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ComputersandElectronicsinAgriculture
journalhomepage:www.elsevier.com/locate/compag
Review
Developmentofsoftcomputingandapplicationsinagriculturalandbiologicalengineering
YanboHuanga,∗,YubinLanb,StevenJ.Thomsona,AlexFangc,WesleyC.Hoffmannb,RonaldE.Laceyd
a
USDA-ARS,CPSRU,141ExperimentStationRoad,Stoneville,MS38776,UnitedStatesUSDA-ARS,APMRU,2771F&BRoad,CollegeStation,TX77845,UnitedStatesc
EngineeringTechnologyandIndustrialDistribution,TexasA&MUniversity,CollegeStation,TX77843,UnitedStatesd
BiologicalandAgriculturalEngineering,TexasA&MUniversity,CollegeStation,TX77843,UnitedStates
b
articleinfoabstract
Softcomputingisasetof“inexact”computingtechniques,whichareabletomodelandanalyzeverycom-plexproblems.Forthesecomplexproblems,moreconventionalmethodshavenotbeenabletoproducecost-effective,analytical,orcompletesolutions.Softcomputinghasbeenextensivelystudiedandappliedinthelastthreedecadesforscientificresearchandengineeringcomputing.Inagriculturalandbiologicalengineering,researchersandengineershavedevelopedmethodsoffuzzylogic,artificialneuralnetworks,geneticalgorithms,decisiontrees,andsupportvectormachinestostudysoilandwaterregimesrelatedtocropgrowth,analyzetheoperationoffoodprocessing,andsupportdecision-makinginprecisionfarming.Thispaperreviewsthedevelopmentofsoftcomputingtechniques.Withtheconceptsandmethods,appli-cationsofsoftcomputinginthefieldofagriculturalandbiologicalengineeringarepresented,especiallyinthesoilandwatercontextforcropmanagementanddecisionsupportinprecisionagriculture.Thefutureofdevelopmentandapplicationofsoftcomputinginagriculturalandbiologicalengineeringisdiscussed.
PublishedbyElsevierB.V.
Articlehistory:
Received1August2009
Receivedinrevisedform9January2010Accepted25January2010Keywords:
SoftcomputingFuzzylogic
ArtificialneuralnetworksGeneticalgorithmsCropmanagementPrecisionagriculture
Contents1.2.
Introduction.........................................................................................................................................Methodsofsoftcomputing.........................................................................................................................2.1.Fuzzylogic...................................................................................................................................2.2.Artificialneuralnetworks...................................................................................................................2.3.Geneticalgorithms..........................................................................................................................2.4.Bayesianinference...........................................................................................................................2.5.Decisiontree.................................................................................................................................Applicationsofsoftcomputinginagriculturalandbiologicalengineering........................................................................3.1.Fuzzylogicapplications.....................................................................................................................
3.1.1.Overview...........................................................................................................................3.1.2.Cropmanagement.................................................................................................................3.1.3.IrrigationandETcalculation.......................................................................................................3.1.4.Soilanalysis........................................................................................................................3.1.5.Precisionagriculture...............................................................................................................3.1.6.Chemicalapplication..............................................................................................................
3.2.Artificialneuralnetworkapplications.......................................................................................................
3.2.1.Overview...........................................................................................................................3.2.2.Cropmanagement.................................................................................................................3.2.3.IrrigationandETcalculation.......................................................................................................3.2.4.Soilanalysis........................................................................................................................3.2.5.Precisionagriculture...............................................................................................................3.2.6.Chemicalapplication..............................................................................................................
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∗Correspondingauthor.Tel.:+16626865354;fax:+16626865372.E-mailaddress:yanbo.huang@ars.usda.gov(Y.Huang).0168-1699/$–seefrontmatter.PublishedbyElsevierB.V.doi:10.1016/j.compag.2010.01.001
108Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127
4.
5.6.7.
Geneticalgorithmapplications..............................................................................................................3.3.1.Overview...........................................................................................................................3.3.2.Cropmanagement.................................................................................................................3.3.3.Irrigation...........................................................................................................................3.3.4.Soilanalysis........................................................................................................................3.3.5.Precisionagriculture...............................................................................................................3.3.6.Chemicalapplication..............................................................................................................
3.4.Bayesianinferenceapplications.............................................................................................................
3.4.1.Overview...........................................................................................................................3.4.2.Cropmanagement.................................................................................................................3.4.3.IrrigationandETcalculation.......................................................................................................3.4.4.Precisionagriculture...............................................................................................................3.4.5.Chemicalapplication..............................................................................................................
3.5.Decisiontreeapplications...................................................................................................................
3.5.1.Overview...........................................................................................................................3.5.2.Cropmanagement.................................................................................................................3.5.3.Precisionagriculture...............................................................................................................3.5.4.Chemicalapplication..............................................................................................................
Fusionofsoftcomputingmethodsinagriculturalandbiologicalengineering....................................................................4.1.Cropmanagement...........................................................................................................................4.2.ETcalculation................................................................................................................................4.3.Soilanalysis..................................................................................................................................4.4.Precisionagriculture.........................................................................................................................Supportvectormachines............................................................................................................................Comparisonandlimitationsofsoftcomputingtechniques........................................................................................Thefuture...........................................................................................................................................References...........................................................................................................................................
3.3.
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1.Introduction
Softcomputingisasetofcomputingtechniques,suchasFuzzyLogic(FL),ArtificialNeuralNetworks(ANNs),andGeneticAlgorithms(GAs).Thesecomputingtechniques,unlikehardcom-puting,whichreferstoahugesetofconventionaltechniquessuchasstochasticandstatisticalmethods,offersomewhat“inexact”solutionsofverycomplexproblemsthroughmodelingandanal-ysiswithatoleranceofimprecision,uncertainty,partialtruth,andapproximation.Ineffect,softcomputingisanintegrationofbiologicalstructuresandcomputingtechniques.FLdevel-opesmulti-valued,non-numericlinguisticvariablesformodelinghumanreasoninginanimpreciseenvironment.ANNsprovidesconfigurationsmadeupofinterconnectingartificialneuronsthatmimicthepropertiesofbiologicalneurons.GAsareawayofsolv-ingproblemsbymimickingthesameprocessesnatureusesthroughselection,recombinationandmutation.
Softcomputingisusedtoachievetractability,robustness,andprovidealowcostsolutionwithatoleranceofimprecision,uncer-tainty,partialtruth,andapproximation.Thismakessoftcomputingcapableofsolvingproblemsthatmoreconventionalmethodshavenotyetbeenabletoprovideinacost-effective,analytical,orcom-pletemanner.Amongsoftcomputingtechniques,FLappearstobethefirstonethathasestablishedfundamentalideasofsoftcomputing(Zadeh,1965,1973,1981).Theestablishedbasicideashaveinfluencedothertechniquesthatarrivedlater.In1986,theParallelDistributedProcessing(PDP)researchgrouppublishedaseriesofresultsandalgorithms(RumelhartandMcClelland,1986).ThisworkgaveastrongimpetustothestudyofmechanismsandstructureofthebrainandprovidedthecatalystformuchofthesubsequentresearchandapplicationofANNs.ThiscanbeviewedasthepointatwhichANNsbecameoneofthesoftcomputingtechniques.GAsweredevelopedbyJohnHollandin1975andpopularizedbyhisstudent,DavidGoldberg(Goldberg,19).Cur-rently,FL,ANNs,andGAsareconsideredascoretechniquesofsoftcomputing.Thecurrentlistofsoftcomputingtechniquesalsoincludesmachinelearning,probabilisticreasoning,andchaosthe-ory.Inthelastthreedecades,softcomputinghasbeenextensivelystudiedandappliedforscientificresearchandengineeringcom-puting.Althoughapplicationsofsoftcomputingtechniquesweresuccessfulinsolvingproblems,themethodologystillhasbeenadvancingtoprovidenewapproachesformoreefficient,robust,andreliablesolutions.SupportVectorMachines(SVMs)(Burges,1998;CristianiniandTaylor,2000)emergedasasetofsupervisedgeneralizedlinearclassifiersandoftenprovidehigherclassificationaccuraciesthanmultilayerperceptronANNs.SVMshaveattractedgreaterinterestinrecentyears.Methodfusionisanotheradvance-mentinsoftcomputingdevelopment,whichcombinesorcascadesdifferentsoftcomputingtechniquestoimprovesystemperfor-manceoveranyindividualtechnique.Neuro-fuzzysystemsareatypicalexampleofsuchafusion(TakagiandHayashi,1991;Horikawaetal.,1992;NieandLinkens,1992;SimpsonandJahns,1993;MitraandPal,1994;JangandSun,1995).Thebehaviorandstabilityofhardcomputingaremorepredictable.Thecomputa-tionalburdenofalgorithmsistypicallyeitherlowormoderate.Thus,itisnaturaltoviewsoftcomputingandhardcomputingascomplementary.Thefusionofthemhasgreatpotentialfordevel-opinghigh-performance,cost-effective,andreliablecomputingschemesthatprovideinnovativesolutionstoproblems(Ovaskaetal.,2002).
Inagriculturalandbiologicalengineering,therehasbeensomeearlyresearchandapplicationsofsoftcomputing(Whittakeretal.,1991;ZhangandLitchfield,1992;Eerikäinenetal.,1993)andinterestinsoftcomputinghasgrownsteadilyinthelastdecade.Asummaryofpapersandreportswerecollectedfromvar-ioussources,particularlythroughsearchesofthetechnicallibraryoftheASABE(AmericanSocietyofAgriculturalandBiologicalEngineers)(http://asae.frymulti.com/)andtheNationalAgricul-turalLibraryofUSDA(UnitedStatesDepartmentofAgriculture)(http://www.nal.usda.gov/).Itwasfoundthat,fromtheearly-1990sto2008,therehavebeen165reportsandpapers(65peerreviewed)onFL,348(193peerreviewed)onANNs,and83(36peerreviewed)onGAs.Itisinterestingtonotethat20reportsandpapers(13peerreviewed)werewrittenonSVMsfrom2003topresent,7(2peerreviewed)ofwhichwerepublishedin2008.Thismaysignify
Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127109
moreinterestinsoftcomputinginthenextdecadeinagriculturalandbiologicalengineering.Soilandwaterstudiesfocusedoncropmanagementanddecisionsupportsystemsforprecisionagricul-tureincludespecialtiessuchasthosehighlightedinGeoderma,aglobaljournalofsoilscience,SSSAJ(SoilScienceSocietyofAmer-icaJournal),JournalofSoil&WaterConservation,andJournalofPrecisionAgriculture.
Inagriculturalandbiologicalengineering,researchersandengineershavedevelopedmethodsforFL,ANNs,GAs,BayesianInference(BI),DecisionTree(DT),andSVMstostudysoilandwaterregimesrelatedtocropgrowth,analyzetheoperationoffoodpro-cessing,andsupportdecision-makinginprecisionfarming.TheyhavealsousedfusiontechniquesthatincludeFL,ANNandGAinsolvingproblems.However,wehavenotfoundapplicationswherefusionwasappliedtosoftcomputingandhardcomputing.Thiscouldbearesearchtopicwithgreatpotential.
Thispaperbrieflyreviewsthedevelopmentofsoftcomputingtechniques.Withtheconceptsandmethods,applicationsofsoftcomputinginthefieldofagriculturalandbiologicalengineeringarepresented.Thefutureofthedevelopmentandapplicationofsoftcomputinginagriculturalandbiologicalengineeringisdiscussed,especiallyinthesoilandwatercontextforcropmanagementandindecisionsupportinprecisionagriculture.2.Methodsofsoftcomputing
Ingeneral,softcomputingincludesthemethodsofFL,neuro-computing,evolutionarycomputing,probabilisticcomput-ing,beliefnetworks,chaoticsystems,andpartsoflearningtheory(http://www.cs.berkeley.edu/∼zadeh/acprco.html).Forresearchanddevelopmentinagriculturalandbiologicalengineering,pri-marymethodsofsignificantutilityincludeFL,ANNs,GAs,BIandDT.
ANNsaremodelarchitecturesandlearningalgorithmsofneuro-computing.GAsareaparticularclassofevolutionarycomputation.BIisamethodtorealizeprobabilisticcomputing.DTisoneoftheinterestingandcommonlyusedarchitecturesusedforlearning,reasoningandorganizationofdatasetsinsoftcomputing.FL,ANNs,GAs,BIandDThavebeenwidelyappliedforresearchanddevelop-mentinagriculturalandbiologicalengineering,especiallywithinthelastdecade.2.1.Fuzzylogic
FLisaformofmulti-valuedlogicderivedfromfuzzysetthe-orytodealwithreasoningthatisapproximate,ratherthanprecise.Incontrasttoyes/noor0/1binarylogic(crisp),FLprovidesasetofmembershipvaluesinclusivelybetween0and1toindicatethedegreeoftruth(fuzzy).Fig.1showsthedifferencebetweenacrispsetandafuzzysetbycomparingthecharacteristicfunctionsofthetwosets.Forthecrispset(Fig.1(a))thecharacteristicfunctionofAisassignedavalueof1or0toeachvalueinX,avaluesetofaphysicalproperty.1forAindicatesthatcorrespondingvaluesinXbelongtothesetA.0forAindicatesthatcorrespondingvaluesinXdonotbelongtothesetA.Theconceptofthecrispsetissuffi-cientformanyapplicationsbutisnotforsomeapplicationsthatrequireflexibility.InthefuzzysetthecharacteristicfunctionofAisassignedavaluebetween0and1,including0and1,toeachvalueinX.1or0forAstillindicatethatcorrespondingvaluesinXbelongordonotbelongtothesetA.Thevaluesbetween0and1forAindicatethatthecorrespondingvaluesinXbelongtothesetAinacertaindegreefromlow,medium,tohighwiththeincreaseoftheAvalue.Fig.1(b)showsatypicalcharacteristicfunctionofthefuzzyset.Withthecharacteristicfunctionthemembershipfunctionforafuzzysetcanbeconstructedtoquantifythemagnitudeofbelong-
Fig.1.Characteristicfunctionsofcrispandfuzzysets(b>d>a>c>0).Characteristicfunctionofacrispset(a)andfuzzyset(b).
ingofeachinput.Themembershipfunctionsmaybedifferentinshapeandinterval.ThelogicoperationssuchasANDandORcanimplementedwiththedifferentmembershipfunctionstogeneratearesultantmembershipfunction.
Inprocessmodelingandcontrol,systemsthatareill-definedandwithuncertaintiescanbemodeledwithafuzzyinferencesys-tememployingfuzzy‘If–Then’rulestoquantifyhumanknowledgeandreasoningprocesseswithoutemployingprecisequantitativeanalyses.Thefuzzyinferencesystemshouldincludethefollowingfunctionalblocks(Jang,1993):
•afuzzificationinterfacethattransformsthecrispinputsintodegreesofmatchwithlinguisticvalues;•aknowledgebasethatincludes
◦arulebasecontaininganumberoffuzzy‘If–Then’rules;
◦adatabasethatdefinesthemembershipfunctionsofthefuzzysetsusedinthefuzzyrules;
•adecision-makingunitthatperformstheinferenceoperationsontherules;and
•adefuzzificationinterfacethattransformsthefuzzyresultsoftheinferenceintoacrispoutput.
Althoughsomeprecedingworkhasbeenindicated(Wilkinson,1963),Dr.LotfiZadehhasbeengenerallyconsideredasthefirstper-sonwhointroducedFLtotheworld.In1965,Dr.Zadehaxiomatizedfuzzysettheory(Zadeh,1965).FLisaninterfacebetweenlogicandhumanreasoning.Humanshavearemarkablecapabilitytoreasonandmakedecisionsinanenvironmentofuncertainty,imprecision,incompletenessofinformation,andpartialityofknowledge,truthandclassmembership.FLisforformalization/mechanizationofthiscapability.FLmimicshumancontrollogic.Itcanbebuiltintoanythingfromsmall,hand-heldproductstolargecomputerizedprocesscontrolsystems.Itusesanimprecisebutverydescriptivelanguagetodealwithinputdataasahumanoperatorwould.Itisveryrobustandtolerantofoperatoranddatainputandoftenworkswhenfirstimplementedwithlittleornotuning.
FLhasbeenappliedtodiversefieldssincethe1970swiththesufficientdevelopmentofsmallcomputingcapability.Ithasbeenappliedinsuchvariedfieldsascontrolsystemsandartificialintel-ligence.In1974,thefirstsuccessfulapplicationoffuzzylogictothecontrolofalaboratory-scaleprocesswasreported(MamdaniandAssilian,1975).Controlofcementkilnswasanearlyindus-trialapplication(HolmbladandOstergaard,1982).Sincethefirst
110Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127
consumerproductusingfuzzylogicwasmarketedin1987,theuseoffuzzycontrolhasincreasedsubstantially.AnumberofCAD(Computer-AidDesign)environmentsforfuzzycontroldesignhaveemergedtogetherwithVLSI(Very-Large-ScaleIntegration)hard-wareforfastexecution.Fuzzycontrolisbeingappliedtovarioussystemsintheprocessindustry(SanthanamandLangari,1994;Tanietal.,1994),consumerelectronics(Hirota,1993;Bonissone,1994),automatictrainoperation(YasunobuandMiyamoto,1985),trafficsystemsingeneral(Hellendoorn,1993),andinotherfields(Hirota,1993;Teranoetal.,1994).
AlthoughFLwasproposedbyProfessorZadehofUniversityofCaliforniaatBerkeley,FLhasbeengainingpopularityonlygradu-allyintheUnitedStates.Thismaybeduetodisappointmentwiththeunfulfilledpromisesof‘artificialintelligence’computingtech-niquesinthe1980s(KhoshnevisandChignell,1985).However,atthesametime,FLproductshavebeenaggressivelybuiltinEuropeandJapan(EET,1991;Smith,1993).Still,theUnitedStatesEPA(EnvironmentalProtectionAgency)hasinvestigatedfuzzycontrolforenergy-efficientmotors(Clelandetal.,1992).NASA(NationalAeronauticsandSpaceAdministration)hasstudiedfuzzycontrolforautomatedspacedocking(OrtegaandGiron-Sierra,1995).Boe-ing,GeneralMotors,Allen-Bradley,Chrysler,Eaton,Whirlpool,andMaytaghavealsoworkedonfuzzylogicforuseinlow-powerrefrigerators,automateddishwashers,improvedautomotivetrans-missions,andenergy-efficientelectricmotors.
Developmentoffuzzysystemshashelpedadvancetechniquesforhandlingimprecisioninsoftcomputing.In1992,theconceptofsoftcomputingwasintroduced(Zadeh,1992).Dr.Zadehenvisionedsoftcomputingasbeingconcernedwithmodesofcomputinginwhichprecisionistradedfortractability,robustnessandeaseofimplementation.Softcomputingservestohighlighttheemergenceofcomputingmethodologiesinwhichtheemphasisisonexploitingthetoleranceforimprecisionanduncertaintytoachievetractabil-ity,robustness,andlowsolutioncost.2.2.Artificialneuralnetworks
ANNsprovideawaytoemulatebiologicalneuronstosolvecomplexproblemsinthesamemannerasthehumanbrain.Formanyyears,especiallysincethemiddleofthelastcentury,inter-estinstudyingthemechanismandstructureofthebrainhasbeenincreasing.Thisincreasingresearchinteresthasledtothedevel-opmentofnewcomputationalmodels,connectionistsystemsorANNs,basedonthebiologicalbackgroundforsolvingcomplexproblemslikepatternrecognitionandfastinformationprocess-ingandadaptation.Intheearly1940s,McCullochandPitts(1943),pioneersinthefield,studiedthepotentialandcapabilitiesofinter-connectingseveralbasiccomponentsbasedonthemodelofaneuron.Lateron,otherslikeHebb(1949),wereconcernedwiththeadaptationlawsinvolvedinneuralsystems.Rosenblatt(1958)coinedthename“Perceptron”anddevisedanarchitecture,whichhassubsequentlyreceivedmuchattention.MinskyandPapert(1969)laterintroducedarigorousanalysisofthePerceptron,ofwhichtheyprovedmanypropertiesandpointedoutlimitationsofseveralrelatedmodels.Inthe1970s,theworkofGrossberg(1976)cametoprominence.Hiswork,basedonbiologicalandpsycho-logicalevidence,proposedseveralnovelarchitecturesofnonlineardynamicsystems.Inthe1980s,Hopfield(1982)appliedaparticu-larnonlineardynamicstructuretosolveproblemsinoptimization.AllofthemconductedpioneerstudiesonthetheoreticalaspectofANNs.
In1986,thePDP(ParallelDistributedProcessing)researchgrouppublishedaseriesofalgorithmsandresults(RumelhartandMcClelland,1986).Thispublicationcontainsanarticleenti-tled“LearningInternalRepresentationsbyErrorPropagation”(Rumelhartetal.,1986a).Thisarticlebroughtrecognitiontoan
Fig.2.ANNnetworkstructure.
ANNtrainingalgorithmnamedBackPropagation(BP),althoughithadalreadybeendescribedinWerbos(1974).ThisBPtrainingalgo-rithmimplementedwiththegeneraldeltarule(Rumelhartetal.,1986a,1986b)gaveastrongimpulsetosubsequentresearchandresultedinthelargestbodyofresearchandapplicationsinANNsalthoughmanyotherANNarchitecturesandtrainingalgorithmshavebeendevelopedandappliedsimultaneously.
Thearchitecture,training/learning,andimplementationofanANNareasimplifiedversionofthestructureandactivitiesofhumanbrain.Forproblemsolving,thehumanbrainusesawebofinterconnectedprocessingunits,neurons,toprocessinforma-tion.Eachoftheneuronsisautonomous,independent,andworksasynchronously.Thevastprocessingpowerinherentinbiologi-calneuralstructureshasinspiredthestudyofthestructureitselfasamodelfororganizinganddesigningman-madecomputingstructures.Comparedwithconventionaldataprocessingmeth-ods,ANNsprovideamodel-free,adaptive,parallel-processing,androbustsolutionwithfaultandfailuretolerance,learning,abilitytohandleimpreciseandfuzzyinformation,andcapabilitytogen-eralize.AnANNisabletomapprocessinputandoutputwithoutunderlyingassumptionaboutthedistributionofdata.ANNsarepowerfulindataprocessingandanalysis.Inmathematics,ANNsarethemodelsdefiningafunction:f(x)|X→Y.EachANNmodeldefinesaclassofsuchfunctions.InANNs,thefunctionf(x)isdefinedbyacombinationoffunctionsgi(x),whichcouldbefurtherdefinedbyacombinationofotherfunctionsri(x),andsoon.ThisrecursivefunctiondefinitioninanANNbringsupanetworkstructurefortheinterconnectionoffunctionunits.Thewidelyusedbinationisthenonlinearweightedsum:f(x)=Acfunctionncom-whereAisapredefinedactivationfunction,suchasi=wg(x),the1ii
c()hyper-bolictangentfunction(Werbos,1974;Rumelhartetal.,1986a,1986b).Fig.2showsatwohidden-layerfeedforwardnetworkbetweeninputxandoutputf.
Thefeedforwardnetworkwithasinglehiddenlayerthatcon-tainsafinitenumberofhiddenneuronsaccompaniedwithanarbitraryactivationfunctionwasproventobeauniversalapproxi-matoronacompactsubsetofrealn-dimensionalEuclideanspaceRn(Horniketal.,19;Cybenko,19).ThistheoryassuresthatANNscanhandleengineeringproblems,whicharehighlycomplexandnonlinear.ANNsprovideapowerfulmethodforpracticallyaccuratesolutionsofpreciselyorimpreciselyformulatedproblemsandforphenomenathatareonlyunderstoodthroughexperimentaldataandfieldobservations.ANNshavebecomethemostpopularsoftcomputingmethodsforsolvingproblemsinengineering.2.3.Geneticalgorithms
EvolutionarycomputingisanArtificialIntelligence(AI)techniquetosolvecombinatorialoptimizationproblems.Itis
Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127111
Fig.3.FlowchartofGAoperation.
implementediniterativeprogresswiththegrowthinapopula-tionselectedinaguidedrandomsearchusingparallelprocessingtoreachthedesiredpoint.Thisoperationwasinspiredbybiologi-calmechanismsofevolution,whichissimilartoDarwin’stheoryonevolution(Darwin,1859).Thereareanumberofpeoplewholaidthetheoreticalfoundationsofevolutionalcomputing:LawrenceJ.FogelandJohnHenryHollandintheUnitedStates(Fogeletal.,1966;Holland,1975),andIngoRechenbergandHans-PaulSchwefelinGermany(Rechenberg,1973;Schwefel,1981).Fogelisregardedasthefatherofevolutionarycomputing.Hollandstudiedthismethodalittledifferentlyandnameditageneticalgorithm.Then,oneofHolland’sstudents,DavidGoldberg,solvedadiffi-cultprobleminvolvingthecontrolofgas-pipelinetransmissionusingthemethodofGAinhisdissertation(Goldberg,19).Gold-berg’sworkgreatlyinspiredsubsequentresearchandapplicationsofGA.
GAisanoptimizationandheuristicsearchtechniquethatusestechniquesinspiredbyevolutionarybiologysuchasinheritance,mutation,selection,andcrossover(alsocalledrecombination).GAworkssimultaneouslyonaset(population)ofpotentialsolutions(individuals)totheproblem.Thealgorithmstartswithasetofsolutions(representingchromosomes)calledasub-population.Thefitnesstowhichsolutionsmeetsomeperformancecriterionisevaluatedandusedtoselect“surviving”individualsthatwill“reproduce”anew,bettersub-population.Then,theindividualswillconductalterationssimilartothenaturalgeneticmutationandcrossover.Theselectionschememakestheprocesstowardshighperformancesolutions.Acarefulselectionofgeneticalgorithmstructureandparameterscanensureagoodchanceofreachingthegloballyoptimalsolutionafterareasonablenumberofiter-ations.Fig.3showsaflowchartofoperationalprocessesofGAs.GAsarecomputationallysimpleyetpowerfulenoughtoprovidearobustsearchfordifficultcombinationalsearchproblemsincom-plexspaces,withoutbeingstuckinlocalextremes(Goldberg,19).Therefore,GAsarepowerfulalternativetoolstotraditionalopti-mizationmethods.GAshavebeensuccessfullyusedinmanyfields,suchasscheduling(Wall,1996;LimandSim,2005),functionopti-mization(Houcketal.,1998),machinelearning(GoldbergandHolland,1988;Grefenstette,1994;Shapiro,1998)andhavebecomeanimportantmethodofsoftcomputing.
2.4.Bayesianinference
Probabilisticcomputingisasoftcomputingtechniquetoper-formprobabilisticreasoning.Theaimofprobabilisticreasoningistocombinethecapacityofprobabilitytheorytohandleuncertaintytomakeinferencewithbelief.Pearl(1988)madeanimportantsur-veyonthistopicwithanemphasisonBayesiannetworks.Grunwald(1997)madeausefulreviewalso.
Bayesianapproacheshavebeenstudiedandappliedexten-sively(Eddy,1982;Edwards,1982;GigerenzerandHoffrage,1995;Jaynes,1996;Lauritzen,2003)byusingBayes’stheorem(Bayes,1763)intheprocessofprobabilisticcomputation.Classicalinfer-encemodelsdonotpermittheintroductionofpriorknowledgeintothecalculations.However,theuseofpriorknowledgewouldsome-timesbeusefultotheprocessevaluation.BI(BayesianInference)isastatisticalinferenceincorporatingpriorknowledgeandpriorprobabilitydistributions.IntheprocessofBIevidenceorobser-vationsareusedtoupdatetheprobabilitythatahypothesismaybetrue.Conventionally,binaryhypothesistestingisusedtosta-tisticallydecidewhichhypothesisistruebetweentwohypotheses.Alternatively,aBayesiandecisionrule,suchasminimumBayesrisk,minimumprobabilityoferror,ormaximumaposterioriprobability(MAP),dependsonthepriorprobabilityofeachhypothesis(Dudaetal.,2001).
BayesianinferenceisbasedontheBayes’theorem(Bayes,1763)thatadjustsprobabilitiesgivennewevidence:P(H|E)=P(E|H)P(H)/P(E)whereisthespecifichypothesis,P(H)isthepriorprobabilityofH,P(E|H)istheconditionalprobabilityofEwhenHhappenstobetrue,andP(E)isthemarginalprobabilityofE(newevidence).TheratioP(E|H)/P(E)representstheimpacttheevidencehasonthebeliefinthehypothesis.Whenthisratioislarge,alargerposteriorprobabilityofthehypothesisgiventheevidencewillbeproducedbymultiplyingthepriorprobabilityofthehypothesisbythisfactor.Whenthisratioissmall,asmallerposteriorprobabil-ityforHwillbeproduced.InBayesianinference,Bayes’theoremisusedtomeasurehowmuchnewevidenceshouldalterbeliefinahypothesis.
BayesianNetworkshavebeenacceptedastoolsfordecision-makingincomplexsituationswithinavarietyofdisciplines(Pearl,1999;Charniak,1991).BayesianNetworksareprobabilisticgraph-icalmodels.Eachofthemodelscharacterizesasetofvariablesandtheirprobabilisticindependencies.Thegraphical,probabilisticmodelsallowthestructuredrepresentationofacognitivepro-cessbasedonalinkandnodestructurewherethestateofparentnodepredictsthestateofthechildnode.ConditionalprobabilitytablesarethenusedtorelatetheparentandchildnodesusingBayesianstatisticalmethodstopredicttheirrelationship.DynamicBayesiannetworks(Ghahramani,1997)aretheBayesiannetworksthatrepresentsequencesofvariables.Thesesequencesareoftenvaluesoftimeseriesorsequencesofsymbols(forexampleproteinsequences).2.5.Decisiontree
DT(DecisionTree)isapopularmethodofmachinelearning.Itwasdevelopedinthe1960s(Magee,19)andcomprisesatree-structuredarrangementofasetofattributestoevaluateandpredicttheoutput.IntheoperationofaDT,thealgorithmisrecursivelylookingfortheattributewiththehighestinformationgain,whichisdeterminedtoevaluatefirst.DTscanbeusedtoidentifythestrategymostlikelytoreachagoal.Theycanalsobeusedasadescriptivemeansforcalculatingconditionalprobabilities.Inoper-ationsresearch,aDTisadecision(classification)model(HillierandLieberman,2005).ADTcanbeusedtovisuallyandexplicitlyrep-resentdecisionsfordecisionsupport.Indataminingandmachinelearning,aDTisapredictivemodel(Teorey,1999;Flamig,2000;
112Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127
WittenandFrank,2000).TheDTdescribesdatabutnotdecisionsfortheresultingclassificationtreeasaninputfordecision-making.Withagraphicalrepresentation,aDTmodelmapsfromobserva-tionsaboutanitemtotheconclusionsaboutitstargetvalue.Inthestructureofthetree,leavesrepresentclassificationsandbranchesrepresentconjunctionsoffeaturesthatleadtothoseclassifications.Themachinelearningtechniqueforinducingadecisiontreefromdataiscalleddecisiontreelearning,or(colloquially)decisiontrees.UsingDTslargeamountsofdatacanbeanalyzedinarelativelyshorttimeforreal-timeapplications(Abrahametal.,2007).3.Applicationsofsoftcomputinginagriculturalandbiologicalengineering
Withthetheoreticaldevelopmentsofsoftcomputing,alargevarietyofsuccessfulapplicationstomanyindustrialsystemshavebeencreated.Duringthelastdecade,interestofapplyingsoftcomputingtechniquestosystemsinagriculturalandbiologicalengineeringhasbeengrowinggreatly.Asinotherfields,softcom-putingplaysanespeciallyimportantroleinprovidingtechniquestointegratehuman-likevaguenessandreal-lifeuncertaintyintoconventionalcomputingprograms.Problemsinsoilandwater,cropmanagementandpostharvesting,precisionagriculture,foodprocessing,foodqualityandsafety,andagriculturalvehicleandroboticshavebeensolvedthroughsoftcomputing-basedclassi-fication,modelingandprediction,andoptimizationandcontrol.Thispaperreviewssignificantpapersforeachoftheseagriculture-relatedareas,organizedbythesoftcomputingtechniqueutilized.3.1.Fuzzylogicapplications
3.1.1.Overview
Insummaryof136relatedpapersandreports,FLhasbeenappliedinsolvingproblemsincropmanagement(17%),soilandwater(16%),foodqualityandsafety(14%),animalhealthandbehavior(10%),agriculturalvehiclecontrol(8%),precisionagricul-ture(7%),greenhousecontrol(7%),agriculturalmachinery(4%),foodprocessing(4%),airqualityandpollution(3%),agriculturalfacilities(2%),agriculturalrobotics(1%),chemicalapplication(1%),andothers(6%)suchasnaturalresourcesmanagementandagricul-turalproductdesign.TheseapplicationshavebeencreatedthroughFLmainlybycontrol(28%),modelingandprediction(24%),clas-sification(24%),fuzzyclustering(9%),rule-basedinference(7%),multisensordatafusion(4%),optimization(1%)andothers(3%)suchasthresholdingandpatterninference.
3.1.2.Cropmanagement
Forcroppestmanagement,Pydipatietal.(2005)usedthecolorco-occurrencemethodfortexturalanalysistodeterminewhetherclassificationalgorithmscouldbeusedtoidentifydiseasedandnormalcitrusleaves.Oneoftheclassificationstrategiesinvesti-gatedwasANNclassifiersbasedontheRBF(RadialBasisFunction)networkswithfuzzyoutputsthatindicateameasureofstrength.Theleveloffuzzinesswasdeterminedbysettinganyvalue<0.5asequivalentto0,andanyvalue>0.5asequivalentto1.ThisisatypicalwayofdealingwiththeoutputofclassifierusingFL,whichhelpsdecidetheoutputclasslabelingwiththeoutputofdecimalnumbers.
Yangetal.(2000a,2003)reportedondevelopmentofanimagecapture/processingsystemtodetectweedsandafuzzylogicdecision-makingsystemtodeterminewhereandhowmuchher-bicidetoapplyinanagriculturalfield.Asinformationconcerningeconomicthresholdsofweedimpactoncropproductivitycannoteasilybeadaptedtoagivenregionoreventoagivenfarm,afuzzylogicapproachwasappliedtoconvertimagedataintosprayercom-mandstoallowfarmerstouseexperiencetoclassifyweedstatus
atagivenlocationinthefield.Thisresearchindicatedthatafuzzylogicsystemisabletounderstandandfacilitatestherepresentationandprocessingofhumanknowledgeincomputerandtheinputs,outputs,andrulesofFLareeasytomodify.
3.1.3.IrrigationandETcalculation
Forirrigationscheduling,Odhiamboetal.(2001a)examinedFLforestimatingdailyreferenceevapotranspiration(ET)withfewerparameterscomparedwiththestandardFAO(FoodandAgricultureOrganization)Penman–Monteithmethod,whichissophisticatedandrequiresseveralinputparameterssomeofwhichhavenoactualmeasurementsbutareestimatedfrommeasuredweatherparameters.Inthisstudy,twofuzzyETmodelsweredevelopedtoestimatereferencegrassET,usingtwoandthreeweatherparam-eters,respectively.TheresultsillustratedthatthefuzzyETmodelscouldyieldaccurateestimationofET.
Al-Farajetal.(2001)developedarule-basedFLcropwaterstressindex(CWSI)usinggrowthchamberdataandtestedthismethodontallfescuecanopiesgrowninagreenhouse.TheupperandlowertheoreticalCWSIbaselinesmayshiftaccordingtonetradiation,wind,andstomatalresistance.ThisstudyproposedfuzzylogictodevelopaFL-CWSIsystemtoovercometheuncertaintyofbaseline.TheFL-CWSIsystemhasjustthreeinputs:canopy-airtemperaturedifferential,vaporpressuredeficit,andshortwaveradiation,andoneoutput:CWSI.Tocalculatethecropwaterstressindexunderdifferentlevelsofsolarradiationandvaporpressuredeficit,150fuzzyruleswereestablishedtorelatethesysteminputsandtheoutput.TheuseofFL-CWSIeliminatedtheneedtocalculateorcal-ibrateempiricalortheoreticalbaselinelimits.TheFL-CWSIwassuccessfullytestedusingindependentgreenhousedata.
ThomsonandRossdevelopedacoupledsensor-andmodel-basedirrigationschedulingmethod(Thomsonetal.,1993;ThomsonandRoss,1996).BasedonthisworkThomson(1998)describedaconceptbywhichreadingsfromsensorscouldbeusedtoreparameterizeoradjustinputstoacropsimulationmodel.Readingsfromsensorsandthemodeledresultswereusedsyner-gisticallyinanadaptivelearningscheme.
3.1.4.Soilanalysis
SoilmappingusingFLhasbeenreportedbyZhuetal.(2001),Bragato(2004),Shietal.(2004),Qietal.(2006),andZhuetal.(inpress).Lark(2000)illustratedhowtodesignsamplinggridsfromimpreciseinformationonsoilvariabilitywithanapproachbasedonthefuzzykrigingvariance.Thisapproachcanderiveafuzzysetofgridspacingsthatwillachieveatargetkrigingvariancewhengivenafuzzyformulationofthesoilpropertyvariogram.Thisfuzzysetofgridspacingscanthenbedefuzzifiedinamoreorlessconservativewaytodefineasamplingscheme.Insupportofprecisionagri-culture,VanAlphenandStoorvogel(2000)developedafunctionalapproachtosoilcharacterizationinvolvedinwaterstress,nitrate-stress,nitrate-leachingandresidualnitrogen-contentatharvestforaprecisionagriculturedecisionsupportsystem.Inthestudy,afuzzyc-meansclassifierwasusedtogroupthesoilprofilesintofunctionalclasses.Fergusonetal.(2003)evaluatedapproachesforsite-specificuseofthenitrificationinhibitorbasedonslopeandsur-facetextureformanagementzonedefinition.Inthisstudy,fuzzyclusteranalysiswasdemonstratedthepotentialtodefinemanage-mentzonesforuseofnitrificationinhibitorsfromeasilyobtainedspatialyieldorsoilECa,ratherthanexpensivegridsamplingofsoilchemicalandphysicalproperties.
3.1.5.Precisionagriculture
Ortizetal.(2008)usedfuzzyclusteringofelevationandslopeoftheterraintodelineaterootknotnematode(RKN)riskzonesforacomparisontestoftwonematicideapplicationratesonnema-todepopulationdensityandcottonlintyield.Theresultsfromthis
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studyclearlyshowedthatRKNcontrolandfinalyieldvariedwithrespecttothenematicidetypeandrateacrossriskmanagementzonesbasedonfuzzyclusteringofterrainelevationandslope,nor-malizeddifferencevegetationindex(NDVI)ofbaresoilreflectance,andapparentsoilelectricalconductivity.
XiangandTian(2007)usedfuzzyinferenceinanANNframeworktodevelopanartificiallyintelligentcontrollerthatauto-maticallyadjustsmultispectralcameraparameters,suchas“gain”and“exposuretime”tocompensateforchangingnaturallight-ingconditionsandtoacquirewhite-balancedimages.Theartificialintelligencecontrolalgorithmdidrequirenomathematicalmodelofthesystem,andprovidedbettercontrolperformancecomparedtoconventionalcontrolmethods.
JonesandBarnes(2000)describedprecisioncropmanagementasamulti-objectivedecision-makingprocessthatmustincorpo-rateadiversityofdata,opinion,preferenceandobjective.Thispaperdevelopedfuzzycompositeprogramming,adistance-basedmulti-objectiveoptimizationproblemthatusesfuzzyrepresenta-tionofuncertaintytocombineremotesensingandcropmodelsfordecisionsupportinprecisioncropmanagement.Thisapproachallowsuserstoexpressindividualorcorporatevaluesandprefer-ences;highlightsthedegreeofimprecisionassociatedwitheachinformationsourceused(i.e.modelaccuracy,uncertaintyincostsandreturns,etc.);highlightsthedegreeofimprecisionassociatedwitheachalternative;facilitatesstructuringofthedecisionpro-cess;reducesseverallevelsofcomplexinformationintoasinglechart;allowsexaminationoftrade-offbetweenalternativesandinterests;andforcesexaminationofinter-relationshipsbetweeninterests.
Ambueletal.(1994)successfullydevelopedandusedafuzzylogicyieldsimulator.TwoexpertsystemmodelsweredevelopedusingFLrules.Inonemodelchemicalandphysicalcharacteristicsofthesoilweremeasuredandcombinedwithlocalmeteorologicaldataasinputparameters.Intheothermodelsoilpropertieswereestimatedratherthanmeasured.Modelpredictedyieldswerethencomparedwithmeasuredyieldsforthosefields.Theresultsindi-catethatonarelativebasis,predictedyieldsgenerallyagreedwithmeasuredyields.
3.1.6.Chemicalapplication
Giletal.(2008)usedlinearmultipleregressionandFLinferencemodelstoevaluatetheeffectsofmicrometeorologicalconditionsonpesticideapplicationfortwosprayqualities(fineandveryfine).Spraylosseswerepredictedusingfuzzyinferencesystems.Interpretableruleswereestablishedforthecharacterizationofmicrometeorologicalparametersusingthetwosprays.Q.Chenetal.(2006)andY.Chenetal.(2006)developedanintelligentpes-ticidespraysystembasedonfuzzycontrolandmachinevisiontoperformsite-specificpesticideapplication.ChoandKi(1999)developedaFLcontrollerforautonomousoperationofaspeedsprayerinanorchard.Theoperationofthecontrollerwasgraph-icallysimulatedundertherealconditionoftheorchard.Machinevisionwasalsousedtodeterminevehicleheadingandfourultra-sonicsensorswereusedtodetectobstaclesduringtheoperation.3.2.Artificialneuralnetworkapplications
3.2.1.Overview
ANNshavethelargestbodyofapplicationsinagriculturalandbiologicalengineeringwhencomparedwithothersoftcomput-ingtechniques.Insummaryofrelated348papersandreports,ANNshavebeenappliedinsolvingproblemsinfoodqualityandsafety(35.34%),crop(22.7%),soilandwater(14.37%),preci-sionagriculture(6.61%),animalmanagement(5.17%),postharvest(2.59%),foodprocessing(2.3%),greenhousecontrol(2.01%),agri-culturalvehiclecontrol(1.15%),agriculturalmachinery(1.15%),
agriculturalpollution(1.15%),agriculturalbiology(1.15%),ecol-ogyandnaturalresources(1.44%),agriculturalrobotics(0.29%),chemicalapplication(0.29%),andothers(2.3%)suchasbioen-ergyandagriculturalfacilities.TheseANNapplicationshavebeencreatedmainlythroughclassification(45.11%),modelingandpre-diction(43.97%),control(4.02%),andsimulation(2.59%),parameterestimation(2.01%),detection(1.15%),dataclustering(0.57%),opti-mization(0.29%)anddatafusion(0.29%)aswell.
Similartoapplicationsingeneralengineeringfields,mostworksinagriculturalandbiologicalengineeringhavebeenaccomplishedusingamultilayerfeedforwardANNtrainedbythefamousBPalgorithm,whichwasinspiredbytheworkofRumelhartetal.(1986a,1986b).Among348collectedpapersandreports210werebasedonmultilayerfeedforwardneuralnetworkstrainedbytheBPalgorithmand83didnotexplicitlystateANNs’structureandtrainingalgorithm.OftheremaindertwelvewerebasedonPNN(ProbabilisticNeuralNetwork);elevenwerebasedonMLP(MultiLayerPerceptron)usingdifferenttrainingalgo-rithmssuchasLevenberg–Marquardtoptimizationprocedure,Broyden–Fletcher–Goldfarb–Shanno(BFGS)optimizationproce-dure,andGA;sevenwerebasedonKohonenSOM(SelfOrganizingMap),whichisapopularunsupervisedtrainingalgorithm;sixwerebaseduponotherunsupervisedtrainingalgorithmssuchasfuzzyART(Carpenteretal.,1991),ART2(CarpenterandGrossberg,1987),andAuto-Associativenetwork(Andersonetal.,1977);fourwerebasedonRBF,whichisaneuralnetworkgoodforfunctionapprox-imation;threewerebasedonLVQ(LearningVectorQuantization);twowerebasedonGRNN(GeneralizedRegressionNeuralNet-work).FinallytenwerebasedonothernetworkstructuressuchasCounter-Propagation(CP),andAdaptiveLogicNetwork(ALN).
3.2.2.Cropmanagement
Inacropfieldstudy,Meyeretal.(2004)conductedadigitalcameraoperationstudyforclassifyinguniformimagesofgrass,baresoil,cornstalksresidue,andwheatstrawresidueusingabariumsulfatereferencepanelbasedoncolor.Theclassificationswereconductedwithacombinationofleast-squaresestimationandBPtrainingtogenerateafuzzyinferencesystem.FuzzyinputvariablesincludedRGBorHSIaveragevaluesalone,withandwith-outmonochromaticlightsources,andwithandwithoutluminanceandbackgroundlightsourcecolortemperaturemeasurementsforeachfuzzyinferencemodel.TheANNsystemprovidedatoolforevaluatingdigitalcameraoperatingperformancebysettingupasimpleclass,supervisedlearningsystemforplant,soilresiduecolorimages.
Inordertodevelopamulti-spectralopticalsystemforremotesensingofnitrogencontentofcrops,Chenetal.(2007)determinedsignificantwavelengthsinimagedataforestimatingnitrogencon-tentofcabbageseedlingleavesbystepwisemulti-linearregressionanalysis.AfeedforwardANNmodelwithcross-learningschemewasfurtherdevelopedtoincreasepredictionaccuracy.TheresultsindicatedthattheANNmodelwithcross-learningusingspectralinformationat490,570,600,and680nmcouldbeusedtodevelopapracticalremotesensingsystemtopredictnitrogencontentofcabbageseedlings.
SuiandThomasson(2006)developedaBPtrainedfeedforwardANNtopredictnitrogenstatusincottonplantsbasedondatafromaground-basedsensingsystem.Thesystemconsistsofamulti-spectralopticalsensorforplantcanopysensing,anultra-sonicsensorforplantheightmeasurement,andadata-acquisitionandprocessingunit.Fieldtestsofthesystemover2yearsinvolvedmeasuringspectralreflectanceandplantheightsimultaneouslyinrealtimeinsitu.Resultsshowedthattheneuralnetworkswereabletopredictnitrogenstatusofthecottonplantsat90%accuracywithtwocategories:deficiencyandnon-deficiency.
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Karimietal.(2005)evaluateddiscriminantanalysisasatoolforclassifyingimageswithrespecttothenitrogenandweedmanage-mentpracticesappliedtotheexperimentalplots,andcomparedtheclassificationaccuracyofthistechniquewiththoseobtainedbyANNandDTalgorithmsonthesamedata.Foridentifyingweedandnitrogenstressesincorn,thediscriminantanalysiswasfoundtoprovidethebestclassificationaccuracyattheearlygrowthstage,whereasbetteraccuracywasobtainedwithANNmodelsatthetasselingandfullmaturitystages.
Tumboetal.(2002b)usedanon-the-gosystemforsensingchlorophyllstatusincornusingBPtrainedfeedforwardANNsandfiber-opticspectrometrytoacquirespectralresponsepatterndataincornfields.Theneuralnetworkmodelincorporatedintothemobilesystemwastrainedusingstaticallycollectedplant-centerspectraldataandchlorophyllreadingsacquiredbySPAD502chlorophyllmeteronthesomedayandinthesamefieldplots.Theneuralnetworkmodelshowedgoodcorrelationbetweenpredictedandactualchlorophyllreadingsofthecalibrationdataset.
Goeletal.(2001)comparedtheDTmethodandANNmethodtoclassifynitrogenstresswithinacornfieldbasedonhyperspectralimages.Goeletal.(2003)alsoevaluatedtheDTandANNclassi-ficationalgorithmsfortheclassificationofhyperspectraldatatodiscriminatebetweendifferentgrowthscenariosinacornfieldtoidentifyweedstressandnitrogenstatusofcorn.Inbothstudies,theANNsobtainedslightlybetterresultsthantheDTs.
Tangetal.(2003)developedatexture-basedweedclassifica-tionmethodconsistingofalow-levelGaborwavelets-basedfeatureextractionalgorithmandahigh-levelANN-basedpatternrecogni-tionalgorithm.Inthisresearch,threespeciesofbroadleafweeds(commoncocklebur,velvetleaf,andivyleafmorningglory)andtwograces,giantfoxtailandcrabgrass,whicharecommoninIllinois,werestudied.Afterprocessing40sampleimageswith20samplesfromeachclass,theresultsshowedthatthemethodwascapableofclassifyingallthesamplescorrectlywithhighcomputationaleffi-ciency,demonstratingitspotentialforpracticalimplementationunderreal-timeconstraints.
Choetal.(2002)usedanANNusingaregularizationmethodtoovercomeoverfittingwithbettergeneralizationfordistinguishingradishfromweedseffectively.Inthisstudy,amachinevisionsys-temusingachargecoupleddevicecamerafortheweeddetectioninaradishfarmwasdeveloped.Shapefeatureswereanalyzedwiththebinaryimagesobtainedfromcolorimagesofradishandweeds.Usingthediscriminantanalysis,thesuccessfulrecognitionratewas92%forradishand98%forweeds.Torecognizeradishandweedsmoreeffectively,anANNwasused.TheANNmodeldistinguishedtheradishfromtheweedswith100%.
Yangetal.(2002)developedaweedrecognitionimagingsys-tembasedonLVQnetworkstoassistintheprecisionapplicationofherbicidesincornfields.Digitalimageswerecollectedandtheintensitiesofthecolorswerecomparedforeachpixeloftheimages.ThepixelintensitiesoftheimageswereusedastheinputsforLVQANNs.TheANNsweretrainedtodistinguishcornfromweeds,aswellastodifferentiatebetweenweedspecies.ThesuccessrateforasingleANNindistinguishingagivenweedspeciesfromcornwasashighas90%,andashighas80%indistinguishinganyoffourweedspeciesfromcorn.
Moshouetal.(2002)usedtheSOMANNinasupervisedwayforaclassificationtaskforaweedspeciesspectraldetector.TheneuronsoftheSOMbecomeassociatedwithlocallinearmappings.Errorinformationobtainedduringtrainingwasusedinanovellearningalgorithmtotraintheclassifier.Theproposedmethodachievedfastconvergenceandgoodgeneralization.
BajwaandTian(2001)developedweeddensitymodelsusingafeedforward,BPtrainedMLPnetworktomapthespatialdistribu-tionofweeddensitybasedonaerialdigitalcolorinfraredremotesensingoverasoybeanfield.Inthisstudy,theANNweeddensity
modelsresultedinR2valuesof0.83–0.83.ThismodelmappedthespatialdistributionofweeddensitywithaR2valueof0.58forafieldnotusedinmodelingformodelvalidation.
Itisquitedifficulttousemachinevisiontodistinguishweedsfromthemaincropinrealtime,duetothesubstantialcomputa-tionalresourcesandthecomplicatedalgorithmsrequired.Yangetal.(2000b)developedANNstoovercomesomeofthesedifficultiesbyinterpretingimagesquicklyandeffectivelytodistinguishyoungcornplantsfromweeds.TheANNswereone-hidden-layerfeedfor-wardnetworkstrainedwiththeBPalgorithm.Inthestudy,atotalof80imagesofcornplantsandweedswereusedfortrainingpur-poses.ForsomeANNs,thesuccessrateforclassifyingcornplantswasashighas100%,whereasthehighestsuccessrateforweedrecognitionwas80%.
Burksetal.(2000)usedthecolorco-occurrencetexturestatisticsasinputvariablesforaBPtrainedANNweedclassificationmodel.Thestudyevaluatedclassificationaccuracyasafunctionofnetworktopologyandtrainingparameterselection.Inaddition,trainingcyclerequirementsandtrainingrepeatabilitywerestudied.
El-Fakietal.(2000)developedandtestedANN-basedweeddetectionalgorithmscapableofdetectingtheleadingweedspeciescompetingwithwheatandsoybeancrops.ThisstudycomparedstatisticaldiscriminantanalysisandtwoANNclassifiers.Theseclassifiersweretrainedandtestedusingthreeweedspecies(John-songrass,redrootpigweed,andyellowfoxtail)withsoybeanandthreeweedspecies(wildbuckwheat,cheat,andfieldbindweed)withwheat.TheresultsshowedthatthestatisticaldiscriminantanalysisclassifierwasmoreaccuratethantheANNclassifiersinclassificationaccuracy.
Suzukietal.(2009)developedadiscriminantmodelforauto-matedweedcontrolusingimageryfromalinescanhyperspectralimagingsensor.Priortodevelopingdiscriminators,explanatoryvariablesforthemodelsweregeneratedfromspectralbandsusingtwomethods:stepwiseselectionmethod(RAW)usingthemul-tivariateteststatisticWilks’LambdaandPrincipalComponentAnalysis(PCA).LinearDiscriminantAnalysis(LDA)andaneuralnetwork(NN)modelswereemployedfordevelopmentofthedis-criminator,resultinginfourdiscriminantmodelstotest:RAW-LDA,RAW-NN,PCA-LDA,andPCA-NN.AccuraciesoftheNNmodelsweresuperiortotheLDA,butsuccessratesforalldiscriminantmodelsweregreaterthan85%.RAWmethodwassuperiortoPCAforpro-cessingspeedbecausePCAselectedvariablescalculatedfromallwavebands.
Inastudyofcropleafareaindices,KollerandUpadhyaya(2005a)developedanANNmodelthatutilizedtheleafareaindex(LAI)val-uesderivedfromaerialimagestotrainandpredictLAIchangesonadailybasis.BasedonthisANNmodel,KollerandUpadhyaya(2005b)predictedtheprocessingtomatoyieldbasedonsoil,crop,andenvironmentalparameters.KollerandUpadhyaya(2005c)fur-therdevelopedaBPtrainedfeedforwardANNmodeltopredictdailyLAIvaluesbasedonsixsetsofmodifiedNDVIvaluesderivedfrombiweeklyaerialimagesobtainedduringthetomatogrowingsea-son.ThetrainednetworkwasabletopredictLAIvalueswithR2valuesof0.96orhigher.ThecumulativeLAIpredictedbytheANNmodelcorrelatedwellwiththemeasuredvalues(R2=0.83).
Walthalletal.(2004)comparedempiricalandANNapproachesforestimatingcornandsoybeanLAIfromLandsatETM+imagery.Inthisstudy,anevaluationofLAIretrievalmethodswascon-ductedusing(1)empiricalmethodsemployingNDVIandanewsoiladjustedindexthatusesgreenwavelengthreflectance,(2)ascaledNDVIapproachthatusesnocalibrationmeasurements,and(3)ahybridapproachthatusesanANNandaradiativetransfermodelwithoutsite-specificcalibrationmeasurements.Comparedtoothermethods,theANN-basedapproachiscomputationallycomplexasmultipleanalyticalstepsmustbecompletedbeforeanestimatecanbeproduced.
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Inthestudyofcropdisease,Pydipatietal.(2005)usedthecolorco-occurrencemethodfortexturalanalysistodeterminewhetherclassificationalgorithmscouldbeusedtoidentifydiseasedandnormalcitrusleavesbasedonaMahalanobisminimumdistanceclassifieraswellasANNclassifiersbasedontheBPalgorithmfortwo-hidden-layerfeedforwardnetworksandRBFnetworkswithfuzzyoutputsgivingameasureofstrength.TheresultsindicatedthatthattheMahalanobisclassifierandtheBPtrainedANNclassi-fierperformedequallywellwhenusinghueandsaturationtexturefeaturesselectedthroughastepwisevariablereductionmethod.
Inastudyofcropgrowth,Hsiehetal.(2001)adoptedadual-hidden-layerfeedforwardANNtrainedwiththeerrorBPalgorithmtoanalyzeexperimentaldataanddevelopstrategiesforadynamicgrowthmodeltosimulatetherelationshipbetweenenvironmentalfactors(temperature,watersupplyanddailyradiation)andcab-bageseedlingquality.Hsiehetal.(2003)continuedtoworkonthemodeldevelopmentofaBPtrained,multilayerfeedforwardANNmodeltoinvestigatetherelationshipbetweenthequalityofcabbageseedlingsandtheirgrowthenvironment.Thisstudydevel-opedandevaluatedthreedifferentANNmodels.Byintegrationofschemesforvariousgrowthstagesandthehistoricalgrowthfactor,themodelcontributesmarkedlyinpredictionability.Theerrorisdecreasedby77%whenthebestmodeldevelopedinthisworkwasused.
Tumboetal.(2002a)trainedasingle-hidden-layerfeedforwardANNusingtheBPalgorithmusingspectralchannelsofthehyper-spectralreflectanceresponsepatternsfromcornplantasinputsforpredictingchlorophyllvaluesastheoutput.TheBPtrainedANNmodelwasdevelopedusingspectralchannelsofthespectralreflectanceresponsepatternsasinputsandchlorophyllreadingsasanoutput.Themodelshowedstrongcorrelationbetweenpre-dictedandactualchlorophyllmeterreadingsfromthesamecornvarietyandsoiltypeasthetrainingset.
Moshouetal.(2001)usedtheSOMANNinasupervisedwayforclassificationofagriculturalplants.Theclassificationmethodwasappliedinaprecisionfarmingapplicationforclassificationofcropsandweedsusingspectralproperties.Theclassificationper-formanceoftheproposedmethodwasproventobesuperiorcom-paredwithotherstatisticalandneuralclassifiers,suchasanoptimalBayesianclassifierintheformofaprobabilisticneuralnetwork.3.2.3.IrrigationandETcalculation
Elgaalietal.(2006)developedaone-hidden-layerfeedforwardANNmodelandaconsumptiveusemodelfortheregionofCol-orado’sArkansasRiverbasintoinvestigatethepossibleeffectsofregionalclimaticchangesonirrigationwatersupplyanddemand.Thetwomodelswereappliedtotheregiontoestimatetheeffectsofclimatechangeonirrigationwaterbalance.
Forselectionofthebestcompromiseirrigationplanningstrat-egyinthecasestudyofJayakwadiirrigationproject,Maharashtra,India,Rajuetal.(2006),basedmultiobjectivelinearprogrammingoptimization,employedKohonenneuralnetworkstosortnon-dominatedirrigationplanningstrategiesintosmallergroups.Theresultsindicatedthattheintegratedmodelmethodologywaseffec-tiveformodelingmultiobjectiveirrigationplanningproblems.
InETcalculation,Brutonetal.(2000)developedfeedforwardANNmodelstrainedwiththeBPalgorithmtoestimatedailypanevaporationusingmeasuredweathervariablesasinputsfromweatherdataofRome,Plains,andWatkinsville,Georgia,USA.Inthisstudy,dailypanevaporationwasalsoestimatedusingmultiplelin-earregressionandthePriestley–TaylormethodandwascomparedtotheresultsoftheANNmodels.TheANNmodelofdailypanevap-orationwithallavailablevariablesasinputswasthemostaccuratemodel.Inoverall,panevaporationestimatedwithANNmodelswasslightlymoreaccuratethanpanevaporationestimatedwithamultiplelinearregressionmodelorthePriestley–Taylorequation.
Odhiamboetal.(2001b)developedafeedforwardANNonaconceptualandstructuralbasisinastudyoneliminationoftrial-and-errorindeterminingtheshapeofthemembershipfunctionsinthefuzzycontrolrulesforestimatingdailyreferenceET.Theresultsofthestudyshowedthattheoptimizedfuzzy–neuralmodelisrea-sonablyaccurate,andiscomparabletotheFAOPenman–Monteithequation.ThisapproachcanprovideaneasyandefficientmeansoftuningfuzzyETmodels.
3.2.4.Soilanalysis
Inthestudyofsoilprofiles,Odhiamboetal.(2004)pre-sentedanapplicationofafuzzy–neuralnetworkclassifierforunsupervisedclusteringandclassificationofsoilprofilesusingground-penetratingradarimagery.FreelandandOdhiambo(2007)usedatwo-layerperceptronneuralnetworkthatperformssupervisedclassificationtoexaminethefeasibilityofusingtexturalfeaturesextractedfromground-penetratingradarfornon-intrusivelymappingsubsurfacesoilconditions.TheANNclassifierwasusedtoassigndatatotheknownsubsurfacecategories.Theresultsofsubsurfacecharacterizationusingextractedtexturalfea-tureswerefoundtobeincloseagreementwithresultsobtainedbycarefulvisualinterpretationofthedata.Thisapproachofground-penetratingradarimageryclassificationwastobeconsideredasanalternativemethodtotraditionalhumaninterpretationonlyintheclassificationofvoluminousdatasets,whereintheextensivetimerequirementwouldmakethetraditionalhumaninterpreta-tionimpractical.
Bajwaetal.(2004)usedamultilayerfeedforwardANNtrainedwithGAtooptimizetheANNtopologyandotherfourunsupervisedandsupervisedmethodstoidentifyaerialhyperspectralimagebandstocharacterizesoilelectricalconductivityandcanopycov-erageinagriculturalfields.Bandselectionwasperformedwithbothunsupervisedandsupervisedapproaches.Fivemethods(threeunsupervisedandtwosupervised)areproposedandcomparedtoidentifyhyperspectralimagebandstocharacterizesoilelectricalconductivityandcanopycoverageinagriculturalfields.Eachhyper-spectralimagebandwasrankedusingallfivemethodsandANNmeasurewasthemostusefulinselectingbandsspecifictoatargetcharacteristicwithminimuminformationredundancy.
FerentinosandAlbright(2002)presentedafeedforwardANNmodelthatwastrainedwiththequasi-NewtonBPalgorithmandpredictspHandelectricalconductivitychangesintherootzoneoflettucegrowninadeep-troughhydroponicsystem.Themostsuit-ableandaccuratecombinationofnetworkarchitectureandtrainingmethodwasonehiddenlayerwithninehiddennodes,trainedwiththequasi-Newtonbackpropagationalgorithm.ThemodelprovedcapableofpredictingpHatthenext20-mintimestepwithin0.01pHunitsandelectricalconductivitywithin5Scm−1.Simplerpre-dictionmethods,suchaslinearextrapolationandthelazymanprediction(inwhichpredictionisthevalueoftheprevioustimestep),gavecomparableaccuracymuchofthetime.However,theyperformedpoorlyinsituationswherethecontrolactionsofthesys-temhadbeenactivatedandproducedrelativelyrapidchangesinthepredictedparameters.Inthosecases,theneuralnetworkmodeldidnotencounteranydifficultiespredictingtherapidchanges.
Additionally,Fidêncioetal.(2001)appliedCPANNandRBFANNinclassificationofsoilsusingnear-infraredspectroscopy.InglebyandCrowe(2001)developedfeedforwardANNmodelswithareduced-memoryLevenberg–MarquardtBPtrainingalgorithmforpredictingorganicmattercontentinSaskatchewansoils.Altendorfetal.(1999)developedasetoffeedforwardANNswithBPtrainingtopredictsoilwatercontentatagivendepthasafunctionofsoiltemperature.
Inthestudyofsoilproperties,ZhangandKushwaha(1999)appliedANNstosimulatetheinteractionbetweensoilandtoolfortillageandsoilbehavior.Schaapetal.(1998)calibratedhierarchical
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ANNmodelsforpredictionofwaterretentionparametersandsaturatedhydraulicconductivityfrombasicsoilproperties.
Inthestudiesofsoiltemperature,Yangetal.(1997a)developedamodelbasedonafeedforwardANNtrainingwiththeBPalgorithmtosimulatedailysoiltemperaturesat100,500and1500mmdepthsofsoilfromOttawa,Ontario,Canada.Yangetal.(2004b)comparedamultivariateadaptiveregressionsplinesmodelwithfeedforwardANNsinsimulationofsoiltemperatureatdifferentdepths.Thecorrelationcoefficientsoflinearregressionfrombothmultivari-ateadaptiveregressionsplinesandANNswerealwayshigherthan0.950.Theresultsdemonstratethepotentialofmultivariateadap-tiveregressionsplinestobeusedasaregressiontechnologyinagriculturalapplications.
AnumberofpapersdevelopingandusingANNshavebeenpub-lishedforsoilpropertystudiesinGeodermaandSSSAJinrecentyears.Anaguetal.(2009)developedsorptionmodelsasafunc-tionofbasicsoilpropertiesusingANNsforestimationheavymetalsorptioninGermansoils.TheresultsofthestudyindicatedthattheANNmodelsperformedbetterthanonmultiplelinearregressionMLRinallcasesfor9heavymetalsusing13soilpropertiesaswellassolutionphaseconcentrationsasinputsandsorbedphasecon-centrationsasoutput.Khalilmoghadametal.(2009)usedANNsinestimatingsoilshearstrengthfrommeasuredparticlesizedistribu-tion,topographicattributes,NDVI,soilorganiccarbon(SOC),andCaCO3.Threeneuralnetworksstructures:multilayerperceptron(MLP),generalizedfeedforward,andmodularfeedforwardnet-workswereusedandcomparedwithconventionalmultiple-linearregressionanalysis.InthecomparisontheimprovementswereidentifiedwithallthreeneuralnetworkmodelsoveraconventionalMLRmodels.Cockxetal.(2009)evaluatedANNsforextractionoftopsoiltexturalinformationfromthedepth-weightedEM38DD(anelectromagneticinductionsoilsensor)signalstopredictthetop-soilclaycontent.EarlierMerdunetal.(2006)comparedANNandregressionpedotransferfunctionsforpredictionofsoilwaterreten-tionandsaturatedhydraulicconductivityanddemonstratedthatANNproducedpromisingresults.
3.2.5.Precisionagriculture
XiangandTian(2007)developedaBPtrainedone-hidden-layerfeedforwardANNinanartificiallyintelligentcontrollerforgainandexposuretimeautomationofamultispectralcameratocom-pensateforchangingnaturallightingconditionsandtoacquirewhite-balancedimages.ThisstudywasundertakentodevelopanartificiallyintelligentcontrollerbasedonanANNwithanadaptiveneuro-fuzzyinferencesystem.Itwasshownthroughexperimentsthatthedevelopedalgorithmwasabletocompletemultispectralcameraparametercontrolwithinthreeiterationsforeachchannel.Theconvergencespeedwasfasterthanwithconventionalcontrolmethods.
Irmaketal.(2006)developedaBPANNmodeltopredictthespatialdistributionofsoybeanyieldsandtounderstandthecausesofyieldvariability.First,aBPtrainedANNmodelwasdevelopedbyrelatingsoybeanyieldtotopography,soil,weather,andsitefactorsandthemodelpredictionswereevaluatedforthesamefieldforindependentyears.Then,thepotentialuseoftheANNmodelwasalsoexploredforpredictingyieldsinindependentfields.Finally,theabilityoftheANNtoattributeyieldlossesduetosoybeancystnematodes(SCN),soilpH,andweedswasevaluated.TheresultsshowedthattheANNmodelcouldpredictspatialyieldvariabilitywell.
Miaoetal.(2006)employedANNanalysistoevaluatetherela-tiveimportanceofselectedsoil,landscapeandseedhybridfactorsoncornyieldandgrainqualityintwoIllinois,USAfields.TheresultsindicatedthattheresponsecurvesgeneratedbytheANNmodelsweremoreinformativethansimplecorrelationcoeffi-cientsorcoefficientsinmultipleregressionequations.Unoetal.
(2005)developedyieldpredictionmodelsusingstatisticalandANNapproachesalongwithvariousvegetationindices.Themodelswereusedtopredictcornyieldfromcompactairbornespectrographicimagerdata.ThestudyshowedthatalthoughnocleardifferencewasobservedbetweenANNsandstepwisemultiplelinearregres-sionmodels,thehighpotentialusefulnessofANNswasconfirmed.Drummondetal.(2003)investigatedsupervisedfeedforwardANNsalongwithstepwisemultiplelinearregressionandprojectionpur-suitregressiontoidentifymethodsabletorelatesoilpropertiesandgrainyieldsonapoint-by-pointbasiswithintenindividualsite-years.Inthestudy,theANNsconsistentlyoutperformedstepwisemultiplelinearregressionandprojectionpursuitregressionandprovidedminimalpredictionerrorsineverysite-year.However,insite-yearswithrelativelyfewerobservationsandinsite-yearswhereasingle,overridingfactorwasnotapparent,theimprove-mentsachievedbyneuralnetworksoverstepwisemultiplelinearregressionandprojectionpursuitregressionweresmall.
Liuetal.(2001)designedafullyconnected,BPtrainedfeed-forwardANNtoapproximatethenonlinearyieldfunctionrelatingcornyieldtofactorsinfluencingyield.Factorsaffectingcropyields,suchassoil,weather,andmanagement,weresocomplexthattra-ditionalstatisticscouldnotgiveaccurateresults.Asanautomaticlearningtool,theANNisanattractivealternativeforprocessingthemassivedatasetgeneratedbyprecisionfarmingproductionandresearch.Inthisstudy,afeedforward,completelyconnected,back-propagationANNwasdesignedtoapproximatethenonlinearyieldfunctionrelatingcornyieldtofactorsinfluencingyield.3.2.6.Chemicalapplication
KrishnaswamyandKrishnan(2002)predictedthenozzlewearratesforfourfannozzlesusingregressionandANNtechniques.AcomparisonoftheregressionmodelandANNmodelshowedthattheregressionandtheneuralnetworkmodelsperformedequallywellforthepredictions.Yangetal.(1997b)usedfeedforwardANNsforsimulationofpesticideconcentrationsinagriculturalsoils.AnANNmodelcanbeexecutedinreal-time,whilethesprayeriswork-inginthefield,inordertoadjustapplicationratestotherealextentoftheproblem.Inthisstudy,anANNmodelwasbuiltandtrainedwithinputsof:accumulateddailyrainfall,soiltemperature,poten-tialET,aswellastillagepracticesandthenumberofdayselapsedafterpesticideapplication.3.3.Geneticalgorithmapplications
3.3.1.Overview
Basedonasummaryof83papersandreports,GAshavebeenappliedinsolvingproblemsincropmanagement(31%),waterman-agement(27%),foodqualityandsafety(11%),foodprocessing(6%),precisionagriculture(4%),agriculturalbiology(4%),agriculturalmachinery(2%),agriculturalfacilities(2%),animalbehavior(2%),andothers(11%)suchasagriculturalvehicle,robotics,andpol-lution.GAsarebasicallyanoptimizationandsearchmethod.Theapplicationsforoptimizationtakethelargestportionofthetotal,66%.GAshavebeenalsousedtoassistwithmodelingandpredic-tion(18%),classification(12%),control(2%),dataclustering(1%)andvaluethresholding(1%).
3.3.2.Cropmanagement
Thorpetal.(2004)usedtheGA-basedimagesegmentationalgo-rithm(Tangetal.,2000)togeneratemeasurementsofpercentvegetationcoverfromthehyperspectralimagescollectedoverasoybeanfield.Fangetal.(2003)estimatedcropleafareaindexbyintegratingacanopyradiativetransfermodelandtheGAoptimiza-tiontechnique.ThismethodwasusedtoretrieveleafareaindexfromfieldmeasuredreflectanceaswellasfromatmosphericallycorrectedLandsatETM+data.YaoandTian(2003)proposedand
Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127117
testedaGA-basedselectiveprincipalcomponentanalysismethodusinghyperspectralremotesensingdataandgroundreferencedatacollectedwithinacornfieldforchlorophyllcontent,plantpop-ulation,andvarioushybrids.TheGA-basedmethodwasusedtoselectasubsetoftheoriginalimagebands,whichcouldreducethedatadimension.Aprincipalcomponenttransformwassubse-quentlyappliedtotheselectedbands.Then,imageprocessingonthereducedfeaturespacecouldbeperformedwithimprovedaccu-racy.Tangetal.(2000)developedamachinevision-basedweeddetectiontechnologyunderoutdoornaturallightingconditions.Inimageprocessing,aGA-based,supervisedcolorimagesegmenta-tionmethodinthehue-saturation-intensitycolorspacewasusedtoseparateplants(cropandweeds)fromthebackground(soil,rocks,andresidue)forthisreal-time,machine-vision-based,in-fieldvari-abilitymappingandselectiveherbicideapplicationsystem.Pabicoetal.(1999)presentedaconceptualframeworkforusingaGAtodeterminecultivarcoefficientsofcropsimulationmodels.
Inastudyofweeddistributionincropfields,Diazetal.(2005)presentedamethodforinducingamodelthatappropriatelypre-dictstheheterogeneousdistributionofwild-oatintermsofsomeenvironmentalvariables.Fromseveralexperiments,distinctrulesetshavebeenfoundbyapplyingaGAtocarryouttheautomaticlearningprocess.Therulesetextractedwasabletoexplainaboutmostofweedvariability.Noguchietal.(1998)developedanintelli-gentvisionsystemforautonomousvehiclefieldoperations.Fuzzylogicwasusedtoclassifythecropsandweeds.AGAwasusedtooptimizeandtunethefuzzylogicmembershiprules.
3.3.3.Irrigation
RajuandKumar(2004)presentedanapplicationofGAforirri-gationplanning.TheGAtechniquewasusedtoevolveefficientcroppingpatternstomaximizebenefitsforanirrigationprojectinIndia.Kumaretal.(2006)presentedaGAmodelforobtaininganoptimaloperatingpolicyandoptimalcropwaterallocationsfromanirrigationreservoir.ThemodelwasappliedtotheMalaprabhasingle-purposeirrigationreservoirinKarnatakaState,India.TheoptimaloperatingpolicyobtainedusingtheGAsissimilartothatobtainedbylinearprogramming.
WardlawandBhaktikul(2004)describedthedevelopmentofaGAtosolveanirrigationwaterschedulingproblem.Theimplemen-tationoftheGAwastooptimizetheutilizationofwaterresourcesinirrigationsystemsoperatingonarotationalbasisalongwithcon-straintsthatrelatetofieldsoilmoisturebalancesaswellascanalcapacities.Caietal.(2001)describedstrategiesforsolvinglargenonlinearwaterresourcesmodelsmanagementwithacombina-tionofGAswithlinearprogramming.
Kuoetal.(2000)presentedamodelbasedonon-farmirriga-tionschedulingandasimpleGAoptimizationmethodfordecisionsupportinirrigationprojectplanning.TheproposedmodelwasappliedtoanirrigationprojectlocatedinDelta,Utahforoptimiz-ingeconomicprofits,simulatingthewaterdemand,cropyields,andestimatingtherelatedcropareapercentageswithspecifiedwatersupplyandplantedareaconstraints.SimulationresultsdemonstratedthatthemostappropriateparametersofGAsforthisstudywere:numberofgenerations,populationsizes,probabilityofcrossover,andprobabilityofmutation.
3.3.4.Soilanalysis
PachepskyandAcock(1998)developedstochasticimagingoftheavailablesoilwatercapacity(AWC)andasoybeancropmodelGLYCIMtosimulatevariabilityanduncertaintyincropyieldesti-matesasrelatedtosoilsamplingdensityandweatherpatternsusingGAs.Parasuramanetal.(2007)estimatedsaturatedhydraulicconductivityusinggeneticprogramming(GP),tree-likerepresen-tationsofGassolutiondomain.InthestudytheperformanceoftheGPmodelswerecomparedwiththeANNmodelsandGPappeared
tobeapromisingtoolforestimatingthesaturatedhydrauliccon-ductivity.
3.3.5.Precisionagriculture
Liuetal.(2001)optimizedfifteeninputfactorswithaGAtodeterminemaximumyieldaftertheANNwastrained.TheANNapproximatedthenonlinearyieldfunctionrelatingcornyieldtofactorsinfluencingyield,wastrained.
3.3.6.Chemicalapplication
Potteretal.(2000)usedGAtooptimizenozzletypeorreleaseheightusingadesireddepositionasmodelinputwithamodelcon-strainonotherfactorssuchasaircrafttypeandspraysystemforaerialpesticideapplicationoptimization.3.4.Bayesianinferenceapplications
3.4.1.Overview
Basedonastudyof46papersandreports,BIhasbeenappliedinsolvingproblemsincropmanagement(28%),foodqualityandsafety(28%),watermanagement(17%),foodprocessing(7%),pre-cisionagriculture(7%),andothers(13%)suchasbioenergyandanimalhealth.BIisbasicallyaclassifierforpatternrecognition.Theapplicationsforclassificationtotal50%.BIalsohasbeenusedtohelpmodelingandprediction(35%),parameterestimation(11%),andoptimizationandcontrol(4%).
3.4.2.Cropmanagement
Inweeddetection,Mathankeretal.(2007)usedaBayesianclas-sifierforclassificationsusingshape,color,spectralimagefeatures.Theclassifierconductedthreeclassificationsusingonlyshapefea-tures,onlygreencolorandspectralenergyfeatures,andallfeaturescombined.Theclassificationaccuracyusingthesefeaturesatdif-ferentresolutionsforweeddetectionvariedfrom80%to87%.Theperformancewasunaffectedbyimageresolutionandshowspoten-tialforfieldapplications.
Foroutdoorfieldplantdetection,TianandSlaughter(1998)developedanenvironmentallyadaptivesegmentationalgorithm.Theresultsoftheenvironmentallyadaptivesegmentationalgo-rithmwereusedtocreateaBayesianclassifierasdecisionsurface.MarchantandOnyango(2003)comparedaBayesianclassifierwithamultilayerfeedforwardANNforplant/weed/soildiscriminationincolorimageswithapreferenceofBayesianclassifieroverANNinthiscase.
3.4.3.IrrigationandETcalculation
ClemmensandKeats(1992)appliedBItothereal-timefeedbackcontrolofabasinirrigationsystem.Bayesianinferenceisappliedtothereal-timefeedbackcontrolofabasinirrigationsystem.Esti-matesoftheKostiakovk(infiltrationparameter)andManningn(Roughnessparameter)wereobtainedduringwateradvancesothattheoptimumcutofftimecanbedeterminedfrom:(1)esti-matesfromobservationofadvancetimeanddistanceandsolutionofthezero-inertiaborderirrigationmodel;and(2)eitherhistoricalestimatesofparametersorsubjectiveestimatesmadebytheirriga-tor.ThestudyshowedthattheBIhassomepotentialforimprovingreal-timecontrolofsurfaceirrigationsystems.
Saydeetal.(2008)proposedananalyticalmethodtoreduceuncertaintyindeterminationofsoilwaterdepletionbyincorporat-ingestimatesoftheuncertaintiesofETandmeasuredsoilmoistureintotheanalysis.UsingaBayesiananalysistheprobabilitydistri-butionsofthetwoestimatorswereincorporatedintoaposterioriprobabilitydistributionofdepletionthatprovidesabetterbasisforirrigationdecisions.
118Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127
3.4.4.Precisionagriculture
Chinchuluunetal.(2007)developedarobustBayesianclassi-fierwithnormaldistributionforcolorsegmentationinacitrusyieldmappingsystemonacanopyshakeandcatchharvester.TheBayesianclassifierworkedrelativelywellonthenon-uniformimages.
3.4.5.Chemicalapplication
LeeandSlaughter(1999)usedBayesianclassifiersindevelop-mentofareal-timeintelligentroboticweedcontrolsystemforselectiveherbicideapplicationtoin-rowweedsusingmachinevisionandprecisionchemicalapplication.3.5.Decisiontreeapplications
3.5.1.Overview
Asummaryof31papersandreportsonDTapplicationsindicatesthatDThavebeenappliedinsolvingproblemsincropmanagement(26%),agriculturalsafety(16%),animalproductionandmanage-ment(13%),foodsafety(13%),water(13%),agriculturalpollution(6%),andothers(13%)suchasprecisionagricultureandbiologi-calcontrol.DTalsoisaclassifier.Theapplicationsforclassificationaccountfor52%ofthetotal.DThasbeenalsousedtoconductalter-nativeinduction(23%),rulerepresentation(13%),patterninduction(6%),andothers(6%)suchasfunctionapproximationandcontrol.3.5.2.Cropmanagement
Karimietal.(2005)compareddiscriminantanalysis,ANNandDTforclassifyingimageswithrespecttothenitrogenandweedmanagementpracticesappliedtotheexperimentalplots.Foriden-tifyingweedandnitrogenstressesincorn,DTcouldnotcompetewiththediscriminantanalysisandANNforbetterresults.Yangetal.(2004a)usedDTstoclassifymultispectralimagesofexperimentalplotshavingdifferentcropandweedpopulations.DTsaredirectlysuitedtoclassificationsincedatarepresentingagivenindividualaresortedthroughthedecisiontreestructuretofalldirectlyintoapre-definedcategory.Inthisstudy,anaircraft-mountedpushb-roomimagingspectrometerwasusedtoobtainscansoftheplotsinoneblue,fivegreen,fivered,andthirteeninfraredbands.Threetypesofinputwere:absolutevaluesofradiancefromthe24wave-bands,vegetationindex(VI),whichconsistsof12inputs,andNDVIwhichconsistsof65inputs.Resultsshowedthatthemostcom-plexclassificationproblem(distinguishingbetween11crop/weedcombinations)wasbestresolvedusingtheNDVIinputs.
Goeletal.(2001)usedaDTmethodtoclassifynitrogenstresswithinacornfieldbasedonhyperspectralimages.Goeletal.(2003)comparedtheDTandANNclassificationalgorithmsfortheclas-sificationofhyperspectraldatatodiscriminatebetweendifferentgrowthscenariosinacornfieldtoidentifyweedstressandnitro-genstatusofcorn.DTtechnologywasappliedtoclassifydifferenttreatmentsbasedonthehyperspectraldata.Varioustree-growingmechanismswereusedtoimprovetheaccuracyofclassification.Misclassificationratesofdetectingallthecombinationsofdifferentnitrogenandweedcategorieswere43,32,and40%forhyperspec-traldatasetsobtainedattheinitialgrowth,thetasselingandthefullmaturitystages,respectively.However,satisfactoryclassificationresultswereobtainedwhenonefactor(nitrogenorweed)wascon-sideredatatime.Inthiscase,misclassificationrateswereonly22and18%fornitrogenandweeds,respectively,forthedataobtainedatthetasselingstage.
3.5.3.Precisionagriculture
Cohenetal.(2006)usedtheDTmethodfordevelopingaspatialdecisionsupportsystem(SDSS)forMedfly(theMediterraneanfruitfly)controlonfruitcropsinIsrael.Thisstudyestablishedthemainstepstoassistthecoordinatorsinthedecision-makingprocedure
inthedevelopmentoftheSDSS.Theoutputisamapthatclassifiesthecitrusplotsintooneofthefollowingblocks:spraying;sprayingisrecommended;sprayingisnotrecommended;no-spraying;nodata.
Yangetal.(2001)usedtheDTalgorithmtodistinguishbetweenmanureandchemicalfertilizertreatmentsforairbornehyperspec-tralimageryclassificationofagriculturalfields.Thesuccessoftheclassificationratewasashighas91%fortheearlyplantingsea-son,99%forthemidplantingseason,and95%forthelateplantingseason.
3.5.4.Chemicalapplication
Murrayetal.(2005)usedtheDTmodeltomodelannualpas-tureproductionforanalysisofpotentialofutilizingvariablerateapplicationtechnologyfromaircraftforimprovedplacementoffertilizer.
4.Fusionofsoftcomputingmethodsinagriculturalandbiologicalengineering
Withthedevelopmentofsoftcomputinginagriculturalandbiologicalengineering,techniqueshaveintegrateddifferentsoftcomputingtechniquesinasynergisticway.ItisadvantageoustoemployANNs,fuzzysystems,andevolutionaryalgorithmsincom-binationinsteadofexclusively(Hoffmannetal.,2005).
Table1listspapersandreportsonfusionofsoftcomputingtech-niquesagriculturalandbiologicalengineeringapplications.ThelistindicatesthattheintegrationofFLandANNsisprobablythemostcommonmethodoffusioninsoftcomputing(thirteenoutoftwenty-ninecollectedpapersandreports).ANFIS(Adaptive-Network-basedFuzzyInferenceSystem)isafuzzyinferencesystemimplementedintheframeworkofadaptiveneuralnetworks(Jang,1993).Byusingahybridlearningprocedure,theANFIScancon-structaninput–outputmappingbasedonbothhumanknowledge(intheformoffuzzy‘If–Then’rules)andstipulatedinput–outputdatapairs.Ithasbeendevelopedandusedtosolveproblemsinagriculturalandbiologicalengineering.4.1.Cropmanagement
Forcropprotection,PearsonandWicklow(2006)developedaneuralnetworktoidentifyfungalspeciesthatinfectsinglekernelsusingprincipalcomponentsofthereflectancespectraasinputfea-tures.TheneuralnetworkwastrainedusingGAsasLestanderetal.(2003)indicatedthattheGAtrainingalgorithmmethodwasmuchlesslikelytooverfitthedata.
Meyeretal.(2004)usedfuzzyinferencesystemsbuiltwithsub-tractiveclusteringinanANFISforadigitalcameraoperationstudyforcolor-basedclassificationsofuniformimagesofgrass,baresoil,cornstalksresidue,andwheatstrawresidue.Forweeddetection,Netoetal.(2003)usedANFISforimageprocessingtoseparateweedfrombackground.AGAwasincorporatedtoadjustthefuzzymem-bershipfunctionstoreducemisclassificationandimproveimagesegmentation.4.2.ETcalculation
BasedonthepreviousresearchonfuzzyETmodels(Odhiamboetal.,2001a),Odhiamboetal.(2001b)furtherstudiedhowtoelim-inatetrial-anderrorindeterminingtheshapeofthemembershipfunctionsinthefuzzycontrolrulesforestimatingdailyreferenceETbyapplicationofafuzzy–neuralsystemthroughfusingfuzzylogicandANNonaconceptualandstructuralbasis.Theneuralcomponentprovidedsupervisedlearningcapabilitiesforoptimiz-ingthemembershipfunctionsandextractingfuzzyrulesfromaset
Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127
Table1
Papersandreportsonfusionofsoftcomputingtechniquesinagriculturalandbiologicalengineering.Year19921997199719972001b20012001200120012001200320032003200320032003200420042004200420062006200620062006200620062007
Author
Linkoetal.KimandChoMorimotoetal.NoguchiandTeraoOdhiamboetal.Liuetal.
JindalandSrisawasQuetal.Miu
MiuandPerhinschiMorimotoetal.JindalandSrithamAndriyasetal.Chtiouietal.Leeetal.Netoetal.
Odhiamboetal.Meyeretal.Goeletal.
JainandSrinivasuluMadeiroetal.Hashimotoetal.Oliveiraetal.
Ferentinosetal.HancockandZhangLakshmietal.
PearsonandWicklowXiangandTian
Fusiontype
ANNmodelingforfuzzycontrol
ANNmodelingplusfuzzycontrolsimulationANNmodelingplusGAparameteroptimizationforfuzzycontrol
ANNsimulationandGAoptimization
ConceptualandstructuralfusionofFLandANNANNmodelingplusGAparameteroptimizationPNNtrainedwithGAALNdecisiontreeFLandGAFLandGA
ANNmodelingplusGAparameteroptimizationPNNtrainedwithGA
FCMclusteringforRBFtrainingSOMwithFCMclusteringANFISmodelingANFISclassification
Fuzzy–neuralnetworkunsupervisedclassification
ANFISclassification
Fuzzyc-meansclusteringforRBFtrainingANNtraininedbyGA
GAparametersearchforANN
ANNmodelingplusGAparameteroptimizationGAparametersearchforANN
ANNparameterizedbyGAANFISclassification
ANNtrainingplusGAparameteroptimizationANNtrainedbyGA
ANNmodelingplusANFIStrainingofFLcontroller
Applicationarea
Extrusioncontrol
BreadbakingprocesscontrolFruitstoragecontrol
119
Pathplanningofanagriculturalmobilerobotbottomofform
ETmodeloptimizationSettingtargetcornyieldsClassificationofsnackfoods
Functionapproximationtoconvertthemeasurementsofanelectronicnoseintoodorconcentrations
Optimizationofdesignandfunctionalparametersofthreshingunits
Optimizationofdesignandfunctionalparametersofthreshingunits
Dynamicoptimizationfortomatocoolstoragetominimizewaterloss
Classificationofeggstodetecteggshellcracks
PredictionoftheperformanceofvegetativefilterstripsColorimagesegmentationofediblebeansPredictionofmultiplesoilproperties
AdaptiveimagesegmentationforweeddetectionClassificationofsoils
Classificationofuniformplant,soil,andresiduecolorimages
PredictionofsedimentandphosphorousmovementthroughvegetativefilterstripsRainfall–runoffmodeling
ApproximationofsugarcanematurationcurvesGreenhousecroppingcontrol
Forecastingofagronomicalperformanceindicatorsinsugarcaneharvest
Greenhousecultivationcontrol
Hydraulicvanepumphealthclassification
AutomaticcalibrationofcomplexwatershedmodelsClassificationofcornkernelsfordetectionoffungiinfection
Outdoorautomaticcameraparametercontrol
ofinput–outputexamplesselectedtocoverthedatahyperspaceofthesitesevaluated.4.3.Soilanalysis
Inastudyofsoilprofiles,Odhiamboetal.(2004)combinedanANNandafuzzysysteminseriesandappliedthefuzzy–neuralnetworkclassifierforunsupervisedclusteringandclassificationofsoilprofilesusingground-penetratingradarimagery.AftertheANNclassifiessoilprofilestripsintoacertainnumberofclustersdeter-mineddynamically,thefuzzymembershipvaluesforeachprofilestripareevaluatedinthesetofclassifiedclusters.Topredictsed-imentandphosphorousmovement,Goeletal.(2004)usedfuzzyc-meanclusteringalgorithmsfortheRBFANNmodelthroughthedatafromvegetativefilterstrips.
Tosimultaneouslypredictwatercontentandsalinityusingthefrequency-responsesoildata,Leeetal.(2003)developedpartialleast-squaresandANFIS(Adaptive-NetworkFuzzyInferenceSys-tem)modelsatdifferentwatercontentandsalinitylevelsmeasuredwiththefour-electrodeWennerarraymethod.4.4.Precisionagriculture
XiangandTian(2007)developedacompleteartificiallyintelli-gentcontrollerbasedonanANNandanANFISforimplementingthecontrollertoautomaticallyadjustmultispectralcameraparam-etersforcompensationofchangesinnaturallightingandtoacquirewhite-balancedimages.Oliveiraetal.(2006)proposedatwo-
stepdecisionsupportsystemstartswithanANNfollowedbyGAsforheuristicsearchtorecommendsuitablesugarcaneareastobeharvested.Liuetal.(2001)designedafeedforward,completelyconnected,BP-trainedANNtoapproximatethenonlinearyieldfunctionrelatingcornyieldtofactorsinfluencingyield.Bystratifiedsamplingbasedonrainfall,someofthedatawereexcludedfromthetrainingsetandusedtoverifytheyieldpredictionaccuracyoftheANN.AftertheANNwasdevelopedandtrained,optimiza-tionofthefifteeninputfactorswasstudiedwithaGAtodeterminemaximumyield.
5.Supportvectormachines
SVMsasanewsetofsupervisedgeneralizedlinearclassifiers,havebeenintroducedtosolveproblemsandhaveattractedgreaterinterestrecentlyinagriculturalandbiologicalengineering.SVMsarecloselyrelatedtoneuralnetworks.Infact,anSVMmodelusingsigmoidkernelfunctionisequivalenttoatwo-layerperceptronneuralnetwork.Usingakernelfunction,SVMsarealternativetrain-ingmethodsforpolynomial,radialbasisfunction,andmultilayerperceptronclassifiersinwhichtheweightsofthenetworkarefoundbysolvingaquadraticprogrammingproblemwithlinearconstraints,ratherthanbysolvinganonconvex,unconstrainedminimizationproblemasinstandardANNtraining.SVMshaveoftenhigherclassificationaccuraciesthanmultilayerperceptronANNs.
SVMs,asasetofsupervisedgeneralizedlinearclassifiers,haveoftenbeenfoundtoprovidehigherclassificationaccuraciesthan
120Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127
Fig.4.PublicationsonapplicationsofSVMsinagriculturalandbiologicalengineer-ing.
otherwidelyusedpatternclassificationtechniquessuchasMLPneuralnetworks.Inagriculturalandbiologicalengineering,thegrowinginterestinSVMsisillustratedinFig.4.Fig.4indicatesthatalthoughthenumberofpeerreviewedpublicationsonthistopic
Table2
PapersandreportsonapplicationsofSVMsinagriculturalandbiologicalengineering.Year2003
Author
FletcherandKong
ApplicationmethodSVMclassification
didnotincreasesteadilyoverthepastfewyears,anincreasingtrendinallpaperssuggestincreasingusageofestablishedtech-niqueswhichdonotrepresentoriginalresearchdevelopments.ThesuccessfulimplementationsofSVMsinagriculturalandbiologicalengineeringarelistedinTable2.
ThegrowinginterestinSVMsaredueto:(1)theirintrinsiceffec-tivenesswithrespecttotraditionalclassifiers,whichresultsinhighclassificationaccuraciesandverygoodgeneralizationcapability;(2)thelimitedeffortrequiredforarchitecturedesign(i.e.,theyinvolvefewcontrolparameters);and(3)thepossibilityofsolvingthelearningproblemaccordingtolinearlyconstrainedquadraticprogrammingmethods(MelganiandBruzzone,2004).
Insoilanalysis,Lamorskietal.(2008)estimatedsoilhydraulicparametersfrommeasuredsoilpropertiesusingSVMs.Theresultsoftheresearchindicatedthatthethree-parameterSVMsperformedmostlybetterthanorwiththesameaccuracyastheeleven-parameterANNs.TheadvantageofSVMwasmorepronouncedatsoilmatricpotentialswherelargerrelativeerrorshavebeenencounteredandthecorrelationbetweenpredictedandmeasuredsoilwatercontentswaslower.Andmostrecently,Twarakavietal.(2009)developedSVMsforestimatingthehydraulicparame-tersdescribingthesoilwaterretentionandhydraulicconductivity.Inestimatingwatercontentsandsaturatedhydraulicconductiv-itiestheSVM-basedmethodpredictedthehydraulicparameters,
Applicationarea
Classifyingfeaturevectorsanddecidewhethereachpixelinhyperspectralfluorescenceimagesofpoultrycarcassesfallsinnormalorskintumorcategories
ClassificationofmilkbyanelectronicnoseClassificationforrecognitionofplantdiseaseClassificationofelectronicnosedata
ClassificationofmodifiedstarchesbyFouriertransforminfraredspectroscopy
Identificationofteavarietiesbycomputervision
Classificationforweedandnitrogenstressdetectionincorn
Detectionofunderdevelopedhazenutsfromfullydevelopednutsbyimpactacoustics
DiscriminationofscreeningofcompoundfeedsusingNIRhyperspectraldata
DiscriminationofwheatclasseswithNIRspectroscopy
Blackwalnutshellandmeatclassificationusinghyperspectralfluorescenceimaging
Simulationofdaily,weekly,andmonthlyrunoffandsedimentyieldfronawatershed
Classificationtodifferentiateindividualfungalinfectedandhealthywheatkernels.
QuantificationofvitaminCcontentinkiwifruitusingNIRspectroscopyClassificationofmeatwithsmalldataset
Predictionofdifferentconcentrationclassesofinstantcoffeewithelectronictonguemeasurements
EstimationofhydraulicparametersfrommeasuredsoilpropertiesClassificationofpaddyseedsbyharvestyear
Predictionofporkmeattotalviablebacteriacountwithhyperspectralimaging
On-lineassessinginternalqualityofpearsusingvisible/NIRtransmissionClassificationofforestdatacovertypes
IdentificationofvarietiesofChinesecabbageseedsusingvisibleandNIRreflectancespectroscopy
Ricewinecompositionpredictionbyvisible/NIRspectroscopyClassificationofintactandcrackedeggs
QuantificationofpearfirmnessusingNIRspectroscopy
Classrecognitionofriceblastwithmultispectralimagingtosupervisevariablespray
Quantitativeassessmentofamyloseandproteincontentinriceaftergammairradiationusinginfraredspectroscopyandchemometrics
Estimationofhydraulicparametersdescribingthesoilwaterretentionandhydraulicconductivity
200420042005200520062006200620062006200720072007200820082008200820082008200820082008200820092009200920092009
Brudzewskietal.Tianetal.
PardoandSberveglieriPiernaetal.Chenetal.Karimietal.Onaranetal.Piernaetal.WangandPaliwalJiangetal.Oommenetal.Zhangetal.Fuetal.Khotetal.Kovacsetal.Lamorskietal.Lietal.
PengandWangSunetal.
TrebarandSteeleWuetal.Yuetal.Dengetal.Fuetal.QiandMaShaoetal.Twarakavietal.
SVMneuralnetworkclassificationSVMclassification
SVMwithRBFkernelofRBFSVMclassificationSVMclassificationSVMclassificationSVMclassificationSVMclassification
Least-squaresSVMclassificationGaussiankernelbasedSVMclassification
SVMmodelingandpredictionMulti-classSVMwithkernelofRBFneuralnetwork
Least-squaresSVMmodelingandprediction
SVMclassification
SVMmodelingandpredictionSVMmodelingandpredictionLeast-squaresSVMclassificationLeast-squaresSVMmodelingandprediction
SVMmodelingandpredictionSVMclassification
Least-squaresSVMclassificationLeast-squaresSVMmodelingandprediction
SVMclassification
Least-squaresSVMmodelingandprediction
SVMclassification
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SVMmodelingandprediction
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whichmostlyimprovedcomparedwiththoseobtainedusingtheANN-basedmethod.
Inthestudiesofcropsforprecisionagriculture,Karimietal.(2006)evaluatedSVMasatoolforclassifyingairbornehyperspec-tralimagestakenoveracornfield.Theclassificationwasperformedwithrespecttonitrogenapplicationratesandweedmanagementpractices,andtheclassificationaccuracywascomparedwiththoseobtainedbyanANNmodelonthesamedata.TheSVMmethodresultedinverylowmisclassificationratesascomparedtotheANNapproachforallcases.DetectionofstressesinearlycropgrowthstageusingtheSVMmethodcouldaidineffectiveearlyapplicationofsite-specificremediestotimelyin-seasoninterven-tions.Tianetal.(2004)usedtheSVMandchromaticitymomentforrecognitionofplantdiseasesbasedonthefeaturesofcolortextureimageofplantdisease.TheexperimentalresultsprovedthattheSVMmethodhadexcellentclassificationandgeneralizationabilityinsolvinglearningproblemwithsmalltrainingsetofsample,andcouldfitforclassificationofplantdisease.
TrebarandSteele(2008)employedaSVMforclassificationofforestdatacovertypes.Inthisstudy,alarge,imbalanceddatasetindifferentforestcovertypeclasseswastransformedintoanumberofnewdatasetsandaSVMwasusedtoconductabinaryclassificationofbalancedandimbalanceddatasetswithvarioussizes.TheuseofdistributedSVMarchitecturesbasicallyreducedthecomplexityofthequadraticoptimizationproblemofverylargedatasets.TheexperimentalresultsofdistributedSVMarchitecturesshowedtheimprovementoftheaccuracyforlargerdatasetsincomparisontoasingleSVMclassifierandtheirabilitytoimprovethecorrectclassificationoftheminorityclass.
6.Comparisonandlimitationsofsoftcomputingtechniques
Therearelimitsonsoftcomputingweneedtobeawareofintheoreticalstudyandpracticalapplication.Tikketal.(2003)stud-iedtheapproximationbehaviorofsoftcomputingtechniques.Inthestudy,theauthorsconductedasurveyoftheresultsofuni-versalapproximationtheoremsachievedthusfarinvarioussoftcomputingareas.Thesetechniquescentermainlyinfuzzycontrolandneuralnetworks.Theauthorspointoutthatthesetechniqueshavecommonapproximationbehaviorinthesensethatanarbi-traryfunctionfromacertainsetoffunctions(usuallythesetofcontinuousfunction)canbeapproximatedwitharbitraryaccu-racyonacompactdomain.Thismeansthatfuzzysystemsandneuralnetworkshavetheabilitytoapproximateanyfunctiontoanarbitrarydegreeofaccuracy.However,fortheapproximation,unboundednumbersof“buildingblocks”(i.e.fuzzysetsorhiddenneurons)areneededtoachievetheprescribedaccuracy.Ifthenum-berofbuildingblocksisrestricted,itisprovedforsomefuzzyandneuralsystemsthattheuniversalapproximationpropertyislost.Therefore,itisreasonabletomakeatrade-offbetweenaccuracyandthenumberofthebuildingblocksindeterminingfunctionalrelationships.Atypicalpracticalapplicationofthisrecommenda-tionistodeterminethenumberofhiddenneuronsincrementallyinANNtrainingforacceptablefunctionapproximationandbettergeneralization.
Comparedtoclassicallogic,FLisnotalwaysaccuratebecausetheresultsareoftenperceivedasanestimate.Also,fuzzysys-temstypicallyrequirethedifficultandtime-consumingprocessofknowledgeacquisitionalthoughtheyprovidetheunderstandableformofknowledgerepresentation.
ANNsarepowerfulcomputingtechniques,whicharedesignedtomimichumanlearningprocessesbyestablishinglinkagesbetweenprocessinputandoutputdata.Thesetechniqueshavebeenwidelyappliedwithadvanceddevelopmentwiththeirunique
advantages,suchasnounderlyingassumptionaboutthedistri-butionofdata,arbitrarydecisionboundarycapabilities,universalapproximationcapabilities,easyadaptationtodifferenttypesandstructuresofdata,abilitytofuzzyoutputvaluestoenhanceclassi-fication,andgoodgeneralizationcapabilities.However,ANNshavesomedisadvantagesincommon,whichneedtobeconsideredinpracticalapplication:
•Blackbox
ANNsareblackboxinnature.Therefore,iftheproblemistofindtheoutputresponsetotheinputinsystemidentification,ANNscanbeagoodfit.However,iftheproblemistospecificallyiden-tifycausal-effectiverelationshipbetweeninputandoutput,ANNshaveonlylimitedabilitytodoitcomparedwithconventionalstatisticalmethods.•Longcomputingtime
ANNtrainingneedstoiterativelydeterminenetworkstruc-tureandupdateconnectionweights.Also,datausedfortrainingmaycontaincertaindegreeofnoises.Therefore,ANNtrainingisatime-consumingprocess.Withatypicalpersonalcomputerorworkstation,theBPalgorithmwilltakealotofmemoryandmaytakeminutes,hours,daysandevenlongerbeforethenetworkconvergestotheoptimalpointwithminimummeansquareerror.Conventionalstatisticalregressionwiththesamesetofdata,onthecontrary,maygenerateresultsinsecondsusingthesamecomputer.•Localminima
Duetoadditionofhiddennodesandlayer(s)andthenonlinear-ityoftheactivationfunctionofeachhiddennodesand/oroutputnodesinnetworkstructure,ANNtraininghasthepossibilitytoproduceforcomplexerrorsurfaceswhichcontainmanyminimasuchasuseofBPalgorithmfortrainingMLPs.Sincesomemin-imaaredeeperthanothers,itispossiblethatthealgorithmwillnotfindaglobalminimum.Instead,thenetworkmayfallintolocalminima,whichrepresentsuboptimalsolutionsinsteadofoptimal.•Overfitting
Withtoomuchtrainingtime,toomanyhiddennodes,ortoolargetrainingdataset,thenetworkwilloverfitthedataandhaveapoorgeneralization,i.e.highaccuracyfortrainingdatasetbutpoorinterpolationoftestingdata.ThisisanimportantissuebeinginvestigatedinANNresearchandapplications(Huang,2009).AlthoughANNshavestrongcapabilitiesoflearningandadapta-tionwitha“blackbox”naturethatdealswithinputsandoutputs,theyrepresentknowledgeimplicitlyandmayproduceresultsthataredifficulttointerpret.ANNsalsomayrequirelongtrainingtimesonnoisydata.Therefore,ANNsmaynotbeneededwhentraditionalmethodsareappropriate.
GAsworkontheirowninternalrulesandaregoodforcomplexorlooselydefinedproblemsusingtheirinductivenaturewithouttheneedtoknowanyrulesoftheproblem.However,withuseofthisinductiveabilityalone,thealgorithmsdonotnecessarilyevolvetotheoptimalsolution.GAsalwayshaveariskfindingasuboptimalsolution.BIusespriorprobabilities.However,priorprobabilitiesareintrinsicallysubjective,whichcanbedifferentfrompersonbyperson.ThismaybethefundamentallimitofBI.
Usually,learningbyDTsisfast,andtheresultiseasilyinter-pretedbyhumanspecialists.However,thelearningcouldproduceoverfitting,theoutputattributeofDTsneedtobecategorical,andeachdecisionislimitedtooneoutputattribute.Theinduc-tionprocessusuallyselectsonlyasmallnumberoftheavailableattributessothatinformationthatisdistributedonalargenumberofattributes(witheachattributecarryingonlylimitedinformationabouttheclass)cannotbehandledadequately,resultinginsubopti-malpredictionaccuracy.Insuchsituations,Bayesianclassifiersand
122Y.Huangetal./ComputersandElectronicsinAgriculture71(2010)107–127
ANNsareoftenusedinstead.SVMshavegainedpopularityinmanytraditionallyANNdominatedfields.UseoftheSVMalwaysfoundtheminimumglobally,whicheliminatesthelocalminimumissuehappenedinANNtraining.However,SVMswereoriginallydevel-opedtosolvebinaryclassificationproblems.Howtoeffectivelyextenditformulti-classclassificationisstillanongoingresearchissue.Typically,amultipleclassclassifiercanbeconstructedbycombiningseveralbinaryclassifiers.Further,allclassescanbeconsideredatonce.HsuandLin(2002)gavedecompositionimple-mentationsfortwosuch“all-together”methods.Theycomparedtheperformancewiththreemethodsbasedonbinaryclassifica-tions:one-against-all,one-against-one,andDirectedAcyclicGraphSVM(DAGSVM).Theexperimentsindicatedthattheone-against-oneandDAGmethodsaremoresuitableforpracticalusethantheothermethods.7.Thefuture
Asdescribedabove,eachsoftcomputingtechniquehasitsownlimitations.Thefusionoftwoorthreeofthesetechniqueswillcon-tinuetobeoneofthemajortrendsinsoftcomputingengineeringapplications.Fuzzyandneuro-fuzzysystemsrepresentknowledgeinanexplicitform,suchasfuzzyrules,ratherthaninanimplicitformasANNsalone.Accordingly,FLandANNsaremergedtoinherittheadvantagesofbothparadigmsandtoavoidtheirdrawbacks.
Recently,withthedevelopmentofelectronicsandinformationtechnologies,3S(remotesensing(RS),globalpositioningsystem(GPS),andgeographicinformationsystem(GIS))technologiesandvariableratetechnology(VRT)havestartedtobecomeavailabletoagriculturalproductionforcropseeding,irrigation,andchem-icalapplication.Foreffectiveapplicationsofthetechnologies,asystemintegrationisneeded.Forthesystemintegration,FLisacriticaltooltoestablish‘If–Then’rulestorepresentextensivehumanknowledgetobuildupaknowledge-basedsystemtocon-nectindependentcomponentstogether.Inthesystemaknowledgebaseobtainstheinformationfromvarioussourcessuchassci-entists,engineers,andfarmersandprovidesadvicesuitedtoageographiclocationbasedonlocalweather,soilandwaterdatafromGPS,GISandtraditionalknowledgearchives.Theweatherdataarecollectedfromthedifferentsensorsonadailybasisforsolarradiation,airtemperature,rainfall,andwindrun.Theinfer-enceengineanalyzesuserqueryandsendsinformationrequeststotheknowledgebaseandmatchesthemwiththestoredknowledgerulesthroughfuzzy‘If–Then’rulesoralgorithmsspecifictothepar-ticulardomainordiscipline.Thenthecontrolsystemoutputsthedecisionoftheinferenceenginetothevariablerateequipmentforcropseedingandchemicalapplication.Acomprehensivemodelbaseincludescropgrowthmodel,healthmodel,perhapsothermodelsthatdescribestheconditionofthecropsothatinformationwillbeprovidedfordecisionsupporttoresultinmoreprecisetim-ingofseeding,moreaccurateuseofseed,fertilizersand,irrigatedwaterinordertoenhancecropproductionandenvironmentalprotectionaswell.Amethodbasecontainslinearandnonlinearmethodsofpatternrecognition,statistics,andsoftcomputingsuchasFL,ANNsandGAs.Inthemodelingprocess,oneormoremeth-odscanbeactivatedtoassembleandgeneratedesignatedmodelstructureandparameters.
ANNshavebeenusedasapowerfultoolinsolvingproblemsinscientificresearchandengineeringapplications.ANNshavetheirownlimitationstorestrictthemasasubstituteoftraditionalmeth-odssuchasstatisticalregression,patternrecognition,andtimeseriesanalysis.Inthenextdecadeorsowithadvanceddevelopmentofcomputerpower,ANNswillcontinuetodevelopnewapplica-tionsinvariousfieldsinagriculturalandbiologicalengineering.Asapowerfulalternativetoconventionalmethods,ANNswillbestud-iedmoretodevelopapproachestoovercomingproblemsofANNsingeneralorinaspecificresearcharea.Infoodscienceandengineer-ing,soilandwaterrelationshipsforcropmanagement,anddecisionsupportforprecisionagriculture,moreapplicationsofANNsmaybeexpected.ANNswillbecontinuouslyappliedstandaloneorfusionwithothersoftcomputingtechniques.Areasofstudymayactivelyinvolvefoodqualityandsafety,soilandwaterresourcesmanage-ment,croppestmanagement,andprecisionagriculture.
ForeffectiveresearchanddevelopmentitmaybepossibletogenerateguidelinesforpredeterminingoptimalANNstructuresandtrainingalgorithms.Forprocessstatisticalmodeling,additionalresearchtopicsmaybetoestablishgenericprocedurestoincludesignificantvariablestoandexcludenon-significantonesfromANNmodelsandtoaddconfidencelimitsontheoutputpredictionsandparameterestimations.ThesedevelopmentswillpermitANNstoalsoutilizethetechniquesofconventionalstatistics.
SVMsappearedasanewtechniquewhichhasadvancedsoftcomputingdevelopment.Inpracticalapplications,SVMsoftenpro-ducedhighclassificationaccuraciesandverygoodgeneralizationcapabilitiescomparedwithANNs.Also,intheprocessofmodel-ingSVMsrequirelesseffortinsettingupcontrolparametersforarchitecturedesign.SVMmodelsareclosetoclassicalMLPneuralnetworks.Usingakernelfunction,SVMsareanalternativetrain-ingmethodforpolynomial,RBFandMLPclassifiersinwhichtheweightsofthenetworkarefoundbysolvingaquadraticprogram-mingproblemwithlinearconstraints,ratherthanbysolvinganon-convex,unconstrainedminimizationproblemasinstandardneuralnetworktraining.WiththeadvantagesofSVMsoverANNsandthegrowinginterestsofSVMs,itcanbeexpectedthatinthenextdecadeSVMswillbemoreactivelyusedinagriculturalandbiologicalengineering.
Nomatterwhichsoftcomputingmethodisused,adaptivelearn-ingcanbeapowerfultoolwhenalsoimplementedtoappropriatelyexploitthepotentialsynergybetweenmethods,somethatcanincludeinputfromsensors.Anexampleofhowthiscanworkinvolvesmodel-basedirrigationschedulingwithassistancefromsoilwatersensors.Thomson(1998)explainedamethodbywhichgranularmatrixsoilwatersensorswereusedtoprovide“feedback”orcorrectiontotwoinputparametersofthewaterbalancecom-ponentofthePnutgro1.02growthmodel(Booteetal.,19).Soilwatersensorsinferredrelativewateruptakeintherootzoneandcorrectedtherootgrowthfunctioninfluencingthedepthofwaterregulation.Thegoalwastoimprovemodelpredictionssothatthemodelcouldrunstand-aloneaftersensorsprovidedcorrectiondataduringseveralsoildryingcycles.Experimentsindicatedtemporalconvergenceofmodel-basedrepresentationsofsoilwaterpoten-tialonsensor-basedrepresentationsastwoparameters(soil–waterparameterDrainedUpperLimitorDUL)androotweightingfactorswereadjusted.
Inthesoilandwatercontextforcropmanagementanddecisionsupportforprecisionagriculturemoreapplicationsofsoftcom-putingtechniques,especiallySVMsstandaloneorfusedwithothersoftcomputingtechniquesandsensor-derivedinformation,maybeexpected.Areasofapplicationmightinvolveclassificationforagri-culturalsoilspatialdistribution,waterresourceoptimizationforirrigationplanning,detectionandclassificationofcropstressandpests(weeds,insectsanddiseases)detection,analysisofremotesensingimagery,studyofcropandyield,andfieldprescriptionsforvariableratechemicalapplication.
Anothertrendinsoftcomputingapplicationsislikelytobethefusionofsoftcomputingandhardcomputing.Althoughnosuccess-fulapplicationsofhardandsoftcomputingfusioninagriculturalandbiologicalengineeringcouldbefoundthusfar,thetechniqueshowsgreatpotentialforfutureresearchoverthenextdecade.Thefusionofsoftcomputingandhardcomputingshouldbeabletopro-videinnovativesolutionstotheproblemswithhigh-performance,cost-effective,andreliablecomputingsystems.Manypublications
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areusefultohelpdevelopsuchcomputingsystems.Ovaska(2005)editedabookthatcombinestheexperienceofmanyinternation-allyrecognizedexpertsinthesoft-andhard-computingresearchworldstopresentpracticingengineerswiththebroadestpossiblearrayofmethodologiesfordevelopinginnovativeandcompetitivesolutionstoreal-worldproblems.Eachofthechaptersillustratesthewide-rangingapplicabilityofthefusionconceptinsuchcriticalareasas•computersecurityanddatamining;
•electricalpowersystemsandlarge-scaleplants;•motordrivesandtoolwearmonitoring;
•userinterfacesandtheWorldWideWeb;and•
aerospaceandrobustcontrol.
Ovaskaetal.(2006)clarifiedthepresentvaguenessrelatedtothefusionofsoftcomputingandhardcomputing.Differentfusionschemeswereclassifiedas12corecategoriesandsixsupplemen-tarycategories,andthecharacteristicfeaturesofsoftcomputingandhardcomputingconstituentsinpracticalfusionimplementa-tionswerediscussedaswell.SickandOvaska(2007)introducedamulti-dimensionalcategorizationschemeforfusiontechniquesandapplieditbyanalyzingseveralfusiontechniqueswherethesoftcomputingpartwasrealizedbyaneuralnetwork.Thecategoriza-tionschemefacilitatedthediscussionofadvantagesordrawbacksofcertainfusionapproaches,thussupportingthedevelopmentofnovelfusiontechniquesandapplications.References
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