I. Introduction
Synthetic aperture radar (SAR) is an active microwave imaging sensor that can obtain the structure, size, and scattering information of targets in all-day and all-weather scenarios. Therefore, it has found wide applications in various tasks, such as terrain mapping, geological exploration, and marine observation. In recent years, new SAR sensors have acquired large amounts of SAR images. More importantly, the interval between targets being redetected is decreasing, and SAR data are updated more frequently than ever. Under this circumstance, SAR is more frequently applied to tasks with strict real-time requirements, such as disaster monitoring and battlefield reconnaissance.