[PDF] REMOTE SENSING & GIS

1136_3REMOTE_SENSING_GIS.pdf

UNIT I REMOTE SENSING

Prepared byT.DINESH KUMARAssistant ProfessorECE,SCSVMV

REMOTE SENSING & GIS

AIM &OBJECTIVESTo provide students an exposure to Remote sensing.To understand the basic concepts ofPassiveRemote Sensing.To learn aboutElectro Magnetic Radiation.To acquire knowledge aboutPlanck"s law-Stefan-Boltzman law.PRE TEST-MCQ TYPE[1]The relation between velocity, wavelength and frequency can be given as _________a) λ = c / rb) λ = c / fc) λ = c / hd) λ = h*c / f[2]Remote sensing uses which of the following waves in its procedure?a) Electric fieldb) Sonar wavesc) Gamma-raysd) Electro-magnetic waves[3]In visible region, the blue light is having a wavelength range of __________a) 0.42-0.52 micrometerb) 0.24-0.52 micrometerc) 0.42-0.92 micrometerd) 0.22-0.32 micrometerUNIT I REMOTE SENSING-CONTENTSDefinition ,Components of Remote Sensing-Energy, Sensor, Interacting Body-Active andPassiveRemote Sensing-Platforms-Aerial and Space Platforms-Balloons, Helicopters,Aircraft andSatellites-Synoptivity and Repetivity-Electro Magnetic Radiation (EMR)-EMR spectrum-Visible,Infra-Red(IR), Near IR, Middle IR , Thermal IR and Microwave-Black Body Radiation-Planck"s law-Stefan-Boltzman law.

THEORYDEFINITIONANDPROCESSOFREMOTESENSINGIntroductionNow-a-daysthefieldofRemoteSensingandGIShasbecomeexcitingandglamorouswithrapidlyexpandingopportunities.Many organizationsspendlargeamountsofmoney onthesefields.Herethequestionariseswhy thesefieldsaresoimportantinrecentyears.Twomainreasonsare there behindthis.1)Now-a-daysscientists,researchers,students,andevencommonpeopleareshowinggreatinterestforbetterunderstanding ofourenvironment.Byenvironmentwemeanthegeographicspaceoftheirstudyareaandtheeventsthattakeplacethere.Inotherwords,we havecometorealize thatgeographic spacealongwiththe datadescribingit,ispartofoureverydayworld;almosteverydecisionwetakeisinfluencedordictatedbysomefact ofgeography. 2) Advancement in sophisticatedspacetechnology(whichcanprovidelargevolumeofspatialdata),along withdecliningcostsofcomputerhardwareandsoftware(whichcanhandlethesedata)hasmadeRemoteSensingandG.I.S.affordabletonotonlycomplexenvironmental/spatialsituationbutalsoaffordabletoanincreasinglywideraudience.REMOTESENSINGAND ITSCOMPONENTS:RemotesensingisthescienceofacquiringinformationabouttheEarth'ssurfacewithoutactuallybeingincontactwithit.Thisisdonebysensingandrecordingreflectedoremittedenergyandprocessing,analyzing,andapplyingthatinformation."Inmuchofremotesensing,theprocessinvolvesaninteractionbetweenincidentradiationandthetargetsofinterest.alsoinvolvesthe

FigureComponents ofRemoteSensing

1. EnergySourceorIllumination (A)-thefirstrequirementforremotesensingis tohaveanenergysourcewhichilluminatesorprovideselectromagneticenergy tothetargetofinterest.2.RadiationandtheAtmosphere(B)-astheenergytravelsfromitssourcetothetarget, itwillcomeincontactwithandinteractwiththeatmosphereitpassesthrough.Thisinteraction maytakeplaceasecond timeas theenergytravelsfrom thetarget to thesensor.3.InteractionwiththeTarget(C)-oncetheenergymakesitsway tothetargetthroughtheatmosphere,itinteractswiththetargetdepending onthepropertiesofboththetargetandtheradiation.4.RecordingofEnergybytheSensor(D)-aftertheenergyhasbeenscatteredby,oremittedfromthe target,werequire asensor (remote-notincontactwiththe target)tocollectandrecord theelectromagneticradiation.5.Transmission,Reception,andProcessing (E)-theenergyrecordedbythesensorhastobetransmitted,ofteninelectronicform,toareceivingandprocessingstationwherethedataareprocessed intoan image(hardcopyand/ordigital).6.InterpretationandAnalysis(F)-theprocessedimageisinterpreted,visuallyand/ordigitallyorelectronically, toextract informationabout thetarget whichwas illuminated.7.Application(G)-thefinalelementoftheremotesensing processisachievedwhenweapply theinformationwehavebeenabletoextractfromtheimageryaboutthetargetinordertobetterunderstandit,revealsomenewinformation,orassistinsolving aparticularproblem.HISTORY OFREMOTESENSING1839-first photograph1858-first photofrom aballoon1903-first plane1909first photofrom aplane1903-4-B/WinfraredfilmWWIandWWII

1960-space

PLATFORMSANDSENSORSTYPESOFPLATFORMSThebaseon whichremotesensorsareplaced toacquireinformationabout theEarth"s surface,iscalled platform.Platformscan bestationarylikeatripod (for field observation)andstationary balloons ormobilelike aircraftsandspacecraft"s.Thetypes ofplatformsdepend upon theneedsas wellasconstraints oftheobservationmission. Therearethreemaintypesofplatforms,namely1)Groundborne2)Airborne3)Space borne.GROUND BORNEPLATFORMS:Theseplatformsareused on thesurfaceoftheEarth.CherryarmconfigurationofRemoteSensingvanandtripodarethetwocommonlyusedgroundborne platforms. Theyhavethecapabilityofviewingtheobjectfrom differentanglesandaremainlyusedforcollectingtheground truth orforlaboratorysimulation studies.AIRBORNEPLATFORMSTheseplatformsare placed within the atmosphereoftheEarth andcan befurtherclassified intoballoonsandaircrafts.a.Balloons:Balloonsasplatformsarenotveryexpensivelikeaircrafts.They haveagreatvarietyofshapes, sizesand performancecapabilities.Theballoonshavelowacceleration,requireno power andexhibit lowvibrations. Therearethreemaintypes ofballoonsystems, viz.freeballoons, Tethered balloonsandPoweredBalloons.Free balloonscanreachalmost thetop ofthe atmosphere;hencetheycanprovide aplatformat intermediatealtitudebetween thoseofaircraftand spacecraft.Thousandsofkilogramsofscientificpayloadscanbeliftedbyfreeballoons.Unlessamobilelaunchingsystemisdeveloped,theflightscanbecarriedoutonlyfrom afixedlaunchingstation.Thefreeballoonsaredependentonmeteorologicalconditions, particularlywinds.Theflight trajectorycannot be controlled. All thesemake extremely difficult topredict whethertheballoons willflyoverthespecific areaofinterest ornot.InIndia,at present, TataInstitute ofFundamentalResearch, Mumbai, has setup aNational balloonfacilityatHyderabad.Teethered balloonsareconnected to theearth stationbymeansofwireshavinghightensionalstrengthandhighflexibility.

The teethered line cancarrytheantenna, powerlinesandgas tubesetc. when windvelocity islessthan35km.perhouratthealtitudeof3000m.,spheretypeballoon is used.When the windvelocityislessthan30kmperhour,naturalshapeballoonsarerestricted to beplaced.Tethered balloonshavethecapabilityofkeepingthe equipmentatafixedpositionforalongtimeandthus,usefulformanyremotesensing programmers.Poweredballoonsrequiresomemeans ofpropulsion tomaintain orachievestationoveradesignatedgeographiclocation. Thesecanberemotelycontrolledandguidedalongwithapath or flyaboveagivenareawithincertainlimitations.b.Aircrafts:Aircraftsarecommonlyusedasremote-sensingforobtainingAerialPhotographs.InIndia,fourtypesofaircraftsarebeingusedforremotesensing operations.Theseareasfollows:DAKOTA: Theceilingheight is5.6to6.2kmandminimumspeedis240km./hr.AVRO: Ceilingheight is 7.5 kmandminimum speed is 600 km./hr.CESSNA:Ceilingheightis9km.andminimumspeedis350km./hr.CANBERRA: Ceiling heightis 40kmandminimum speedis560 km./hr.Thefollowingspecialaircraftsarebeingusedinabroadforremotesensingoperations in highaltitudephotography.U-2:Ceilingheightis21km.(forstrategicphotographic).Minimumspeedis798 km./hr.ROCKELLX-15(ResearchCraft):Ceilingheightis108kmandspeedis6620km./hr.The advantagesofusingaircraftsasremotesensingplatformare: highresolution ofdatarecorded, possibilityofcarryinglargepayloads,capabilityofimaginglargeareaeconomically,accessibilityofremoteareas,convenienceofselectingdifferent scales,adequate controlatall time, etc.However, dueto limitations ofoperatingaltitudesandrange,theaircraftfinds itsgreatestapplications inlocal orregional programmeratherthanmeasurements onglobalscale.Besidesall these,aircraftshave been playingan importantrolein thedevelopment ofspaceborneremotesensing Techniques.Testingofsensorsand varioussystemsand subsystems involvedin space borneremotesensingprogrammeisalways undertaken in awell-equippedaircraft.

SPACEBORNEPLATFORMSPlatformsin space,i.e. satellitesarenotaffectedbythe earth"satmosphere.Theseplatformsmovefreelyintheirorbitsaroundtheearth. Theentireearthoranypartoftheearthcanbecoveredatspecifiedintervals. Thecoveragemainlydependsontheorbitofthesatellite.Itisthroughthesespaceborneplatforms,wegetenormousamount ofremotesensingdataandasaresult.RemoteSensinghasgainedinternationalpopularity. Accordingtotheorbitalmode,therearetwotypesofsatellites-GeostationaryorEarthsynchronousand sun-synchronous.PASSIVE ANDACTIVESENSORSRemotesensorsaretheinstruments which detect various objects on the earth"s surfacebymeasuringelectromagnetic energyreflectedor emittedfrom them.Thesensorsaremountedon theplatforms discussedabove.Different sensorsrecord different wavelengths bands ofelectromagneticenergycomingfromtheearth"s surface.Asfor example,an ordinarycameraisthemostfamiliartypeof remotesensorwhichusesvisibleportionofelectromagneticradiation.Classificationof SensorsRemotesensorscan beclassified in different waysasfollows.On theBasis of Sourceof EnergyUsed:On thebasis ofsourceof energyusedbythesensors, theycan beclassified into twotypes-ActivesensorsandPassivesensors.ACTIVESENSORSActivesensorsusetheirownsourceofenergyandearthsurfaceis illuminated bythisenergy. Thenapart ofthisenergyisreflectedbackwhichisreceivedbythesensortogetherinformationabouttheearth"ssurfacewhenphotographiccamerauses itsflash, itactsasanactivesensor.Radarand laseraltimerareactivesensors.Radariscomposedofatransmitterandareceiver.Thetransmitteremitsawave,whichstrikesobjectsandisthenreflected orechoedbacktothereceiver.Thepropertiesofanactivesensorare:1)It usesbothtransmitterandreceiverunitstoproduceimagery,henceitrequires highenergylevels.2)ItmostlyworksinmicrowaveregionsofEMR spectrum,whichcanpenetratecloudsandisnotaffectedbyrain.3)Itisanall-weather,day-nightsystemandindependentofsolarradiation.4)TheRADARsignaldoesnotdetectcolour informationortemperatureinformation,butitcandetecttheroughness, slopeandelectricalconductivityoftheobjects understudy.

PASSIVESENSORSPassivesensorsdonothavetheirownsourceofenergy.Theearthsurfaceisilluminatedbysun/solarenergy.Thereflectedsolarenergyfromtheearthsurfaceortheemittedelectromagneticenergybytheearthsurfaceitself isreceivedbythesensorPhotographiccameraisapassivesensorwhen it isusedinsunlight,withoutusingitsflash.Thepropertiesofapassivesensorare:1)Itisrelativelysimplebothmechanicallyandelectricallyanditdoesnothavehigh powerrequirement.2)The wavebands,wherenaturalremittance orreflected levelsarelow,highdetectorsensitivitiesand wideradiationcollectionaperturesarenecessarytoobtainareasonablesignal level. Therefore,mostpassivesensorsarerelativelywidebandsystems.3)It depends upongoodweatherconditions.

Figure activeandpassivesensorOntheBasisofFunctionofSensors:Onthebasisoffunctionofsensors,theyaredivided into twomaintypes-FramingSystemandScanningSystem.Framingsystem:Inframingsystem,twodimensionalimagesareformedatone singleinstant.Here,alensisusedtogatherthelightwhichispassedthroughvariousfiltersand thenfocusedon aflat photosensitivetarget.Inordinarycamera,thetargetisfilmemulsion,whereasinvidiconcamera,thetargetiselectricallychargedplate.ScanningSystem:Inscanningsystem,asingledetector/anumberofdetectors withspecificfieldof view,issuedwhichsweepsacrossa scene inaseriesofparallel linesandcollectdataforcontinuouscellstoproduceanimage. MultiSpectralScanner,MicrowaveRadiometer,MicrowaveRadar,OpticalScannersarefewexamples ofscanningsystem sensors.

OntheBasisofTechnicalComponentsoftheSystem:Thesensorscanbeclassifiedinto threecategoriesonthebasisoftechnicalcomponentsofthesystemandthecapabilityof thedetection.Theseare:1)Multispectralimagingsensorsystems2)Thermalremote sensingsystems3)Microwaveradarsensingsystems.Themultispectralor multibandimagingsystemsmay useconventionaltypecamerasormay useacombination ofbothcamerasandscannersforvarious bandsofelectromagneticenergy.Asforexample,ReturnBeamVidicon(RBV)sensorofLandsatusesbothphotographicandScanningsystems,whichissimilartoanordinaryTVcamera.Thethermalsystem usesradiometers,photometers,spectrometers,thermometerstodetectthetemperaturechanges wheremicrowavesensingsystemsusetheantennaarraysforcollectinganddetectingtheenergyfrom theterrainelements.ELECTROMAGNETICSPECTRUMThefirstrequirementforremotesensingistohaveanenergysourcetoilluminatethetarget(unlessthesensedenergyisbeingemittedbythetarget).Thisenergyisintheform ofelectromagneticradiation.Allelectromagneticradiationhasfundamentalpropertiesandbehaves in predictablewaysaccordingto thebasics ofwavetheory.Electromagneticradiationconsistsofanelectricalfield(E)whichvaries in magnitude inadirectionperpendicular tothedirectioninwhichtheradiationistraveling,andamagneticfield(M)orientedatrightanglestotheelectricalfield.Boththesefields travelatthespeedoflight(c).Twocharacteristicsofelectromagneticradiationare particularlyimportanttounderstandremotesensing.Thesearethewavelengthandfrequency.Electromagneticradiation(EMR)asanelectromagneticwavethattravelsthrough spaceatthespeed oflight C which is 3x108meters persecond. Theoreticalmodel ofrandom mediaincludingtheanisotropiceffects,random distribution discretescatters,roughsurfaceeffects,havebeenstudiedforremotesensingwithelectromagneticwaves.

Light-canbethoughtofasawaveinthe'electromagneticfield'oftheuniverseWavelength

Frequency(howmanytimespeak passespersecond)Figure Wavelength and frequencyThewavelengthisthelengthofonewavecycle,whichcanbemeasuredasthe distancebetweensuccessivewavecrests.Wavelengthisusuallyrepresentedby theGreek letter lambda (λ).Wavelengthismeasuredinmetres(m)or somefactorof metressuchasnanometres(nm,10-9metres),micrometres(?m, 10-6 metres) (?m, 10-6 metres)orcentimetres(cm,10-2metres).Frequencyreferstothenumberofcyclesofawavepassingafixedpointperunitoftime.Frequencyisnormallymeasuredinhertz(Hz),equivalenttoonecyclepersecond,and various multiples ofhertz.Wavelengthandfrequencyarerelatedbythefollowingformula:

Therefore,thetwoareinverselyrelatedtoeachother.Theshorterthewavelength,the higherthefrequency.Thelongerthewavelength,thelowerthefrequency.Understanding thecharacteristicsofelectromagneticradiationintermsof their wavelengthandfrequency iscrucial to understandingtheinformation to beextractedfromremotesensingdata.Theelectromagneticspectrumrangesfromthe shorterwavelengths(includinggammaandx-rays) to thelonger wavelengths (including microwavesandbroadcastradiowaves). Thereareseveralregionsoftheelectromagnetic spectrumwhichareusefulforremote sensing.

Figure ElectromagneticSpectrumWAVELENGTH REGIONSIMPORTANT TO REMOTESENSING:UltravioletorUVFor the mostpurposesultravioletor UV of thespectrumshortestwavelengthsarepracticalforremotesensing.Thiswavelengthbeyondthe violetportionofthevisiblewavelengthshenceitname.Someearthsurfacematerialsprimarilyrocksandmaterialsareemit visibleradiation when illuminatedbyUVradiation.VisibleSpectrumThelightwhichoureyes-our"remotesensors"-candetectispartofthevisiblespectrum.Itisimportanttorecognizehowsmallthevisibleportion isrelativetotherestof the spectrum.There isalotofradiationarounduswhichis"invisible"tooureyes,butcanbe detectedby otherremotesensinginstrumentsandusedtoouradvantage.Thevisiblewavelengthscoverarangefromapproximately0.4to0.7?m.Thelongestvisiblewavelengthisredandtheshortestisviolet. Commonwavelengthsofwhatweperceiveasparticularcoloursfromthevisibleportionofthespectrumarelistedbelow.Itis importanttonotethatthis is theonlyportion ofthespectrum wecanassociatewith theconceptofcolours.

Violet:0.4-0.446 ?mBlue:0.446-0.500 ?mGreen:0.500-0.578 ?mYellow:0.578-0.592 ?mOrange`:0.592-0.620?mRed:0.620-0.7?mBlue,green,andredaretheprimarycoloursorwavelengthsofthevisiblespectrum.Theyaredefinedassuchbecausenosingleprimarycolourcanbecreatedfromtheothertwo,butallothercolourscanbeformedbycombiningblue,green,andredinvariousproportions.Althoughweseesunlightasauniformorhomogeneouscolour,itisactuallycomposedofvariouswavelengthsofradiationinprimarily theultraviolet,visibleandinfraredportionsofthe spectrum.The visible portionofthisradiationcanbe showninitscomponentcolourswhensunlightispassedthroughaprism,whichbendsthelightin differingamountsaccordingtowavelength.Infrared(IR)The nextportionofthespectrumof interestisthe infrared(IR)regionwhichcoversthewavelengthrangefromapproximately 0.7?mto100?mmorethan100timesaswideasthevisibleportion.The infraredcanbedividedinto3categoriesbasedontheirradiationproperties-thereflectednear-IR middleIRand thermalIR.ThereflectednearIRcoverswavelengthsfromapproximately0.7?mto1.3?miscommonlyused toexposeblackandwhiteandcolor-infrared sensitivefilm.Themiddle-infraredregion includesenergywith awavelength of1.3 to 3.0?m.The thermalIRregionisquite differentthanthe visibleandreflectedIRportions,asthisenergy isessentiallytheradiationthatisemittedfromtheEarth'ssurfaceintheformofheat. ThethermalIRcovers wavelengthsfromapproximately3.0?m to 100?m.MicrowaveThiswavelength(orfrequency)intervalintheelectromagnetic spectrumiscommonlyreferred toas aband,channel orregion. Theportionofthespectrumofmorerecentinteresttoremotesensing isthe microwaveregionfromabout1mm to1m.Thiscoversthelongestwavelengthsusedforremotesensing.The shorterwavelengthshavepropertiessimilartothethermalinfraredregionwhilethe longerwavelengthsapproachthewavelengthsusedforradio broadcasts.

WAVE THEORY AND PARTICLE THEORYLight can exhibit both a wave theory, and a particle theory at the same time. Much ofthe time,light behaves like a wave. Light waves arealso called electromagnetic wavesbecause they aremade up of both electric (E ) and magne tic (H ) fields. Electrom agnetic fieldsoscillateperpendicular to the direction of wave travel, and perpendicular to each other. Lightwaves areknown as transverse waves as they oscillate in the direction traverse to thedirection of wavetravel.

Electromagnetic propagationWaves have two important characteristics-wavelength and frequency.The sine wave is thefundamental waveform in nature. When dealing with light waves, we refer to the sine wave.The period (T ) of the wavef or m is one ful l 0 to 360 deg ree sw eep. The rela tionship offrequency and the period is given by the equation: f = 1 / T T = 1 / f The waveforms are alwaysin the time domain and go on for infinity. The speed of a wave can be found by multiplying thetwo units together. The wave's speed is measured in units of length (distance) per second:Wavelength x Frequency = Speed As proposed by Einstein, light is composed of photons, avery small packetsof energy. The reason that photons are able to travel at light speeds is due tothe fact that they have no mass and therefore, Einstein's infamous equation-E=MC2 cannot beused. Another formula devised by Planck, is used to describe the relation betweenphotonenergy and frequency-Planck's Constant (h)-6.63x10-34 Joule-Second. E = hf(or)E = hc /? Eis the photonic energy in Joules, h is Planks constant and f is the frequency in Hz.PARTICLE THEORYThe basic idea of quantum theory is that radiant energy is transmitted in indivisiblepacketswhose energy is given in integral parts, of size hv, where h is Planck's constant =6.6252 x 10-34J-s, andv photons.The dilemma of the simultaneouswaveandparticle wavesofelectromagnetic energy may beconceptuallyresolvedbyconsideringthatenergy isnotsuppliedcontinuously throughoutawave,butratherthatitiscarriedby photons.

Theclassicalwavetheorydoesnotgivetheintensityofenergyatapoint in space, butgivestheprobabilityoffindingaphotonat thatpoint.Thustheclassicalconceptofawaveyieldstotheideathatawavesimply describes theprobabilitypathforthemotion oftheindividual photons.Theparticularimportanceofthequantumapproachforremotesensing isthat it providestheconceptofdiscreteenergy levelsinmaterials.Thevaluesandarrangementof these levelsaredifferentfordifferentmaterials.Informationaboutagivenmaterialisthusavailable inelectromagneticradiationasaconsequenceoftransitionsbetweentheseenergy levels.Atransitiontoahigherenergy leveliscausedby theabsorptionofenergy,orfroma highertoalowerenergyleveliscausedby the'emissionofenergy.Theamountsofenergyeitherabsorbedoremittedcorrespondpreciselytotheenergy differencebetweenthetwo levelsinvolvedinthetransition.Becausetheenergylevelsaredifferentforeachmaterial,theamountofenergy aparticularsubstancecanabsorboremitisdifferentforthatmaterialfromanyothermaterials.Consequently,thepositionandintensitiesofthebandsinthespectrumofagiven materialarecharacteristicto that material.STEFAN-BOLTZMANN LAWStefan-Boltzmannlaw,also knownasStefan's law, describes thepowerradiatedfromablackbodyin terms ofitstemperature.Specifically,theStefan-Boltzmannlaw states that thetotalenergyradiatedperunitsurfaceareaofablack bodyacrossall wavelengthsperunittime(alsoknownas theblack-bodyradiantexistenceoremissivepower),is directlyproportionalto thefourth poweroftheblack body'sthermodynamictemperatureT:

WIEN'S DISPLACEMENT LAWWien's displacement law states that the black body radiation curve for different temperaturespeaks at a wavelength inversely proportional to the temperature. The shift of that peak is adirect consequence of the Planck radiation law which describes the spectral brightness of blackbody radiation as a function of wavelength at any given temperature. However it had beendiscovered by Wilhelm Wien several years before Max Planck developed that more generalequation, and describes the entire shift of the spectrum of black body radiation toward shorterwavelengths as temperature increases.Formally, Wien's displacement law states that thespectral radiance of black body radiation per unitwavelength, peaks at the wavelength λmaxgiven by:

λmax= b/Twhere T is the absolute temperature in degrees kelvin. b is a constant of proportionality calledWien's displacement constant, equal to 2.8977721(26)×10-3 m K. [1], or more conveniently toobtain wavelength in microns, b≈2900?m K. If one is considering the peak of black bodyemission per unit frequency or per proportionalbandwidth, one must use a differentproportionality constant. However the form of thelaw remains the same: the peak wavelengthis inversely proportional to temperature (orthe peak frequency is directly proportional totemperature).Wien's displacement law may be referred to as "Wien's law", a term which is alsousedfor the Wien approximation.APPLICATIONS

Figure exampleof passive and active remote sensing Figureexample of Remote sensing platforms of satellite, manned aviation and low-altitudeUAV

POSTTEST-MCQ TYPE[1]Which of the following field is used by the EM waves?a) Solar fieldb) Polarized fieldc) Electric fieldd) Micro field[2]Which of the following is not a principle of remote sensing?a) Interaction of energy with satelliteb) Electromagnetic energyc) Electro-magnetic spectrumd) Interaction of energy with atmosphere[3]Which among the following waves is having less wavelength range?a) 0.03mmb) 0.03nmc) 0.03md) 0.03km[4]In visible region, the blue light is having a wave length range of __________a) 0.42-0.52 micrometerb) 0.24-0.52 micrometerc) 0.42-0.92 micrometerd) 0.22-0.32 micrometer[5]Among the following, which describes Stefan-Boltzmann formula?a) M = σ/T4b) M = σ-T4c) M = σ+T4d) M = σ*T4[6]Which of the following can act as an example for air-borne platform?a) LISS-IIIb) Dakotac) MOSd) LISS-II

[7]Which of the following has the maximum value in an electric or magnetic field?a) Wave lengthb) Focal lengthc) Frequencyd) Amplitude[8] If the intensity of wave length decreases, the energy released will ___________a) Increaseb) Decreasec) Remain samed) Zero[9]The wave length sensed in remote sensing are __________a) Nano meters and gigameters rangeb) Nano meters and deci meters rangec) Nano meters and micro meters ranged) Nano meters and meters range[10]In an EM field, which filed is placed horizontal?a) Gamma raysb) Sonar fieldc) Electric fieldd) Magnetic field[11]Which among the following wave is not employed in case of remote sensing?a) X-rayb) Visible rayc) Thermal IRd) Radio waves[12]Which of the following waves can be used in case of remote sensing?a) UV raysb) X-raysc) Gamma raysd) Visible rays

[13]EM waves varies from ______ to ________a) Meters to nano-metersb) Meters to micro-metersc) Nano to micro-metersd) Centimeters to nano-meters[14]Strength of signal doesn"t depend upon which of the following factors?a) Energy fluxb) Dwell timec) Altituded) Reflection[15] Energy flux may affect which of the following?a) Lensb) Strength of the signalc) Apertured) Declination[16]Which among the following indicates the correct expansion of Wi-FS?a) Wide Field Sensorb) Wireless Fidelity Sensorc) Wide Fidelity Sensord) Wireless Field Sensor[17]IRS 1A and 1B satellites can carry which of the following sensors?a) LISS-IVb) LISS-IIIc) LISS-Id) LISS-V[18]Blue, green, and red are the_________of the visible spectrum.a) primary coloursb) primaryfrequentc)secondarycoloursd)secondary frequent

CONCLUSIONIn this unit, the student would have understood the concept of remote sensingandgotanexposure towardsbasic concepts of Passive Remote Sensing.The Electro Magnetic Radiationand its types were discussed. The Planck"s law and Stefan-Boltzman law were explained.Thewavelength regions important to remote sensingwere seen. Theexamplesof passive and activeremote sensingwere discussed.REFERENCES1. Anji Reddy, Remote Sensing and Geographical Information Systems, BS Publications 2001.2. M.G. Srinivas, Remote Sensing Applications, Narosa Publishing House, 2001.3.Lillesand T.M. and Kiefer R.W. Remote Sensing and Image Interpretation, John Wiley andSons, Inc, New York.4. Janza.F.J., Blue, H.M., and Johnston, J.E., "Manual of Remote Sensing Vol.I, AmericanSociety of Photogrammetry, Virginia, U.S.A, 1975.ASSIGNMENT1.Describe the History of Remote Sensing.2.Explainthesignificance of EMR in remote sensing?3.Identifythedifferenttypesof Electromagnetic radiation?4.With an exampledifferentiateactivepassive remote sensing system and passive remotesensing system.5.On thebasis of function of sensors,identifythe different types sensors being used.

UNIT II EMR INTERACTION WITHATMOSPHERE AND EARTHMATERIALSPrepared byT.DINESH KUMARAssistant ProfessorECE, SCSVMV

REMOTE SENSING & GIS

AIM &OBJECTIVESTo provide students an exposure to Remote sensing.To understand the basic concepts ofAtmospheric characteristics.To learn aboutthe significance of Atmospheric windowsused in remote sensing.To acquire knowledge aboutEMR interaction withdifferent materials.PRE TEST-MCQ TYPE[1]Diameter of sun can be given as ____________a) 1.39 * 107kmb)1.9 * 106kmc) 1.39 * 106kmd) 1.39 * 1016km[2]Which of the following can be changed while interaction of EM wave with a surface?a) Intensityb) Diffractionc) Wave lengthd) Direction[3]Which of the following indicates a volume phenomenon?a)Refractionb) Reflectionc) Transmissiond) DiffractionUNITII REMOTE SENSING-CONTENTSAtmospheric characteristics-Scattering of EMR-Raleigh, Mie, Non-selective and RamanScattering-EMR Interaction with Water vapour and ozone-Atmospheric WindowsSignificance of Atmospheric windows-EMR interaction with Earth Surface Materials-Radiance, Irradiance, Incident, Reflected, Absorbed and Transmitted Energy-Reflectance-Specular and Diffuse Reflection Surfaces-Spectral Signature-Spectral Signature curves-EMR interaction with water, soil and Earth Surface.

THEORYENERGY INTERACTIONSWITHTHEATMOSPHEREBeforeradiationusedforremote sensingreachestheearth'ssurfaceithasto travelthroughsomedistance oftheEarth'satmosphere.Particlesandgasesin theatmospherecanaffecttheincoming lightandradiation.Theseeffectsarecausedby the mechanisms ofscatteringandabsorption.

FigureEnergy InteractionwithAtmosphereSCATTERINGScattering occurswhenparticlesorlargegasmoleculespresentintheatmosphere interactwithandcause theelectromagneticradiationtoberedirectedfromitsoriginalpath.Howmuchscatteringtakesplacedepends onseveralfactorsincluding thewavelengthoftheradiation,theabundanceof particles orgases,andthedistancetheradiation travels throughtheatmosphere. Therearethree(3)types ofscatteringwhich takeplace.RAYLEIGHSCATTERINGRayleighscatteringoccurswhenparticlesarevery smallcomparedtothewavelength oftheradiation. Thesecould bearticles suchas small specksofdust ornitrogenand oxygen molecules.Rayleigh scatteringcauses shorterwavelengthsofenergytobescatteredmuch morethan longerwavelengths. Rayleighscatteringisthedominantscattering mechanismintheupperatmosphere.Thefactthattheskyappears"blue" duringtheday isbecauseofthisphenomenon.Assunlightpassesthroughtheatmosphere,theshorterwavelengths(i.e.blue)ofthevisiblespectrumarescatteredmorethantheothervisiblewavelengths.

FigureRayleighScatteringAtsunriseandsunsetthe lighthastotravelfarther throughtheatmospherethanatmiddayandthescatteringoftheshorterwavelengthsismorecomplete; this leaves agreaterproportion ofthelongerwavelengths to penetratetheatmosphere.ABSORPTIONAbsorptionisthe othermainmechanismatworkwhenelectromagneticradiation interacts withtheatmosphere.Incontrasttoscattering,this phenomenoncauses moleculesintheatmospheretoabsorbenergyatvariouswavelengths.Ozone,carbon dioxide,andwatervaporare the threemainatmosphericconstituentswhichabsorbradiation.Ozoneserves toabsorbtheharmful(tomostlivingthings)ultravioletradiationfor thesun.Withoutthisprotectivelayer intheatmosphere ourskinwould burnwhenexposedtosunlight.Carbondioxidereferredtoasagreenhouse gas.This isbecauseittendstoabsorbradiationstrongly inthefarinfraredportionofthe spectrumthatareaassociatedwiththermalheatingwhichservestotrapthisheat inside theatmosphere.Watervapourintheatmosphereabsorbsmuchof theincoming longwave infraredandshortwavemicrowaveradiation(between22?mand1m).The presenceofwatervapourintheloweratmospherevariesgreatlyfromlocationto locationandatdifferenttimesoftheyear.Forexample,theairmassabove a desert wouldhavevery littlewatervapourtoabsorbenergy,whilethetropicswouldhave highconcentrations ofwatervapour(i.e. high humidity).

MIESCATTERINGMie scatteringoccurswhentheparticlesarejustaboutthe samesizeasthe wavelengthoftheradiation.Dust,pollen,smokeandwatervapourarecommoncausesof Miescatteringwhichtendstoaffectlongerwavelengthsthanthoseaffectedby Rayleigh scattering.Miescatteringoccursmostly inthelowerportionsoftheatmospherewherelarger particlesaremoreabundantand dominateswhencloudconditionsareovercast.Thefinalscatteringmechanismof importance iscallednonselectivescattering.This occurswhen theparticlesaremuch largerthan thewavelength oftheradiation.Water dropletsandlargedustparticlescancause thistype of scattering.Nonselective scatteringgetsitsnamefromthefactthatallwavelengthsarescatteredaboutequally.Thistypeofscatteringcausesfogandcloudstoappearwhitetooureyesbecauseblue,green,andredlightareallscatteredinapproximatelyequalquantities(blue+green+ redlight=white light).ATMOSPHERICWINDOWSWhileEMRistransmittedfromthesuntothesurfaceoftheearth,itpassesthrough theatmosphere.Here,electromagneticradiationisscatteredandabsorbedbygasesanddustparticles.Besidesthemajoratmosphericgaseouscomponentslike molecular nitrogenandoxygen,otherconstituentslike water vapour,methane,hydrogen,heliumandnitrogencompoundsplay importantroleinmodifyingelectromagneticradiation.Thisaffectsimagequality.Regionsof theelectromagnetic spectruminwhichtheatmosphere istransparentarecalledatmospheric windows.Inotherwords,certainspectralregionsoftheelectromagneticradiationpassthroughtheatmospherewithoutmuchattenuationarecalledatmosphericwindows.Theatmosphereispractically transparentinthevisibleregionoftheelectromagneticspectrumandtherefore,manyofthesatellitebasedremotesensingsensorsaredesignedtocollectdatainthisregion.Someofthecommonlyusedatmosphericwindowsareshown in thefigure.Theyare:0.38-0.72microns(visible),0.72-3.00microns(nearinfra-redandmiddle infra-red),and 8.00-14.00 microns (thermal infra-red).Transmission100%UVVisibleInfraredEnergyBlocked0.3Wavelength (microns)1101001 mm.

FigureAtmosphericwindowsSPECTRALSIGNATURECONCEPTS-TYPICALSPECTRALREFLECTANCECHARACTERISTICSOFWATER, VEGETATIONANDSOILAbasicassumptionmadeinremotesensingisthataspecifictargethasan individualandcharacteristicmannerofinteracting withincidentradiation.Themannerofinteractionisdescribedby thespectralresponseofthetarget.Thespectralreflectancecurvesdescribethespectralresponse ofatargetina particularwavelengthregionofelectromagnetic spectrum,which,inturndependsuponcertainfactors,namely,orientationofthesun(solarazimuth),theheightoftheSuninthesky (solarelevationangle),thedirectioninwhichthesensorispointingrelativetonadir(thelookangle)andnatureofthetarget,thatis, stateofhealthofvegetation.Every objectonthesurfaceoftheearthhasitsuniquespectralreflectance.The figureshowstheaveragespectralreflectancecurvesforthreetypicalearth'sfeatures:vegetation, soilandwater.Thespectralreflectancecurvesfor vigorousvegetationmanifeststhe"Peakandvalley"configuration.The valleysinthe visibleportionof the spectrumare indicative of pigmentsinplantleaves.Dipsinreflectancethatcanbeseenatwavelengthsof0.65µm,1.4µmand1.9µmareattributabletoabsorptionofwaterby leaves.Thesoilcurve showsamoreregularvariationofreflectance.Factorsthatevidentlyaffectsoilreflectancearemoisturecontent,soiltexture,surfaceroughness,andpresenceoforganicmatter.The termspectralsignaturecanalsobeusedforspectralreflectancecurves.Spectralsignatureisa set ofcharacteristicsbywhich amaterialoranobject maybeidentified onanysatelliteimage orphotographwithinthegivenrangeofwavelengths.

FigureSpectralreflectanceCurveSometimesspectralsignaturesare used to denotethe spectralresponseofatarget.Thecharacteristicspectralreflectancecurve.The figureforwatershowsthatfromabout0.5µm,areductioninreflectancewithincreasing wavelength,sothatinthenearinfraredrange,thereflectanceofdeep,clearwaterisvirtually azero.However,thespectralreflectanceofwaterissignificantlyaffectedby thepresenceofdissolvedandsuspended organicandinorganicmaterialandby the depthofthewaterbody.The figureshowsthespectralreflectancecurvesforvisibleandnear-infraredwavelengthsatthesurfaceandat20 mdepth.Suspended solids inwaterscatter thedownwellingradiation,thedegreeofscatter beingproportionaltotheconcentrationandthecolorof thesediment.Experimentalstudiesinthefieldandinthe laboratoryaswellasexperiencewithmultispectralremotesensinghaveshownthatthe specifictargetsarecharacterizedbyanindividualspectralresponse.Indeedthesuccessful developmentofremotesensing ofenvironmentoverthepastdecadebearswitnesstoits validity.Intheremainingpartofthissection,typicalandrepresentativespectralreflectancecurvesforcharacteristictypesofthesurfacematerialsareconsidered.

Imagineabeachona beautifultropicalisland.ofelectromagneticradiationwiththe toplayerofsandgrainsonthe beach.Whenanincidentrayofelectromagneticradiationstrikesanair/graininterface,partof therayisreflectedandpartofitistransmittedintothesandgrain.Thesolidlinesinthefigurerepresenttheincidentrays,anddashedlines1,2,and3representraysreflectedfrom the surface buthave never penetrateda sandgrain.Foragivenreflecting surface,allspecularraysreflectedinthesamedirection,suchthattheangleofreflection(theanglebetweenthereflectedraysandthe normal,orperpendicular tothereflecting surface)equalstheangleofincidence(theanglebetweentheincidentraysandthesurfacenormal). Themeasureofhowmuchelectromagneticradiationisreflectedoffasurfaceiscalleditsreflectance,whichisanumberbetween0and1.0.Ameasureof1.0meansthe100%oftheincidentradiationisreflectedoffthesurfaceandameasureof0means that 0%isreflected.ATMOSPHERIC INTERACTIONS WITH ELECTROMAGNETIC RADIATIONAll electromagnetic radiation detected by a remote sensor has to pass through the atmospheretwice, before and after its interaction with earth's atmosphere. This passage will alter the speed,frequency, intensity, spectral distribution, and direction of the radiation. As a result atmosphericscattering and absorption occurs. Theseeffects are most severe in visible and infraredwavelengths, the range very crucial in remote sensing. During the transmission of energythrough the atmosphere, light interacts with gases and particulate matter in a process calledatmospheric scattering. The two major processes in scattering are selective scattering and non-selective scattering. Rayleigh, Mie and Raman scattering are of selective type. Non selectivescattering is independent of wavelength. It is produced by particles whose radii exceed 10micrometer, such as, water droplets and ice fragments present the clouds.This type of scattering reduces the contrast of the image. While passing through the atmosphere,electromagnetic radiation is scattered and absorbed by gasses and particulates. Besides the majorgaseous components like molecular nitrogen and oxygen, other constituents like water vapour,methane, hydrogen, helium and nitrogen compounds play an important role in modifying theincident radiation and reflected radiation. This causes a reduction in the image contrast andintroduces radiometric errors.

Regions of the electromagnetic spectrum in which the atmosphere is transparent are calledatmospheric windows. The atmosphere is practically transparent in the visible region of theelectromagnetic spectrum and therefore many of the satellite based remote sensing sensors aredesigned to collect data in this region. Some of the commonly used atmospheric windows are0.38-0.72 micrometer (visible), 0.72-3.00 micrometer(near infrared and middle infrared) and8.00-14.00 micrometer(thermal infrared).The figureshows relative scatter as a function of wavelength from 0.3 to 1 micrometerof thespectrum for various levels of atmospheric haze.The characteristics of all the four types ofscattering in the order of their importance in remote sensing aregiven in the table

ATMOSPHERIC PROPERTIESThe main part of the radiance measured from high flying aircraft or satellite stemsfrommultiplescattering in the atmosphere. Therefore, the remaining signal can be interpreted in terms ofsuspensions only after a careful correction for the atmospheric contribution. For this reason thevarying optical parameters of atmosphere must enter the radiative transfer calculations.Before we study theeffectsof solar radiation and atmospheric properties, we shall consider themass quantities which determine the spectral upward radiance. The source of the shortwaveradiation field in atmosphere is the Sun emitting in a broad spectral range.The extraterrestrial irradiance at the top of the atmosphere, the solar constant, depends on theblack body emission of the Sun's photosphere and on the scattering and absorption process in theSun's chromosphere. Important Fraunhofer lines caused by the strong absorption inthe Sun'schromosphere show some prominent drops in the spectral distribution of the solar radiation.Thefigure shows the solar irradiance at the top of the earth's atmosphere to be between 0.4 and 0.8micrometeras determined by Necked and Labs.

Figure Solar irradiance at the top of the atmosphere illuminating the Earth between0.4micrometer-0.8micrometer

EMR INTERACTION WITH OZONEOzone is a trace gas in the atmosphere mainly confined to stratospheric heights between 20and40 km with a maximum concentration near 25 km. At these levels, ozone dominates the shortwave radiation budget, while at other heights its influence isnearly negligible. The Chappuisband of ozone in the visible spectrum is the only ozone band used to detect the oceanicconstituents from space. The transmission of the chlorophyll fluorescence to the top of theatmosphere is hindered through the absorption by water vapour and molecular oxygen in theirvibration action bands. In order to study the selective gaseous absorption in the radiative transfercalculationsthe transmission functions of o2and H2oare computedfrom absorption lineparameters by explored through areas of Lorentz's theory ofcollision broadening. Thecontribution from resonance broadening is negligible in the spectral region considered. Also theDoppler line broadening, which is small whencompared with Lorentzline widths, is neglectedsince the area absorption takesplace in the atmospherebelow 40 km.The transmission functions areaveraged/over 1 nm wavelength intervals. The reduction in thesolar flux due toabsorptionand scattering by aclear mid-latitude summer atmosphere. Responsestudies for the temperature and pressure dependenceof the transmission functionhave beenperformed and showonly a weak influence for the temperature effect. Thepressure impact is notnegligible and has to be accounted for. Air molecules are smallcompared to the wavelength ofthe incoming sunlight. Hence, the extinction throughmolecular scattering can be determinedwith Rayleigh theory. The necessary property for the determination of the scatteringcoefficientof the vertical profile of theatmospheric pressure has been estimatedSince molecularscattering within the atmosphere depends mainly on pressure, the scatteringcoefficient can be estimatedby climatological measurement.Atmosphericspectral turbidityvariations are caused by variations in aerosolconcentration, composition and size distribution.The vertical distribution of the aerosolsistaken and the phase functions of aerosols are nearlywavelength independent within thevisible and near infrared. For the radiative transfercalculations the scattering functions are estimated by Mie theory. The range ofatmosphericturbidity values used to study the effects of aerosol scattering on themeasuredspectral radiancescorrespond to horizontal visibilities at the surface between6 and 88 km.

Atmospheric effects on Spectral Response PatternsThe energy recorded by a sensor is always modified by the atmosphere betweenthe sensor andthe ground. As shownin Figure, the atmosphere influences theradiance recorded by a sensorintwo ways, namely, (a) it attenuates or reduces theenergyilluminating a ground object and (b) theatmosphere acts as a reflector itselfadding the pathradiance to the signal detected by the sensor.These two atmosphericeffects are expressedmathematically as follows

Atmosphericeffects influencingtheSpectral RadianceThe irradiance (E) is caused by directly reflected 'sunlight' and diffused 'skylight',which is thesunlight scattered by the atmosphere. The amount of irradiance dependson seasonal changes,solar elevation angle, and distance between the earth and sun.EMR INTERACTION WITH EARTH SURFACE MATERIALSWhen electromagnetic energy is incident on any feature of earth's surfacesuchas a water body,various fractions of energy get reflected, absorbed, andtransmitted as shown in Figure.

Figure Basic interactions between Electromagnetic Energy and a water body Applying the principle of conservation of energy,therelationship can be expressed as:

All energy components are functions of wavelength, (I ) . In re mote se nsing, theamountofreflected energy ER(A.) is more important than the absorbed and transmittedenergies.

Therefore, it is more convenient to rearrange these terms liketransmittance and can be denotedas p(A. ), c x.( A.) and y( A.) . Si mpl y, it can be understoodthat, the measureof how muchelectromagnetic radiation is reflected off a surface iscalled its reflectance.

The reflectance range lies between 0 and 1. A measure of 1.0means that 100% of the incidentradiation is reflected off the surface, and a measure'0' means that 0% is reflected. Thereflectance characteristics are quantified byspectral reflectancep(A. ) whic h is expressed asabove.Thefundamental equation by which the conceptual design of remotesensingtechnology is built.If S (A.) is a zero, then p(A.), that is, the reflectance isone, whichmeans, thetotal energyincident on the object is reflected and recorded by sensing systems. Theclassical example of thistype of object is snow (white object). If S (A.) is one, then (A.) is a zero indicating that whateverthe energy incident on the object, iscompletely absorbedby that object. Black body such as lampsmoke is anexample of this type of object.Therefore it can be seen that the reflectance variesfrom0 (black body) to 1 (white body). Whenwe divide the incident energy on both sidesof the balance equation, we get the proportions ofenergy reflected, absorbedand transmitted which vary for different featuresof the earthdepending on the materialtype. These differences provide a clue to differentiate betweenfeatures of an image.Secondly, from the wavelength dependency of the energy components, it is evidentthat evenwithin a given feature type, the proportionofreflected, absorbed, andtransmittedenergy"smayvary at different wavelengths. Thus two features which areindistinguishablein one spectralrange,may exhibit a marked contrast in anotherwavelength band. Because many remote sensingsystems operate in the wavelengthregions in which reflected energy predominates, thereflectance properties of terrestrialfeatures are very important.Radiant energy, which like all other energies expressed in Joules, is the energyassociated withelectromagnetic radiation. The rateof transfer of radiant energy iscalled the flux and has wattsas the units of power. Density implies distribution overthe surface on whichthe radiant energyfalls. If radiant energy falls upon a surfacethen the term irradiance (E) is usedin place of radiantflux density. If the flow ofenergy is away from the surface, as in the case of thermal energyemitted by theearth or incomingsolarenergy which is reflected by the earth, then the termradiantexistenceor radiant emittance as measured in units of Wm-is used.Radiance (L) is defined as the radiant flux density transmitted from asmall areaon the earth'ssurface and viewed througha unit solid angle. It is measured in wattsper square meter persteradian(Wm-2 S.1). The concepts of the radian and steradianareillustrated in Figure.

The other important terms we come across remote sensingtechnology is 'reflectance' denotedbye. Itis defined as the ratio between the irradianceand the radiant emittanceof an object. Whenremotely sensed images collected overa time periodare to be compared, it is most appropriate toconvert the radiancevalues recorded by the sensor into reflectance in order to eliminate theeffects ofvariable irradiance over the seasons of the year.The reflectance characteristic of earth's surface features may be quantified bymeasuring theportionof incident energy that is reflected. It is a dimensionless quantity.The quantitiesdescribed above are very often used to refer to particular narrowwavebands rather than to thewhole spectrum. The terms are then precededby theword'spectral', as in 'spectral radiance for agiven waveband is the radiant flux densityin the waveband per unit solid angle per unitwavelength.The sun'slight is the form of electromagnetic radiation most familiar to human beings. The lightas reflected by physical objects travels in a straight line to the observer's eye. Onreaching theretina, it generates electrical signals which are transmitted tothe brainby the optic nerve. Thesesignals are used by the brain to construct an image of theviewer's surroundings. This is theprocessof vision and it is closely analogous to theprocessof remote sensing; indeed, visionitself is a form of remote sensing. The set ofan electromagnetic waves iscalled theelectromagnetic spectrum, which includesthe range from the long radio waves, through themicrowave and infrared wavelengthsto visiblelight waves and beyond them to the ultravioletand to the short wave X-andgamma rays.

Figure (a) The angle formed when arc length s equals r, the radius of the circle, is equalto 1 radian. Thus, angle a = sIr radians. There are 21t radians (360 degrees) in a circle.(b) A steradian is the solid (three-dimensional) angle formed when the area delimited onthe surface of the sphere is equal to the square of the radius of the sphere.

SPECTRAL REFLECTANCE CURVESA basic assumption made in remote sensingis that a specific target has an individual andcharacteristic manner of interacting with incident radiation. The manner of interaction isdescribed by the spectral response of the target.The spectralreflectance curves describe the spectral response ofa target in a particularwavelength region of electromagnetic spectrum, which, in turn depends upon certain factors,namely, orientation of the sun (solar azimuth), the height of the Sun in the sky (solar elevationangle), the direction in which the sensor is pointing relative to nadir (the look angle) and natureof the target, that is, state of health of vegetation.

Figure Solar Elevation and azimuth angles. Elevation is measured upwards from theHorizontal plane. Azimuth is measured clockwise from north. The zenithangle is measuredfrom the surface angle, and equals 90 minus elevationangle, in degrees.Every object on the surface of the earth has its unique spectral reflectance.The figureshows theaverage spectral reflectance curves for three typical earth'sfeatures: vegetation,soil and water.The spectral reflectance curves for vigorousvegetationmanifests the"Peak-and-valley"configuration. The valleys in the visibleportion of the spectrum are indicative of pigments inplant leaves. Dips in reflectancethat can be seen at wavelengths of 0.65 nm, 1.4 nm and 1.9 nm,areattributable to absorption of water by leaves. The soil curve shows a more regularvariationof reflectance. Factors that evidently affect soil reflectance are moisturecontent,soil texture,surface roughness, and presence of organic matter.The termspectral signature can also be used for spectral reflectance curves. Spectral signatureisa set of characteristics by which a material or an object may be identified on anysatellite imageor photograph within the given range of wavelengths. Sometimes&spectralsignatures are usedto denote the spectral response of a target.

FigureSpectral Reflectance Curves or Spectral Signatures of Typical Features ofearth's Surface.The characteristic spectralreflectance curve is show in figurefor water shows thatfrom about0.5nm, a reduction in reflectance with increasing wavelength, so that inthe near infrared range,the reflectance of deep, clear water is virtually a zero.However, thespectral reflectance of wateris significantly affected by thepresence of dissolved and suspended organic and inorganicmaterial and bythedepth of the water body.Figureshows the spectral reflectance curves forvisibleand near-infrared wavelengthsat the surface and at 20 m depth.

FigureSpectral reflectance curves for water at different depths

The suspended solidsin water scatter the down welling radiation, the degree of scatter beingproportional tothe concentration and the colour of the sediment. Experimental studies in thefield andin the laboratory as well as experience with multispectral remote sensing have shownthat the specific targets are characterized byan individual spectral response. Indeedthesuccessful development of remote sensing of environment over the past decadebears witness toitsvalidity.In the remaining part of this section, typical and representativespectral reflectance curves forcharacteristic types of the surface materials are considered.Imagine a beach on a beautifultropical island.This figure shows interactionsof electromagnetic radiation with the top layer ofsand grains on the beach. When anincident ray of electromagnetic radiation strikes an air/graininterface, part ofthe rayis reflected and part of itis transmitted into the sand grain. The solidlines in the figurerepresent the incident rays, and dashedlines 1, 2, and 3 represent rays reflectedfrom the surface but have never penetrated a sand grain. The latter are called specularrays byVincent and Hunt (1968), and surface-scattered rays by Salisbury and Wald(1992); these raysresult from first-surface reflection from all grains encountered. For a givenreflecting surface, allspecular rays reflected in the same direction, such thattheangle of reflection (the angle betweenthe reflected rays and the normal, orperpendicular to the reflecting surface) equals the angle ofincidence (the anglebetween the incident rays and the surface normal).

Figureinteraction between electromagnetic radiation and the top layer of particlescomprising a mat surface. Solid lines (I) represent incident rays, lines 4 and 5

The measure of how much electromagnetic radiation is reflected off a surfaceiscalled itsreflectance, which is a number between 0 and 1.0.A measure of 1.0means the 100% of theincident radiation is reflected off the surface and a measureof0 means that 0% is reflected. Inthe case of first-surface reflection, this measure is called the specular reflectance, which will bedesignated here as rs (A). The A inparentheses indicates that specular reflectance is a function ofa wavelength.The reason thatrS(A) is a function of a wavelength is that the complex index of refraction ofthereflecting surface material is dependent on a wavelength. The term complex means that thereis areal and imaginary part to the index of refraction.Every material has acomplex index of refraction, though for some materials at somewavelengths, only thereal part of the complex index of refraction may be nonzero.For a sandgrain withcomplex index of refraction N( A) = n(A)[1-ik(A)], thespecular reflectance isexpressed by Fresnel's equationasfollows:

The final reflectance of a specular ray bouncing off multiple grains of sand issimply themultiplicative product of specular reflectance from the entire encounteredair/grain interface. Forinstance, if the specular reflectanceof three grains for aparticular wavelengthof electromagneticradiation were 0.9, 0.8 and 0.7, respectively,the final reflectanceof a specular ray bouncing offall three grains would be(0.9)(0.8)(0.7)= 0.504. The specular reflectance of the beach surface,RS(A), is theaverageofall the individual specular ray reflectance.Raysof electromagneticradiation that have been transmitted through someportion of one or more grains arecalledvolume rays. These are shown as dashedlines 4 and 5 in Figure. The equation for the volumereflectance, r5(A), of a sandgrainis complicated because it depends on both the transmittanceof the grain andthe interface reflectance of the top of that grain and the underlying grain (s).

The averagerS(A ) for all the gr ains in the beach from which electromagneticradiationisreflected is defined as the volume reflectance of the beach,RS(A). Thetotal reflectance of thebeach,RT(A), is the averaged sum of the specular and volumereflectance, asfollows

The dependence ofRSA and RV(A) are markedly different, as demonstrated inFigurefor thecase of a uniform grain size and varying wavelength. Three importantobservations canbesummarizedfrom the above discussion on the beautiful beachisland.(i) The spectral locations of absorption bands dependon chemical compositionof the material;for example, quartz and calcite absorption bands in the thermalinfrared wavelength region havedifferent spectral locations becauseSi ando ions in quartz are connected by a "spring" with adifferent bond strengththan that ofthe" spring" connecting Ca and 0 ions in calcite.(ii) The brightness, or magnitude, of the spectral reflectance depends primarilyon the size of thereflecting grains.(iii) Absorption bands appear as reflectance minimain transparent materials(such as quartz andcalcitein the visible wavelength region), whereasabsorption bands appear as reflectance maximain opaque materials.

FigureAbsorption coefficient, specular reflectance, volume reflectance, and totalreflectance vswavelength for a spectral feature.

Note that when we use the terms transparent or opaque toexplain opticalbehavior, we mustdesignate both a wavelength region and the material because thecomplex indexof refraction ofany material is generally non-constant over a largerange of wavelength.To consider the effect on reflectance of mixing several minerals together, let ustake the simplercaseof a particulate medium consisting of several mineral constituents,with air filling theinterstices between particles.It is possible for us to estimate thespectral reflectanceof a mixed-mineral particulate sample by using a linearcombinationofthe reflectance spectra of its mineralconstituents, weighed by the percentage ofarea on the sample's surface that is covered by eachmineral constituent. The followingequation demonstrates this estimation forthe total spectralreflectanceof a mixedparticulate sample at wavelengthA.

Figure Diagrams of the illumination and reflection geometries of (a) hemisphericalreflectance. (b) directional hemispherical reflectance, and (c) bi-conical reflectance

Thus so far we have talked about volume reflectance and specular reflectance on the basis ofwhether electromagnetic rays did or did not penetrate one or moregrainsin a soil or rocksurface. Now we need to define some reflectance terms that relate to themanner in which the soilor rock surface is illuminated, as well as, how thereflected energyfrom its surface is measured.The most fundamental term forreflectance used in this book is defined as spectral hemisphericalreflectance or diffusereflectance.APPLICATIONS

Figure example of atmospheric electromagneticwindow Figure example of EMRinteraction with earth surface materials

POSTTEST-MCQ TYPE[1]When emissivity is zero, what will be the value of reflectance?a) Oneb) Zeroc) Tend) Not equal to one[2]Generally, the value ofreflectance varies from __________a) 10-20b) 0-10c) 0-1d) 0-0.5[3]The reflectance characteristic of earth's surface features may be quantified by measuring____________a)the portion of reflectedenergy that istransmitted.b) the portion of incident energy that is reflected.c)the portion of incident energy that is refracted.d)its speed and velocity.[4]Which of the following can be changed while interaction of EM wave with a surface?a) Intensityb) Diffractionc) Wave lengthd) Direction[5]Find the transmittance, if the transmitted and incident energies are given as 156J and 987Jrespectively.a) 0.51b) 0.45c) 0.15d) 0.5

[6]The set of_______________is called the electromagnetic spectrum.a) Electricwavesb)Magneticwavesc) Tsunamiwavesd)Electromagnetic[7]The energy recorded by a sensor is always modified by the atmosphere between__________and ________a)satellite and groundb)space and satellitec) sensor and groundd)sensor and satellite[8]Bluelight+Greenlight+ Redlight=a)Red lightb)White lightc) Black lightd)Greenish blue light[9]____________serves toabsorbtheharmful(tomostlivingthings)ultravioletradiationfor thesun.a)Mesosphereb)Ozonec)Lithosphered)Ionosphere[10]__________occurs when particles or large gas molecules present in theatmosphere interact with and cause the electromagnetic radiation to be redirected from itsoriginal path.a) Radianceb)Irradiancec)Greenhouse gasd) Scattering

CONCLUSIONIn this unit, studentswould have understood the concept of remote sensingandthebasicconceptsof atmospheric characteristics like scattering of EMR and its typeswere discussed. Thesignificance of atmospheric windows used in remotesensingwaselaborated. Theknowledgeabout EMR interaction with different materialswasexplained.Thusthevolume reflectance andspecular reflectance on the basis of whether electromagnetic rays did or did not penetrate one ormoregrainsin a soil or rocksurfacewas discussed.REFERENCES1. Anji Reddy, Remote Sensing and Geographical Information Systems, BS Publications 2001.2. M.G. Srinivas, Remote Sensing Applications, Narosa Publishing House, 2001.3.Lillesand T.M. and Kiefer R.W. Remote Sensing and Image Interpretation, John Wiley andSons, Inc, New York.4.Janza.F.J., Blue, H.M., and Johnston, J.E.,Manual of Remote Sensing Vol.I,AmericanSociety of Photogrammetry, Virginia, U.S.A, 1975.5.Barrow., G. M.,1962, Introduction to Molecular Spectroscopy, New York,McGraw-Hill.6.Mather, P. M., 1987, Computer Processing of Remotely Sensed Images: An Introduction,John Wiley & Son.7.Fisher., J., 1989, Thepixel, a snare and a delusion, International Journal of RemoteSensing,18, pp. 679-6858.Hunt., G. R, Salisbury, J. W., and Lenyoff, C. J., 1973, Visible and Near InfraredSpectraofMinerals and Rocks. V11. Acidic Igneous Rocks, Modern Geology,Vol.4, pp 217-224.9.Curran.,P., 1989, Principles of Remote Sensing, Longman, London.ASSIGNMENT1.Describe about thespectral signature concepts.2.Identify, what are the characteristic of EMR interaction with soil particles.3.Describe as how does EMR interact with Ozone?4.Listout the different types of scattering in remote sensing.5.List out the primary absorbentsof electromagnetic energy in the atmosphere.S

UNIT III OPTICAL AND MICROWAVEREMOTE SENSINGPrepared byT.DINESH KUMARAssistant ProfessorECE, SCSVMV

REMOTE SENSING & GIS

AIM &OBJECTIVESTo provide students an exposure to Remote sensing.To understand thedifferentEarth Resources Satellites.To learn aboutSatellite Sensors.To acquire knowledge aboutSide Looking Airborne Radar andSynthetic ApertureRadar.PRE TEST-MCQ TYPE[1]Blue, green, and red are the_________of the visible spectrum.a) primary coloursb) primaryfrequentc)secondarycoloursd)secondary frequent[2]The altitudinal distance of a geostationary satellite from the earth is about:(a) 26,000 kmb)30,000 kmc) 36,000 kmd)44,000 km[3]_________ is a device that converts electrons to photons or vice-versa.a) Antennab) Electron gunc) Photon amplifierd) Microwave tubeUNIT III OPTICAL AND MICROWAVE REMOTE SENSING-CONTENTSSatellites-Classification-Based on Orbits-Sun Synchronous and Geo Synchronous-Based on Purpose-Earth Resources Satellites, Communication Satellites, Weather Satellites,Spy Satellites-Satellite Sensors-Resolution-Spectral, Spatial, Radiometric and TemporalResolution-Description of Multi Spectral Scanning-Along and Across Track Scanners-Description of Sensors in Landsat, SPOT, IRS series-Current Satellites-Radar-Speckle-Back Scattering-Side Looking Airborne Radar-Synthetic Aperture Radar-Radiometer-Geometrical characteristics

THEORYIntroductionRemote sensing of the surface of the earth has a long history, dating from theuse of camerascarriedby balloons and pigeons in the eighteenth and nineteenthcenturies. The term 'remotesensing'is used to refer to the aircraft mounted systemsdeveloped for military purposesduring the early part of the 20thcentury. Air bornecamera systems are still a very importantsource ofremotely sensed data. Although photographic imaging systems have many uses, thisunitis concerned with image data collected by satellite sensing systems which ultimatelygenerate digital image products.Space borne sensors are currently used to assist in scientific and socioeconomicactivitieslikeweather prediction, crop monitoring, mineral exploration, waste landmapping, cyclonewarning, water resources management, and pollution detection. All this has happened in ashort period of time. The quality of analysis of remote sensing dataand the varied types ofapplications to which the science of remote sensing isbeing put to use are increasingenormously as new and improved spacecraft arebeingplaced into the earth's orbit. Theprimary objectives, characteristics and sensorcapabilities of the plethora of remote sensingsatellites circling this planet, are discussedin thisunit.An attempt is made to classify the satellites into threetypes, namely,earthresources satellites, meteorological satellites, and satellites carrying microwavesensors. Thisclassificationis not rigid. For instance, most of themeteorologicalsatellitesare also capableof sensing the resources of the earth. Before turning to the individualsatellite's descriptionand the corresponding sensors and capabilities, a brief overviewofsatellite systemparameters is presented in the following paragraphs.Satellite System ParametersA brief overview of the most important satellite system parameters which describethefunctions and operationsof the remote sensing systems are presented in thissection. Broadly,the system parameters are of twotypes: instrumental and viewing.The principal instrumentalparameters, namely, wavelength or frequency,polarization,and sensitivity or radiometricresolution are determinedby the design of the transmitter, receiver, antenna, detectors, anddata handling system. The principal viewingparameters are determinedby both theinstrument design and the orbital parametersof thesatellite. Revisit internal, resolution,swath width, illumination and/ or observationangle and mission lifetime are the importantviewing parameters of any satellite sensingsystem.

Instrumental ParametersAll of the remote sensing systems make use of information carried byelectromagneticradiation,of which there is an infinite range of possible frequenciesor Wavelength.Inpractice, however, the transparency or otherwise of the earth'