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

• 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?

DopplerScatt Overview

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.

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

Radial Velocity Pointing Calibration

` · (vp � vs)

` = sin ✓[x cos�+ y sin�]� cos ✓z

�vr� =

` · vp@�

��

Radialvelocitysensitivities

��(↵) = a0 +X

an cos(n↵) + bn sin(n↵)

Calibrationmodela isantennarotationanglefromencoder

Errorsinlookangleq isfromrangeandisveryaccurate.

AirplanevelocityfromIMUisO(cm/s)

Beforecalibration

Aftercalibration

Radial Velocity STD Per Measurement

Radial Velocity Standard Error 200m Cell

Correction for Wind-Driven Component

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.

GMF ChallengesModel Resolution and Direction

Non-Wind Driven Surface Currents

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

GHRSST 2017-04-18

Sentinel 3 Image on 2017-04-18

12CourtesyofJ.Molemaker &SPLASHteam,SPLASHReportApril20

Radial VelocitiesNo Wind Correction

PredominantWind&WaveDirection

Wind Corrected Radial Velocities

Modulation of s0

s0 showssignificant“instantaneous”modulationbysurfacevelocityandatoilspillplume.Potentialeffectsduetosurfactants,kinematicmovingframeeffectsofstress,orSSTneedfurtherinvestigation.

DopplerScatt Vector Velocity Estimation

Badazimuthdiversity

Goodazimuthdiversity

Retrieved Surface Velocity Components

Retrieved Surface Velocity Errors

NCOM U Surface Velocity

NCOMrunat250mresolutionwithspecialtuningforriverinputs.DatacourtesyofG.Jacobs&NRLNCOMteam

DopplerScatt U Surface Velocity

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

Plume track fore-looking radial velocity

Plume track aft-looking radial velocity

Submesoscalefront

DopplerScatt physical measurements–Engineering Flight June 22nd 2016

Aft-lookingresidualradialvelocities

Fore-lookingSurfaceradialvelocityfromDoppler,aftersubtractingplatformmotionandroughBraggcontribution.Noticetidallyinducedinternalwavesatthecontinentalshelf.

Velocity(m/s)

Fore-lookingbackscattercrosssectioncorrespondingtoradialvelocity.NoticeincreasedbrightnessduetowindstrengtheningoffPointSur.

Preliminary Retrievals with Wind CorrectionInternal Wave Changes

Speed&Dire

T=0 T~30min T~90min T~120min

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

Measuring Winds and Currents with DopplerScatt · Measuring Winds and Currents with DopplerScatt E....

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