大气信道模型

《大气信道模型》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、组会报告张鑫2011年11月17日大气信道模型主要内容★大气信道对自由空间光通信的影响光束消光及其模型大气湍流及其模型★近期学习的其他内容★下一步工作大气信道对自由空间光通信的影响光束消光——激光光束在传播过程中强度的降低，即衰减。大气湍流——导致空间光强度波动、光束方向的随机变化、接收角波动等。光束消光BeamExtinction☞基本概念☞基本规律☞分子消光☞气溶胶消光基本概念和基本规律概念：激光束在含有原子、分子或颗粒的介质中传播时产生衰减的现象。起因：吸收（分子）和散射（气溶胶）。基本规律：朗伯定律——在物理状态保持稳定的情况下，消光过程在辐射强度和物质数

2、量上都是线性的。分子消光分子消光模型——描述由分子吸收产生的透光比损失FASCODEModelLOWTRANModelMODTRANModelFASCODEModel（1）FASCODE——line-by-linemodel,determinestheopticaldepthasafunctionofeitherwavenumberorwavelength.Anabsorptionlinehasthreeprimarycharacteristics:thecentralpositionofthelineVo;thestrengthorintensityofthel

3、ineS;theshapefunctionfortheabsorptionline.Thenaturallineshape(orLorentzprofile)isgivenbyThisprofileismostimportantintheloweratmosphereunderconditionsofrelativelyhighpressure.FASCODEModel（2）ThetransmittanceTofaregionistheratioofincidentpowertoemergentpower,andtherelationbetweentransmit

4、tanceandopticaldepthisimplicitlydefined:Totaltransmittanceforapathofinterestisdeterminedbyfindingthetransmittancesforeachhomogeneouslayerorregionthatcomposesthepath,andthenmultiplyingthemtogethertogettheresultanttotaltransmittance.MODTRAN&LOWTRANModelMODTRANModel——abandmodel,calculate

5、sthespectrallyaveragedatmospherictransmittance,doesnotobeytheLambertlaw(exceptfortheverynarrowspectralwindowsoverwhichanabsorptioncoefficientcanbeconsideredtobeconstant,whichismuchlessthanalinewidth),thefundamentaloutputoftheMODTRANmodel:thefull-pathtransmittance,ratherthantheopticald

6、epthoranextinctioncoefficient.LOWTRANModel——aninitiallowresolutiontransmittancecode.evolve气溶胶消光气溶胶模型——气溶胶颗粒数量的集中情况ModifiedGammaDistributionJungeFunctionShettleandFennModelNavyAerosolModel(NAM)AdvancedNavyAerosolModel(ANAM)模型简介Theaerosolparticlenumberconcentrationisdefinedasthenumberof

7、particlesperunitvolumeperradiusincrement:ModifiedGammaDistribution——themoderadius(in)thatcorrespondstotheradiusatwhichisamaximum；N——thetotalnumberdensityinparticlesper；a,b,,and——fouradjustableparametersthatallowthefunctiontobefittoalargevarietyofmodels.JungeFunctionc(r)isnowdefinedast

8、henum