measuring winds and currents with dopplerscatt · measuring winds and currents with dopplerscatt e....
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Measuring Winds and Currents with DopplerScatt
E. Rodríguez, D. Perkovic-Martin, T. Gal, N. Niamsuwan, B. Stiles, A. Wineteer
Jet Propulsion LaboratoryCalifornia Institute of Technology
1©2017CaliforniaInstituteofTechnology.Governmentsponsorshipacknowledged.
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• Both are essential climate variables that have a tight two-way coupling
– Stress and stress derivatives drive both horizontal and vertical circulation
– Currents provide a moving reference frame for stress and also modulate winds through heat
transport/SST
• A case was made to the ongoing US NRC Decadal Survey by multiple RFI 1 and 2 responses with
broad support from the winds community
– Decadal survey recommendations for future measurements expected by the end of 2017
• Concepts for simultaneous measurements of winds and currents using small modifications of
available technology have been put forward in China (Dong et al, OVWST2106), Europe (Stoffelen
et al, Ardhuin et al, SKIM), and the US (WaCM team).
• DopplerScatt (NASA IIP) is a proof of concept instrument to validate measurement physics,
algorithms, technology readiness.
Why Winds and Surface Currents?
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DopplerScatt Overview
3
DopplerScatt Overview• ScanningDopplerradardevelopedunderNASA’sIIPprogram• BecomingoperationalunderNASAAITTprogram• DataProducts:1. Vectoroceansurfacecurrents2. Vectoroceansurfacewinds3. Radarbrightnessmaps(sensitivetosurfactantssuchasoilfilms)• Mappingcapabilities:25kmswath;maps200kmx100kmareain
about4hrs;200mdataproductresolution;~5-10cm/sradialvelocityprecision.
• Currentstatus:– Instrumenthardwarecompleted– Instrumentcurrentlyundergoingfinalcalibrationandvalidation– CalVal campaigns:SPLASH(Submesoscale Processesand
Lagrangian AnalysisontheShelf)inMississippiRiverPlume(CARTHE)&TaylorOilPlatformPlume(NOAA),April18-28;KISS-CANONinMontereyBayMay1-4.
PotentialUsesforScientificUse
• Observationofmesoscaletosubmesoscale transitioninsurfacecurrentcirculationwithassociatedwinddrivers.
• Observationofinternalwavesandevolutionoversynopticscales
• Improvedunderstandingofair-seainteractionbysimultaneousmeasurementsofsurfacecurrents,windstress,andSST(separatesensorthatcanbeaccommodatedinNASAKingAirplatform).
• Improvedunderstandingofmechanismsleadingtoupwelling• Understandingofinteractionsofriverplumesandocean
circulation,includingmixing
PotentialforOperationalUse
• Highresolutioncharacterizationofcirculationincoastalshippingareas
• Trackingofsurfacesurfactants(e.g.,oil)withsimultaneousmeasurementsofsurfacecurrentsandwindstoaidmodelsinpredictionofdispersal
• Understandingbeacherosion• Planningforoilplatformsitingandsafety
DopplerScatt radial surface currents and biological surfactants (white) at Columbia River mouth.
DopplerScatt instrument. It has been deployed on a DOE King Air and will transition to an operational instrument in the NASA King Air B200.
©2017CaliforniaInstituteofTechnology.Governmentsponsorshipacknowledged.
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Doppler Current Measurement Concept
DopplerPhaseDifference:DF =2kDr=fDdtRadialvelocitycomponent:vr =Dr/dt =DF/(2kdt)
Vectorcurrentsareestimatedbycombiningmultiple(≧2)azimuthobservationsandprojectingvectortotheoceansurface.
• Radarsprovidecoherentmeasurements:boththephase andtheamplitude ofascatteredsignalaremeasured.
• Thephase isproportionaltothe2-waytraveltime(orrange)• Theamplitude isproportionaltothescatteringstrengthofthetraget• Doppler measurements,fD,areobtainedbymeasuringthephasedifferencebetween
pulses,DF.Noiseisreducedbycombiningmultiplepulses.4©2017CaliforniaInstituteofTechnology.Governmentsponsorshipacknowledged.
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Radial Velocity Pointing Calibration
5
vr =
ˆ
` · (vp � vs)
ˆ
` = sin ✓[x cos�+ y sin�]� cos ✓z
�vr� =
@
ˆ
` · vp@�
��
Radialvelocitysensitivities
��(↵) = a0 +X
n
an cos(n↵) + bn sin(n↵)
Calibrationmodela isantennarotationanglefromencoder
Errorsinlookangleq isfromrangeandisveryaccurate.
AirplanevelocityfromIMUisO(cm/s)
Beforecalibration
Aftercalibration
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Radial Velocity STD Per Measurement
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Radial Velocity Standard Error 200m Cell
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Correction for Wind-Driven Component
8
A wind driven component is estimated by binning Doppler velocities relative to wind direction to make a wind driven current GMF. The current estimates of the GMF are still being refined but preliminary estimates over a large range of wind speeds shows near universal behavior independent of waves and wind speed.
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GMF ChallengesModel Resolution and Direction
Non-Wind Driven Surface Currents
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Todayandtonight(Tuesday18April)
VisibleSatellite+RadarWinds(10AMCDT)
WavesSSS+Currents
WindsfromtheSE5-10kts.Increasingto10-15knotstonight.Mostlyclear.Seas2-3feet,waveperiod6-7s.Nearshorefreshwaterwithwestwardcurrents.
ModelwasruninrealtimebyM.Curcic,datawereprovidedbyB.Kerns,RSMAS
SPLASHSubmesoscale ProcessesandLagrangian AnalysisontheShelf
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GHRSST 2017-04-18
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Sentinel 3 Image on 2017-04-18
12CourtesyofJ.Molemaker &SPLASHteam,SPLASHReportApril20
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Radial VelocitiesNo Wind Correction
13
PredominantWind&WaveDirection
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Wind Corrected Radial Velocities
14
PredominantWind&WaveDirection
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Modulation of s0
15
PredominantWind&WaveDirection
s0 showssignificant“instantaneous”modulationbysurfacevelocityandatoilspillplume.Potentialeffectsduetosurfactants,kinematicmovingframeeffectsofstress,orSSTneedfurtherinvestigation.
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DopplerScatt Vector Velocity Estimation
16
Badazimuthdiversity
Badazimuthdiversity
Goodazimuthdiversity
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Retrieved Surface Velocity Components
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Retrieved Surface Velocity Errors
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NCOM U Surface Velocity
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NCOMrunat250mresolutionwithspecialtuningforriverinputs.DatacourtesyofG.Jacobs&NRLNCOMteam
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DopplerScatt U Surface Velocity
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Columbia River Internal Wave Tidal Bore
Clockwise from top left:
1. Satellite SAR image of the Columbia river plume from Aug 9th
2002, Nash & Moum, Nature, 2005 showing internal waves generated by the plume. Another feature has been conjectured to be a submesoscale front (Akan et al, JGR submitted. J. McWilliams, personal communication)
2. DopplerScatt September 13th
Track 1 fore-looking radial velocity
3. DopplerScatt September 13th
Plume track fore-looking radial velocity
4. DopplerScatt September 13th
Plume track aft-looking radial velocity
Submesoscalefront
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DopplerScatt physical measurements–Engineering Flight June 22nd 2016
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Aft-lookingresidualradialvelocities
Fore-lookingSurfaceradialvelocityfromDoppler,aftersubtractingplatformmotionandroughBraggcontribution.Noticetidallyinducedinternalwavesatthecontinentalshelf.
Velocity(m/s)
Fore-lookingbackscattercrosssectioncorrespondingtoradialvelocity.NoticeincreasedbrightnessduetowindstrengtheningoffPointSur.
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Preliminary Retrievals with Wind CorrectionInternal Wave Changes
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Speed
Speed&Dire
ction
T=0 T~30min T~90min T~120min
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Surface ocean vector winds and surface currents are tightly coupled essential climate
variables and must be measured simultaneously to improve our present understanding of the
coupled ocean-atmosphere system. These measurements will allow significant advances in
understanding of topics ranging from large-scale circulation in the tropics, air-sea interaction along
western boundary currents, to basic physical processes such as the vertical circulation of the ocean
and its role in the upwelling of nutrients that governs the ocean’s biological productivity.
Measurements with a resolution of 5 km or better would also improve significantly our
understanding of ocean-atmosphere variability from 10km to 200km, which is not yet well
observed. These measurements will also have significant impact for applications ranging from
fisheries, coastal shipping, and disaster management, especially if they can be made at high
resolution (5km or better) near the coasts. The international ocean vector wind community
endorses the pursuit of such simultaneous measurements , including the first global observation of
surface currents, which are being advocated by teams from the United States, Europe, and China.
Candidate Statement
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