Measuring Wave Breaking and Spectral Evolution in Coastal Waters with Interferometric Synthetic Aperture Radar

Airborne and spaceborne interferometric synthetic aperture radars (InSARs) produce surface velocity measurements at very high spatial resolution over a large area. The spatial mapping can be used to generate the surface velocity strain and local acceleration fields for highlighting ocean surface processes such as wave breaking and rip current formation. Also, coherence between signals from two interferometric channels is a descriptor of the correlation of the surface roughness that scatters back the radar signals and reflects the ocean surface turbulence condition. On the ocean surface, wave breaking is a major source of turbulence that causes surface roughness decorrelation, thus the coherence parameter serves as an independent means for detecting surface wave breaking. The results of breaking detections using the properties of surface roughness decorrelation and critical local acceleration are comparable. In this paper, we investigate the wave breaking detection in the surf zone and along a cross-shore transect using the surface decorrelation method and the critical local acceleration method. Also explored are the functional dependences of breaking properties (e.g., breaking probability, fraction and intensity) on various wind and wave parameters. The large spatial coverage of airborne or spaceborne operation further offers the opportunity to investigate the evolution of surface wave spectrum in high spatial resolution (sub-kilometer). This capability is very useful for monitoring the coastal wave and current environment. The analysis results from InSAR wave mapping are especially suitable to serve as wave model boundary condition input as well as calibration and validation of modeled output over the coverage area of InSAR measurements.