Digital Analysis of Remotely Sensed Imagery

"JayGao’sbookontheanalysisofremotesensingimageryisawell-written,easy-to-read,andinformativetextbestservinggraduatestudentsingeosciences,andpractitionersinthefieldofdigitalimageanalysis.AlthoughDr.Gaostatesthathehastargetedhisbookatupper-levelundergraduatesandlower-levelpostgraduatestudents,itsrigoranddepthofmathematicalanalysiswouldchallengemoststudentswithoutpriorexperienceinremotesensingandcollege-levelmathematics.Thebookcoversalotofgroundquickly,beginningwithabasicexplanationofpixels,digitalnumbersandhistogramsandadvancingrapidlythroughadescriptionofthemostwell-knownsatellitesystemstodatastorageformats,rectificationandclassification.Itbestservesstudentswhohavealreadytakenanintroductorycourseinremotesensing.Followingathree-chapterdescriptionofthebasicstheremainingelevenchaptersarededicatedtothedescriptionofthemostcommonimageprocessingsystemsandthedetailsoftheimageanalysisfunctionswhichcanbecarriedout.Thelargestportionofthetextcoversclassification–spectralandspatial,neuralnetworks,decisiontreesandexpertsystems–andisaninvaluablereferencetoanyoneinterestedinunderstandingimageanalysisterminologyandthealgorithmsbehindthesedifferentsystems.ThelastchapterofthetextisaddressedtopractitionerswishingtointegrateremotesensingimagedatawithGISand/orGPSdata.Thetextisnicelystructuredsothatindividualchapterscaneasilybeskippedwhentheircontentisnotofinteresttothereaderwithoutimpairingtheunderstandingoflaterchapters."Thefirstthreechaptersofthebookcoverintroductorymaterialthatthereadershouldbefamiliarwithforthemostpart,butalsoincludesaveryhandysummaryoftoday’ssatellitesystems.Chapteroneaddressesbasicmaterial,suchaspixelDN,coordinates,featurespace,histograms,andspatial,spectral,temporalandradiometricresolutionnormallycoveredinanintroductorycourseinremotesensing.Chaptertwopresentsaveryinformativeandup-to-dateoverviewoftoday’ssatelliteinstrumentsincludingmeteorological,oceanographic,earthresources,hyperspectralandradarinstruments.Instrumentandorbitalparametersarepresentedintabularformandmakeiteasytolookuptechnicaldetailssuchasspectralandspatialresolution,orbittype,repeatcycleandotherinstrumentcharacteristicsquickly.Writtenexplanationsareclear,readableandprovidelotsofinterestinginsightandusefultidbitsofinformationsuchaspotentialproblemsandthecostofimagery.Fortechniciansandprogrammersthethirdchapterprovidesdetailsonstorageformats,includingdescriptionsofBSQ,BILandBIPbinaryformats,andthemostcommongraphicsformatslikeGIF,TIFFandJPEGtogetherwithdatacompressiontechniques.Non-technicianscanskipthischaptersinceimageprocessingsoftwarewillgenerallytakecareofformatconversionsinternallywithoutaneedforunderstandingthenuancesofeach."Chaptersfourwillbeofinteresttoanyoneconsideringthepurchaseofimageprocessingsoftware,ortryingtounderstandthedifferencesbetweensystems.Gaoprovidesausefuloverviewofexistingsoftware–IDRISI,ERDASImagine,ENVI,ERMapper,PCI,eCognitionandGRASS.Abriefhistoryofeachprovidesusefulbackground,andadiscussionofthefeaturesofeachtogetherwithacomparison(alsogivenintabularform)isinformativetoanyoneconsideringapurchase."Chapterfivecanalsobeviewedasastand-alonereferenceonrectification,butalsoservesasanexcellentoverviewoftheproblemsofdealingwithmappingonacurvedsurfaceandhasparticularapplicationforgeographersandcartographers.Itdiscussesthesourcesofgeometricdistortion,coordinatedsystemsandprojections,howimagerectificationisdone–includingtheuseofgroundcontrolpointsandimplicationsfortheorderoftransformationemployed.ThereisaniceexampleshowinghowaccuracyisinfluencedbythenumberofGCPsemployedforSPOTandLandsatTM.Fornon-technicalstudentsthetransformationmathematicscanbeskipped.Aratherminimalsectiononimagesubsettingandmosaickingisincluded.Chaptersixcontinuesinmuchthesameveinasthepreviouschapter,butdiscussingimageenhancement–techniquesthatimprovethevisualqualityofanimage.Thetermsintroducedhere,suchasdensityslicing,linearenhancement,stretching,andhistogramequalization,willbefamiliartousersofimageprocessingsoftwareandGaoprovidesausefulexplanationofeachinturn.Otherapplication-orientedutilitiessuchasbandratioing,vegetationindices,IHSandTasseledCaptransformationsandprincipalcomponentanalysisarepresentedinaformwhichisunderstandabletostudentswithgoodmathematicalgrounding."Theremainderofthetextdeals,toalargeextent,withthetopicofclassification.Chapterseveninitiallydiscusseselementsofimageinterpretation,butthendevotesthechaptertoadetailedpresentationofthemostcommon(andaffordable)ofthese-spectralanalysis.Gaopresentsthedifferentalgorithmsusedtodefinespectraldistance,andthendevotestexttoadiscussionoftheinnerworkingsofunsupervisedclassificationsystems.Thesectiononsupervisedclassificationisaveryusefulreferenceforanyoneundertakingthisprocess–describinghowtosetabouttheclassificationprocess,thedifferencesbetweenthedifferentclassifiers,andhowtochooseanappropriateone.Theconceptsoffuzzylogicandsub-pixelsclassifiersarealsopresentedbriefly."Fromthispointon,thetextbecomesmuchmorespecializedandtechnicalandisgearedtowardsgraduatestudents,thosecarryingoutresearchprojects,andthoseinterestedinalgorithmicdetail.Chapter8isthefirstdealingwithartificialintelligenceanddescribesthefundamentalsofneuralnetworks.Itprovidessufficientinformationforatechnically-mindednon-specialisttounderstandtheworkingsofsuchasystemandservesasagoodintroductiontosomeonewhoisconsideringthisfieldofresearch.Chapternineoffersanexplanationofdecisiontreeswithbothadescriptiveverbalapproachandwithmathematicalalgorithmicdetail.Chaptertenaddressesspatialclassifiers–inparticulartheanalysisoftexture.Thischapteragainleansmoreheavilytowardsmathematicsandthedetailismoresuitedtoreaderswithastrongtechnicalbent.Gaogoesontodiscusstheprocessofimagesegmentationandthencethefundamentalsofobject-orientedclassification.Thereisausefuloverviewoftwopopularsoftwarepackages–eCognitionandFeatureAnalyst–togetherwithadiscussionofthestrengthsandweaknessesofobject-basedclassification.Chapterelevenpresentsanoverviewofexpertsystems.Thisisanadvancedfieldofartificialintelligenceandisanambitiousundertakingtodescribeinfiftyorsopages.Itisaninterestingreadforsomeonetryingtogainasuperficialknowledgeoftheworkingsofsuchasystemandtheassociatedterminology,butforanyonewishingtoworkinthefield,amuchmorein-depthcoverageisnecessary."Atthispoint,thestudentwhowasjusttryingtounderstandthebasicsofimageprocessingandclassification(andwhoskippedchapterseightthrougheleven)shouldresumereadingasthelastthreechaptersprovideveryhelpfulpracticalinformation.Chaptertwelveprovidesausefuldiscussiononthemethodologyforassessingtheaccuracyofaclassificationandincludessourcesofinaccuracyandinterpretationofanerrormatrix.Itprovidesworkedexamplesofaccuracyassessmentsusingsimplemath.Thisisavaluableadditiontothetextandpresentsanimportantprocessthatisoftenoverlookedinreportingclassificationresults.Chaptersthirteenandfourteenalsodealwithverypracticalmatters.Chapterthirteendescribesproceduresforhandlingtheanalysisoftemporalchangesviaavarietyofchangedetectionalgorithms,andchapterfourteenintroducestheuseofGISandGPSdatainimageanalysis."Dr.Gaohaswrittenanexcellenttextdescribingtechnicalinformationinaveryreadablemanner.Hisbookwillserveasagoodtextforacourseinremotesensing/imageanalysis,assumingthatthestudenthasreceivedinstructioninthefundamentalsofremotesensingandbeenintroducedtosomeimageprocessingsoftware.Studentswishingtobecomeadeptatthepracticalitiesoffundamentalimageprocessingskillsandclassificationcaneasilyskipthemidsectionofthetext,whereasthosewhoarekeentolearnaboutmoresophisticatedclassifierswillgainthefundamentalsofthesefromthissection.OverallIfoundthebookveryinformativeandapleasuretoread."ReviewedbyHelenM.Cox,PhD.AssociateProfessor,DepartmentofGeography,CaliforniaStateUniversity,Northridge