Video Estimation of Foreshore Topography Using Trinocular Stereo
Keywords:Nearshore, swash, image processing
Previous researchers have shown that topographic response to swash processes is typically rapid and occasionally substantial. However, the methods used to document these fluctuations were often labor intensive, and usually resulted in only a few estimates at a limited number of survey locations. We present an automated technique for the detection of small- and large-scale variations in foreshore topography that has both high spatial and temporal resolution. This technique utilizes trinocular (three view) stereogrammetry to recover topographic Information from a set of synchronous, overlapping video images. The foreshore topography is mapped by following the movement of the sharply defined foamy runup edge that visibly contrasts with the darker, underlying, saturated beachface. Under field test conditions, the video method has a vertical accuracy of between 1 and 3 cm, comparable to that of traditional surveying methods and to theoretical expectations. The advantages of this new technique are that the topography estimates are extremely dense on the order of thousands of estimates within a 100 m2 region, that estimates can be made on a wave by wave basis, and that sampling requires minimal manpower. This method may prove useful in the study of rapid foreshore sediment transport dynamics, such as the formation of beach cusps.