Study Of Electromagnetic Scattering From Rough Sea Surfaces

Rough sea surfaces are formed with the interaction, which is nonlinear, of sea- surface wind and gravity and surface-tension of sea water. Also nonlinear is the interaction of sea surfaces with electromagnetic waves. So nonlinear theory and method should be employed in the study of EM scattering from rough sea surfaces. Also applied in this area should be numerical computation techniques and intelligent methods that have been used extensively in other modern sciences and technology. Study of EM scattering from rough sea surfaces is divided into such several aspects as modeling sea surfaces, calculating EM scattering, analysis of echo and parameters retrieval of sea surfaces in this paper. Following are the important work and conclusions. 1 Three typical sea power spectrum including new D-B-J spectrum are introduced and analyzed. Sea surfaces are modeled with analytical statistical model, numerical statistical method, fractal function and the hybrid of statistics and fractal. 2 Kirchhoff approximation is modified with the 2th order iterative solution of integral equation of EM field. 5PM and TS are amended with the curvature of the rough sea surfaces. Two methods are presented to compute the slope probability density function used in TS model, and this makes it possible to calculate EM scattering from fractal surfaces with TS. 3 Moment method (MM) is employed to calculate EM scattering from rough sea surfaces as nonconductors. 4 FDTD is used to compute the EM scattering from rough sea surfaces with objects on them while incident wave is plane and nonplane. 5 MM and FDTD are combined with beam simulation method to extend the size of rough surfaces calculated, whose efficiency is shown with numerical results. 6 The variations of EM scattering coefficient versus wind speed and TM wave polarization are discussed. EM scattering from fractal rough sea surfaces is calculated to conclude that the echo is also fractal and the amplitude distribution satisfies the K-distribution. The relation between the fractal dimension, the shape parameter of K-distribution of the echo and the sea surface parameter is obtained. 7 The retrieval of wind speed and the temperature of sea water is conducted with ANN and GA.