Numerical and experimental studies of ship wakes for wide area surveillance

Wide Area Surveillance refers to the continuous monitoring and tracking of the earth’s surface by using air and space-borne satellites. Many countries routinely do WAS for military and intelligence purposes. The present work is an application of the same for maritime ship detection in the seas, using the basic premise that a wake produced by a vessel can be more prominently captured than the ship alone. At the free surface, synthetic aperture radar images of a ship's wake show long dark and bright streaks known as Kelvin and turbulent wake. This Kelvin wave wake travels more than 100 kilometres away from the ship and contains important information about the ship. In our paper, we have done an assessment study on different ship’s wake signatures by employing a combination of numerical simulations and validation with experiments. Though the initial part of the paper deals with straight line motion, an application of the same to a ship turning is also investigated at the end. Reverse calculations for detection of ship forward velocity using dispersion relations are carried out from their wake signature. This study is part of the research carried out by the Indian Navy with the collaboration of our department. Based on the results of our study, we can say that the method is promising and can be used for routine monitoring of the coast and open sea.