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.

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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.@en