1. Cross-Polarized SAR: A New Potential Technique for Hurricanes Will Perrie and Biao Zhang Bedford Institute of Oceanography Dartmouth, Nova Scotia, Canada
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. 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. 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. 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. 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. 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. Hurricane Bertha – 12 July 2008 Hurricane wind-speed retrievals with C-2PO
12. Hurricane Earl on Sep 02, 2010 at 22:59 UTC VV polarization VH polarization RADARSAT-2 dual-polarization SAR image
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. 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. 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. 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. 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
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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 .
