The Study Of Sea Wave Slope Probability Distribution Inversion Based On Low-incidence Radar

The slope of sea wave is an important physical parameter of ocean.A number of processes occurring at or near the air-sea interface are closely related to the sea wave slope.Accquiring the distribution of wave slopes accurately has important physical significance and high order parameters of wave slope can also provide new approach to accquire some unknown parameters of ocean.Although in most circumstances,sea wave slope probability density function(PDF)is expressed as a Gaussian distribution,there is evidence to suggest that it follows a quasi-Gaussian,which can be represented by Gram-Charlier seres to fourth order.The empirical formulae of statistical parameters of slope PDF have all been derived by optics method previously.However,these results cannot be simply extrapolated to the case of microwave observation of the sea surface,because of diffraction effects which limit the sensitivity of the observations to scales larger than 2 to 5 times the electromagnetic wavelength,and now there are no empirical formulae specially designed for microwave band.Aiming at such requirement,the main research targets of this paper is inverting the parameters of quasi-Gaussian from PR data and establishing empirical formulae of quasi-Gaussian slope PDF suitable for Ku-band.Inverting high order parameters of sea wave slope has very strict requirements for the inversion model accuracy,so we propose a new high-precision low-incidence radar sea surface scattering model named FGO4 model as the inversion model.The paper study the physical optics model based on quasi-Gaussian sea wave slope PDF,and conpute the backscattering coefficient based on the scattering characteristics under the small incidence;and then,introduce the geometrical optics of second order(GO2),quasi-specular model(QS),and propose a “filtered” GO4 model(FGO4 model)combining the advantages of QS model and geometrical optics model of to fourth order(GO4)and simulate to verify the accuracy and the physical meaning of parameters of FGO4 model.Then,confirm the range of incidence and wind speed for FGO4 inversion using simulation.In this paper,the other important research content is quasi-Gaussian sea wave slope inversion based on microwave remote sensing measurement data.Here,the data set we choose for inversion is the data of Ku band low-incidence spaceborne precipitation radar.And we use the FGO4 model proposed in this paper and two-dimensional nlinear least-squares fitting method,invert all the statistical parameters of quasi-Gaussian slope PDF from PR radar measurements.We also establish the empirical formulae of all the seven parameters varing with wind speed under the Ku band.Besides,the impacts of wave conditions(swell or wind sea)and the impacts of angles between wind and wave direction on slope PDF parameters are also studied...