| Generally,the radar platform was NOT moving in the traditional electromagnetic scattering model of sea surface,where back scattering coeefficients were calculated in varies conditions.These models provide numerous simulation results for the study of the electromagnetic scattering of sea surface,and provide solid foundation to explain scientific phenomenon of electromagnetic scattering from sea surface.Nevertheless,radar platforms are moving in most realistic scenarios of remote sensing.It is neccesary to consider the flight process of the motion radar platformhe in sea surface electromagnetic scattering.Therefore,based on the traditional small slope approximation and the actual monitoring mode of airborne radar from aircraft and missiles,spatiotemporal dynamic scattering models in sidelooking and front-looking platform are simulated with the uniform speed for horizontal or oblique moving,respectively.Consquently,the time series of sea clutter and its doppler spectrum and statistical distribution are presented under different conditions of sea surface environments or radar platform parameters.This paper provides technical support for the development of ocean remote sensing technology.The main work of this paper is as follows:1.The method and process of sea surface modeling are introduced in detail.Peculiar to sidelooking and front-looking moving radar,three-dimensional spatiotemporal dynamic sea surfaces are presented with spatiotemporal coherence.For the long strip sea surface model based on moving platform,FFT is optimized to reduce the computational complexity and the simulation time.2.The small slope approximation is applied into the calculation of electromagnetic scattering from three-dimensional sea surface.The applicability of the small slope approximation is studied on the size of sea surface model and the mesh number of unit wavelength.Furthermore,the effect of incident angle,wind speed,etc,on RCS are discussed in detail.A parallel acceleration technology,Open MP,is combined with the sea surface modeling and the small slope approximation to optimize the simulation model and achieve excellent acceleration effect.3.The influence on the characteristics of the Doppler spectral shift and broadening is studied by considering moving radar platform.The time series of sea clutter and its Doppler spectrum are simulated under different sea environment and radar platform parameters.The result shows that the Doppler spectral shift of echo is particularly sensitive to the velocity of moving platform with the premise of non-crosswind incidence,and the velocity of moving platform will expand the Doppler spectral broadening,too.4.The statistical characteristics of backscattered echoes from moving radar platform are studied.The optimum amplitude distribution model matching,amplitude ratio distribution and phase difference distribution of sea clutter of moving radar platform are discussed under different incident angles,frequency and wind speed.The results show that the clutter from moving rader platform matches well with Weibull distribution when the wind speed of sea surface is small,but when the wind speed increases,it tends to lognormal distribution.It is also pointed out that the moving platform can shorten the decorrelation time of sea clutter according to the results of amplitude ratio and phase difference. |
