The Simulation And Electromagnetic Calculation Of The Sea And The Ship Wake

With the rapid development of marine remote sensing and radar tracking technology, the detection of the sea and the targets on it has been becoming more of a concern, especially the detection of ships on the sea has become the main content of the ocean research. The ship targets in actual complicated sea background are difficult to be detected, so inverting ship targets' information through their wakes has been one of the most important research directions in marine target detection. In this thesis ship's Kelvin wakes, two-dimensional linear and nonlinear seas were simulated, and the ship's Kelvin wakes under ocean background were given, then corresponding electromagnetic scattering calculations were carried out at last. The main research contents of this thesis can be divided into the following three parts: sea's modeling, ship's Kelvin wakes' modeling and the electromagnetic scattering calculation of them.First, several common modeling methods of sea were described, and the modeling method based on sea wave spectrum was chosen, besides several common wave spectra were given. Then we used the linear superposition method and the linear filter method, and two-dimensional linear seas with different wind speeds and different wind directions were obtained. Considering that the real sea is non-linear, a common method of non-linear sea modeling was introduced, namely the CWM(Choppy Wave Model). Then non-linear seas were obtained with the linear sea results, and those results, compared with corresponding linear ones, were in line with characteristics of seas in real situation.Second, appropriate ship models were selected to simulate Kelvin wakes, which were the most common ones of ship' wakes, then Kelvin wake results with different parameters were obtained. Combined with Kelvin wakes' simulation, corresponding comparison and analyses of the factors influencing Kelvin wakes were conducted. Superimposing Kelvin wakes on linear and non-linear seas simulated before, we got Kelvin wakes on linear and non-linear seas, then we changed the wind speed above seas and ship's speed, ship's Kelvin wakes on the seas with different wind speeds and different ship speeds were obtained, after the results being analyzed, a factor that wakes with high sea-station and low ship speed are easily been drowned was obtained.Finally, the Debye formula was used to calculate the seawater's permittivity with radar incident waves in different frequencies. While calculating the electromagnetic scattering of electrically large sea, taking the characteristics of the sea simulated into consideration, the Kirchhoff Approximation was adopted, then distributions of the sea's electromagnetic scattering coefficients with different wind speeds, different wind directions, different incident wave frequencies and different polarization mode on incident angles, scattering angles, incident azimuth angles and scattering azimuth angles were obtained, and corresponding analyses were conducted. And based on this, electromagnetic scattering calculations of Kelvin wakes on linear and non-linear seas were conducted, the effects of factors such as wind speed, wind directions and ship speed on them are obtained.