WANGs6019501图像处理作业.docx

WANGs6019501图像处理作业.docx

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WANGs6019501图像处理作业

Question1:

Selecttheimagesyouwanttousefromthedataset.PerformafuzzyclassificationonselectedLANDSAT8OLIimagesusingR.Storescreenshotsofyourclassifications（waterclassonly）inanMSWorddocument.Specifyandmotivateyourchoicesoftheimagestoinclude,ofthenumberofclassesandoftheparameterm.Rememberthattheaimoftheclassificationistoseechangesinthesurfaceareaofthelakethroughtime.

First,Ineedtoselecttheappropriateimagestodotheclassification.Theprincipleofmyselectionisthattryingtoselecttheimageswhichhaveaslesscloudinthelakeareaaspossibleandthewaterareashouldbeasclearaspossible.Andthedateofimagesshouldbedifferent.Finally,Iselectfiveimagestodothefollowingwork.Theyarelc81690602013198.img,lc81690602013182.img,lc81690602013168.img,lc81690602013150.imgandlc81690602013246.img,separately.

TheimagesIselected

ThenIneedtodotheclassificationoftheseimages,respectively.ThefirstthingIneedtodoisdeterminingtheparameterswhichneedfortheclassifications.

Ncl—thenumberofclasses.ForeachimagesItrydifferentNclwhichare3,4and5,respectively.AndthenIchoosethefinalNclastheonewhichmakethewaterareamostclearlyaftertheclassification.Finally,theNclis5forlc81690602013198.img,lc81690602013182.img,lc81690602013168.img,lc81690602013150.imgand4forlc81690602013246.img.

m—theparameterwhichrepresenttheleveloffuzziness.Therangeofparametermis[1,infinite）.Thefuzzinesswillincreasedasmincrease.Ifmequalto1,thefuzzyclassificationwillturntoacrispclassification.Itryseveralvaluesofm,andknowingifthemsettingtotoolarge,theiterationwillnotworkwell,themeanofclasseswillhardtoseparate.Andtheconfidencevaluewillbelow.ThenIsearchforsomearticlesaboutit,itseemsthatmequalto2willbetheempiricalbestvalue.SofinallyIselectthemequalto2.

Aftertheiterationofclassification,Ineedtoidentifywhichclassiswater.Asknowingthereflectionspectrumofthewater,thewaterhasthelowestreflectanceinband4-6,SoIcanidentifythewaterclassbycode:

Andtheresultoffuzzyclassificationsshowsbelow,intheseimagesthepixelvaluesarethemembershipvaluesofwaterclass.

lc81690602013150.img

lc81690602013168.img

lc81690602013182.img

lc81690602013198.img

lc81690602013246.img

Question2:

Foreachofthemembershiptowaterimagesyouobtained,groupthepixelsbelongingtothelakeintoalakeobject.IncludescreenshotsofthelakeobjectsinyourWorddocument.Explainandmotivatehowyoumadetheobjects.

AsIneedtoseechangesinthesurfaceareaofthelakethroughtime,it’sbettertocreatethelakeobjectsfortheimages.Thenit’sconvenienttoseethechangesbyobjectsovertime.

Thefirstthingtogroupthelakeobjectissettingthethresholdvalue

thr—thevalueofthreshold.Itdeterminesthatweatherthepixelcouldbeapartofthelakeobjectornotbycomparingitsmembershipwiththreshold.Isawthehistogramofmembershipofwaterclassandtriedseveralthresholdvaluestoseetheresultsofgroupingobjects.FinallyIchoose0.8asmythresholdtogroupthelakeobjects.

Whenaninitialpixelisdefined,itwillgrowin8directions,anypixelwhichadjacenttoitwillbejudgedbythreshold.Ifthemembershipvaluelargerthanthreshold,thisadjacentpixelwillbeincludedinthelakeobjectandwillgrowin8directionsagaindependonitself.Afterthegrowth,Iwillobtainmanysegmentsoflakeobjects,andthebiggestsegmentisLakeNaivasha.

FrompreviousexerciseIknowthelargestsegmentisLakeNaivasha,andthesecondlargestsegmentisLakeOloiden.Inthisassignment,IonlyrecordtheareasofLakeNaivashatoseethechangesthroughtime.Theresultofgroupinglakeobjectshowsblow:

lc81690602013150

lc81690602013168

lc81690602013182

lc81690602013198

lc81690602013246

Question3:

Calculatethesurfaceareaofthelakeforeachdate.ExplainhowyoucalculatedthelakesurfaceareaandshowtheresultforallLANDSAT8OLIimagesinatableandagraph.

ThesurfaceareaofLakeNaivashaisthesumofthenumberofpixelswhichinthelargestsegmentofthelakeobjectmultipliedbythepixelsize.ThesurfaceareasarecalculatedbyR.Theresultsare:

Thelakesurfaceareaeachdata

Originalimages

SurfaceareaofLakeNaivasha（m2）

lc81690602013150

125640900

lc81690602013168

129148200

lc81690602013182

134766900

lc81690602013198

127805400

lc81690602013246

135562500

Question4:

Evaluateyourresult.Didthesurfaceareachangeovertime?

Whatcanyousayabouttheuncertaintiesofthesurfaceareaestimatesandtheuncertaintiesinthechangesinsurfacearea.

Theuncertaintiesarisebothinthesurfaceareaestimatesandthechangesinsurfacearea.

First,theuncertaintiescomefromtheprocessing.Theparameterssettingfortheclassificationandgroupingobjecthastheinfluenceofuncertainties.Differentnumberofclassesordifferentparameterm,willleadtodifferentmembershipofallclasses.Andalsodifferentthresholdvaluewillleadtodifferentresultsoflakeobjects.Thatallwillleadtouncertaintiesonsurfaceareaestimatesandchangesinsurfacearea.

Then,theuncertaintiescomefromtheenvironment.FromtheimageIseecloudsshadowandalgainthelakearea.ThatwillmakeproblemswhenIdoclassificationtoidentifywater.Andleadtolessaccuracyonclassificationandgroupingobjects.

Question5:

Ifyoucomparethisresultwiththeresultoftheexercisesonfuzzyclassificationandobjectmonitoring,whereyouperformedsimilarproceduresonaseriesofLandsatETM+images,whatcanyousayaboutthedifferences?

ComparingtheseresultwiththepreviousexercisewhichIhavedonewiththelandsatETM+images.AsonlytwoimagesinLandsatETM+weretakenin2013andthedateare20130530and20130615,covertthesedatetoJuliandayare150and166.

Sothecorrespondingimagestopreviousexercisearelc81690602013150andlc81690602013168.

Thefuzzyclassificationandobjectmonitoringoftheseimages:

lc81690602013150vsl20130530

lc81690602013168vsl20130615

ComparingwithLandsatETM+images

images

Area

lc81690602013150

125640900

l20130530

125692200

lc81690602013168

129148200

l20130615

129022200

Andifyouseeonthegraph,itwillmoreclearly:

FromthetableandthegraphIseetheresultsfromthesetwodatasetsarequitesimilar.Buttherestillhavesomesmalldifference.Thatmaybebecausethespectralresolutionofthesetwodatasetaredifferent,andalsootherreasons.Forexamplethetimeoftakingthesepicturesarenotactuallythesame,andtheparametersIsettingtodoclassificationandobjectmonitoringarenottotallythesame.

Question6:

IfyoucomparetheNDVIplotshowwiththelakeareaplot,canyouseearelationshipbetweenthem?

Whichrelationshipdoyousee?

Didyouexpecttoseearelationshipbetweentheseplots?

Why（not）?

HistogramofNDVIperimageperpolygon

PlotofmeanNDVIofdifferentdate

ThechangeofsurfaceareaofthelakeandthechangeofmeanNDVIisrelevant.

Fromtheabovelinecharts,IseethechangeofmeanNDVIvaluesisalmosttheinversechangeoflakesurfacearea.Thatmeanwhenthesurfaceareaoflakeisincreased,themeanNDVIvalueisdecreased.ItistheexpectedrelationshipthatIwanttosee.Becausewhenthelakesurfaceareaisincreased,theareaofwaterincreased,theareaofplantsdecreased,thatleadtothedecreasingofNDVI.