Experimental Demonstration of Ambiguous Staggered SAR with Waveform Alternation for Coastal Surveillance

Abstract

Maritime surveillance using synthetic aperture radar (SAR) calls for both wide swaths and high resolution. This enables monitoring of wide areas with high detection probabilities and low false alarm rates at short time intervals. Ambiguous SAR modes have proven effective for ship monitoring in remote offshore regions. They deliver high-resolution SAR images over wide swaths that can be effectively exploited for ship detection, even though they are corrupted by significant ambiguities of ships and sea clutter. Building upon the successful demonstration of the staggered ambiguous mode using TerraSAR-X, this paper presents the results of a further experimental acquisition, carried out near the Dutch coast, where an ultra-wide ground swath of 160 km is imaged at an azimuth resolution of 2.2 m by introducing in the staggered ambiguous mode alternation of up- and downchirp waveforms. 79 small ships were detected in the data set, some of which even near the coast and despite the presence of first-order range ambiguities caused by land scatterers, as these ambiguities are very blurred and manifest as noise like disturbances. These results are of fundamental importance for incorporating the ambiguous modes into existing and future SAR systems as an efficient additional mode for ship monitoring, suitable for both open sea and coastal surveillance.