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Cross-Polarized SAR: A New Potential Technique for Hurricanes

Cross-Polarized SAR: A New Potential Technique for Hurricanes. Will Perrie and Biao Zhang Bedford Institute of Oceanography Dartmouth, Nova Scotia, Canada. SAR-wind models. PR vs. incidence angle, from quad-polarization data.  Compared to other PR models ….

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Cross-Polarized SAR: A New Potential Technique for Hurricanes

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  1. Cross-Polarized SAR: A New Potential Technique for Hurricanes Will Perrie and Biao Zhang Bedford Institute of Oceanography Dartmouth, Nova Scotia, Canada

  2. SAR-wind models PR vs. incidence angle, from quad-polarization data.  Compared to other PR models … PR dependence onincidence angle We develop a polarization ratio model to improve wind speed retrievals…

  3. SAR PR ocean wind models Nonlinear Least Squares fit …. PR Model I only incidence angle dependence PR Model II with additional wind speed dependence

  4. Mouche et al #2 Our #1model Mouche et al #1 downwind Dataset Thompson et al Mouche et al #1 crosswind Johnsen et al Vachon&Dobson Elfouhaily Our #2 model PR PR from RADARSAT-2

  5. SAR winds from CMOD5.N and our model#I + R2 HH pol image Dataset 14.1 m/s 12.9 m/s 12.4 m/s 11.6 m/s 15.9 m/s 16.6 m/s Zhang, B., W. Perrie, and Y. He (2011), Wind speed from RADARSAT-2 quad-polarization images using a new polarization ratio model, J. Geophys. Res., doi:10.1029/2010JC006522. 17

  6. C-band models Co-Polarization Model:CMOD5.N HH VV HV 1:wind speed, wind direction, incidence angle. 2: NRCS_VV saturated under high winds. VH Cross-Polarization Ocean model: C-2PO U10 U10 Correlation coefficient for C-2PO = 0.91 1: only wind speed dependence. 2: NRCS_VH not saturated under high winds.

  7. R2 Quad-Polarization Ocean Backscatter Measurements Dataset NRCS_VV, NRCS_HH depend on incidence angle, wind direction NRCS_VV saturates U10 U10 NRCS_HV, NRCS_VH not sensitive to incidence angle, wind direction no NRCS_HV saturation C-2PO corr coeff = 0.91 U10 U10

  8. Hurricane wind-speed retrievals with C-2PO Hurricane Bertha – 12 July 2008

  9. Hurricane Ike – 10 Sept 2008

  10. Hurricane Bill – 22 Aug 2009

  11. Hurricane Danielle – 28 Aug 2010

  12. Hurricane Earlon Sep 02, 2010 at 22:59 UTC VH polarization VV polarization RADARSAT-2 dual-polarization SAR image

  13. Hurricane Earlon Sep 02, 2010 at 22:59 UTC Winds -buoy #41001 is 18.1 (m/s) C-2PO is 16.0 CMOD5.N is 17.4 H*Wind is 16.8 H*Wind (m/s) CMOD5.N(m/s) C-2PO model (m/s)

  14. Comparison of C-2PO and CMOD5. SAR wind retrievals eyewall? rain? gradients? Along track-SFMR (hr) time series SFMR-measured 10s rain rates (mm/hr) time series (hr)

  15. Hurricane Earl C-2PO CMOD5.N Comparisons of C-2PO and CMOD5.N SAR-retrieved winds U10 (Sep 02, 2010 at 22:59 UTC)with collocated H*Wind

  16. Hurricane Ike dual-polarization SAR image at 23:56 UTC on Sep 10, 2008 VV polarization VH polarization CMOD5.N + wind directions via H*Wind C-2PO model U10

  17. Hurricane Ike C-2PO CMOD5.N Comparisons of C-2PO and CMOD5.N SAR-retrieved winds U10 (23:56 UTC, on September 10, 2008) with collocated H*Wind CMOD5.N  bias of -4.89 m/s and RMS error of 6.51 m/s C-2PO  bias of -0.88 m/s and RMS error of 4.47 m/s

  18. Summary • C-2PO model presented • insensitive to wind direction, radar incidence angle • easy mapping of observed cross-pol NRCS to wind speed • avoids errors in wind speed retrievals that occur in CMOD5.N • in quad-pol data, C-2PO does not seem to saturate • potential for hurricane wind retrievals • dual-pol Earl:high wind comparisons R2 SAR – airborne SFMR • Earl: C-2PO bias= -0.89 m/s, RMSE= 3.23 m/s, CMOD5.N bias= -4.14 m/s, RMSE= 6.24 m/s. • Reasons for under-estimates: • CMOD5.N is saturated in high winds • co- and cross-polarized NRCS calibration error • CMOD5.N and C-2PO do not account for rain, high sea states, eye gradients, e.g. dampen the NRCS  biases in wind speeds • inaccurate wind directions for CMOD5.N.

  19. Some other sources… • Paul Hwang et al. TU2.T10.4 (11:20) Wind retrieval with cross-polarized SAR returns • Vladimir Zabeline et al. TH2.T02.2 RADARSAT Application in ocean wind measurements Hwang, P. A., B. Zhang, and W. Perrie, 2010: Depolarized radar return for breaking wave measurements and hurricane wind retrieval. Geophys. Res. Lett.,37, L01604, doi:10.1029/2009GL041780. Vachon, P.W. and J. Wolfe, (2010), C-band cross-polarization wind speed retrieval, IEEE Geosci. Remote Sens. Lett., 7, 456-459. Zhang, B., and W. Perrie (2010), C-band Quad-Polarization ocean backscatter measurements: A new polarization ratio model. SEASAR2010, January 25-29, Frascati, Italy. Zhang B., W. Perrie, and Y. He, 2011: Wind speed retrieval from RADARSAT-2 quad-polarization imagesusinga new polarization ratio model. J. Geophys. Res., 116, doi:10.1029/2010JC006522. Zhang, B., W. Perrie (2011), Cross-polarized synthetic aperture radar: a new measurement technique for Hurricanes, under review - Bulletin of the American Meteorological Society (BAMS).

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