Unified Coordinate System Algorithm for Terahertz Video-SAR Image Formation

Video synthetic aperture radar (ViSAR) is a novel imaging mode where the radar system forms a sequence of SAR images while the radar platform is flying. To achieve a high frame rate, ViSAR system typically operates in the terahertz (THz) band. In this paper, the unified coordinate system algorithm (UCSA) improving on the polar format algorithm (PFA) is proposed for THz ViSAR images formation, which is based on the more accurate wavenumber domain signal model derived by second-order Taylor expansion. Considering the small synthetic angle feature of THz ViSAR, the UCSA divides two-dimensional resampling into range and azimuth resampling using the chirp z-transform to reduce the processing complexity in ViSAR imaging. Through the analysis in this paper, it can be known that THz PFA images are free from the quadratic phase errors. However, the PFA images are oriented to different directions and exist image distortion caused by linear phase errors (LPE). Through an image resampling, the UCSA corrects the LPE and rotates the images to the unified coordinate system simultaneously. The effectiveness of UCSA is validated by a ground-based experiment performed by a 0.3 THz radar system.