Abstract
A new algorithm for ship wake detection is developed with the aim of ship heading and velocity estimation. It exploits the Radon transform and utilizes merit indexes in the intensity domain to validate the detected linear features as real components of the ship wake. Finally, ship velocity is estimated by state-of-the-art techniques of azimuth shift and Kelvin arm wavelength. The algorithm is applied to 13 X-band SAR images from the TerraSAR-X and COSMO/SkyMed missions with different polarization and incidence angles. Results show that the vast majority of wake features are correctly detected and validated also in critical situations, i.e., when multiple wake appearances or dark areas not related to wake features are imaged. The ship route estimations are validated with truth-at-sea in seven cases. Finally, it is also verified that the algorithm does not detect wakes in the surroundings of 10 ships without wake appearances.
Highlights
Maritime traffic monitoring is gaining great advantages from spaceborne SAR imagery
Several international projects are investigating an operational ship monitoring system [1,2,3,4], and many experimental results are available on ship detection in SAR images [5,6,7,8,9,10]
A central dark line is the signature of the turbulent wake, which is aligned with the ship longitudinal axis
Summary
Maritime traffic monitoring is gaining great advantages from spaceborne SAR imagery. Several international projects are investigating an operational ship monitoring system [1,2,3,4], and many experimental results are available on ship detection in SAR images [5,6,7,8,9,10]. Since wakes appear in SAR images as dark or bright straight lines, the existing algorithms for wake detection exploit the classical linear feature detection methods, such as Radon [18] or. Results on 250 wakes extracted from medium to low resolution SAR data (Radarsat-1, ERS, Seasat) [14] show that the accuracy of the computed velocity is within about percent of the true speed for most of the images, provided that the wakes exhibit a clear appearance and are not closely aligned with the azimuth direction. From the literature, the bright/dark dots in the transformed domain are detected considering their angular distance as foreseen by hydrodynamics [17] They are validated as representative of the ship wake components by means of novel merit indexes in the intensity domain. Algorithm validation is performed on 13 X-band SAR images from the TerraSAR-X and COSMO/SkyMed missions, with different polarization and incidence angles
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