MIMO-TOPS MODE FOR HIGH-RESOLUTION ULTRA-WIDE-SWATH FULL POLARIMETRIC IMAGING

The novel TOPS mode can achieve wide swath imaging coverage at the cost of impaired azimuth resolution. MIMO-SAR systems combined with multi-channel SAR signal reconstruction in azimuth and digital beamforming (DBF) on receive in elevation can overcome the inherent contradiction between swath width and azimuth resolution of conventional SAR systems. This paper derives a novel spaceborne MIMO-TOPS mode for high-resolution ultra-wide-swath full polarimetric imaging. In such an imaging scheme, different polarimetric waveforms with different elevation beam pointing directions and short time delays are transmitted in a single pulse repetition interval (PRI) by different sub-aperture antennas in azimuth. Besides improving the desired signal-to-noise ratio (SNR) and suppressing ambiguous energy in elevation, a novel DBF on receive approach including two steps is adopted to separate different echoes corresponding to sub-pulses with different polarizations. The design example of a full polarimetric MIMO-TOPS SAR system, which allows for the imaging capacity to cover an ultra wide swath of 400 km with a high azimuth resolution of 3 m, is given to validate the proposed imaging scheme.