Study On The Propagation Of EM Wave In The Evaporation Duct Over The Sea And Inversion Problem Based On The Neural Network

Both of the parametric characteristics and forming conditions of evaporation duct over the sea are described in this paper, and the impact of atmospheric duct on the propagation of electromagnetic wave is analyzed here. The concept of atmospheric boundary layer is then introduced, and both of standard atmosphere and atmospheric layer near sea surface are presented detailedly. The expression of modified refractivity under different atmospheric layers is given here, and the characteristics of modified refractivity profile of neutral atmospheric layer and stable atmospheric layer are analyzed through comparison. Three evaporation duct models are introduced: U.S. model (PJ), European model (MGB) and recently developed model (Babin). Two solutions to solve the field distribution of electromagnetic wave under atmospheric duct are presented, ray tracing method and parabolic equations method, which are used to obtain field distribution and propagation path loss under both standard atmosphere and evaporation duct, and the difference due to different polarization states is also analyzed. Finally, both of the principle of neural network method and the method to inverse atmospheric modified refractivity profile are given, and heights of different evaporation ducts are inversed using the power of sea clutter echo. The inversion results in certain range of height are reliable through comparisons and analyses.