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  • Put markers every 90 degrees for the GMF plots to differentiate the two GMFs
  • Put markers every 90 degrees for the GMF plots to differentiate the two GMFs
  • X-Winds & L2B color scatter plots
  • X-Winds & L2B color scatter plots

TU1.T10.2.pptx TU1.T10.2.pptx Presentation Transcript

  • A Novel Ocean Vector Winds RetrievalTechnique for Tropical CyclonesPeth Laupattarakasem1, Suleiman Alsweiss1, W. Linwood Jones1, and Christopher C. Hennon21Central Florida Remote Sensing LaboratoryUniversity of Central FloridaOrlando, Florida 328162University of North Carolina AshevilleAsheville, NC 28804IGARSS 2011Vancouver, CanadaJuly 26, 2011
  • Outline
    SeaWinds OVW measurements in hurricanes
    Radar backscatter geophysical model function
    X-Winds OVW retrieval algorithm
    wind direction retrieval
    wind speed retrieval
    X-Wind Comparisons with H*Wind & QuikSCAT standard L2B OVW product
  • SeaWinds Hurricane Measurements
    Historically Ku-band scatterometers have under estimated hurricane wind speeds
    Issues
    Inadequate spatial resolution (25 km IFOV)
    Rain contamination (backscatter & attenuation)
    Geophysical OVW retrieval algorithm
    Developed for global winds
    Not optimized for tropical cyclones
  • Extreme Winds Sigma-0 Geophys Model Function (XW-GMF)
    Special QuikSCATGMF developed for hurricanes
    Training dataset of 35 QScat hurricane overpasses
    3-D GMF: so = f(ws, relative wdir, atmostransmis)
    WS: one-minute sustained 10m wind speeds from NOAA HRD H*Wind surface wind analysis
    Relative wind direction c:the difference between wind direction and the radar azimuth look
    Atmostransmissivity: inferred from simultaneous observations of QRad H-pol brightness temperatures
  • Hurricane Geophysical Model Function (GMF)
    30 m/s
    H-pol so, dB
  • GMF C0- CoeffDependence 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 Transmissivity
    Rain attenuation is corrected implicitly through use of the QRad H-pol brightness temperature Tbh
    GMF = f(ws, rel_wdir, Tbh)
    Tbh
    140 k
    160 k
    190 k
  • X-Winds OVW retrieval Algorithm
    Attributes
    Assumes cyclonic wind direction rotation about TC center
    Assumes rain effects are primarily absorptive
    Rain volume backscatter is neglected
    Empirical 3-D XW-GMF accounts for backscatter saturation with wind speed & rain absorption
    Uses sequential scalar wind direction and wind speed estimation
    Not traditional ocean vector wind “maximum likelihood estimation” retrieval
  • Scalar Wind Direction Estimation
    Relies on anisotropy of measured difference between forward and aft looking backscatter measurements
    Dsomeas = (sofore – soaft) @ top-of-the-atmos
    Typical hurricane image
    Latitude Index
    Dso - linear units
    Longitude Index
  • Wind Direction Modeling of Dso
    so anisotropy model for single radar azimuth look
    Taking the difference between fore & aft radar looks yields
    Wind direction solutions (aliases) are roots of
    Yields ambiguous wind direction solutions
    typically ~ 6 – 8
  • Wind Direction Alias Removal
    Keep ambiguities within window ±30 from CCW spiral
    Multi-pass median filter and populate missing pixels through interpolation
    Use smoothed TC wind field for wind speed estimation
    Wind Directions Ambiguities Retrieved Wind Direction Field
  • X-Winds Scalar Wind Speed Estimation
    Use 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
    |(someas – GMF)|
    4 σ0 flavors
    HF HA VF VA
    Wind Speed (m/s)
  • Results and Performance Evaluation
    X-Winds OVW retrievals
    - L2B-12.5km OVW product- H*Wind surface wind analysis
  • Hurricane Fabian Rev#21898
    X-Winds
    L2B-WS 12.5km
    H*Wind Analysis
  • Hurricane Ivan Rev#27217
    X-Winds
    L2B-WS 12.5km
    H*Wind
  • Wind Speeds Comparison (10 revs)
    X-Winds QSCAT L2B-12.5km
    TbH-pol
    TbH-pol
  • Wind Speeds Comparison (10 revs)
    X-Winds QSCAT L2B-12.5km
    TbH-pol
    TbH-pol
  • Wind Direction Comparison (10 revs)
    X-Winds QSCAT L2B-12.5km
    TbH-pol
    TbH-pol
  • Wind Direction Comparison (10 revs)
    X-Winds QSCAT L2B-12.5km
    TbH-pol
    TbH-pol
  • Conclusion
    A new OVW retrieval algorithm has been developed for SeaWinds
    Specifically tailored for tropical and extra-tropical cyclones
    Performance evaluated using comparisons with H*Wind surface wind analysis and L2B-12.5km
    Better agreement with H*Wind
    A new (11-year) SeaWindsTC OVW data set will be produced starting next year 2012