Multistatic UAV SAR Joint Synchronization Based on Multiple Direct Wave Pulses Exchange

Multistatic unmanned aerial vehicle synthetic aperture radar (MUAV-SAR) 3-D imaging system suffers from the time and phase synchronization errors among multiple stations. The classical two-way direct wave pulse exchange synchronization method introduces the p-ambiguity phase error and causes limited time phase synchronization accuracy with multiple system nodes, leading to 3-D image defocusing. An MUAV-SAR joint synchronization method based on multiple direct wave pulses exchange is proposed to solve the p-ambiguity problem robustly and improve the synchronization accuracy significantly. First, the p-ambiguity phase error is estimated through the comparative calculation of delay-phase information extracted from direct wave pulses and the high estimated success probability (99.73%) of the p-ambiguity can be achieved through the noise smoothing. Second, the synchronization accuracy is improved, that is, the time and phase errors are reduced to about (2/N)1/2 of the existing method by utilizing N stations information fusion to jointly process redundant information of direct wave pulses from multiple synchronization links. Finally, a four-station UAV SAR real data experiment verifies the effectiveness of the proposed approach.