Study On High Frequency And Ultra High Frequency Ocean Surface Scattering

With the development of the economic construction and national defense construction, the studies on near-shore ocean dynamics environment are more and more pressing demanded. Real-time monitored the near-shore ocean dynamic environment effectively, may provides the scientific basis for the near-shore marine enviroment, and avoids the great losses under the condition of poor enviroment of the ocean dynamics. The costal ocean remote sensing technology is urgently needed. For the limitation of the theory and technology, the present ocean remote sensing technology is unsuitable for the near-shore application. A new scattering model is used to characterize the electromagnetic scattering from the sea.In this work, simulation approaches are realized, improved and assessed.1. By using perturbation method with Maxwell equations, boundary conditions and fluic dynamic equations, this paper studies the three-dimensional rough surface scattering, derives second-Doppler spectrum and modifies the electromagnetic coupling coefficient. For the modified fluid coupling coefficient, the numerical solution of the radio scattering cross section is more precise. The second-order Doppler echo spectrums are invered under 13MHz, 25MHz and 300MHz incident frequencies.2. According to the second Green Vector Theorem, the representation of the far electromagnetic scattering wave is derived by using Kirchhoff stationary phase approximation.The second-order Doppler spectrum of three-dimentional rough ocean surface is derived for the first time.The influence of the wind speed, radar incident frequency is analyed.3. Based on the Gaussian sea surface model, the series expansions of the slope of three-dimention Gaussian sea surface model is used with small slope approximation,to obtain the second order doppler spectrum, and simulations of 13MHz,25MHz and 300MHz are implemented.4. Combination of the small perturbation method and Kirchhoff approximation is applied for derivation of the Two-scale model. Adopting the A.K.Fung sea-spectrum model, the second echo spectrum is derived by Two-scale model with considering the gravity waves and capillaries. The result of the second echo spectrum is compared with other scholars’results and the real sea echo.For summarize, this thesis is focused on the electromagnetics scattering from the ocean surface and the efficiency, accuracy and applicability of different methods serve as the main subjects.