Surface Wave Breaking Caused by Internal Solitary Waves: Effects on Radar Backscattering Measured by SAR and Radar Altimeter

Abstract

Breaking surface waves play a key role in the exchange of momentum, heat, and gases between the atmosphere and the ocean. Waves break at the ocean’s surface at high or medium wind speeds or in the absence of wind due to shoaling of the seafloor. However, surface waves also break due to interactions with internal solitary waves (ISWs). In this paper, we revisit surface wave breaking caused by ISWs and how ISWs are manifested in synthetic aperture radar (SAR) images acquired by the TerraSAR-X and Sentinel-1 satellites and in high-resolution radar altimeter data acquired by the SAR altimeter (SRAL) onboard the Sentinel-3A satellite. X-band TerraSAR-X images acquired at low wind speeds suggest that meter-scale surface breaking waves resulting from large-scale ISWs are associated with large modulations in backscatter at HH and VV polarizations that cannot be explained by present theories. Furthermore, Sentinel-1 C-band SAR satellite images acquired at moderate to high wind speeds also exhibit large radar signatures from surface wave breaking at VV and VH cross-polarizations. Finally, new observations from the Sentinel-3 SRAL altimeter show clear evidence of significant wave height (SWH) variations along the propagation paths of ISWs. The SWH signatures are unique in showing that the surface wave energy does not return to its unperturbed level after an ISW passes, most likely because intense meter-scale wave breaking results in surface wave energy dissipation. In summary, these results show that surface wave breaking contributes significantly to radar remote sensing of ISWs.