A novel technique for ship wake detection from optical images

Abstract

Monitoring ships at sea is of great importance for both civilian and military purposes. Since ship wakes are more distinct than hulls, wakes are widely employed for ship detection from satellite imagery. In this paper, a novel approach was proposed to detect ships from optical imagery. Candidate wakes were first obtained by the normalized Radon transform of an image with the ship hull in the center. False wakes were then removed by pixel value verification, turbulent wake identification, included angle verification, and contrast verification. Meanwhile, bright edges of turbulent wakes were detected after turbulent wake identification. Detected wakes were verified with wakes delineated through visual inspection. By implementing the proposed technique to optical imagery, reflectance at the near-infrared (NIR) band of GF 1 and Sentinel 2 MSI and the panchromatic band of Landsat 8 OLI showed the best accuracies. Total recalls of turbulent and Kelvin wakes were 93.5% and 91.2%, respectively, while total precisions were 93.7% and 93.8%, respectively. Positions, directions, and endpoints of wakes were also obtained with good accuracy. The categories of wakes were confirmed by the wake features and the spatial relationships between wakes. Factors influencing the accuracy of the developed method and comparison with state-of-the-art wake detection methods were then discussed.