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ID:59180444
大小:3.10 MB
页数:32页
时间:2020-09-26
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1、ElectroMagneticRadiation(EMR)Lecture3August9,2006WaysofEnergyTransferEnergyistheabilitytodowork.Intheprocessofdoingwork,energyisoftentransferredfromonebodytoanotherorfromoneplacetoanother.Thethreebasicwaysinwhichenergycanbetransferredincludeconduction,convection,andradiation.
2、•Mostpeoplearefamiliarwithconductionwhichoccurswhenonebody(moleculeoratom)transfersitskineticenergytoanotherbycollidingwithit(physicalcontact).Thisishowapangetsheatedonastove.•Inconvection,thekineticenergyofbodiesistransferredfromoneplacetoanotherbyphysicallymovingthebodies.A
3、goodexampleistheconvectionalheatingofairintheatmosphereintheearlyafternoon(lessdenseairrises).•ThetransferofenergybyelectromagneticradiationisofprimaryinteresttoremotesensingbecauseitistheonlyformofenergytransferthatcantakeplaceinavacuumsuchastheregionbetweentheSunandtheEarth
4、.Jensen,2000RemotesensingandEMRremotesensingneedsanenergysourcetoilluminatethetarget(unlessthesensedenergyisbeingemittedbythetarget).ThisenergyisintheformofelectromagneticradiationSource:StanAronoff,2005MGSTES6–50µm1.DescribetheEMRWavemodelParticlemodel1A.WavemodelElectromagn
5、eticwaveconsistsofanelectricalfield(E)whichvariesinmagnitudeinadirectionperpendiculartothedirectioninwhichtheradiationistraveling,andamagneticfield(M)orientedatrightanglestotheelectricalfield.Boththesefieldstravelatthespeedoflight(c).Jensen,2000Threecharacteristicsofelectroma
6、gneticwaveVelocityisthespeedoflight,c=3x108m/swavelength(ג)isthelengthofonewavecycle,ismeasuredinmetres(m)orsomefactorofmetressuchascentimetres(cm)10-2mmicrometres(µm)10-6mnanometres(nm)10-9mFrequency(v)referstothenumberofcyclesofawavepassingafixedpointperunitoftime.Frequency
7、isnormallymeasuredinhertz(Hz),equivalenttoonecyclepersecond,andvariousmultiplesofhertz.unlikecandגchangingaspropagatedthroughmediaofdifferentdensities,vremainsconstant.Hertz(Hz)1kilohertz(KHz)103megahertz(MHz)106gigahertz(GHz)109Theamplitudeofanelectromagneticwaveistheheighto
8、fthewavecrestabovetheundisturbedpositionTraveltimefromtheSuntoEarthi
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