VIDEO ESTIMATION OF FORESHORE TOPOGRAPHY USING TRINOCULAR STEREO

Previous researchers have shown that topographic response to swash pro cesses is typically rapid and occasionally substantial. However, the m ethods used to document these fluctuations were often labor intensive and usually resulted in only a few estimates at a limited number of su rvey locations. We present an automated technique for the detection of small- and large-scale variations in foreshore topography that has bo th high spatial and temporal resolution. This technique utilizes trino cular (three view) stereogrammetry to recover topographic information from a set of synchronous, overlapping video images. The foreshore top ography is mapped by following the movement of the sharply defined foa my runup edge that visibly contrasts with the darker, underlying, satu rated beachface. Under field test conditions, the video method has a v ertical accuracy of between 1 and 3 cm, comparable to that of traditio nal 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 m(2) region , that estimates can be made on a wave by wave basis, and that samplin g requires minimal manpower. This method may prove useful in the study of rapid foreshore sediment transport dynamics, such as the formation of beach cusps.