Measurement And Analysis Of Key Atmospheric Optical Parameters Of Site Testing For Optoelectronic System

When a laser beam propagates in the atmosphere,there are linear and nonlinear effects,such as beam wander,spread and phase distortion,that reduce the laser energy and power density in the propagation path.The topic Laser Beam Propagation in the Atmosphere(LBPA)studies those effects,aiming to avoid or lessen the influence of atmosphere on the beam.LBPA is an important content for the testing and evaluation of optoelectronic systems,as well as a necessary step for the application of optoelec-tronic system.The system efficiency and technical development is limited by the site condition,so it is crucial to evaluate the atmospheric and optical conditions for a site.In this thesis,experiment data is analyzed with the help of numerical simulation.Several appropriate data processing techniques are introduced to analyze the data and evaluate the uncertainty of key parameters of site condition.The main work is summarized as following:1.Collection and analysis of massive data of the site testing for optoelectronic sys-tems.Multi-year meteorological observation data is collected,and the national distribution of different parameter is given.Conventional meteorological param-eters are used to estimate aerosol optical depth over China.The precision of estimation algorithm is verified by the observed data of sun photometers.At-mospheric optical turbulence data measured at multiple stations throughout the country is analyzed.The logarithmic probability distributions of atmospheric co-herence length and isochoric angle are given.Considering the layered charac-teristics of optical turbulence,the coherent length ratio is defined to evaluate the contribution of near-surface optical turbulence to the whole layer of optical tur-bulence.Conventional sounding data in many years is analyzed to establish the wind speed pattern according with the actual site when local Greenwood wind speed models for different seasons are fitted.2.According to the characteristics of optical turbulence data,an improved version of Hilbert-Huang Transform is introduced to analyze the measured profiles of high-resolution optical turbulence.The Complete Ensemble Empirical Mode Decom-position decomposes the measured optical turbulence profiles into components at different scales.Different methods are used to explore the physical meaning of each component;then variance contribution rate is defined to evaluate the con-tribution of vibration in different components to the original profile;finally the quantitative description of optical turbulence profile is given.It is suggested that the optical turbulence model should contain a trend term and some fine struc-tures of specific scales.An intrinsic optical turbulence model is defined in which profiles of different orders can be embedded into varying components of differ-ent scales in the original profile.The influence of different components in optical turbulence profile on the calculation of some integral parameters is analyzed.The calculation results of different order optical turbulence models are compared by taking the turbulent momentums corresponding to atmospheric coherence length,isochoric angle and scintillation index as examples.3.The thermal blooming effect is related to many parameters such as wind speed and atmospheric extinction coefficient in the propagation path.In a typical prop-agation scenario,global sensitivity analysis methods are introduced to explore the sensitivity of the numerical model of thermal distortion parameter to different in-put factors.Elementary Effect Test is used to qualitatively evaluate the influence of each parameter on the numerical model of thermal distortion parameter,di-viding input parameters into important parameters and unimportant parameters.Variance-Based Sensitivity Analysis is used to quantitatively evaluate the sen-sitivity of those important parameters,indicating that those parameters can in-fluence thermal distortion parameter either directly or through interactions with other parameters,and the interactions between these parameters have a greater influence on thermal distortion parameter.The confidence intervals of sensitiv-ity statistics are calculated by the bootstrap method,and the confidence of each sensitivity index is given.4.The applications of artificial intelligence algorithm in atmospheric optics are ex-plored.Multilayer perceptron is constructed to estimate the near-surface optical turbulence.The input features are selected by Partial Mutual Information-based Selection and Genetic Algorithm-based Selection and the optimal number of neu-rons is determined by trial and error.The data is divided into training set,veri-fication set and testing set.The training set and verification set are used to train and optimize the neural network,and the testing set is used to evaluate the gen-eralization performance of the neural network.The results show that the perfor-mance of multilayer perceptron is good when the training and testing data come from the same site,while the generalization ability of multilayer perceptron is questionable when the training and testing data come from different sites.The generalized Hufnagel-Valley model is used to fit the average optical turbulence profiles of several regions.Taking the least root mean square of the logarithmic measured and fitted profiles as the optimization objective,the Genetic Algorithm is introduced to derive the seven parameters in the generalized Hufnagel-Valley model.The data used in this paper comes from the site testing project of photoelectric sys-tem.As for the content,on one hand massive data is analyzed revealing the variation characteristics;on the other hand,based on the indepth understanding of the data,the accuracy of several key parameters,such as aerosol optical depth,atmospheric coher-ence length,isochoric angle and thermal distortion parameters,are evaluated.As for the method,on one hand,the traditional data processing method is adopted;on the other hand,some new methods are introduced,which not only overcome the limitations of traditional methods,but also provide a new perspective to study related problems.As for the conclusion,it can be used not only in photoelectric site testing project,but also in theoretical researches and practical applications of atmospheric optics.