Remote sensing: Its Application & Types

What is remote sensing? what are its application and various types of remote sensing in detail with graphic visuals.

1. Remote Sensing and GIS
Dr. Sanjeev Kumar
Department of Geology
School of Earth and Environmental Sciences
Babasaheb Bhimrao Ambedkar University, Lucknow
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Definition of Remote Sensing
Aformalandcomprehensivedefinitionofappliedremotesensingasgiven
byNationalAeronauticsandSpaceAdministration(NASA)isasfollows:
“Theacquisitionandmeasurementofdata/informationonsome
property(ies)ofaphenomenonobject,ormaterialbyarecordingdevice
notinphysicalintimatecontactwiththefeature(s)undersurveillance;
techniqueinvolveamassingknowledgepertinenttoenvironmentsby
measuringforcefieldselectromagneticradiationoracousticenergy
employingcameras,radiometersandscanners,lasers,radiofrequency
receivers,radarsystem,sonar,thermaldevices,seismographs,
magnetometers,gravimeters,scintillometers,andotherinstrument”.

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Anotherdefinitions:
"RemoteSensingisthescienceandartofobtaininginformationaboutanobject,area,or
phenomenonthroughtheanalysisofdataacquiredbyadevicethatisnotincontactwith
theobject,area,orphenomenonunderinvestigation.“
or
Remotesensingistheacquisitionofinformationaboutanobjectorphenomenonwithout
makingphysicalcontactwiththeobjectandthusincontrasttoon-siteobservation.
The another definition of remote sensing is given by American
Association of Photogrammetry and Remote Sensing 1988 as follows:
“Theart,scienceandtechnologyofobtainingreliable
informationaboutphysicalobjectsandtheenvironment,throughthe
processofrecording,measuringandinterpretingimageryanddigital
representationofenergypatternderivedfromnoncontactsensor
systems”.

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2005:IRS cartosatfor DEM generation
2007: IRS cartosat2 with 80 cm panchromatic band
2013: Landsat 8 OL1/T/RS with 11 bands (freely downlodable)
2014: World view 3.30 resolution

6. Stages in Remote Sensing
i.Emission of electromagnetic radiation, or EMR (sun/self emission)
ii.Transmission of energy from the source to the surface of the earth, as
well as absorption and scattering
iii.Interaction of EMR with the earth’s surface: reflection and emission
iv.Transmission of energy from the surface to the remote sensor
v.Sensor data output
vi.Data transmission, processing and analysis
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7. •Energy Source or Illumination (A)
•Radiation and the Atmosphere (B)
•Interaction with the Target (C)
•Recording of Energy by the Sensor (D)
•Transmission, Reception, and Processing (E)
•Interpretation and Analysis (F)
•Application (G)
Remote Sensing Process Components
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Applications of Remote Sensing

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13. Electromagnetic Radiation
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15. Electromagnetic Energy
Wave Theory -c =??????x ??????
Speed of Light (c) = wavelength xfrequency (??????x ??????)
c = 3 x 10
8
m/sec (the speed of light) = 186,000 miles/sec
Wavelength (??????) –the distance from
one wave peak (or crest) to the next
is the wavelength
Frequency(??????)-thenumberof
peakspassingafixedpointina
spaceperagiventimeunit
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16. ElectromagneticSpectrum
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Major regions of the electromagnetic spectrum

23. Types of Remote Sensing
RemoteSensingcanbeeitherpassiveoractive.ACTIVEsystemshave
theirownsourceofenergy(suchasRADAR)whereasthePASSIVE
systemsdependuponexternalsourceofillumination(suchasSUN)or
selfemissionforremotesensing.Thisisdescribedisgivenbelow:
Activeremotesensing:Emitsenergyinordertoscanobjectsand
areaswhereuponasensorthendetectsandmeasurestheradiationthatisreflected
orbackscatteredfromthetarget.RADARisanexampleofactiveremotesensing
wherethetimedelaybetweenemission
andreturnismeasured,establishingthe
location,height,speedsanddirectionof
an object.
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Active remote sensing create their own electromagnetic energy that
1.Istransmittedfromthesensortowardtheterrain(andislargely
unaffectedbytheatmosphere)
2.Interactswiththeterrainproducingabackscatterofenergy
3.Isrecordedbytheremotesensor’sreceiver.
The most widely used active remote sensing include:
•Activemicrowave(Radiodetectionandranging;RADAR),
whichisbasedonthetransmissionoflongwavelengthmicrowaves(e.g.
3-25cm.)throughtheatmosphereandthenrecordingtheamountof
energybackscatteredfromtheterrain.
RadarwasinvestigatedbyA.H.TaylorandL.C.Youngin1922.

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•SONAR (Sound navigation ranging) , which is based on the
transmission of sound waves through a water column and then recording the
amount of energy backscattered from the bottom or from objects within the
water column
•LIDAR(Lightdetectionandranging),whichisbasedonthe
transmissionofrelativelyshortwavelengthlaserlight(e.g.1040nm)
andthenrecordingtheamountoflightbackscatteredfromtheterrain.

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31. PassiveRemoteSensing:detectnaturalradiationthatisemittedor
reflectedbytheobjectorsurroundingareabeingobserved.Reflectedsunlight
isthemostcommonsourceofradiationmeasuredbypassivesensors.
Examplesofpassiveremotesensorsincludefilmphotograph,infrared,and
radiometers.
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Special Sensor Microwave/ Imager (SSM/I)
•OneofthefirstpassivemicrowavesensorswastheSpecialsensor
Microwave/imager(SSM/I)onboardtheDefenseMeteorologicalSatellite
Program(DMSP)satellitesince1987.Thedepartmentofdefensealsorelease
thedatatothescientificcommunity.
TRMM Microwave Imager (TMI)
•TheTropicalRainfallMeasuringMission(TRMM)issponsoredbyNASA
andtheNationalSpaceDevelopmentAgency(NASAD)ofJapantostudy
thetropicalrainfallandtheassociatedreleaseofenergythathelpstopower
globalatmosphericcirculation.
•TheTRMMMicrowaveImagerisapassivemicrowavesensordesignedto
providequantitativerainfallinformationovera487mile(780km.)swath.
•Itmeasurestheintensityofradiationatfivefrequencies:10.7(45km
spatialresolution),19.4,21.3,37,85.5GHz(5kmspatialresolution).

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Advanced Microwave Scanning Radiometer (AMSR -E)
AMSR-E measures total water-vapor content, total liquid water content,
precipitation, snow-water equivalent, soil moisture (using the 6.925 and 10.65
GHz frequencies), sea surface temperature (SST), sea surface wind speed, and
sea ice extent.

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Types of Remote Sensing System
1. Visual remote Sensing System:

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2. Optical remote Sensing System:

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Optical remote sensing systems are classified into the following types, depending on the
number of spectral bands used in the imaging process.
Panchromaticimagingsystem:Thesensorisasinglechanneldetectorsensitivetoradiation
withinabroadwavelengthrange.Ifthewavelengthrangecoincidewiththevisiblerange,
thentheresultingimageresemblesa"black-and-white"photographtakenfromspace.The
physicalquantitybeingmeasuredistheapparentbrightnessofthetargets.Thespectral
informationor"colour"ofthetargetsislost.Examplesofpanchromaticimagingsystemsare:
•IKONOS PAN
•SPOT HRV-PAN
Multispectralimagingsystem:Thesensorisamultichanneldetectorwithafewspectral
bands.Eachchannelissensitivetoradiationwithinanarrowwavelengthband.Theresulting
imageisamultilayerimagewhichcontainsboththebrightnessandspectral(colour)
informationofthetargetsbeingobserved.Examplesofmultispectralsystemsare:
•LANDSATMSS
•LANDSATTM
•SPOTHRV-XS
•IKONOSMS

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SuperspectralImagingSystems:Asuperspectralimagingsensorhasmanymore
spectralchannels(typically>10)thanamultispectralsensor.Thebandshavenarrower
bandwidths,enablingthefinerspectralcharacteristicsofthetargetstobecapturedbythe
sensor.Examplesofsuperspectralsystemsare:
•MODIS
•MERIS
HyperspectralImagingSystems:Ahyperspectralimagingsystemisalsoknownasan
"imagingspectrometer".Itacquiresimagesinaboutahundredormorecontiguousspectral
bands.Theprecisespectralinformationcontainedinahyperspectralimageenablesbetter
characterizationandidentificationoftargets.Hyperspectralimageshavepotential
applicationsinsuchfieldsasprecisionagriculture(e.g.monitoringthetypes,health,moisture
statusandmaturityofcrops),coastalmanagement(e.g.monitoringofphytoplanktons,
pollution,bathymetrychanges).Anexampleofahyperspectralsystemis:
•Hyperion on EO1 satellite

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3. Infrared Remote Sensing:

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Theamountofthermalradiationemittedataparticularwavelengthfromawarmobject
dependsonitstemperature.Iftheearth'ssurfaceisregardedasablackbodyemitter,its
apparenttemperature(knownasthebrightnesstemperature)andthespectralradianceare
relatedbythePlanck'sblackbodyequation,plottedintheabovefigureforseveral
temperatures.Forasurfaceatabrightnesstemperaturearound300K,thespectralradiance
peaksatawavelengtharound10µm.Thepeakwavelengthdecreasesasthebrightness
temperatureincreases.Forthisreason,mostsatellitesensorsformeasurementoftheearth
surfacetemperaturehaveabanddetectinginfraredradiationaround10µm.
Besidesthemeasurementofregularsurfacetemperature,infrared
sensorscanbeusedfordetectionofforestfiresorotherwarm/hotobjects.Fortypicalfire
temperaturesfromabout500K(smoulderingfire)toover1000K(flamingfire),the
radianceversuswavelengthcurvespeakataround3.8µm.SensorssuchastheNOAA-
AVHRR,ERS-ATSRandTERRA-MODISareequippedwiththisbandthatcanbeused
fordetectionoffirehotspots.

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Planck'slawdescribesthespectraldensityofelectromagneticradiationemittedbya
blackbodyinthermalequilibriumatagiventemperatureT,whenthereisnonetflow
ofmatterorenergybetweenthebodyanditsenvironment.

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4. Microwave Remote Sensing:

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Themicrowaveenergyrecordedbyapassivesensorcanbeemittedbythe
atmosphere(1),reflectedfromthesurface(2),emittedfromthesurface(3),ortransmitted
fromthesubsurface(4).Becausethewavelengthsaresolong,theenergyavailableisquite
smallcomparedtoopticalwavelengths.Thus,thefieldsofviewmustbelargetodetect
enoughenergytorecordasignal.Mostpassivemicrowavesensorsarethereforecharacterized
bylowspatialresolution.
Applicationsofpassivemicrowaveremotesensingincludemeteorology,hydrology,
andoceanography.Bylooking"at",or"through"theatmosphere,dependingonthe
wavelength,meteorologistscanusepassivemicrowavestomeasureatmosphericprofilesand
todeterminewaterandozonecontentintheatmosphere.Hydrologistsusepassive
microwavestomeasuresoilmoisturesincemicrowaveemissionisinfluencedbymoisture
content.Oceanographicapplicationsincludemappingseaice,currents,andsurfacewindsas
wellasdetectionofpollutants,suchasoilslicks.

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5. Radar Remote Sensing:

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6. Satellite Remote Sensing

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7. Airborne Remote Sensing:

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8. Acoustic and near-acoustic remote sensing

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Atmospheric Constituents

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Interaction with atmosphere

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Atmospheric window for various wavelength of EMR

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Figureisageneralizeddiagramshowingrelativeradiationtransmissionof
differentwavelength.GreyzonesmarkedinFig.showtheminimalpassageof
incomingand/oroutgoingradiationwhereaswhiteareasdenoteatmospheric
windows,inwhichtheradiationdoesnotinteractmuchwithairmoleculesand
hence,isnotabsorbed.Mostremotesensinginstrumentonairorspace
platformsoperateinoneormorethesewindowsbymakingtheirmeasurements
withdetectorstunedtospecificfrequencies(wavelength)thatpassthroughthe
atmosphere.However,somesensors,especiallythoseonmeteorological
satellite,directlymeasureabsorptionphenomenon,suchasthoseassociated
withcarbondioxideandothergaseousmolecules.

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iv.RamanScattering:Ramanscatteringiscausedbyatmospheric
particles,whicharelarger,smaller,orequal,tothatofwavelengthofthe
radiationbeingsensed.Theatmosphericparticlesmaybegaseousmolecules,
waterdroplets,fumes,ordustparticles.TheEMRhasanelasticcollisionwith
theatmosphericparticles,whichresultsineitherlossorgainofenergyand
thusanincreaseordecreaseinwavelength.
Theeffectwasdiscoveredin1928byC.V.RamanandhisstudentK.S.
Krishnaninliquids,andindependentlybyGrigoryLandsbergandLeonid
Mandelstamincrystals

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❖Absorptionistheprocessbywhichradiantenergyisabsorbedandconverted
intootherformsofenergy.Theabsorptionoftheincidentradiantenergymay
takeplaceintheatmosphereandontheterrain.Anabsorptionbandisarange
ofwavelength(orfrequencies)intheelectromagneticspectrumwithinwhich
radiantenergyisabsorbedbyasubstances.

64. 4. Refraction: When EMR encounters substances of different densities,
like air and water, refraction takes place. Refraction refer to bending of light when
it passes from one medium to another.
Refractionoccursbecausethemediaareofdifferentdensitiesandthe
speedofEMRisdifferentineach.Theindexofrefraction(n)isameasureofthe
opticaldensityofasubstances.Thisindexistheratioofthespeedoflightina
vacuum,c(3X10
8
m/s),tothespeedoflightinasubstancessuchasthe
atmosphereorwater,Cn
n=c/Cn
Thespeedoflightinasubstancescanneverreachthespeedoflightin
avacuum.Therefore,itsindexofrefractionmustalwaysbegreaterthan1.For
exampletheindexofrefractionfortheatmosphereis1.0002926.
Withintheatmospherethereisacontinuousmovementsofair.An
effectproducedbythemovementofmassesofairwithdifferentrefractive
indicesiscalledatmosphericshimmer.Theeffectofshimmercanbemost
easilydetectedinthetwinklingofstars.Shimmerresultsinblurringon
remotelysensedimages.

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Reflection:Reflectionistheprocesswherebyradiation‘bouncesoff’an
objectlikethetopofacloud,awaterbody,ortheterrestrialearth.Reflection
differsfromscatteringinthatthedirectionassociatedwithscatteringis
unpredictablebutincaseofreflectionitispredictable.Reflectionexhibits
fundamentalcharacteristicsthatareimportantintheremotesensing.
First,theincidentradiation,thereflectedradiationandaverticaltothe
surfacefromwhichtheanglesofincidentandreflectionaremeasuredallliein
thesameplane.Second,theangleofincidenceandtheangleofreflectionare
approximatelyequal.
Aconsiderableamountofincidentradiationfluxfromthesunis
reflectedfromthetopofcloudsandothermaterialsintheatmosphere.This
resultsinrecordingofsomeextraamountofenergybythesensorinadditionto
thereflectedenergyfromtheterrain(target).Blurredimageandappearanceof
cloudontheimageryarethemainproblemsassociatedwithatmospheric
reflection.

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