Preliminary study for in-site observation of wave runup on a natural beach using an unmanned aerial system
|關鍵字:||波浪溯升;無人飛機;鏡頭變形;邊緣偵測;Wave runup;Unmanned aerial vehicle;Lens distortion;Boundary detection|
Runup is an important factor in the coastal sediments. Few previous studies on in-site wave runup were fulfilled due to complexity of runup in a natural beach and limited for in-site observation. In this study an unmanned aerial system with a full-chip camera was set up to have living recording the whole process of wave runup. Through bilinear transformation between image coordinates and world coordinates for each picture instant wave runup along the shoreline was computed to explore its characteristics. Some techniques of image processing were used to obtain clear waterline of each picture, including the image binarization, enhancement, morphological and the Canny algorithms, and piecewise linear regression. An applicable method of bilinear beach slopes instead of the equivalent slope method was proposed to closely represent the actual beach profile. A comparison of R_(2%) between the measured and estimated ones by empirical formula of Mase (1989) shows less difference by the mean squared error of 0.096m and bias of -0.043 m, indicating relative values of 27.1% and 12.1%, respectively. The new-moon beach as the present research base has a submerged small bar. According to the long wave theory, the transmitted coefficient of a long wave over the submerged bar is about 0.93, which has slight effect on runup. Northern waves during the winter time, have southward velocity component to push water to the trough of the submerged bar and to increase runup at this portion. Wave runup on Topography of the natural beach is commonly complex so that wave runup on the natural beach are different and have time delay in different positions. This is an interesting academic topic and the results are valuable to coastal engineering.
|Appears in Collections:||Thesis|