Landsat Tutorial.docx

Landsat Tutorial.docx

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LandsatTutorial

AnIntroductoryLandsatTutorial

WelcometotheworldoftheLandsatSatellitesandtheirviewoftheEarthweliveon!

TheimagescontainedonthissetofCD-ROMswereobtainedbyLandsat-5,oneofaseriesofsatellitesbuiltandlaunchedbytheNationalAeronauticsandSpaceAdministration（NASA）oftheUnitedStatesofAmerica. TheLandsatsatellitesobservetheEarth,andthedatathattheycollecthavebeenusedforalmost30yearstostudytheEarth'senvironment,resources,andnaturalandman-madechangesontheEarth'ssurface.

TheLandsatseriesinitiatedtheeraofEarthobservationfromspacefornon-militarypurposes. Landsat-typedataarenowcollectedbysatellitesystemsbuiltbyothercountriesandcommercialenterprises,butLandsatdataarethestandardforEarthobservations,andLandsatistheonlysystemofitstypewiththemissiontocollect,archive,anddistributedataofalltheEarth'slandsurface.

ThefirstLandsatwaslaunchedonJuly23,1972. ThissatellitecarriedonboardtwoinstrumentstolookattheEarth'ssurface-aReturnBeamVidicon（RBV）andaMulti-SpectralScannerSystem（MSS）.

Landsat-1,originallycalledtheEarthResourcesTechnologySatellite（ERTS-1）,wasfollowedbyLandsats-2,-3,-4,-5,and-7. Landsat-6unfortunatelyfailedtoreachorbit. ReturnBeamVidiconsandMulti-SpectralScannerSystemswereflownonthefirstthreeLandsats. TheMSSprovedtobeamoreusefulandreliableinstrumentthattheRBV.  Landsats-4and-5wereequippedwithanMSSandanimprovedversionoftheMSS,theThematicMapper（TM）.  Landsat-6carriedan"EnhancedThematicMapper"（ETM）only,andLandsat-7iscarryingan"EnhancedThematicMapper-plus,"orETM+. TheoperatingdatesoftheLandsatsatellitesandtheinstrumentsonthemarelistedonTable1.

Launched

Retired

Instruments

Landsat-1（ERTS-1）

July23,1972

January,1978

RBV,MSS

Landsat-2

January22,1975

July,1983

RBV,MSS

Landsat-3

March5,1978

September,1983

RBV,MSS

Landsat-4

July16,1982

June,2001*

MSS,TM

Landsat-5

March1,1984

MSS,TM

Landsat-6

October5,1993

October5,1993

ETM

Landsat-7

April15,1999

ETM+

              Table1.LandsatSatellites,theirOperationalPeriods,andTheirInstruments.

*TheLandsat-4sensorswerenotoperationalafterJuly,1987;thesatellitewaslaterusedformaneuvertesting.

ThedataontheseCD-ROMs,calledtheGeoCoverdataset,covertheUnitedStatesofAmerica,includingAlaskaandHawaii. ThedatasetwasproducedbytheEarthSatelliteCorporationforNASAandcontainsapproximately900TMimages,orscenes. EachLandsatsceneisabout115mileslongand115mileswide（or100nauticalmileslongand100nauticalmileswide,or185kilometerslongand185kilometerswide）. ThisdatasetcoverstheUnitedStatesaround1990andcamefromobservationsacquiredbytheLandsat-5satellite. Becauseofsatelliteschedulingconstraintsandcloudcoverobscuringtheground,thescenesintheGeoCoverdatasetwerenotallobserved（acquired）onthesamedayorwithinthesamemonth,butincludescenesacquiredwithinayearortwoof1990. Withineachimageorpicture,thesmallestpictureelement,orpixel,coversasquare28.5metersonaside. Nomatterhowmuchyouzoominonanimage,thesmallestsquarethatyoucanseewillbe28.5metersonaside-evenifthereareonlyafewbigsquaresonyourscreen. Thatdatasquareisabout94feetonaside,oranareaofaboutonefifthofanacreorabout0.08hectare. TheTMpixelsizeenablesobservationoflargenaturalfeatures,suchasvolcanos,rivers,andforests,andlargeman-madefeatures. Majorhighways,officebuildings（suchasthePentagonorUSCapitolbuilding）,cityparksandagriculturalfields,airports,majorbridgesanddamsareapparent,butnarrowstreets,creeksandstreams,individualhouses,andautomobilescannotbediscerned.

Sincethedataarespreadover4CD-ROMs,theUnitedStateswasbrokenupintosmallerareascalledtilesormosaics. CollectionsoftileswereputoneachCD-oneCD-ROMcoverstheeasternUnitedStates,anothercoversthecentralUnitedStates,athirdCD-ROMcoversthewesternUnitedStates,andonefinalCD-ROMcoversAlaskaandHawaii.  Eachtilecoversanareaof6degreesoflongitude（12degreesoflongitudeatlatitudesabovethan60degrees,affectingonlyAlaskandata）by5degreesoflatitude. AdescriptionofthetilingschemecanbefoundintheGeoCoverProductDescriptionSheet（GeoCover.doc;alsoAppendix3.）. Technicallyspeaking,thesedatawereorthorectified（geometricallycorrectedsothattheywouldappearastheywouldonamap,alwayslookingstraightdownandnotfromofftoaside）. Thenthedatawereprojected（displayed）usingtheUniversalTransverseMercatorprojectiontominimizethedistortioncausedbytakingapieceofasphereandflatteningit.

TheTMinstrumentonLandsat-5andtheETM+instrumentonLandsat-7observetheEarthwith7differentfiltersor"bands". Bands1,2,3,4,5,and7onbothinstrumentsaresensitivetolightenergyfromthesunreflectedbythesurfaceoftheEarth. Eachbandissensitivetoadifferentpartofthereflectedsolarenergy. Thepartsofthereflectedenergyaredefinedbythelengthofthelightwaves. Thus,band1oftheTMandETM+instrumentsrecordsreflectedlightenergyonlyintherangeof0.45microns（µm-amicronisonemillionthofameterlong）to0.52µm. Thehumaneyeseesreflectedlightinthatbandofwavelengthsasthecolorblue;hence,band1issometimesreferredtoastheblueband. Inasimilarmanner,bands2and3oftheTMandETM+instrumentsrecordreflectedgreenandredlight,respectively.

TMandETM+bands4,5,and7recordreflectedlightinwavelengthsthathumaneyescannotdetect. Thesebandsarereferredtoasnearinfrared（NIR,band4）andshortwaveinfrared（SWIR,bands5and7）.

Band6oftheTMandETM+instrumentsisdifferentfromalltheotherbandsbecauseitdoesnotrecordreflectedlightenergy,butratherheatenergyemittedbytheEarth'ssurface.

Inadditiontothesebands,theETM+instrumentalsohasaneighthband,calledthepanchromaticsharpeningband. ETM+band8issensitivetoreflectedlightenergyacrossabroadrangeofwavelengthsthatincludesblue,green,redandnearinfrared. Thispanchromaticbandhasaspatialresolutionof15meters,ratherthanthe28.5or30metersofbands1,2,3,4,5and7. ThesensitivitiesofMSS,TMandETM+bandsarelistedinTable2.

Band

RBV

MSS

TM

ETM+

1

.48-.57µmgreen

.45-.52µmblue

.45-.52µmblue

2

.58-.68µmred

.52-.6µmgreen

.53-.61µmgreen

3

.69-.83µmIR

.63-.69µmred

.63-.69µmred

4

.5-.6µmgreen

.76-.9µmNIR

.75-.9µmNIR

5

.6-.7µmred

1.55-1.75µmSWIR

1.55-1.75µmSWIR

6

0.7-0.8µmIR

10.4-12.5µmTIR

10.4-12.5µmTIR

7

0.8-1.1µmIR

2.08-2.35µmSWIR

2.1-2.35µmSWIR

8

.52-.9µmpanchromatic

Table2. LandsatInstrumentBands.IR=infrared;NIR=nearinfrared;SWIR=short

wavelengthinfrared;TIR=thermalinfrared（longwavelength）;andµm=micronormicrometer.

Whatdothedifferentbandsmeantouswhenwelookatthedata?

 Tofindoutwhateachindividualbandseesbest,orbetterthantheothers,checktheLandsat-7imagesshowninAppendix2. Theindividualbandimagesappearasgrayscaleimages-likeold-fashionedblack-and-whitephotographs. However,theycanbecombinedtoformcompositeimages,withadifferentgrayscaleimagefeedingadifferentcolorgun（typicallyared-green-blue,orRGBcombination）. Therearemanyband-colorcombinationsthattellusefulstories. Threedifferentandoftenusedcompositesaresummarizedbelow.

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TrueColor:

  Forthetruecolorrendition,band1isdisplayedinthebluecolor,band2isdisplayedinthegreencolor,andband3isdisplayedintheredcolor. Theresultingimageisfairlyclosetorealistic-asthoughyoutookthepicturewithyourcameraandwereridinginthesatellite. Butitisalsoprettydull-thereislittlecontrastandfeaturesintheimagearehardtodistinguish.

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False-Color,alsocalledNearInfraredorNIR:

  Inthisimage,band2isdisplayedinblue,band3isdisplayedingreen,andband4isdisplayedinred. Thisrenditionlooksratherstrange-vegetationjumpsoutasabrightredbecausegreenvegetationreadilyreflectsinfraredlightenergy!

 Itissimilartopicturestakenfromaircraftwhenusinginfraredfilmandisveryusefulforstudyingvegetation.

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Short-WavelengthInfrared,orSWIR:

  InthisSWIRimage,band2isdisplayedinblue,band4isdisplayedingreen,andband7（or5）isdisplayedinred. Thisrenditionlookslikeajazzeduptruecolorrendition-onewithmorestrikingcolors.

ThisisthebandcombinationwasusedintheGeoCoverdataset. ItisbuiltintotheGeoCoverdataandcannotbechanged. Further,thecontrastandbrightnesshavebeenalteredintheGeoCoverdatasettomakeamoreconsistentoverallmosaic.

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TheappearanceofdifferentsurfacefeaturesforthedifferentcompositeimagesissummarizedonTable4.

TrueColor

Red:

     Band3 

Green:

 Band2

Blue:

    Band1

FalseColor

Red:

     Band4

Green:

 Band3 

Blue:

    Band2

SWIR（GeoCover）

Red:

     Band7

Green:

 Band4

Blue:

    Band2

Treesandbushes

OliveGreen

Red

Shadesofgreen

Crops

Mediumtolig