Design of Passive Modes and Parameter Estimation Methods for Localizing Terrestrial Emitters via SAR Systems

Synthetic aperture radar (SAR) systems employ active imaging modes to collect observation data. However, restrictions such as power constraints often necessitate SAR systems to operate with a limited operational duty cycle, resulting in considerable idle time per orbit. This article introduces two innovative observation modes for SAR systems, aiming to effectively utilize this idle time for localizing terrestrial emitters, such as radar and communication systems, in the azimuth-range plane of SAR observation geometry. The proposed modes leverage passive observation capability of SAR systems and work in low power during time slots not dedicated to active imaging. The implementation first involves establishing observation geometries and positioning planes for SAR systems moving along linear and circular trajectories. Next, two passive observation modes are designed, utilizing two azimuth receive beams to gather observations from distinct angles along linear and circular trajectories, respectively. Subsequently, parametric models of beam center crossing times (BCCTs) are then developed, with the emitter coordinate as model parameters. Analytical and numerical positioning methods are proposed by inversing the model parameters. Additionally, Cramer-Rao lower bounds (CRBLs) are derived for the emitter coordinate under the proposed observation modes, and it is demonstrated that the proposed estimators achieve these theoretical bounds. Finally, several simulation experiments are conducted to analyze the performance of the proposed modes and methods.