大氣信道模型主要內(nèi)容★大氣信道對自由空間光通信的影響

光束消光及其模型大氣湍流及其模型★近期學(xué)習(xí)的其他內(nèi)容★下一步工作大氣信道對自由空間光通信的影響光束消光——激光光束在傳播過程中強(qiáng)度的降低，即衰減。大氣湍流——導(dǎo)致空間光強(qiáng)度波動、光束方向的隨機(jī)變化、接收角波動等。光束消光BeamExtinction?基本概念?基本規(guī)律?分子消光?氣溶膠消光基本概念和基本規(guī)律概念：激光束在含有原子、分子或顆粒的介質(zhì)中傳播時產(chǎn)生衰減的現(xiàn)象。起因：吸收（分子）和散射（氣溶膠）?；疽?guī)律：朗伯定律——在物理狀態(tài)保持穩(wěn)定的情況下，消光過程在輻射強(qiáng)度和物質(zhì)數(shù)量上都是線性的。分子消光分子消光模型

——描述由分子吸收產(chǎn)生的透光比損失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氣溶膠消光氣溶膠模型——?dú)馊苣z顆粒數(shù)量的集中情況

ModifiedGammaDistributionJungeFunctionShettleandFennModelNavyAerosolModel(NAM)AdvancedNavyAerosolModel(ANAM)模型簡介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.小結(jié)由于光束消光產(chǎn)生的大氣鏈路損耗：T(s)是透光比：是總消光系數(shù)：Fortypicalclearairconditions,;forhazeconditions(withavisibilityofroughly4km),;infogconditions,;foradensefogwithavisibilityof10m,.大氣湍流模型?折射率結(jié)構(gòu)參數(shù)

——與波長、氣溫、氣壓有關(guān)，隨地面高度h的變化而變化?空間光功率譜密度——用來描述?大氣湍流模型——描述折射率結(jié)構(gòu)參數(shù)折射率結(jié)構(gòu)參數(shù)折射率結(jié)構(gòu)方程

ForlocallyhomogeneousandisotropicturbulenceWithintheinertialsubrange

空間光功率譜密度KolmogorovspectrumNon-KolmogorovspectrumTatarskiispectrumModifiedvonKarmanspectrumKolmogorovspectrum是三維波矢，范圍是適用條件：：infinite(m)，：negligiblysmall(mm)在有奇點(diǎn)Non-Kolmogorovspectrum：折射率結(jié)構(gòu)參數(shù)，單位為特別地，當(dāng)Non-KolmogorovspectrumKolmogorovspectrumTatarskiispectrum使用Gaussian方程來截短Kolmogorovspectrum

isthecutoffathighwavenumbers在有奇點(diǎn)ModifiedvonKarmanspectrum適用條件：Itisfiniteandisotropicfor大氣湍流模型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