The paper analyzes the problem of achieving a coherent operation in Geostationary SAR (GEOSAR) missions intended for continuous monitoring of land surfaces. In contrast to LEOSAR missions, GEOSAR uses very long SAR integration times (from minutes to hours). Accordingly phase errors due to orbit perturbations, radar master oscillator drift, atmosphere propagation and other sources must be conveniently compensated during SAR processing to avoid image defocusing. A network of Active Radar Calibrators (ARC) distributed on the observed scene is proposed, providing echo envelope and phase observations before Synthetic Aperture Processing. In this way the radar antenna phase center trajectory and other phase error sources can be continuously tracked and compensated using a pyramidal sub-aperture processing approach.

Peer Reviewed