Topographic features of the Bristol Channel sea-bed: a comparison of SEASAT (synthetic aperture radar) and side-scan sonar images

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Abstract
Side-scan sonar data collected in 1977 and 1983 from the Bristol Channel are compared with 1978 SEASAT images, in order to determine the limiting physical dimensions of positive and negative topographic features detectable by SEASAT. The identification of sea-bed topography is related to a change in current speed which, in turn, is controlled bythe relief:water-depth ratio. In a water depth of 45mwith a surface current speed of about 70cms −1, for example, features > 11 m in relief and with a spacing > 500 m are visible. The widths of tone-change bands on SEASAT images are found to be related to the ‘effective’ widths of the topographic features that are modifying the flow conditions. The tone-change band sequence is related to positive and negative relief of the bed, under a particular current direction.