外文翻译原文-无线传感器网络水质监测：赞比亚实例

WirelessSensorNetworksforWaterQualityMonitoring:ACaseofZambiaNchimunyaChaamweDepartmentofElectronicsandInformationEngineeringHuazhongUniversityofScienceandTechnologyWuhan,CAbstractWaterqualitymonitoringisaveryimportantundertakingthatwouldensuresafeandcleanwaterbeingdeliveredtotheendusers.Waterqualitymonitoringisessentialincontrollingphysical,chemicalandbiologicalcharacteristicsofwater.Toensureacompleteandanallinclusivemonitoringoftheundergroundwaterandsurfacewater,datasamplingneedtobecarriedoutatmanydifferentlocationswithinandwithoutthestudyphenomenon.ThecurrentwaterqualitymonitoringmethodsinZambiaaremostlysparseandmanual.ThispaperproposestheuseofWirelessSensorNetworkstomonitorwaterqualityusingcheap,effectiveandefficientsensorsthathavetheabilitytosense,processandtransmitthesenseddata.Keywords-Zambia;Water;Waterqualitymonitoring;WirelessSensorNetworks(WSNs);SensorsI.INTRODUCTIONWaterqualitymonitoringisthequantifiablemeasurementofwaterqualityvariablessuchassuspendedsediments,temperature,nutrientsandpathogensinthewaterovertimeandwaterqualityontheotherhandreflectsthecompositionandcharacteristicsofwaterasaffectedbynaturalcausesandmansactivities,expressedinmeasurabletermsandrelatedtointendeduseofthewaterlikedrinking1.Therearethreeavailableprimarymethodsofwaterqualitymonitoringandtheyincludediscrete,mechanicalandautomated.Discretemonitoringisthecommonandtraditionalmanualmethodwhichinvolvesthetakingofasampleofwatertosendtoalaboratoryforanalysis.Mechanicalwaterqualitymonitoringisthemethodwhereacontainercontainingsamplebottlesisleftatthewaterbodythatmechanicallyobtainssamplesofwater,whicharelatersenttoalaboratoryforanalysis.Automatedwaterqualitymonitoring(AWQM)isthemethodofplacingwaterqualitysensorsintothewaterbody,whichiscontinuouslymeasuredbythesensorsandtheinformationisstoredinmemory.Theultimateandprimaryobjectiveofwaterqualitymonitoringistoensurethatsafeandcleanwaterisdeliveredtotheconsumer.Cleanandsafewaterismorepreciousthangoldoroilbecausewaterislife.AccordingtodatafromthestatisticsofficeofZambia2theproportionofhouseholdsinZambiawithaccesstosafewaterwas59percentby2006.This59percentisnotassuredofsafeandcleanwaterallthetimeduetothepoormonitoringmethodscurrentlyavailableinthecountry.Forinstanceaccordingto3atleast1000peoplevisitedtheclinicsandhospitalscomplainingofstomachpains,vomitingandseverediarrheaofwhich13wereadmittedafterdrinkingwaterallegedtohavebeencontaminatedbyanearbymine.ThiswasafteracidiceffluentsfromMopaniCopperMinesaccidentallyenteredthewatersystemofaprivatewaterutilitycompany.ThisincidencehappenedinnorthernZambiainJanuary2008.Thistragedycouldhavebeenpreventedwithaneffectivewaterqualitymonitoringprogram.TheEnvironmentalCouncilofZambia(ECZ),thebodyinchargeofenvironmentalpolicyissuesinZambiawarnedthatthecountrywasexpectedtoexperienceincreasingair,waterpollutionduetomoreminingactivities4.ThemajordiseaseoutbreaksinZambiaaremainlyattributedtothewaterbornediseases.Inordertocurbtheseoutbreaks,therearecertaininterventionsthatcanbeemployedandtheyincludepromotionofsafedrinkingwatersupplyforthecommunitiesandwaterQualitymonitoringwhichisatthecentreofactivities5.Recentadvancesinwirelesscommunicationshavemotivatedthedevelopmentanduseofextremelysmall,low-costsensorsthatpossesssensing,signalprocessingandwirelesscommunicationcapabilities.Awirelessnetworkconsistingofalargenumberofsmallsensorswithlowpowertransceiverscanbeaneffectivetoolforgatheringdatainavarietyofenvironmentsincludingwaterqualitymonitoring.Thedatacollectedbyeachsensoriscommunicatedthroughthenetworktoasingleprocessingcentrecalledthesinkthatusesallreporteddatatodeterminecharacteristicsoftheenvironmentordetectanevent6,7.TheuseofWSNstoimplementmonitoringsystemstakesadvantageoftherapidandflexibledeploymentofsensornodes.Thedeploymentissoflexiblethatthesensornodescanbeeitherthrowninthefieldasamassorplacedonebyoneinthesensorfield.Theycanbedeployedbydroppingfromaplaneorplacedonebyonebyeitherahumanorarobot.Waterqualitymonitoringentailsplacingthesensornodesintothewaterthatiseitherstaticormoving.UnderwaterSensorNetworks(UWSNs)shareanumberofcommonpropertieswithgroundsensornetworks,suchasthelargenumberofnodesandlimitedenergyandsoon.UWSNsthougharedifferentinsomeaspectsfromtheordinarygroundsensortechnology.First,radiocommunicationswhicharethecommonmodeofcommunicationinordinarygroundsensor978-1-4244-4713-8/10/$25.002010IEEEnodesdonotworkwellunderthewater.Theymustbereplacedbyacousticcommunications.Second,whilemostgroundsensorsarestatic,underwatersensornodesmaymovewithwatercurrentsandotherunderwateractivities8.ThispaperlooksatwhyWSNsarethebestalternativetothecurrentmethodsofmonitoringwaterqualityinZambiabyconsideringcertainpropertiesofWSNsanditalsoconsiderstheresearchworkgoingontoimprovetheseproperties.Thepaperisdividedinsections,insectionII,thepaperdiscussesthecurrentmethods,insectionsIII,thepaperdiscussessimilarwork,insectionIVitlooksatthepropertiesofWSNsthatwouldgivethemanedgeovercurrentmethodsandinsectionVthepaperconcludes.II.WATERQUALITYMONITORINGMETHODSINZAMBIAThewaterqualitymonitoringmethodsusedinZambiacanbecategorisedintofour;operationalmonitoring,laboratorymethods,biologicalindicatorsandmonitoringwells.Thesemethodsfallunderthediscreteandmechanicalmethodsofwaterqualitymonitoring.A.OperationalMonitoringOperationalmonitoringisawaterqualitymonitoringmethodthatinvolveswellsetandplannedobservationsormeasurementstomakesurethatthecriticalcomponentsofasafewatersupplyareoperatingproperly.Forinstancemakingsurethatpipesthatdeliverwatertohouseholdsisnotbroken,ensuressafewater.Operationalmonitoringisbasedonsimpleandrapidobservationsortests,suchasturbidityorstructuralintegrity,ratherthancomplexchemicalanalyses9.B.LaboratoryMethodsThisisthemostlywidelyusedmethodforsurfacewaterqualitymonitoringinZambia.Itisusedbyboththewatercompaniesinchargeofdeliveringwatertothecommunitiesandalsobyresearchers.Samplesofwaterarecollectedusingcontainersandsenttothelabstobeanalysedfortemperature,conductivity,alkalinity,dissolvedoxygen(DO),biochemicaloxygendemand(BOD),totalsuspendedsolids(TSS),pH,chlorides,sulphates,nitratesandmetalsusingstandardmethods10.Accordingtotheauthorsof11intheirstudyoftheimpactofeffluentscontainingzincandnickelmetalsonstreamandriverwaterbodiesobtainedthelevelsofpollutantsbycollectingwaterandsedimentsamplesfromselectedsites.Thecollectedsampleswereanalysedusingatomicabsorptionspectrophotometermethod.Thismethodworksinsuchawaythatfirstly,thewavelengthatwhichthemetalcouldbedetectedisestablished.Thenthesolutionisaspiratedintotheflamewhereitisvaporized.Atomsofthemetalareexcitedtohigherlevels.Theenergyabsorbedbythemetalsismeasuredandtheconcentrationisthenreadfromthecalibrationcurveobtainedbyanalysingstandardsolutions.C.BiologicalIndicatorsFishandotherlivingorganismsareusedasbiologicalindicatorsofwaterqualityespeciallyinstreamsandriverswhicharesourcesofwaterforthemajoritypoorZambians.Theauthorsof12intheirresearchobservedthatpollutanteffluentloadsfrommining,industrialandagriculturalactivitiesdischargedintotheKafueRiverBasinovertheyearshadledtodeteriorationinqualityoftheriverwaterandtheenvironmenttoanextentthattherewasadecreaseinbothfishcatchesandsizesincertainareasoftheKafueRiver.D.MonitoringWellsAmonitoringwellisdefinedasawelldesignedandinstalledapparatususedtoobtainrepresentativegroundwaterqualitysamplesandhydrogeologicinformationfromanaquifer.Thegeneralpurposeofmonitoringwellsistoprovidecontrolledaccessforsamplinggroundwaternearwastestorageortreatmentfacilityinordertodetectseepageandmonitortheeffectsofcontaminantsinseepageongroundwaterquality13.TheuseofmonitoringwellsisthemostlyusedmethodtomonitorundergroundwaterqualityinZambia.Thismethodismostlyappliedinminingareaswhicharethemajorpollutantsofundergroundwater.Whenusingmonitoringwellsthelevelsofconcentrationsofcontaminantsarefrequentlymonitoredtodetermineiftheyareincreasing,decreasing,orremainingthesame.Monitoringusingmonitoringwellsisalsoperformedatandinthevicinityofwatersupplysourcestodeterminethequalityandtrendsofindicatorsofwaterquality.Figure1.ExampleofFishindicatingthatthewateriscontaminatedFigure2.ExampleofhowamonitoringwelllookslikeIII.SIMILARWORKWSNshavebeenproposedandarebeingproposedforuseinanumberofapplications.TheycanbeusedinthemilitarywhereWSNscanbepartofthemilitarycommand,control,andsurveillance,controlandtrackingenemies14.WSNscanalsobeusedinindustry,inhospitalsandsoon.AnumberofresearcheshavebeendoneontheuseofWSNsforwaterqualitymonitoring,in15aprojectwhichcarriedoutcalledunderwatersensornetworksformonitoringwaterqualitywasreportedandtheultimategoaloftheprojectwastoimplementahierarchicalwaterqualitysensornetworkstructurethatwouldreducethecostofwaterqualitysensornetworksandincreasethenumberofsensornodedeployedinagivenarea.Toachievetheabovethewholenetworkwasdividedintoseveralclustersbasedonsignalstrength.Likeordinaryclusteringeachclusterwouldhaveaheadnodewhichreceivescollecteddatafromothernodesinthecluster.Theclusterheadnodeswouldthensendthegathereddatatothesink.In16aprojectwasreportedthatusedWSNstomonitorgroundwaterquality.TheprojectentailedunderstandingtheprevalenceofarsenicinBangladeshgroundwater.Anotherprojectwasreportedin16thatusedWSNstomonitorsuppressnitratepropagationthroughsoilsandgroundwaterinCalifornia.suppresssuppressIn17areportwasgivenaboutthedesignandimplementationofasensornetworkthatisdesignedtospecificallycollecttemperaturedataintheBalticSeainacost-efficientmanner.In18aWSNdescribedasanaqueoussensornetwork(ASN)thatisabletoautonomously,continuously,in-situandinreal-timemonitorstreams,lakes,oceanandstreamswasproposed.TheauthorsindicatedthattheASNwillgobeyondensuringsafedrinkingwaterqualitybutcouldbeatoolforbiologistsseekingtomonitorthetemperature,flowcharacteristics,andchemicalenvironmentofaquaticcommunities.In19aWSNtermedthe“SmartCoast”wasproposed.ThisisaWirelessSensorNetworkforwaterqualitymonitoring.Thesystemcanbeusedtoinvestigateparameterssuchastemperature,phosphate,dissolvedoxygen,conductivity,pH,turbidityandwaterlevelanditallowsdatatobeviewedinrealtimeviatheinternetbyremoteusers.Thesystemcanalsobeusedtomapthespatialandtemporaldistributionofpollutantsandmayassistintheidentificationofpossiblepollutionsources.IV.PROPERTIESOFWSNSThispaperisproposingtheuseofinexpensivesensornodesinthemonitoringofbothgroundwaterandsurfacewaterasproposedby11.Inthissection,thepaperdiscussessomeofthepropertiesofWSNsnetworksthatmakethemtheidealalternativetothecurrentwaterqualitymonitoringmethodsinZambia.Thepaperalsolooksatsomeoftheresearchworkthathasbeendonetoimprovetheseproperties.A.CostandSizeThecostofasinglesensornodedependsontheapplicationandvariesfromhundredsofUSDollars(fornetworksofveryfew,butpowerfulnodes)toafewcents(forlarge-scalenetworksmadeupofverysimplenodes)20.ThecostofsensornodesmakesitaffordableevenforthepoorestofthepoorcountriestoimplementWSNsforthemonitoringofwaterquality.Similarly,thesizeofsensornodesdependsontheneedsoftheapplication;theyvaryfromthesizeofashoeboxtoamicroscopicallysmallparticle21.Toobtainafullscalemonitoringofthesurfaceandundergroundwater,sampledataneedbecollectedatmanydifferentplacesandthisrequiresalargenumberofsensingdevices.Awirelesssensornetworkthatusescheapandsmallsensorsmeetsthisrequirement.B.FaultToleranceFaulttoleranceisconsideredasoneofthemostcriticalissuesinWSNssincesensornodesarevulnerableandpronetofailureduetoenergydepletion,hardwarefailure,communicationlinkerrors,maliciousattack,andsoon.Accordingto22faulttoleranceistheabilityforasystemtoperformclosetooptimalinthepresenceoffaults.Accordingto23faulttoleranceinWSNsmayexistatfourlevels,hardwarelayer,softwarelayer,networkcommunicationlayer,andapplicationlayer.Thispropertyisvitalinasfaraswaterqualitymonitoringisconcernedbecauseofthesomanyactivitiesthathappeninriversandstreams,likefishingthatwoulddisturbthesensors.FaulttoleranceinWSNshasalsoreceivedalotofattentionfrommanyresearcherstomakethesystemalmostentirelyfaultless.Forinstance,in24astudyproposedtheplacementofwhatareknownasrelaynodes(RN)whicharemuchstrongerandcostlythatwouldcommunicatewithordinarysensornodesandotherRNsinordertoprolongthenetworklifetimeincaseofsomefailuresamongordinarynodes.C.LifeTimeWirelessSensorNetworklifetimeisdefinedasthetimeperiodinwhichthenetworkisabletoperformthesensingfunctionsandtransmitdatatothesink25.Thelifetimeofasensornetworkcanrangefromhourstoanumberofyearsdependingontheapplication21.AWSNwithalifetimeofanumberofyearswouldservewellforwaterqualitymonitoringwhichisalifelongactivity.Thelifetimeofthesensornetworklargelydependsontheenergycontainedintheindividualnodes.Thisisanotherareathathasreceivedalotofinterestfromresearchersandanumberofenergyefficiencyalgorithmshavebeenandbeingproposed26-32.Themostcommonapproachbymanyresearchersisthatofclusteringthesensornodesinordertoreducethenumberofnodesinvolvedinthetransmitionofdatawhichrequiresfarmoreenergythansensing.Theapproachworksinsuchawaythateachclusterwillhaveaclusterheadinchargeofreceivingdatafromtheothernodesintheclusterandthentransmittingthedatatootherclusterheads(hierarchical)ordirecttothesinkorbasestation(singlelevel).E.DeploymentSensornodesinthephysicalenvironmentmaybedeployedatrandomorplacedatchosensamplepoints.Deploymentofsensorsmaybeaone-timeactivityoracontinuousprocess,weremorenodesaredeployedatanytimeduringtheuseofthenetwork33.Assensornodesarereasonablycheapandsmallinsize,densernetworkscanbedeployedandthiscanallowthemonitoringofallpossibleplacesintheundergroundwaterandsurfacewater.Sensornodescanalsobedeployedinsideorveryclosetothestudyareamakingitpossibletosenseanypossiblechangesintheenvironmentalinthequickestpossibletime34.ThisrapidandflexibledeploymentofsensorsinWSNscanbetakenadvantageofinsomeareasinsurfacewaterwhichcanotherwisebedifficulttoaccessifusingtheothermethods.Nodedeploymenthasitsownchallengesandthesolutionshavebeenablytackledbyresearchers.Forinstancetheauthorsof35proposedtheusingofmobilenodestorelocateandmovetoareaswheresomenodesarenotfunctioningorwheresomenodesareabsent.D.CoverageCoverageinWSNsreflectsonhowwellanareaismonitoredbysensornodesoritisthemeasurementofthedegreeofcoveragebysensornodes36.Thecoveragecaneitherbesparseordense,indensecoveragethesensornodesaredeployedonalmosteveryareaofinterest.TherehasbeensomeresearchonimprovingthecoverageofWSNsevenbyusingsparselydeployedsensornodes.Theauthorsof37proposedwhattheycalledanoptimalpolynomialtimealgorithm.Thealgorithmusesgraphtheoreticandcomputationalgeometryconstructstosolvethebestandworstcasecoverageproblem.Theauthorsof38proposedwhattheyreferredtoasafullylocalizedalgorithm.Itworksinsuchawaythateachsensornodemakesadecisionaboutitspositionwithtwomessageexchangeswithitsneighborhood.Thefirstmessageexchangedisasimple“hello”message.Thismessagegatherspositionsofallneighboringnodesofaparticularnode.Then,eachnodecomputesitsownrelayset,itdoesthisbytakingthefurthestneighborasthefirstnode,andthenaddingneighborsfarthestfromwhatiscalledtheisobarycentreofalreadyselectedrelays,untiltheareacoveredbyneighborsisfullycovered.Thesecondmessagebroadcaststhisrelaysettoneighbors.Theauthorsof39alsoproposedwhattheycalledaCoverageConfigurationProtocol(CCP).Accordingtotheauthors,thisprotocolcandynamicallyconfigurethenetworktoprovidedifferentfeasibledegreesofcoveragerequestedbyapplications.TheauthorssaythisflexibilitygivestheWSNtheabilitytoself-configureitselfforawiderangeofapplicationsandenvironmentswithdiverseorchangingcoveragerequirements.E.ConnectivityAnetworkissaidtobeconnectedifthereisalwaysanetworkconnectionbetweentwonodes21.Lossofconnectivitybetweensensornodesinmultihoproutinginthepathbetweensourceanddestinationmayleadtothepartitionofthenetwork.Waterqualitymonitoringrequiresanetworkwithhighconnectivitytoensurecontinuousandreliableinformationpassingtothebasestation.Anumberofresearcheshavebeenandbeingcarriedouttosolvetheproblemofconnectivity.Theauthorsof40proposedtheuseofwhattheytermedcooperativetransmissiontoconnectpreviouslydisconnectedpartsofanetworkandthiswouldsolvetheseparationproblemofmulti-hopnetworkscausedbyfailureofsomenodeornodes.Accordingtothesameauthors,cooperativetransmissionworksinsuchawaythatagroupofnodescouldcombinetheiremissionpowertocomeupwithahigheremissionpower.Withthishigheremissionpower,thenodescanreachdestinationsthatareveryfarawaythusimprovingtheconnectivity.Theauthorsof41proposedanalgorithmthatwoulddynamicallyconfigurethenetworkinordertoachieveahighdegreeofconnectivityandcoverage.Theauthorsof42proposedwhattheycalledanAdaptiveSelf-ConfiguringsEnsorNetworksTopology(ASCENT).Accordingtotheauthors,ASCENTworksinsuchawaythateachnodeassessesitsconnectivityandadaptsitsparticipationinthemulti-hopnetworktopologybasedonthemeasuredoperatingregion.F.TopologyAccordingtotheauthorsof21networktopologyisanimportantpropertybecauseitaffectsnetworkcharacteristicssuchaslatency,robustness,andcapacity.Thecomplexityofdataroutingandprocessingalsodependsonthetopology.InWirelesssensornetworksnodescandirectlycommunicatewitheachotherwithoutanyinfrastructureorthesensornodescanbeusedasroutersthatwillforwardmessagesovermultiplehopsonbehalfofothernodes26.Inamulti-hop,anetworkmayformanarbitrarygraph,butoftenanoverlaynetworkwithasimplerstructureisconstructedsuchasatreeorasetofconnectedstars21.Deployingnodesforundergroundandsurfacewatermonitoringrequirescarefulhandlingoftopologymaintenanceandanumberofalgorithmstosolvethisproblemhavebeenproposed.Theauthorsof43proposedwhattheycalledaHighlyAdaptiveDistributedRoutingAlgorithm.Theauthorssaythealgorithmisdistributedinthatnodeswilljustmaintaininformationaboutadjacentnodes.Thisalgorithmassumesthatallroutesareloop-free,andprovidesmultipleroutesforanysource/destinationpairwhichrequiresaroute.Theauthorsalsosayifthereareanychangesinthetopologyofthenetwork,theprotocolquicklyreestablishesvalidroutes.Inaneventofanetworkpartitionduetofailurebyanodethisprotocoliscapableofdetectingthepartitionanderasesalldistortedrouteswithinagiventime.G.SelfHealingSelfhealingisoneofthemostimportantfeaturesofwirelesssensornetworks.Itistheabilityforthenetworktorepairitselfwhen