The internal waves wake will be generated when an underwater vehicle sails in stratified ocean. Such internal waves signals could be detected by synthetic aperture radar (SAR). The characteristics of the internal waves depend on vehicles, stratified fluid and motion properties. The SAR images of the internal wave are also affected by the magnitude and direction of the sea surface wind. The internal waves generated by an underwater vehicle in a two-layered fluid were simulated based on a hydrodynamic theoretical model. The rough sea surface influenced by wind were simulated by the P-M wind wave spectrum. The SAR images were calculated based on the internal wave signals under rough sea surface by the two-scale method. The numerical simulation shows that the internal wave wake could be identified in the SAR images under appropriate speed and depth of the vehicle. As the ship speed increases, the internal wave wake tends to be close to the center axis of the track. The visibility of the wake is also related to the wind speed. At low wind speed, the wake has high visibility. Under moderate sea conditions, the wake can be identified by removing noise caused by surface wind waves, while the wake is difficult to recognize at high wind speed.
1.INTRODUCTION
When a submerged vehicle sails in ocean, it will produce hydrodynamic wakes similar to those of ships, which are difficult to eliminate for a long time. The types of wakes can be divided into Kelvin waves, Internal waves and Turbulent wakes (Zhang et al. 2003). And in synthetic aperture (SAR) radar remote sensing images, the wake often lasts for a long time and has a wide range, and may still exist even under moderate sea conditions (Lyden et al.1988). The SAR imaging of wakes can be influenced by various factors, such as marine environmental factors (sea conditions, stratification, terrain, etc.), submersible factors (speed, depth, etc.), radar factors (polarization mode, angle of incidence) (Yeremy et al. 2001).
