Study On The Refractive-index Power Spectrum Of Oceanic Optical Turbulence Based On Hill Model 4

The light,as a tool carrying and routing information,has been widely used in underwater wireless communication and underwater measuring.But the propagation of light in ocean is always affected by oceanic turbulence.Researches about this are based on the oceanic refractive-index power spectrum(ORIS)which characterizes the statistics of refractive-index in turbulence.In 1999,the power spectrum of refractive-index in ocean has been modeled by V.V.Nikishov and V.I.Nikishov for Kolmogorov case,and the model has been widely used in the community.But this model was queried in 2018 because a scalar model(Hill model 1)on which it is based has low precision.Then,based on Hill model 4 which has high precision,Yi spectrum was proposed for oceanic optical turbulence,and this spectrum behaves well when the Prandtl number equals 7 and the Schmidt number equals 700.Meanwhile,since 1990,the Atmospheric Optics has used Hill model 4 to develop the refractive-index power spectrum.A further comparison between researches about ocean and those about atmosphere shows a faster development of the latter which has obtained Non-Kolmogorov models for nonclassical turbulence,and has paid more on using structure coefficient to characterize the strength of optical turbulence and using inner scale to characterize the minutia of optical turbulence.The above studies of atmospheric optical turbulence could provide a good reference for researches about oceanic optical turbulence.In considering above,this dissertation thesis contains three parts: Studying on classical oceanic optical turbulence,and proposing an oceanic Kolmogorov power spectrum of refractive-index based on Hill model 4 for wide-ranged Prandtl number and Schmidt number;Studying on non-classical oceanic optical turbulence,and developing a non-Kolmogorov power spectrum of refractive-index for oceanic optical turbulence;Studying on parametric characterization of oceanic optical turbulence,and obtaining the equivalent structure coefficient and the equivalent inner scale of above oceanic power spectra of refractive-index.The main contents are as follows.Firstly,a refractive-index Kolmogorov power spectrum of oceanic optical turbulence is obtained based on Hill model 4 for the oceanic environment in which Prandtl number and Schmidt number are wide-ranged.In this work,Hill model 4,as a differential equation,is numerically solved and numerically fitted in a wide range of Prandtl number and Schmidt number.Based on the fitted result,Kolmogorov spectrum of scalar is obtained.It can describe temperature spectrum and salinity spectrum,and it agrees well with the curves of Hill model 4.Then,the temperature-salinity co-spectrum is derived by using Nikishov analogy method.By combining the scalar spectrum and the co-spectrum,an oceanic refractive-index Kolmogorov power spectrum(Kolmogorov ORIS)is developed.In addition,the variation of parameters in spectrum with environment and wavelength is considered,and the relations between Kolmogorov ORIS and averaged temperature,average salinity,temperature-salinity gradient ratio,wavelength are built up.Based on above results,the influence of averaged temperature,average salinity,temperature-salinity gradient ratio and wavelength on light propagation is discussed,and we find that the statistics of light propagation corresponding to our Kolmogorov ORIS agree well with those corresponding to Hill model 4.Then,a non-Kolmogorov power spectrum of oceanic optical turbulence is proposed,which refers to the nonclassical turbulence.In this work,the scalar spectrum we obtained based on Hill model 4 is extended to a non-Kolmogorov form which agrees well with the structure function of refractive-index.Next,the concept of spectral correlation is introduced to deduce the temperature-salinity co-spectrum in non-Kolmogorov case.And then,a non-Kolmogorov ORIS is obtained by combining the non-Kolmogorov scalar spectrum and the non-Kolmogorov co-spectrum.Finally,in considering the significance of structure coefficient and inner scale in the studies about light propagation,an equivalent structure coefficient and an equivalent inner scale of ORIS are obtained.In this work,the plane wave scale pattern in oceanic turbulence is studied.According to the scale pattern,we obtain the equivalent structure coefficient and the equivalent inner scale by comparing the wave structure function of plane wave in oceanic turbulence with those in atmospheric turbulence.To verify whether the equivalent structure coefficient can describe the turbulence strength,and whether the equivalent inner scale can describe the turbulence minutia,we analyze them from three aspects: plane wave angular spectrum distribution,optical scintillation and the minutia of refractive-index.The analysis shows that the equivalent structure coefficient can describe the turbulence strength,and the equivalent inner scale can describe the turbulence minutia.