Numerical simulation study on thermal trailing wake of targets at sea

The infrared trailing wake of a moving target at sea is a significant factor in the detection and identification process. Therefore, it is imperative to conduct infrared simulation and analysis for the trailing wake of a moving target at sea. Initially, the geometric modelling of the wake for the moving target is conducted based on the Kelvin wake and turbulent wake model, and the geometric model of the wake with sea surface is formed by the linear superposition method combined with the sea surface wave height spectrum model. Subsequently, the BRDF solution model for the optical parameters of the wake on the sea-air trans-medium surface is established by combining the Monte Carlo-light ray tracing method, and the discrete coordinate method is employed to carry out the rapid simulation of the background radiation of the sea surface with the wake. Finally, the distribution of the wake geometry and infrared radiation field of target at 300K seawater temperature is calculated and analysed, based on the calculation results of the trailing wake temperature field of a typical Wigley ship type travelling at a uniform speed on a calm sea surface. The results demonstrate that the width of the trailing wake and the sea surface disturbance caused by a large ship are significantly larger than those of a small ship in terms of geometric dimensions. However, in the infrared radiation simulation imaging results, the distribution of the trailing wake radiation characteristics of the target at different scales in the same infrared wavelength band is consistent. Furthermore, the infrared radiation in the mid-waveband (3-5 μm) of the trailing wake is higher than that of the surrounding sea surface, while the opposite is true for the long-waveband (8-14 μm). This phenomenon can be attributed to the fact that, when imaging is conducted from a fixed angle, the geometry of the trailing wake prompts alterations in the slope of the wavelet surface and the foam structure of the sea surface. Concurrently, the reflected radiation entering the detector in different bands is subject to modification due to the influence of the optical parameter BRDF on the surface of the wavelet surface. This ultimately leads to the distribution of the radiation characteristics according to the geometric shape of the wake. The infrared simulation imaging model of the trailing wake for the moving target at sea can be used as a reference to provide simulation models for the analysis of the infrared trailing wake of different types of targets sailing in different sea areas.