Determination of the Spatial Pattern of Wave Directions in the Inhomogeneous Coastal Ocean by Marine Radar Image Sequences

Remotely sensed images of the ocean are a useful tool for revealing wave direction information in the spatial domain. Considering wave inhomogeneities in a coastal area, this paper addresses issues concerning the analysis of local wave directions using a simultaneous time series of X-band radar echo intensities. The method employed to analyze the directional wave information in our paper is based on a cross-spectral analysis of radar echo intensity time series from several neighboring locations constituting a spatial array within a small area. Compared with simultaneous sea surface elevation records, which have demonstrated their efficacy for estimating directional wave information, the spatial wave features present in radar image sequences are more sensitive to environmental factors and image noise. To confirm the practicality of this approach, we examined the relationship between the wave directions estimated from the X-band radar and moored buoy data. Most mean wave directions and dominant wave directions estimated from the radar images are consistent with the buoy results. In most cases, the differences between the radar and buoy wave directions are within ±30°. We also present a radar image case with an obvious refracted wave pattern. The results estimated from this image case demonstrate the feasibility of determining the spatial pattern of wave directions from a highly inhomogeneous wave field.