Detection of ship wake using an airborne magnetic transducer

Wakes induced by motion of vessels may extend for tens of kilometers and exist for hours under certain conditions in open sea. This forms a useful feature for long-range ship detection. We present a method for passively detecting a ship wake using measurements obtained by an airborne SQUID magnetic transducer that measures the first-order gradients of the magnetic signature induced by the wake. Analytical formulas of wake magnetic gradients are derived to provide guidelines for designing the airborne detector. We also derive probability bounds of wake detection for cross-correlation and square-law detectors, which can be used to predict the expected performance.