Coprime Synthetic Aperture Radar (CopSAR): A New Acquisition Mode for Maritime Surveillance

In this paper, we propose a synthetic aperture radar (SAR) technique able, in the case of bright targets over a dark background, to reduce the amount of data to be stored and processed, and, at the same time, to increase the range swath, with no geometric resolution loss. Accordingly, the proposed approach can be usefully employed in ocean monitoring for ship detection. The technique consists of a new SAR acquisition mode and of very simple processing. It is based on the adaptation of the coprime array beamforming concept to the case of SAR systems: two interlaced sequences of pulses are transmitted, with two sub-Nyquist pulse repetition frequencies (PRFs) that are equal to the Nyquist PRF divided by two coprime integer numbers. Each sequence is separately processed via standard SAR processing, and the two final aliased images are combined in a very simple way to cancel aliasing. We call the proposed approach "coprime SAR" (CopSAR). Three different implementations are proposed, and the effectiveness of the CopSAR concept is demonstrated by using both simulated and real SAR data. It turns out that the significant data amount reduction and the range swath increase are only paid with a reduction of the target-to-background ratio and with the presence of a (nonstringent) limit on ship azimuth size.