| The effects of atmospheric optical turbulence strongly restricts the performance of electro-optical engineering in marine environment,such as optical remote sensing imaging,free space optical communication and laser propagation in atmosphere.The accurate assessment of the influence of atmospheric optical turbulence on the electro-optical system depends primarily on the turbulence information,especially the atmospheric refractive index structure parameter Cn2 which is an important parameter to quantitatively describe the intensity of atmospheric optical turbulence.In marine environment,Cn2 can provide effective guidance on the optimal working time of laser engineering system for atmospheric transmission and the setting of key parameters of the electro-optical system.Because of the complexity of the underlying surface of the ocean,the current detection technology of Cn2 is always expensive,and a longstanding measurement for many climates and seasons are not available,which cannot meet the application of the electro-optical engineering.Therefore,some models have been established to estimate Cn2 from routine meteorological parameter.In this paper,we estimate Cn2 in marine environment using the sea surface data measured on the observation platform in the South China Sea at Maoming and the sounding data measured by the meteorological balloons equipped with sensors in open sea,respectively.The results are compared with those in different environments.We also evaluate the feasibility and reliability of the models with quantitative statistical analysis.The main work and conclusions of the article are as follows:1.The author summaries some boundary layer turbulence models,such as Bulk,Tatarski and Wynggard models,which based on similarity theory,and some outer scale profile models,such as Dew an,HMNSP99,Coulman and Jackson models,which based on Tatarski model.Besides,the artificial neural network model and Thorpe outer scale model are added.2.The Cn2 of the atmospheric boundary layer of the sea,the sea-land interface and the inland area are estimated by using the routine meteorological data from the integrated observation platform over sea and on the coast of Marine Meteorological Science Experiment Base at Bohe of Maoming,China Meteorological Administration,and from the 35 meters tower in Hefei,respectively.We also analyze the results of models estimation and the factors of estimation errors.The results of marine atmospheric boundary layer shows that the average relative error of the Bulk method which considers the contribution of temperature,humidity,and temperature-humidity correlation term to the turbulence is 3.97%,which is slightly higher than 3.82%of the Wynggard model which only considers the contribution of temperature to the turbulence.However,the correlation coefficient between the estimates of Bulk method and the measurements is 0.65,which is significantly higher than 0.56 of the Wynggard model.It means the contribution of humidity and temperature-humidity correlation term to the turbulence in the marine environment is unignorable.As atmospheric optical turbulence models usually have regional characteristics,a set of similarity functions are fitted using the datasets from the 35 meters tower in Hefei.Then the similarity functions succeed in coupling with Bulk method to estimateCn2 in Hefei.3.Based on 30 sets of sounding data obtained at Marine Meteorological Science Experiment Base at Bohe of Maoming and the Hufnagel model,an empirical model for Cn2 profile is fitted,which is appropriate to the variation of the turbulence profile on the coast.Based on the HMNSP99 outer scale model,a new outer scale model of Maoming is obtained by fitting the sounding data and used to estimate Cn2 of Maoming.The new estimated Cn2 are then compared with measurements and the results from the Dewan,HMNSP99 and Coulman outer scale models,respectively.It is found that the new Maoming outer scale model has a best result,the correlation coefficient between the estimates and the measurements is 0.92,while the average relative error is the lowest,only 2.96%.In addition,according to 10m resolution sounding data in Kuerle,we extend the Thorpe outer scale model from troposphere to stratosphere,the correlation coefficient between the estimates of Thorpe outer scale model and the measurements is 0.73,and the average relative error is only 2.44%.4.The atmospheric optical turbulence profiles of inland area(Hefei),sea-land interface(Maoming)and open sea are estimated by using the Dewan,HMNSP99 and Coulman outer scale models combined with the Tatarski optical turbulence parameterization scheme,respectively.The estimates are compared with the observed Cn2 profiles in Hefei and Maoming.The results show a good consistency both in trend and magnitude,which provides a support for estimating Cn2 profiles of open sea with this model.Besides,the consistency of the estimates of the Dewan,HMNSP99 and Coulman outer scale models in open sea are compared.We can conclude that the outer scale of the open sea is less than 10 meters,and jitter violently with height,and less than 1 meter above 20 kilometers.Cn2 is approximately 10-14 to 10-19 m-2/3,and decreases with height.5.This paper analyses the relationships among the Cn2 profiles,wind shear,temperature gradient,and the reciprocal of Richardson number.It is found that a strong,thin turbulent layer often corresponds to sharp fluctuations of wind shear,temperature gradient,and the reciprocal of Richardson number.It is concluded that the estimates of Cn2 profile using the HMNSP99 outer scale model which includes both wind shear and temperature gradient is more in line with the actual turbulence variation.The research work of this paper shows that the turbulence models can well accomplish the estimation of Cn2 in marine environment.It can accumulate data and provide useful method for the development of Cn2 model and the study of turbulence characteristics in marine environment.However,the turbulence models still need to be modified and improved to meet the needs of higher accuracy. |
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