Extraction of Phase-Resolved Wave Data from X-Band Radar Imagery

Abstract

Typically, phase-resolved measurements of the sea surface are limited to single-point time series from in situ sensors, or arrays of multiple in situ sensors. The deployment of such devices is costly and time intensive, and the wave data they provide is limited in its spatial coverage and directional accuracy. Several remote sensing options, including optical video and X-Band marine radars, offer the possibility of full 2D reconstruction of the phase-resolved directional sea on spatial scales of kilometers.

Ocean waves are visible in radar imagery as the ubiquitous backscatter from short wind ripples is modulated by the longer gravity waves. However, a robust mechanism for extracting surface elevation information from the radar intensity data does not yet exist. The vast majority of past studies investigating wave information in radar imagery are limited to the retrieval of bulk parameters such as significant wave height (e.g. Young et al., 1985; Nieto Borge et al., 1999). More recently, several studies have investigated the extraction of phase resolved wave parameters (Nieto Borge et al., 2004; Dankert & Rosenthal, 2004) but are limited to methods requiring buoy calibration, or impractically high radar installation.

The present study investigates a more widely applicable method for reconstructing the phase-resolved sea surface from X-Band radar imagery. The methodology was developed by the authors previously (Simpson et al., 2017) and consists of an assimilation algorithm built on a physics-based wave model. The scope of work under the Link Fellowship was to assess performance of the algorithm using two field datasets.