Dispersive surface classification: local analysis of optical image sequences of the water surface to determine hydrographic parameter maps

Abstract

The appearance of the sea surface is a spatio-temporal phenomenon. Features observed on the water surface are, e.g. wave fields or wind streaks. The acquisition and analysis of image sequences therefore allows a complete (spatio-temporal) representation of the sea state. Ship- or land-based nautical radars are used in the field and optical sensors are used in hydraulic wave tanks to acquire image sequences. A technique using a combination of image sequences acquired from CCD cameras and in situ data sets is used to observe and analyze the spatio-temporal sea surface wave field in a hydraulic wave tank. A new image sequence processing method, called DiSC (Dispersive Surface Classificator), was developed to create maps of physical parameters for inhomogeneous, dispersive surfaces. The analysis technique allows the determination and representation of hydrographic parameters such as the near-surface current-velocity vector, the water depth, and the full-directional wave spectra. DiSC, applied to image sequences of the sea surface, is useful for impact studies on maritime structures, beach studies, and other studies in wave facilities. The analysis method also has been tested for nautical X-band radar image sequences. The presented method enables oceanographers and offshore and coastal engineers to study the spatio-temporal behaviour of wave fields in nature and in hydraulic wave tanks for monitoring and planning purposes.