Egmond-an-Zee (Netherlands) and Teignmouth (UK)

Sea level; Other wave statistics; Wave height and period statistics; Transport in the water column; Bathymetry and Elevation

Sea level recorders; synthetic aperture radars; wave recorders

Shallow coastal seas: function and impacts of change: Theme 2 - Process experiments at small-scale: X-band radar Description The X-band radar project uses a standard marine X-band radar to produce images of the sea surface. A sequence of 64 radar images are recorded at intervals corresponding to the antenna rotation rate of about 2.25 seconds. Filtering The wave images can be filtered to leave individual wave frequencies. Averaging the image sequences When all the images in an image sequence is averaged, the wave signal tends to cancel out leaving persistent targets showing clearly above the sea clutter. Small objects such as buoys can be identified in the averaged images even in heavy sea conditions where such targets would be lost in the sea clutter signal of a single image. Breaking waves Breaking waves give a stronger signal than non-breaking waves on the radar. The average images can be used to identify areas of breaking waves which are related to the location of submerged sand bars. The technique has recently been used experimentally to follow the movement of an inshore sand bar at Egmond in the Netherlands. Wave and bathymetry analysis The image sequences can be analysed to produce maps of wavelength, celerity (wave speed) and direction. The changes in the wave behaviour caused by shoaling as the waves move into shallow water are used in a wave inversion algorithm to produce an estimated map of the water depth causing that wave behaviour. By subtracting the tidal water levels from the calculated water depths, bathymetric maps can be produced. Further work This is an ongoing research project at POL, and future work will be directed to improve the accuracy of the bathymetric estimates in very shallow water where linear wave theory breaks down, and the calculated depths are overestimated.

Proudman Oceanographic Laboratory
Joseph Proudman Building 6 Brownlow Street
Liverpool
Merseyside
L3 5DA
United Kingdom