Slide 1

A Novel Ocean Vector Winds RetrievalTechnique for Tropical Cyclones

Peth Laupattarakasem1, Suleiman Alsweiss1, W. Linwood Jones1, and Christopher C. Hennon2

1Central Florida Remote Sensing LaboratoryUniversity of Central FloridaOrlando, Florida 328162University of North Carolina AshevilleAsheville, NC 28804

IGARSS 2011Vancouver, CanadaJuly 26, 2011

1OutlineSeaWinds OVW measurements in hurricanesRadar backscatter geophysical model functionX-Winds OVW retrieval algorithmwind direction retrievalwind speed retrievalX-Wind Comparisons with H*Wind & QuikSCAT standard L2B OVW productSeaWinds Hurricane MeasurementsHistorically Ku-band scatterometers have under estimated hurricane wind speedsIssuesInadequate spatial resolution (25 km IFOV)Rain contamination (backscatter & attenuation)Geophysical OVW retrieval algorithmDeveloped for global windsNot optimized for tropical cyclonesExtreme Winds Sigma-0 Geophys Model Function (XW-GMF)Special QuikSCAT GMF developed for hurricanesTraining dataset of 35 QScat hurricane overpasses3-D GMF: so = f(ws, relative wdir, atmos transmis)WS: one-minute sustained 10m wind speeds from NOAA HRD H*Wind surface wind analysisRelative wind direction c: the difference between wind direction and the radar azimuth lookAtmos transmissivity: inferred from simultaneous observations of QRad H-pol brightness temperaturesPut markers every 90 degrees for the GMF plots to differentiate the two GMFs4Hurricane Geophysical Model Function (GMF)

H-pol so , dB 30 m/sGMF C0 - Coeff Dependence on Wind Speed

C0 , dB 10 20 40 60 Wind Speed, m/s GMF Anisotropy with Wind Speed

C1 , linear units C2 , linear units 10 20 40 60 Wind Speed, m/s 10 20 40 60 Wind Speed, m/s

XW-GMF Atmospheric TransmissivityRain attenuation is corrected implicitly through use of the QRad H-pol brightness temperature TbhGMF = f(ws, rel_wdir, Tbh)Tbh

140 k160 k190 kPut markers every 90 degrees for the GMF plots to differentiate the two GMFs8X-Winds OVW retrieval AlgorithmAttributesAssumes cyclonic wind direction rotation about TC centerAssumes rain effects are primarily absorptiveRain volume backscatter is neglectedEmpirical 3-D XW-GMF accounts for backscatter saturation with wind speed & rain absorptionUses sequential scalar wind direction and wind speed estimationNot traditional ocean vector wind maximum likelihood estimation retrieval Scalar Wind Direction EstimationRelies on anisotropy of measured difference between forward and aft looking backscatter measurementsDsomeas = (sofore soaft) @ top-of-the-atmos

Latitude IndexLongitude IndexDso - linear unitsTypical hurricane imageWind Direction Modeling of Dsoso anisotropy model for single radar azimuth look

Taking the difference between fore & aft radar looks yieldsWind direction solutions (aliases) are roots of

Yields ambiguous wind direction solutions typically ~ 6 811Label color scaleEdit title to include sig0f and sig0aMake equations bigger

Wind Direction Alias RemovalWind Directions AmbiguitiesRetrieved Wind Direction Field

Keep ambiguities within window 30 from CCW spiralMulti-pass median filter and populate missing pixels through interpolationUse smoothed TC wind field for wind speed estimation

12X-Winds Scalar Wind Speed EstimationUse smooth TC wind field as estimated true wind direction and calculate relative wind direction c = (radar az est-wind dir)Find 1-D wind speed solution for each so flavor (V- & H-pol, fore & aft direction) that satisfies this relationship

X-Winds Wind Speeds Retrievals

Wind Speed (m/s)|(someas GMF)|4 0 flavors HF HA VF VA14- L2B-12.5km OVW product - H*Wind surface wind analysisX-Winds OVW retrievals

Results and Performance EvaluationHurricane Fabian Rev#21898

X-WindsH*Wind AnalysisL2B-WS 12.5km16Hurricane Ivan Rev#27217

X-WindsH*WindL2B-WS 12.5km17

Wind Speeds Comparison (10 revs)X-Winds QSCAT L2B-12.5km

TbH-polTbH-polX-Winds & L2B color scatter plots18

Wind Speeds Comparison (10 revs)X-Winds QSCAT L2B-12.5km

TbH-polTbH-polX-Winds & L2B color scatter plots19Wind Direction Comparison (10 revs)

TbH-polX-Winds QSCAT L2B-12.5kmTbH-pol20Wind Direction Comparison (10 revs)

TbH-polX-Winds QSCAT L2B-12.5kmTbH-pol21ConclusionA new OVW retrieval algorithm has been developed for SeaWindsSpecifically tailored for tropical and extra-tropical cyclonesPerformance evaluated using comparisons with H*Wind surface wind analysis and L2B-12.5kmBetter agreement with H*WindA new (11-year) SeaWinds TC OVW data set will be produced starting next year 201222