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TU1.T10.5.ppt

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TU1.T10.5.ppt

  1. 1. Cross-Polarized SAR: A New Potential Technique for Hurricanes Will Perrie and Biao Zhang Bedford Institute of Oceanography Dartmouth, Nova Scotia, Canada
  2. 2. PR vs. incidence angle, from quad-polarization data.  Compared to other PR models … PR dependence on incidence angle We develop a polarization ratio model to improve wind speed retrievals… SAR-wind models
  3. 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 -0.0802 C 0.0333 B 0.5474 A Fitted values Coefficient -0.0505 Q2 -0.0006 Q1 0.9559 P3 -0.0162 P2 0.0012 P1 Fitted values Coefficient
  4. 4. Dataset Mouche et al #2 Our #1model Mouche et al #1 downwind Mouche et al #1 crosswind Johnsen et al Thompson et al Elfouhaily Our #2 model Vachon&Dobson PR PR from RADARSAT-2
  5. 5. Dataset 17 SAR winds from CMOD5.N and our model#I + R2 HH pol image 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.
  6. 6. Co-Polarization Model: CMOD5.N Cross-Polarization Ocean model: C-2PO 1:wind speed, wind direction, incidence angle. 2: NRCS_VV saturated under high winds. 1: only wind speed dependence. 2: NRCS_VH not saturated under high winds. Correlation coefficient for C-2PO = 0.91  VV  HH  HV  VH U 10 U 10 C-band models
  7. 7. Dataset R2 Quad -Polarization Ocean Backscatter Measurements NRCS_VV saturates no NRCS_HV saturation NRCS_HV, NRCS_VH not sensitive to incidence angle, wind direction NRCS_VV, NRCS_HH depend on incidence angle, wind direction U 10 U 10 U 10 U 10 C-2PO corr coeff = 0.91
  8. 8. Hurricane Bertha – 12 July 2008 Hurricane wind-speed retrievals with C-2PO
  9. 9. Hurricane Ike – 10 Sept 2008
  10. 10. Hurricane Bill – 22 Aug 2009
  11. 11. Hurricane Danielle – 28 Aug 2010
  12. 12. Hurricane Earl on Sep 02, 2010 at 22:59 UTC VV polarization VH polarization RADARSAT-2 dual-polarization SAR image
  13. 13. Hurricane Earl on Sep 02, 2010 at 22:59 UTC H*Wind (m/s) Winds -buoy #41001 is 18.1 (m/s) C-2PO is 16.0 CMOD5.N is 17.4 H*Wind is 16.8 CMOD5.N (m/s) C-2PO model (m/s)
  14. 14. Comparison of C-2PO and CMOD5. SAR wind retrievals Along track-SFMR (hr) time series SFMR-measured 10s rain rates (mm/hr) time series (hr) eyewall? rain? gradients?
  15. 15. Hurricane Earl Comparisons of C-2PO and CMOD5.N SAR- retrieved winds U10 ( Sep 02, 2010 at 22:59 UTC) with collocated H*Wind C-2PO CMOD5.N
  16. 16. dual-polarization SAR image at 23:56 UTC on Sep 10, 2008 Hurricane Ike VV polarization VH polarization CMOD5.N + wind directions via H*Wind C-2PO model U10
  17. 17. Comparisons of C-2PO and CMOD5.N SAR- retrieved winds U10 (23:56 UTC, on September 10, 2008) with collocated H*Wind Hurricane Ike 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 C-2PO CMOD5.N
  18. 18. Summary <ul><li>C-2PO model presented </li></ul><ul><li>insensitive to wind direction, radar incidence angle </li></ul><ul><ul><li>easy mapping of observed cross-pol NRCS to wind speed </li></ul></ul><ul><li>avoids errors in wind speed retrievals that occur in CMOD5.N </li></ul><ul><li>in quad-pol data, C-2PO does not seem to saturate </li></ul><ul><ul><li>potential for hurricane wind retrievals </li></ul></ul><ul><li>dual-pol Earl : high wind comparisons R2 SAR – airborne SFMR </li></ul><ul><li>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 . </li></ul><ul><li>Reasons for under-estimates: </li></ul><ul><li>CMOD5.N is saturated in high winds </li></ul><ul><li>co- and cross-polarized NRCS calibration error </li></ul><ul><li>CMOD5.N and C-2PO do not account for rain, high sea states, eye gradients, e.g. dampen the NRCS  biases in wind speeds </li></ul><ul><li>inaccurate wind directions for CMOD5.N. </li></ul>
  19. 19. Some other sources… <ul><li>Paul Hwang et al. TU2.T10.4 (11:20) Wind retrieval with cross-polarized SAR returns </li></ul><ul><li>Vladimir Zabeline et al. TH2.T02.2 RADARSAT Application in ocean wind measurements </li></ul><ul><li>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. </li></ul><ul><li>Vachon, P.W. and J. Wolfe, (2010), C-band cross-polarization wind speed retrieval, IEEE Geosci . Remote Sens . Lett ., 7 , 456-459. </li></ul><ul><li>Zhang, B., and W. Perrie (2010), C-band Quad-Polarization ocean backscatter measurements: A new polarization ratio model. SEASAR2010 , January 25-29, Frascati, Italy. </li></ul><ul><li>Zhang B., W. Perrie, and Y. He , 2011 : Wind speed retrieval from RADARSAT-2 quad-polarization image s using a new polarization ratio model. J . Geophys . Res ., 116 , doi:10.1029/2010JC006522. </li></ul><ul><li>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). </li></ul>

Notas do Editor

  • Figure 2a. Polarization ratio (PR) as a function of incidence angle, from RADARSAT-2 quad-polarization observations and our PR models, as well as selected empirical and theoretical PR models from the literature.
  • Comparisons of observed NRCS in VV polarization (x-axis) from RADARSAT-2 measurements with equivalent values (y-axis) calculated from the various empirical and theoretical PR models in the literature: (a) Model 2 from Mouche et al . [2005] (M2005), (b) Model with incidence angle dependence from this study, (c) Model 1 from Mouche et al . [2005] (M2005), (d) Model with from Horstmann et al . [2000] (H2000), (e) Model from Johnsen et al . [2008] (J2008), (f) Model with from Thompson et al . [1998] (T1998), (g) Model with Eq.(5) from Elfouhaily [1996] (E1996), (h) Model with wind speed and incidence angle dependence from this study, and (i) Model with from Vachon and Dobson [2000] (V2000).
  • SAR wind map retrieved by our PR model with only incidence angle dependence and CMOD5.N, from a RADARSAT-2 SAR image as shown in Figure 6a. The colorbar denotes wind speed, in units of m/s. The black arrow indicates wind direction (with 0  to the east) .
  • a)-b) Normalized radar cross section (NRCS) versus wind speed, for six 5  incidence angle bins between 20  and 50  for (a) VV polarization, (b) HH polarization. In (a), include CMOD4, CMOD5, CMOD5.N. c)-d) Normalized radar cross section (NRCS) versus wind speed, for six 5  incidence angle bins between 20  and 50  for (a) HV polarization, (b) VH polarization. The solid line corresponds to a linear fit, with correlation coefficient of 0.97.
  • RADARSAT-2 dual-polarization SAR image acquired over Hurricane Earl at 22:59 UTC on September 2, 2010, (a) VV polarization and (b) VH polarization.
  • RADARSAT-2 dual-polarization SAR image acquired over Hurricane Earl at 22:59 UTC on September 2, 2010, (a) VV polarization and (b) VH polarization. Colorbar shows sigma-naught in VV polarization ( ) and in VH polarization () in dB, respectively. SAR-retrieved wind speeds from (c) the CMOD5.N model and , with e xternal wind directions from NOAA HRD H*Wind are overlaid , and (d) from the C-2PO model and . Colorbar shows wind speeds at 10-m height () in m/s.
  • Comparisons of C-2PO and CMOD5.N SAR- retrieved wind speeds (at 22:59 UTC, on September 2, 2010) with collocated SFMR-measured along-track 10s averaged surface winds during 22:30~23:30 UTC, on September 2, 2010, (a) time series plot, (d) gives SFMR-measured 10s path-integrated rain rates (mm/hr).
  • Comparisons of C-2PO and CMOD5.N SAR- retrieved wind speeds (at 22:59 UTC, on September 2, 2010) with collocated SFMR-measured along-track 10s averaged surface winds during 22:30~23:30 UTC, on September 2, 2010, (b) and (c) scatter plot s
  • A RADARSAT-2 dual-polarization SAR image acquired over Hurricane Ike at 23:56 UTC on September 10, 2008, (a) VV polarization and (b) VH polarization. Colorbar shows sigma-naught in VV polarization ( ) and in VH polarization () in dB, respectively. SAR-retrieved wind speeds from (c) the CMOD5.N model and , with e xternal wind directions from NOAA HRD H*Wind are overlaid , and (d) from the C-2PO model and .
  • Comparisons of C-2PO and CMOD5.N SAR- retrieved wind speeds (at 23:56 UTC, on September 10, 2008) with collocated H*Wind derived wind speeds at 01:30 UTC, on September 11, 2008 .

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