global DEM acquisition will be employed during the Science Phase. The challenges explicitly arise from a pursuit monostatic formation with a drifting phase of libration and a very large cross track baseline phase in a bistatic configuration. These challenges led to updates in the roll steering tool in order to be able to handle these formations. Additionally, a performance evaluation suite was developed, delivering estimates of the improvements achieved in terms of noise equivalent sigma zero (NESZ) performance by the use of roll steering as well as estimates of the NESZ degradation if roll steering would not be used. The output of the described analyses is a proposal for the attitude steering table update sequence during the TanDEM-X Science Phase based on performance considerations. Practical considerations like a maximum feasible update rate of the space-craft table are also taken into account.