Remote Sensing - DePaul University GIS Collaboratory 遙感- DePaul大學地理信息系統(tǒng)實驗室

RemoteSensingJanuary20,2006Geog258:MapsandGISOutlinesPrinciplesofremotesensingThreekeyaspectsofresolutionofremotelysensedimageAerialphotovs.satelliteimageClassifyingaerialphotographGeometricdistortionofaerialphotographClassifyingsatelliteimagePrinciplesofremotesensingWhatyouseeistheamountofelectromagneticenergyreflectedbyobject;needsenergysource,object,sensorElectromagneticenergycanbedividedintodifferentspectralbands(visiblelight,NIR,microwave)givenitswavelengthElectromagneticspectrumElectromagneticenergyinteractswithobjectdifferentlySnowreflectsmostofenergy(that’swhyitlooksbright)Drysoilabsorbsmostofenergy(that’swhyitlooksdark)HowobjectinteractswithelectromagneticenergyisafunctionofwavelengthsbasisofimageinterpretationSpectralreflectancesignatureElectromagneticradiationinteractswithatmosphereaswell.Someradiations(invisible,NIRandmicrowavebands)passthroughatmosphererelativelywellAtmosphericwindowElectromagneticspectrumSpectralsignatureExplainwhywaterlooksdarkishblue;Explainwhyvegetationlooksgreenish;ExplainwhysandlooksreddishyellowAtmosphericwindowItshowshowmuchelectromagneticradiationtransmitsatmosphereInwhichbands,is%transmissionhigh?Advantageofusingthosebands?CompareaerialphotoandsatelliteimageintermsofspectralbandsOpticalsensorInfraredsensorRadarsensorAerialphotographDifferentkindsofimagePancromaticimageTrue-colorimageFalse-colorimagePancromaticimageIfairbornecamerasuseblack/whitefilmorsatellitesensorsuseasingleband,itproducespancromaticimage(grayscaleimage)ColorcompositeColorprimaries:RGB(Red,Green,Blue)ManycolorsareformedbycombiningcolorprimariesinvariousproportionsLookinsideyourinkjetcolorprinter.Didyoureallybuy100differentcolorcartridges?SameprinciplesapplytoproducingcolorimagestakenfromairbornecamerasorsatellitesensorsTrue-colorimageSeeTable9.1(p.182)HowmanybandsareusedforLandsat4and5?What’sthespectralrange(andcorrespondingcolors)forbandname3,2,1?Eachbandcollectsdifferentimages(SeeFigure9.27atp.182)Toproducecolor-image,bands321areassignedtoRGBrespectivelyThecolorofresultingimageresembleswhatwouldbeobservedbyhumaneyesThat’swhyit’scalledtrue-colorimageFalse-colorimageIfthreebandsarearbitrarily(i.e.doesn’thavetobeRGBbands)assignedtoRGBlayers,itproducesfalse-colorimageSPOTXS1(greenband)

SPOTXS2(redband)

SPOTXS3(NearIRband)

R=XS3(NIRband)

G=XS2(redband)

B=XS1(greenband)

Whydoesvegetationappearredinthiscolorcomposite?Whydoesvegetationappeardarkingreenbandinpancromaticimage?WhydoesvegetationappearbrightinNIRbandinpancromaticimage?ThreekeyaspectsofresolutionsSpatial:pixel(grain)size;minimumdistancewhichcanberecordedAerialphotohasofcoursehigherresolutionTemporal:howoftenistheimagerecordedForsatelliteimage,itcanberegular(satellitesareorbitingtheearthinregulartimeinterval)Spectral:howmanybandsareusedSatellitesensorsusedifferent#bands;mostofthemlessthan10(e.g.TMuses7bands);sensorswith#band>10arecalledhyperspectral(e.g.MODIS)ImportantindeterminingthefitnessofuseTypesofsensorsystemsPassiveRelyonexternalenergysourceOpticalsensor(reliantonsolarenergy)ActiveSensoritselfsendsoutradiation(likeflashcamera)Radarsensor(reliantonmicrowave)Whichonecanrecordtheimageofearthatnight,andwhichonecan’t?AnotherreasonforthepopularityofRadarimagingistheabilityofmicrowavetopenetrateatmosphere(e.g.clouds);seeFigure9.4(p.164)SowhatwouldbetheadvantageofRadarimagingcomparedtoopticalimaging?Aerialphotographyvs.Satelliteimaging

(AirborneRSvs.SpaceborneRS)Whichbeganearlier?(withthedevelopmentofwhat?)Whichwouldhaveahigherspatialresolution?(inwhichaltitude?)Aretheyanalogordigital?(outputformat)Whichismoreflexible?(cansatellitebelaunchedanytime?)Whichwouldprovidegeographiccoverageinasystematicmanner?Whichisequippedwithwiderspectralbands?(doesairphotohasthermal-infraredsensors?)Howwouldpost-processingbedifferent?ClassifyingaerialphotoFilmemulsion{black-and-white,true-color,color-infrared}Camera’sheight{high,mid,low-altitude}Camera’svantagepoint{vertical,oblique}Whencolor-infraredfilmswereinvented,andforwhichpurpose?GeometricdistortionofairphotoAerialphotogivesusperspectiveview(itdistortsgeometryofgeographicfeatures)TransformationfromcentraltoparallelperspectiveresultsinplanimetricallycorrectphotoororthophotoSourcesofgeometricdistortionCameratiltsScaleisnotuniformSourcesofgeometricdistortionVariationsinterrainRememberphotoisflat(2D)andobjectsshouldbeseenfromthepointofinfiniteheightintheplanimetricallycorrectphoto.Intheaerialphoto,a’isdisplacedoutwardtoab’isdisplacedinwardtobduetoterrainvariationsClassifyingsatelliteimageSpatialresolution{high,low}Typesofenergysource{passive,active}Typesofspectralbands{pancromatic,multispectral,hyperspectral}Specialpurposes{earth-observing,meterological,thermal-infrared}Fromthelistofearthobservingsatellite,,placethesensorsinclassificationschemesaboveReviewquestio