This paper presents a novel approach in the instrumental error analysis of Synthetic Aperture Radars (SAR) based on active phased array antennas (APAA). A residual post-calibration error exists due to differences between the calibration and operational excitations of the transmit/receive modules (TRMs) for those source errors that are monitored by the internal calibration facility. Analytical expressions are derived for the residual post-calibration errors and validated through intensive simulations of some instrumental errors for a specific sensor architecture. Alternative internal global calibration strategies are proposed to reduce the impact of the post-calibration error. The simulations show that the proposed elevation dependent calibration can provide a substantial reduction of the post-calibration errors even in the case of relaxed tolerance of the TRM weight setting errors.

This paper presents an initial analysis of the possibilities for velocity and acceleration measurement with the Bi-Directional SAR imaging mode (BiDi). It comprises single satellite single path acquisitions as well as a constellation of two satellites. The translational velocity components into azimuth and range directions are simulated. A BiDi approach for measuring the azimuth velocity from one satellite with one receiving channel is proposed. Image examples acquired with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites show velocity and acceleration effects on ships and the proposed BiDi velocity approach is verified. Interferometric fringes were observed on anchoring ships. A first approach into the understanding of rotational effects was achieved by simulation of rotational fringes.