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

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

SAR PR ocean wind models CoefficientFitted values A B C Nonlinear Least Squares fit …. CoefficientFitted values P P P Q Q PR Model I only incidence angle dependence PR Model II with additional wind speed dependence

DatasetDataset Mouche et al #2Our #1modelMouche et al #1 downwind Mouche et al #1 crosswindJohnsen et al Thompson et al ElfouhailyOur #2 model Vachon&Dobson PR PR from RADARSAT-2

DatasetDataset 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: /2010JC

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 C-band models

DatasetDataset 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 C-2PO corr coeff = 0.91

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

Hurricane Ike – 10 Sept 2008

Hurricane Bill – 22 Aug 2009

Hurricane Danielle – 28 Aug 2010

Hurricane Earl on Sep 02, 2010 at 22:59 UTC VV polarization VH polarization RADARSAT-2 dual-polarization SAR image

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)

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?

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-2POCMOD5.N

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

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 m/s and RMS error of 6.51 m/s C-2PO  bias of m/s and RMS error of 4.47 m/s C-2POCMOD5.N

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= m/s, RMSE= 3.23 m/s, CMOD5.N bias= m/s, RMSE= 6.24 m/s. Reasons for under-estimates: 1)CMOD5.N is saturated in high winds 2)co- and cross-polarized NRCS calibration error 3)CMOD5.N and C-2PO do not account for rain, high sea states, eye gradients, e.g. dampen the NRCS  biases in wind speeds 4)inaccurate wind directions for CMOD5.N.

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: /2009GL Vachon, P.W. and J. Wolfe, (2010), C-band cross-polarization wind speed retrieval, IEEE Geosci. Remote Sens. Lett., 7, 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 images using a new polarization ratio model. J. Geophys. Res., 116, doi: /2010JC 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).