大气信道模型

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;thestrengthorintensityofthelineS;theshapefunctionfortheabsorptionline.Thenaturallineshape(orLorentzprofile)isgivenbyThisprofileismostimportantintheloweratmosphereunderconditionsofrelativelyhighpressure.FASCODEModel（2）ThetransmittanceTofaregionistheratioofincidentpowertoemergentpower,andtherelationbetweentransmittanceandopticaldepthisimplicitlydefined:Totaltransmittanceforapathofinterestisdeterminedbyfindingthetransmittancesforeachhomogeneouslayerorregionthatcomposesthepath,andthenmultiplyingthemtogethertogettheresultanttotaltransmittance.MODTRAN&LOWTRANModelMODTRANModel——abandmodel,calculatesthespectrallyaveragedatmospherictransmittance,doesnotobeytheLambertlaw(exceptfortheverynarrowspectralwindowsoverwhichanabsorptioncoefficientcanbeconsideredtobeconstant,whichismuchlessthanalinewidth),thefundamentaloutputoftheMODTRANmodel:thefull-pathtransmittance,ratherthantheopticaldepthoranextinctioncoefficient.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Theaerosolparticlenumberconcentrationisdefinedasthenumberofparticlesperunitvolumeperradiusincrement:ModifiedGammaDistribution——themoderadius(in)thatcorrespondstotheradiusatwhichisamaximum；N——thetotalnumberdensityinparticlesper；a,b,,and——fouradjustableparametersthatallowthefunctiontobefittoalargevarietyofmodels.JungeFunctionc(r)isnowdefinedasthenumberofparticlesperunitvolumeandperlogarithmoftheradius.bothpandvisdependentupontheparticularcharacteristicsoftheaerosol.Theexponentvcanvaryovertherange2<v<4,withthelowervaluetypicallyfoundinfogconditions.ShettleandFennModel（1）——themoderadius(radiusforwhichthedistributionismaximized)——adistributionwidthparameter.ShettleandFennmodelincludefourmodels(rural,urban,maritime,andtropospheric).Thetroposphericmodelcontainsonlyasinglelog-normaldistribution,whiletheotherthreemodelscombinetwolog-normaldistributions.ShettleandFennModel（2）Theruralmodel——representaerosolsthathavenourbanorindustrialsources.Theaerosolisamixtureofwatersolublecomponentsand"dust-like“components.Thecomplexrefractiveindexisdeterminedbytherelativeweightingofthecomponentsinthemixture.Theurbanmodel——modifiestheaerosolmixbyincludingcombustionproductsandotherindustrialproducts.Themaritimemodel——hastwocomponents:(I)asea-saltcomponent,and(2)acontinentalcomponent.Thecontinentalcomponentisidenticalwiththemixturedefinedintheruralaerosolmodelexceptthatthelargestparticlesareeliminatedduetoassumedfalloutbythetimetheairmasshastransportedouttotheopenocean.NavyAerosolModel(NAM)NAMiswidelyusedtomodeltheeffectsofaerosolextinctioninmarineenvironments.Theaerosoldistributionisassumedtoberepresentableasasumoverfourlognormallydistributedmodes:Limitations——NAMwasdesignedtodetermineextinctionatasingleheightabovetheoceansurface,namely10m.Inaddition,itwasdesignedtorepresentaerosolextinctionconditionsthatoccuroveropen-oceanconditions,andnotnecessarilytheactualconditions.AdvancedNavyAerosolModel

ItwasdevelopedtocorrectsomeofthelimitationsanddeficienciesfoundinNAM.ANAMintroducesaheightdependenceforaerosolparticleconcentrationsfromthesurfaceuptoseveraltensofmeters.——heightabovethewatersurface；——windspeedmeasuredata10mheight.小结由于光束消光产生的大气链路损耗：T(s)是透光比：是总消光系数：Fortypicalclearairconditions,;forhazeconditions(withavisibilityofroughly4km),;infogconditions,;foradensefogwithavisibilityof10m,.大气湍流模型☞折射率结构参数

——与波长、气温、气压有关，随地面高度h的变化而变化☞空间光功率谱密度——用来描述☞大气湍流模型——描述折射率结构参数折射率结构参数折射率结构方程

ForlocallyhomogeneousandisotropicturbulenceWithintheinertialsubrange

空间光功率谱密度KolmogorovspectrumNon-KolmogorovspectrumTatarskiispectrumModifiedvonKarmanspectrumKolmogorovspectrum是三维波矢，范围是适用条件：：infinite(m)，：negligiblysmall(mm)在有奇点Non-Kolmogorovspectrum：折射率结构参数，单位为特别地，当Non-KolmogorovspectrumKolmogorovspectrumTatarskiispectrum使用Gaussian方程来截短Kolmogorovspectrum

isthecutoffathighwavenumbers在有奇点ModifiedvonKarmanspectrum适用条件：Itisfiniteandisotropicfor大气湍流模型GurvichModelSLC-DayModelHufnagel-ValleyModel(HVModel)HV-NightModelGreenwoodModelGurvichModel（1）Inthismodelprofilesareclassifiedintofourgroupsdependentonthemeasured(orestimated)valueofattheheight（1）For（strongturbulence）（2）ForGurvichModel（2）（3）For（4）For（weakturbulence）GurvichModel（3）GurvichModel（4）GrachevaandGurvichdevelopedtheso-called‘simple’modelsofturbulence:A.Modelforthe‘best’atmosphericconditions(weakturbulence):B.Modelforthe‘worst’atmosphericconditions(strongturbulence):C.Modelfor'average'atmosphericconditions(geometricalmeanvalueofthetwopreviousprofiles):GurvichModel（5）SLC-DayModelTheSubmarineLaserCommunication-Day(SLC-Day)modelisfrequentlyusedtodescribedaytimeturbulenceconditionsatinlandsites.Hufnagel-ValleyModel（1）TheHufnagel-Valley(HV)modelisoneofthemostpopularmodelsforinlandsitesanddaytimeviewingconditionssinceitpermitsvariationsinhigh-altitudewindspeedandnear-groundturbulencelevels.A——thenominalvalueofatthegroundV——theestimatedhigh-altitudermswindspeedinm/sinthe5-20-kmaltituderangeHV-21model——

Hufnagel-Valle