Calculated Radar Images of Ship Wakes from Simulated Wake Hydrodynamic Models

摘要

Calculations of radar scatter images from simulated ships wakes are presented for two ships, the Quapaw and a DDG class vessel. Three ship speeds were used for each, scaled so that the Froude numbers were the same for both vessels. Two radar scattering mechanisms were used: Bragg scatter and an empirical sea spike model. No Doppler effects are considered (important to SAR image formation) so that the model is one for a real-aperture radar. Both vertical and horizontal transmit polarizations were used, with like polarizations received, for a single depression angle of 45 degrees. Two flight aspects were considered: parallel and perpendicular to the axis of the wake, with the radar beam perpendicular to the direction of flight. Simulated wake elevations and slopes are calculated using the slender ship method published recently by Keramidas (1987). The results show a relatively weak modulation from the Bragg scatter contribution, which would probably be masked by moderate sea conditions. The most significant result is the occurrence of the maximum image brightness from a narrow V-wake. This image feature is associated with a region of large slope, but moderate wave height, due to the interaction of the superposition of the Kelvin wakes from the bow, stern, and ship body contributions. Because of the aspect of the high slope region, the radar echo from this region is significant only for radar beam illumination perpendicular to the wake axis. For perpendicular flight aspect, the radar image consists primarily of the Bragg return for both polarizations and yields only the Kelvin wake. Suggestions are made for improving both the radar scatter model and the hydrodynamic model. (fr)