Comparison of radar and video observations of shallow water breaking waves

Simultaneous microwave and video measurements of shallow water breaking waves are presented. A comparison of the data from the two sensors shows that short-duration spikes in the measured X-band radar cross section are highly correlated with the presence of breaking waves in the video imagery. In addition, the radar backscatter from shallow water breaking events is responsible for 40% to 50% of the total cross section, which is a much larger contribution than typically observed for deepwater breaking events. Based on estimates of the area of individual breaking regions determined from digitized video images, the radar cross section per unit area of the turbulent breaking region is shown to be well approximated by a value of -1.9 dB at 31° grazing. Finally, there are some differences between the radar and video signals that suggest that microwave radar may be less sensitive than video techniques to relict foam not associated with active wave breaking. In general, the results indicate that radar is a very good detector of shallow water breaking waves and suggest that radar can be used for the measurement of the spatial and temporal variations of wave breaking.