Quad-polarization SAR features of ocean currents

Type Article
Date 2014-09
Language English
Author(s) Kudryavtsev Vladimir1, 2, 3, Kozlov I.1, Chapron Bertrand1, 4, Johannessen J. A.3
Affiliation(s) 1 : Russian State Hydrometeorol Univ, Satellite Oceanog Lab, St Petersburg, Russia.
2 : Inst Marine Hydrophys, Dept Remote Sensing, Sebastopol, Russia.
3 : Nansen Environm & Remote Sensing Ctr, Bergen, Norway.
4 : IFREMER, Lab Oceanog Spatiale, Plouzane, France.
Source Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-09 , Vol. 119 , N. 9 , P. 6046-6065
DOI 10.1002/2014JC010173
WOS© Times Cited 57
Keyword(s) quad-polarized SAR, SAR imaging of ocean current, radar scattering, wave-current interaction, wave breaking
Abstract A methodology is demonstrated to exploit the polarization sensitivity of high-resolution radar measurements to interpret and quantify upper ocean dynamics. This study particularly illustrates the potential of quad-polarization synthetic aperture radar (SAR) measurements. The analysis relies on essential characteristics of the electromagnetic scattering mechanisms and hydrodynamical principles. As the relaxation scale of centimeter-scale ocean surface scatters is typically small, radar signal anomalies associated with surface manifestations of the upper ocean dynamics on spatial scales exceeding 100 m are mostly dominated by nonresonant and nonpolarized scatters. These “scalar” contributions can thus efficiently trace local breaking and near-breaking areas, caused by surface current variations. Using dual copolarized measurements, the polarized Bragg-type radar scattering is isolated by considering the difference (PD) between vertically and horizontally polarized radar signals. The nonpolarized (NP) contribution associated with wave breaking is then deduced, using the measured polarization ratio (PR) between polarized signals. Considering SAR scenes depicting various surface manifestations of the upper ocean dynamics (internal waves, mesoscale surface current features, and SST front), the proposed methodology and set of decompositions (PD, PR, and NP) efficiently enable the discrimination between surface manifestation of upper ocean dynamics and wind field variability. Applied to quad-polarized SAR images, such decompositions further provide unique opportunities to more directly assess the cross-polarized (CP for HV or VH) signal sensitivity to surface roughness changes. As demonstrated, such an analysis unambiguously demonstrates and quantitatively evaluates the relative impact of breakers on cross-polarized signals under low to moderate wind conditions.
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