Characterization of Polarized SAR Scattering of Breaking Waves Caused by Internal Solitary Waves

Abstract

Internal solitary waves (ISWs) resonate with meter-scale surface waves, which causes crests to overturn and waves to break strongly, generating many whitecaps. We analyze the polarized SAR characteristics of ISWs based on nonpolarized scattering theory and polarization decomposition theory. The surface breaking waves induced by ISWs generate short-scale waves carrying Bragg waves on the one hand, which enhances the polarized Bragg scattering (PD) contribution at the decimeter or centimeter scale and generate additional nonpolarized scattering (NP) contribution through specular scattering on the other hand. The copolarized scattering intensity in ISW regions is always higher than that in unperturbed sea surface under both L and C bands, with higher PD and NP contributions. The average PD is 1.3 (1.7) times higher than that of the unperturbed sea surface, and the average NP is approximately 82% (165%) higher than that of the sea surface. The PD and NP values associated with the convergent zones are always larger than those associated with the divergent zones, indicating that breaking waves mainly occur in convergence. The results of $\bm{HA}\alpha$ decomposition show that the scattering mechanism of ISWs is surface scattering with reduced scattering entropy and mean scattering angle. We construct compact polarization based on fully polarized SAR, and extract polarization parameters that indicate increased degree of polarization at ISWs, which supports our inference of enhanced specular scattering.

Keywords

• Breaking waves
• internal solitary waves
• nonpolarized scattering
• polarimetric SaR