Cross-Polarized SAR: A New Potential Technique for Hurricanes
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Cross-Polarized SAR: A New Cross-Polarized SAR: A New Potential Potential Technique for Technique for Hurricanes Hurricanes Will Perrie and Biao Zhang Bedford Institute of Oceanography Dartmouth, Nova Scotia, Canada
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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 …. - PowerPoint PPT Presentation
Transcript of Cross-Polarized SAR: A New Potential Technique for Hurricanes
Cross-Polarized SAR: A New Cross-Polarized SAR: A New PotentialPotential Technique for Hurricanes Technique for Hurricanes
Will Perrie and Biao ZhangBedford Institute of OceanographyDartmouth, 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 modelsSAR-wind modelsSAR-wind modelsSAR-wind modelsHH0
VV0
σ
σPR
HH0
VV0
σ
σPR
SAR PR ocean wind models SAR PR ocean wind models SAR PR ocean wind models SAR PR ocean wind models
Coefficient Fitted values
A 0.5474
B 0.0333
C -0.0802units]Linear [ )exp(PR CBA
Nonlinear Least Squares fit ….
Coefficient Fitted values
P1 0.0012
P2 -0.0162
P3 0.9559
Q1 -0.0006
Q2 -0.0505
units][Linear )(PR 10 QUP
3*2*1)( 2 PPPP 2*1)( QQQ
PR Model I only incidence angle dependence
PR Model II with additional wind speed dependence
DatasetDatasetDatasetDatasetMouche 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
DatasetDatasetDatasetDataset
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SAR winds from CMOD5.N and our model#I + R2 HH pol image
14.1 m/s12.9 m/s
12.4 m/s11.6 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.
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
VVHH
HV VH
U10 U10
C-band models
DatasetDatasetDatasetDatasetR2 Quad-Polarization Ocean Backscatter Measurements
NRCS_VV saturates
no NRCS_HV saturation
NRCS_HV, NRCS_VHnot sensitive to incidence angle, wind direction
NRCS_VV, NRCS_HHdepend on incidence angle, wind direction
U10U10
U10 U10
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-2PO CMOD5.N
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
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
Summary 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: 1) CMOD5.N is saturated in high winds2) co- and cross-polarized NRCS calibration error3) CMOD5.N and C-2PO do not account for rain, high sea states, eye gradients, e.g.
dampen the NRCS biases in wind speeds4) inaccurate wind directions for CMOD5.N.
Some other sources…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 images using a 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).
