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Marine radar imaging of nearshore bar structure: biases due to tidal and RMS wave height variations

We present results of an experiment using a marine radar to image the surface roughness patterns due to wave breaking and energy dissipation over coastal offshore sand bars. Data were collected at the US Army Coastal Engineer Field Research Facility research pier, Duck, NC. The experiment was designed to compare marine radar and video imaging mechanisms of wave breaking and dissipation that is responsible for surface expression of the bar using the two methods. The approach uses half-hourly averages of a sixty-second sequence of thirty-two images of wave propagating onshore. This averaging causes individual wave patterns to smear out to a weak background level, and the region of enhanced wave breaking and dissipation over the bar to stand out in the image. The experiment studies the bar location shore-normal biases associated with the effects of local mean tide height and rms wave height in their role of determining the location of wave breaking and dissipation relative to the bar position. In this work we show examples of the analysis used, with comparisons made between video imaging and the radar imaging approaches. Quantitative comparisons of offshore bias are presented at the conference