Ship Wakes in Optical Images

Ship wakes are more distinct than the hulls and can be visually observed in optical images. In this paper the wakes of 2836 ships in 32 optical images with different resolutions are observed and summarized. The ships are divided into four types according to the hull and wake features: fishing vessels, motorboats, cargo ships, and warships. The results show that each ship type has characteristic wakes, and there are significant differences among the categories. The probabilities of occurrence of different types of wakes and their components are shown. Turbulent wakes are inevitable. The probability of occurrence of Kelvin wakes is small and less than 40%. The visibilities of internal waves that are generated by only cargo ships are very low as a result of the harsh formation conditions. Turbulent wakes should be preferentially detected. Low-resolution images are more suitable for the detection and positioning of hulls and wakes, while high-resolution images with more details are convenient for further analysis of the size, velocity, and draft of ships. The study on the cause of the formation of the features of ship wakes in optical images proves that the classification of the wakes is reasonable and that the features of wakes can be used to initially identify the type of ship.