T. Meissner, F. Wentz, J. Scott, K. Hilburn Remote Sensing ... · Remote Sensing Workshop November...

T.Meissner,F.Wentz,J.Scott,[email protected]

ESAOceanSalinityScienceandSalinityRemoteSensingWorkshopNovember26- 28,2014MetOffice,Exeter,UK

Outline1. AquariusADPSVersion3.0

� MajorUpdatesfromV2.0

2. LocalBiases� RainEffectsversusGeophysicalModelFunction

3. RainImpact:Atmosphere

4. RainImpact:SurfaceSplashing

5. RainImpact:Freshening

6. FreshwaterLensing

7. Summary

AquariusADPSVersion3.0OfficialAquariusProduct.ReleasedJune2014.

ADPSV2.0 ADPSV3.0

� SurfaceRoughnessCorrection� BasedonNCEPwindspeeds

� ReflectedGalaxy� Physicalmodel:

Oceansurfacemodelledasensembleoftiltedfacets:GeometricOptics

� SurfaceRoughnessCorrection� BasedonAquariuswindspeeds� HH-polactiveandH-polpassive

� ReflectedGalaxy� GeometricOptics(about90%)� Empiricalcorrection:Symmetrization

betweenascendinganddescendingswaths

� Q/CFlagging� degradedconditions� undetectedRFI

� AntennaPatternCorrection� Reducedbiasesoverland+ice� Reducedbiasesin3rd Stokes

� ΔSSS(SST)biasadjustment� mitigateslargescalebiases

Ascending(PM)– Descending(AM)Biases

Month

Latitude

GO(V2.0) GO+empiricaladjustment(V3.0)

Performance:LocalBiasesAquarius- ARGO

� Freshbiasesintropicsandsubtropics� Saltybiasesatmid-highlatitudes

� BiggestinNPacific� Seasonalpattern

Month

Latitude

2-year:09/2011– 08/2013

CausesofRegionalBiasesandMitigation"Real"

Aquariusiscorrectshouldnotbecorrected

"Fake"shouldbecorrected/mitigated

� Raininducedfreshening� Mainlytropics(ITCZ)� Stratificationofupperoceanlayer.� Aquariusmeasureswithinfewcm

ofsurface.� Insitumeasurementsatvarious

depth:� ARGO:5m� HYCOM:upperlayer?� mooredbuoys:1m

� ErrorsinthegeophysicalmodelfunctionthatisusedintheSSSretrievalandthathasazonalsignature.

� Rain� splashingeffectonsurface� atmosphere

� UndetectedRFI� enteringthroughsidelobes� makesSSSartificiallylow� issueincertainareas(China,

Japan,Indonesia,…)

Itisessentialtoseparatetheeffects.

RainMeasurementandFiltering

� Approach:1. FilteroutrainatorclosetoAquariusobservation.2. ChooseobservationsthatarenotimpactedbyundetectedRFI.3. Dealwiththemodelfunctiondependentbiases.4. Estimateatmosphericeffectsandsurfacesplashing.5. Leftwiththerealfreshening.

� CONAEMicrowaveRadiometer(MWR):KandKa–band§ OnAquariusplatform§ WasoperatinguntilApril2014§ AllowsrainmeasurementatthelocationandtimeofAquariusobservation§ Rainratesarenotverygood(no18GHzchannel)§ Allowsrainflagging:Aquariusobservationrainfree§ AvailableatRSSftpserver

ftp://Aquarius_mwr:[email protected]/aquarius_mwr/rss_l2c_h5/§ WillbeavailableatPO.DAAC

� MicrowaveImagers§ SSMIS(F17),WindSat:1hourwithinAquarius(sameequatorialcrossingtime)§ TMI:crossingtimeshiftingrelativetoAquarius§ CandetectrainwithintimewindowofAquariusobservation

AquariusSSS:AllEvents– RainFiltered

About30%ofthefreshbiasesatlowlatitudesareduetorain.Thesaltybiasesathighlatitudesarenotduetorain.

CausesofSSTDependentBiases� GeophysicalModelFunctionGMFthatisusedintheretrievals

� 0.1KuncertaintyinGMFis0.2psuuncertaintyinSSS� Dielectricconstantofseawater� Oxygenabsorptionmodelusedforatmosphere(non-resonantcontinuum)� Surfaceroughnessmodel� ErrorinauxiliarySSTfieldthatisusedintheretrievals(coldwater)� UndetectedRFI� Acombinationofsuch� Wearecurrentlytrackingthatdown.ImprovementplannedforV4.0.

� "Biasadjusted"SSSproduct� providedinV3.0inadditiontostandardproduct

SSSAQ- HYCOM

ImpactonPerformanceLocalBiases

V3.0norainfilter

biasadjustedrainfilter

ImpactonPerformanceTripleColocationStatistics

Global.RainFiltered

EstimatedIndividualErrorsσ[psu]AQ– HYCOM– ADPRCARGOσ[psu]

TripleCollocation:Assumethat errorsinthe3productsareindependent

3o monthlyaverages1.5o monthlyaverages

“Errors”inHYCOM/ARGOduetosamplingAQUARIUS HYCOM ARGO

V3.0 0.24 0.27 0.16 0.19SSTbiasadjusted 0.18 0.22 0.16 0.19

Std.Dev.ofMonthlyAveragesvs.ARGO

ADPSwithSST-biasadjustment

CAP

ADPSwithoutSST-biasadjustment

RainInducedEffects(1)1. Realfreshening

� Aquarius(fewcmofsurface)versusARGOorHYCOM(5mdepth)

2. Atmosphericabsorption� AquariusL2SSSretrieval

usescloudwaterfromNCEPforatmosphericcorrection.

3. Surfacesplashing?

Wewillnowshowthatabout80-90%oftheobservedeffectismostlyduetorainfreshening.

LowwindsSurfacelayerstratified

HighwindsSurfacelayermixed

AtmosphericCorrection

� AquariususesNCEPliquidcloudwaterforatmosphericraincorrection.

� NCEPmissesmostoftherain.Itunderestimatesthecloudwaterbycloseto100%andthusitisbasicallyuselessinrain.

� FutureversionwilluseCMORPHaccumulatedrainproduct.

ImpactonSalinityRetrieval� AssumethatSSM/Igivescorrect

cloudwater.

� AtmosphericabsorptionincreasesTBandthusgivesaSSSthatistoolow.

� Theatmosphericraincorrectionalgorithmissupposedtocorrectthat.

� NCEPunderestimatesthecloudwatercontentandthereforeundercorrectstheatmosphericeffect.

� OurcurrentAquariusV3.0SSSistoolow/freshinrain.� 0.2psuinhighrain.

� FuturereleaseswilluseCMORPH

NCEP

CMORPH3hr

RainSplashing:WindSpeed� WhencomparedtoNCEPthescatterometer(HH- pol)windspeedshowsanincreaseatlowwindspeedsandhighrainrates.

� Likelyduetosurfacesplashing.

� NCEPwindspeedbestgroundtruthinrain?

� Howdoesthateffectthesalinityretrievalsinrain?

Rainsplashing:SurfaceemissivityAnalyzeX-pol:X=β·H - VCombinationofV-polandH-polthatisinsensitivetoSSSβ= 1.18 (innerhorn),1.33 (middlehorn),1.54 (outerhorn)Itishowever,verysensitivetoroughness

V-polH-polX-pol

SSS

∆TB

Wind

∆TB

RainEffectonX-polTBmeasured- model

� ThereisverylittleraininducedexcessemissivityonX-pol.

� Partofthelittleeffectweareseeingcouldbeactuallyduetoundercorrectingtheatmosphericeffect.

� Scatterometerwindisusedinroughnesscorrection.Scatterometerwindisproxyforroughness.

� TheresultsindicatethatitisNOTwarrantedtoperforma"rainsplashcorrection"intheADPSalgorithmbyforcingtheAquariusSSStoHYCOM.

horn1 horn2 horn3

RainInducedEffects(2)

About80-90%oftheobservedeffectisduetorainfreshening.Therestisduetoatmosphere+surfacesplashing.

Lowwinds:fresheningisabout- 0.13to- 0.15psu/(mm/h)

LowwindsSurfacelayerstratified

HighwindsSurfacelayermixed

RainFresheninginTropicsAquariusversusHYCOM,ARGO,mooredBuoys

FreshwaterLensingRainRatesfromMicrowaveimager

Rainwithin1hourofAquarius

Fresheningatsurfacecomparedwith1m/5m

NorainatAquariusRain0- 1hourbeforeAQFreshwaterlensingvisible

Norainwithin1hourbeforeAquarius

Rain1- 12hoursbeforeAQupperlayerhasmixed

Aquarius– PMEL(1m)

Aquarius– HYCOM(5m?)

Aquarius– ARGO(5m)

SummaryandConclusions� Whencomparingsatellitesalinitywithgroundtruthweneedtocarefully

separatebiasesthatareduetoinaccuraciesintheGMFfrombiasesthatareduetostratificationwithintheupperlayer.

� AquariusADPSV3.0mitigatestheGMFbiasesbutkeepsthestratification.� Estimatedaccuracy:

0.22psu(1.5degmonthly).0.18psu(3.0degmonthly).

� RainfresheningfromAquarius� Observeddifferencebetweensurfaceand5mlayer:0.17psu/(mm/h)atlowwindspeeds.

� Smallerrorduetoinadequateatmosphericcorrectionandsurfacesplasheffects.

� Thescatterometerwindspeedisagoodproxyforsurfaceroughnessincludingrainsplashing.Nooronlyverysmallcorrectionforrainsplashingeffectsiswarranted,ifscatterometerwindspeedsareusedinthesurfaceroughnesscorrection.

� Instantaneousfresheningestimatedtoabout0.13to0.15psu/(mm/h)atlowwindspeeds.

� ConsistentwithSMOSresults.

� SurfacefreshwaterlensingisvisibleinAquariusdata1– 3hoursafterrainevent.

BackupSlides

AquariusSSS:AllEvents– RainFilteredGlobalAverageasTimeSeries

� Globaldifferencerain– no-rainissmall� 0.04psu/0.02K.� Timedependence(month)veryweak.

� Globallyitdoesnotrainthatmuch!

� Compensationtoaccountofthefactthatwedonotrainfilterincalibrationcanbedoneeeasily.� Addone-timesmallTAnumberforeachofthe6channelsincalibration.

RainImpactonSensorCalibration� V3.0senorcalibration:

� Matchesglobal7-dayaverageofAquariuswithHYCOM� Doesnotdorainfiltering.

� Consequence:TheV3.0AquariusSSSaretoosalty� Globalbias.� Stratificationintropics:

Aquariusseesrainfreshening,whichisreal,butHYCOMdoesnot.Itthereforeblamesthemismatchtothesensorcalibration.

� ThecorrectwaywouldbetofilterAquariusobservationsforrainbeforematchingthemtoHYCOM(orARGO).

� Howmuchdoesthatamountto?

� Study:Computedmonthlyclimatologyofnon-rainfilteredminusrainfilteredAquariusobservations.� TimeframewhereMWRisavailableforrainflagging.� InadditionuseMWimagers(SSMIS,WindSat,TMI)tofilteroutrainwithin1hour

beforeAquariusobservation.

MWRRainRates� AvailableatRSSFTPsite

� ftp://Aquarius_mwr:[email protected]/aquarius_mwr/rss_l2c_h5/

� SpaceandtimecollocatedtoAquariusL2swath.

� Format:� HDF5� samestructureasAquariusADPSL2files� samenameconventionforgranules

� Variables� time,latitude,longitude(matchesADPSL2)� cloudwater,rainrate,liquidwaterattenuationatL-band� windspeed,watervapor

� Documentationonprocessingalgorithmandfilecontent

� PO.DAAC?

� UseinAquarius� Foranalysisonly.NotpartofL2processing.� RainFlagging� RainRates:notverygood(37GHzchannelsaturates)

AquariusADPSversusCAPPerformanceAnalysis

� Exactlythesameensembleofsamplesusedforallcomparisons� SameQ/C

� Two-typesofStandardDeviations� 1.44Secsingleretrievals� Retrievalsfirstaveragedoveramonth

� CAPisVersion2.5.1� ADPS

� withoutandwithSST-biasadjustment

MeanandStd.Dev.(1.44sec)vs.SSTErrordominatedbyroughness

StdDev

Bias


CAP


1. CAPisnoisieratADPSon1.44seccycle.2. CAPhasappliedanSSTflatteningbymakinganadjustmentofthe

dielectricconstant.Thisoneofmanywaystodothat.

MeanandStd.Dev.(1.44sec)vs.WindErrordominatedbyroughness

StdDev

Bias


CAPADPSwithoutSST-biasadjustment

• CAPisnoisieratADPSon1.44seccycle.• Noiseisincreasingwithincreasingwindspeed.

Std.Dev.ofMonthlyAveragesvs.HYCOMErrordominatedbylocalSST-dependentbiases


CAP


Std.Dev.ofMonthlyAveragesvs.ARGO


CAP


T. Meissner, F. Wentz, J. Scott, K. Hilburn Remote Sensing ... · Remote Sensing Workshop November...

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