An automatic ship and ship wake detection system for spaceborne SAR images in coastal regions

摘要

An automatic ship and ship wake detection system for spaceborne SAR images is described and assessed. The system is designed for coastal regions with eddies, fronts, waves and swells. The system uses digital terrain models to simulate synthetic SAR images to mask out land areas. Then a search for ship targets is performed followed by wake search around detected ship candidates. Finally, a homogeneity test and wake behavior test are performed which reduces the number of false alarms substantially. The system is demonstrated with ERS-1 SAR images and its performance is assessed using Seasat and ERS-1 images. No other information about the ships was available, hence, the basis for the assessment is through comparison with human visual interpretation of the same data. The number of lost ships (ship-like targets) was 7-8% for both Seasat-A and ERS-1. No false ships were detected. The number of lost or false wakes (wake-like features) was higher in ERS-1 images than in Seasat-A images and was nearly 15%. Taking into account the extremely strong variations in sea state in some of the selected scenes, the automatic detection performance is considered to be very good. In addition, the requirement of analyzing a 3-look ERS-1 scene of 100 km/spl times/100 km in less than eight minutes has been achieved on a workstation.