Analysisofwindprofilerdatainthecontextofbird

migrationSTSM-2015CostActionES1305-European

NetworkfortheRadarsurveillanceofAnimalMovement(ENRAM)

NadjaWeisshaupt

[ThisSTSMwasproposedtocomplement theanalysisofwindprofilerdata,which ispartof thePhD project of Nadja Weisshaupt at Aranzadi - Society of Sciences. The PhD was initiated inSeptember2013andwilllastthreeyears.ItisajointprojectofbiologistsfromAranzadi-Societyof Sciences and engineers from Euskalmet – Basque agency for meteorology/University of theBasque Country. It aims at characterizing the migration phenology of birds passing the Bay ofBiscay on their journey between Central/Northern Europe and the Iberian Peninsula and tocomplementinformationfromexistingringingdata.TheassessmentofthesignificanceoftheBay

Methodology

Pre-STSMdatacollectionThedataanalysedinthisSTSMwascollectedatthewindprofilersiteinPuntaGalea,SpaininMarch2015.RadardatawasobtainedfromthelocalL-bandwindprofiler.Simultaneousrecordingswerecollectedbyathermal-imagingcamera,whichwassetupverticallyonthesouthsideoftheradarandasclosetotheradaraspossible.Thesouthernsidewaschosenbecausebirdsinspringmigrationwereanticipatedtocrosstheradarbeaminaboutthisdirectionontheirjourneynorthwards,providedtheyflythroughthemainlobe.Thisshouldincreasetheprobabilityofrecordingthesamebirdsastheradar.

Thermal-imagingdatawasthenvideotapedforfourhoursfromsunsetattheradarsiteonoverall10nightsinMarch2015.Thepurposeofthesesimultaneousrecordingswastoestablishareferenceandpotentialsupportforinterpretingthequantitativeandtemporalpatternsintheradardataof2015.

Therecordingsyieldedavarietyofbirdcounts.Inanexploratorycampaigninspring2014countsbetween0-1100birdswererecorded.In2015,numberswerelower,rangingfrom1to502birds.FortheSTSM,basedonthesetwofieldseasons,birdcountsbetween0-100birdswereclassifiedas“weakmigration”,100-400birdsas“moderatemigration”,400-700birdsas“strongmigration”andabove700birdsas“verystrongmigration”.Thusin2015,thecameradatabaseincludedweaktostrongmigrationevents.ExamplesofsnapshotsareincludedintheAppendix.

Allbirdtargetspassingthescreenweretime-stampedandclassifiedastofirst,second,third,fourthhourofrecordingtofacilitateposteriorcomparisonofmigrationintensitywithradardata.Furthercommentsastoflocksize,other/unidentifiedtargetsetc.wereadded,ifapplicable.Inthepresenceofclouds,itwaspossibletoseethewinddirectionbasedoncloudmovement.

NadjaWeisshaupt’srolewastoprovidethecameradatabaseandherornithologicalbackgroundtocomplement/supporttheinterpretationoftheradardataanalysis,whichwasperformedasfollows.

STSM

TimeseriesTheanalysisandinterpretationofthetimeseriesdataandisacomplextaskbecauseitisbasedonrawdataandmanyscattererscouldbemixedtogether.

of Biscay as a geographical barrier formigrating landbirds is important from an ecological andevolutionary point of view and regarding the conservation of Basque coastal ecosystems asstopoversites.]

Forthisreasonitisveryimportanttoidentifytheleastcomplexsignals,thestrongestsignalsandindividualsignalsinthedata.Acertainleewayindatainterpretationhasbeentakenintoaccountintheresults.Onlysignalswhereuncertaintyabouttheinterpretationwasconsideredlowweretakenintoaccountinthestudy.

Thesignaldepictstheradialvelocityofthescatterersrelativetothebeamposition.Thismeanstheprojectionofthemovementofthescattererinthedirectionofthebeam.Whentheantennaispointingvertically,radialvelocityistheverticalmovementofthescatterer.Forthisreasontheverticalbeamischosentodiscardinformationrelatedtothehorizontalmovementandtoassociatethesignalswithverticalmovementofthebirds(weassumethattheselectedscatterersarebird).Thefirstassumptionisthattheonlyverticalmovementofthebirdisthewingbeat.Thereforethereturnechoesgiveusinformationofthewingbeatpatternsofthebirds.

ForthepresentSTSMweselectedtheverticalbeamofthelowmode.Theadvantageofthismodeisthatwithitsrangeof2kmitcoversapproximatelythesamerangeasthecamera,whichreachesupto3km.Insomecases,thehighmodeisusedasaverificationtool.

BirdtargetsItiswellknownthatbirdechoesarestrongerthanatmosphericsignals.Thereforethefollowingassumptionsweremade:

1. Thebirdcouldbedetectedinthesidelobesbeforecrossingthemainlobeoronlybythesidelobesifitdoesn’tpassoverthemainlobe.Thepathofthebirdmodifiesthesignal.

2. Thestrongechoofthebirdorotherechoesofequalorstrongerintensityhaveanimpactontherange-weightingfunction(RWF).Therange-weightingfunctiondetermineshowindividualscatterer’scontributionsareweightedasafunctionofrangeinaresolutionvolume.

3. Thereceivercouldbesaturatedbecauseofstrongechoesandwhileitisrecovering,theechoreturnsignalsaremodified(thereceivercannotworkunderspecifications,theamplificationofthereturnsignalcouldbeincorrect).

4. Thetimeseriesplotsarenormalizedplots.Thefeaturesofeachgatearerepresentedindependentlyandtheamplitudescannotbecomparedvisuallybetweengatestoevaluatethestrength/presenceorabsenceofanecho.

BiologicalinformationOneofthemostimportantpointsofthisSTSMisthattheinterpretationofthesignalsrequiresbiologicalknowledge.Thereforethermalimagingdatawascrucialandwasconsideredinthisstudytogetherwithknowledgeaboutbiologicalbehaviourofbirds.

Inputdata1. Windprofilerdataatthemomentlevelwasreviewedinordertoidentifythedaysofbird

migrationforMarch2015andcomparedwiththedatabaseofthecameracampaign.

2. Timeseriesanalysis.Itisimportanttobefamiliarwiththisdata,toknowthecharacteristicsofanatmosphericversusanon-atmosphericsignal.

3. Asitisdifficulttoanalysefrequenciesinthetimeseriesdata,spectrogramswerecreatedduringtheSTSMtobetterunderstandthefrequenciesoftheechoes.Thepatternsareeasiertoidentifyinthespectrogramsalthoughacombinationofbothtimeseriesandspectrogramsisbest.

4. Thevideorecordingswereusedtoverifysinglebirds,groupsofbirdsorothertargetsandtoconfirmclearairconditions,visibilityconditionsandincaseoflowclouds,winddirection/strength.

DataanalysisThefollowingstepsdescribetheapproachfordataanalysis.

1. Windprofilerdatawasanalysedatthemomentlevelofallbeamsandinbothmodes.Thentheverticalbeamofthelowmodewasselectedforthestudy.

2. Featuresofthemomentdatatakenintoaccountforanalysis:intensityofbirdcontaminationduringthesampleddays(numberofprofilesandgatesthatcouldberelatedtobirdcontamination),manual(visual)identificationofthelayersofbirdcontamination,timeaftersunsetwhendatastartedtoshowsignsofbirdcontamination.

3. Byusingtheinformationofthecamerathedayswereclassifiedinfourgroupsbasedonbirdcountsasdescribedpreviously:

a. Lowcontamination.

b. Moderatecontamination.

c. Highcontamination.

d. Veryhighcontamination

Thefeaturesassociatedwitheachbirddetectedbythecamerawerepreviouslydescribedinaseparateanalysis(notENRAM-related).

4. Theanalysisofthetimeseriesstartedwithadayofmoderatemigrationaccordingtothecamera.Theaimwastoidentifyapatternofasinglebirdinthetimeseries.

5. Combiningthetimeseriesdataandthespectrogramplotstoidentifythefrequenciesassociatedwithverticalmovementsinsinglescatterersandstrongestsignals.Thespectrogramshowsthefrequenciesineachgate.

6. InformationextractedfromtimeseriesandspectrogramswascollectedinWordandExcelsheets:time(tofindtime-stampedtargetsinthesimultaneouscamerarecordings),gatesinwhichthetargetswerelocated,anykindofcommentsonparticularrepetitivepatterns,screenshotsofspecial/extraordinarypatterns,doubtstobeclarifiedwithourhostVolkerLehmannetc.

7. Thestudyisrepeatedforeachintensitygroup.Thespectraldataisusedtoverifytheresultsofapreviousassessmentatspectrallevel.

Results

Atthemomentlevel.Themomentplotsdisplaythethreemomentsradialvelocity,spectralwidthandsignal-to-noiseratio(SNR)inacontourplot.TheX-axisrepresentsthetimeandtheY-axisrepresentstheheight.

Themainobservationsatthemomentlevelare:

1. Thereareslightdifferencesbetweenthebeamsatthemomentlevel.Thelowmodeshowsmoredetailsofthebirdpatternsinthecourseoftimeandacrossthegates.Thelowmodematchesthesamplingheightofthecamera.

2. Furtherworkisneededtoinvestigatedifferencesbetweenthebeams.

3. March2015,isamonthinwhichthereareclearconditionsfrom5to10,from16to18andattheendofthemonth.HighervaluesofSNRandspectralwidth,andastrongvariabilityofradialvelocityandspectralwidthareassociatedwithbirdcontamination.

4. Thebirdcontaminationislinkedtotheareaassociatedtobirdfeaturesinthecontourplotsatthemomentlevel.Thisareamightbecorrelatedtobirddensity.Themomentlevelshowstheefficiencyofthesignalprocessingtechniquetoidentifyatmosphericsignals,notbirdsignals.

BirdcharacteristicsLowcontamination-15March2015(startingatabout19:00)

Highcontamination-17March2015(startingatabout19:00)

Aftersunsetthereisstrongdiscontinuityinthethreemoments.

AtthetimeserieslevelThetimeseriesplotsshowthetimeseriesoftheI-Qsignalsforeachgate(Y-Axis)plottedagainsttime(X-Axis).

Lowcontamination:

Generallybirdechoeshaveanellipticalshape.Thestrongsignalandtheweightingfunctionappliedinthesignalprocessingcausethemultiplicationofthepatternsintoseveralgates.Intheaboveexample,threegatesarecontaminatedbyonebird.Itisidentifiedasonebirdbasedonthecodificationoftheellipse(i.e.thepatternshapingtheellipse).Thebirdislocatedinthe“strongest”gate,i.e.thegatewherethebirdsignalexhibitsthegreatestsignal-to-noiseratio(differencetosurroundingnoise).

Theellipseappearstocontaininformationonwingbeatpatterns(e.g.continuousorpause-flapping-pause-flappingetc.),however,thisaspectneedsfurtherinvestigation.

Moderatecontamination:

Thedensityoftheellipseshasincreasedacrossheightandtime.Theanalysisispotentiallymoredifficultbecausebirdscouldmutuallymaskeachotherinthesamegate.Neighbouringgatescannotbecomparedvisuallybecauseofnormalization(seeintroduction).

Highcontamination:

Withincreasingdensitytheriskformixedellipsescontainingseveralbirdsaugments,i.e.birdsignalscanbeconcatenatedtoformlongellipses.Ahighdegreeofexpertiseandfamiliaritywiththiskindofdataisrequired.Inmanycasesitisdifficulttoseparateordistinguishbetweenthedatafromthemainlobeandthesidelobesalthoughthedatafromthemainlobecontainsinformationonthemovementofthebird-ifitpassesperpendicularlytothebeam,thefrequencyiszero.

AstheanalysisofthefrequenciesisverycomplexbasedonthesinusoidalcurveintheI-Qdata,spectrogramswerecreatedforthesampleddates.Thecombinationofbothplottypesfacilitatestheanalysisandrevealsmanyfeaturesofthedataveryusefulnotonlyforornithologiststudiesbutalsoformeteorology.

Spectrogramsvs.timeseries-differentpatternsandsomeexplanations

Thedifferencesbetweenthetimeseriesplotsandspectrogramsareillustratedonthebasisof5March2015.

Belowatimeseriesplotof5Marchwiththeframeindicatingthesignals,whicharefurtherdetailedinthespectrograms.

Spectrograms

Thespectrogramisacontourplotrepresentingthesignalstrengthalongthefrequencies(Y-axis)againsttime(X-axis)foreachgate.

Example1

Startingatthebottom,abirdisidentifiedinthetimeseriesinthegates2-3-4,theellipseandthecodificationoftheellipseisidenticalsoitisassumedthatitisonesinglebird.Thespectrogramanalysisrevealstheverticalfrequenciesandtheheightinwhichthebirdisflying.Itispossibletodeterminetheflightaltitudeintimeseriesbutitiseasierbasedonthemaximumsignal-to-noisevalueofthespectrogram.

Gate2

Gate3

Gate3containsthestrongestsignalandthusdefinestheflightaltitudeofthebird.Thefrequenciesindicateanoscillatingzigzag.Theseoscillationsarebeingfurtherexploredatthis

moment,buttheyareprobablyassociatedwithwingbeatpatternswhenthebirdcrossesthebeam.

Example2.Sometimesbirdsdonotcrossthemainlobeandthusexhibitfrequenciesotherthan0(noperpendicularmovementrelativetoradar).Gate8

Example3

Inthefollowingspectrograms,thebirdisflyingatanaltitudeof0.86km,longerellipsesareobservedandthetargetneedsmoretimetocrossthebeamatthisheight.

Gate14

Thesearesomeofthemainfeaturesrelatedtothespectrogram.Thepowerfulinformationresultingfromcombiningtimeseriesandspectrogramhashelpedusunderstandthemovementsofthebirdswhentheycrossthebeams.Thecodificationsoftheellipsesarebeingstudiedinmoredetailatthemomentandmoreresearchisneededtocompletethework.

VerificationwiththespectralinformationIndayswithhighbirddensities,thespectraldatawasanalysedincombinationwiththetimeseries.Themainresultofthisstudywasthatifthesignalofabirdisveryclearinagate,thebirdisremovedbysignalprocessing.Theproblemliesintheadjacentgatescontainingafuzzyornoisycopyofthebirdsignalwhichisnotremoved.Therefore,itwasconcludedthatspectralinformationprovidesanerroneouspictureonmigrationparameters(e.g.flightaltitude).

Additionally,indaysofweakmigrationwithonlysinglebirds,thesignalprocessingworkedreliablyandcleanradardataeffectively.Thusonlythetimeseriescontainedaccurateinformationonbirds.

VerificationbycameraThecamerarecordingsprovideddataonoverallmigrationintensityandtargetidentification(occurrenceofsinglemigrantsvs.groups,otherobjects)whichwillbefurtheranalysedincombinationwithtimeseriesandspectrograms.However,sofaritisnotquitecleartowhatextentandhowreliablytheameradataonsmallsingletargets(passerines)actuallycoincideswithsingletargetsobservedintimeseries,i.e.ifonebirdpassingoverthecameraisexactlythesamebirdwhichwillbeseenanddepictedinthetimeseriesasthesamplingvolumeisdifferent.Currently,thisissueseemsoflessimportanceincaseoflargerobjects(airplanes)orlargerflocksofbirds.Furtheranalysiswillprobablyshedmorelightonthisaspect.

Othertargetsvs.birdsOn15March,birdsweredetectedduringprecipitationevents.Birdsignalsarecompletelydifferentfromprecipitationsignals(seebelow).

Thelowerthreegatesshowonesinglebird(locatedinthesecondgateat0.19km)andtheuppergatesshowprecipitation(gates0.31-0.49km).

Conclusions&outlooks

TheSTSMenabledtheresearcherstoperformpioneerworkintheanalysisoftimeseriesdata.Itwaspossibletoevaluatethereliabilityandtheinformationcontentofthedifferentdatalevels

(momentsvs.spectravs.timeseries)andtoidentifycharacteristicsofdifferenttargets.Theresultsshownarepreliminaryandrepresentaselectionofthevarietyfoundinwindprofilerdata.Dataanalysisison-going.Futureworkwillfocusonamoredetailedanalysisoftargetidentification(e.g.birdsvs.otherobjects,classificationofbirds)andtoextractandanalysefurtherbirdmigrationparametersthatwerenotreliablyaccessiblebasedonmoments,spectraandconsensusdata.Theseparametersincludethedeterminationandrefinedanalysisofflightaltitudeandmigrationintensity(incombinationwiththermal-imagingdata)aswellastheevaluationofapotentialimpactofweatherconditionsonmigrationdynamics.Furtherparameterswillbeextractedifpossible.

TheresultswillbepublishedincollaborationwiththehostofthisSTSM.