側掃聲納影像在邊坡之應用研究

Abstract

傳統上以側掃聲納進行水下地貌的探勘，取得良好的聲學影像，透過回散射訊號的特性辨認目標物、海床上的紋理和波痕，並能與多音束地形資料相互對照，但通常在較平緩的區域下進行。而許多的水下人造建物都位於沿岸，或是在邊坡上，例如：堤防、水庫壩堤、水力發電設施等。在斜坡上為了使側掃聲納的影像更清晰，過去研究指出可調整拖魚旋轉的角度便能展示出良好的影像，不過當旋轉角度不合適，很容易造成影像強弱分佈不均，坡面上地貌難以辨識的問題。另外，為了在邊坡上做影像測繪，以旋轉拖魚的方向使收錄的影像更清楚，容易造成影像定位上的誤差，本研究利用斜打的成像幾何，計算拖魚指向位置，透過平面投影的方式，在每次乒發聲波的剖面上取得聲波在斜坡上的反射點以及高程值，計算反射點與拖魚的距離，以及投影點的距離，重新輸出成新的座標系統，於是我們可以將水深資料與側掃聲納影像匹配在一起，結果不但在影像上能得到讀取斜坡上的地貌資料，也能同時讀取地形資訊。本論文將此方法應用於日月潭邊坡上之水力發電設施，透過此方法去繪出進水口、出水口柵欄，以及壩堤影像，並分析他們成效。

Traditionally side scan sonar underwater topography exploration and achieved good acoustic image, identifying the target, seabed texture and ripples through the back scattering signal characteristics, and can be cross-referenced with the multibeam terrain data, but It is usually carried out in a relatively flat area. Many things are built man-made underwater terrain located along the coast, or also on the underwater slope, for example: embankments, embankment dam reservoirs, hydroelectric facilities and so on. On a slope in order to make the image clearer side-scan sonar, past research indicates that the main tone mapping according to the slopes and side-scan sonar beams pointing to adjust the angle of rotation and drag fish ranging study the angle of rotation of the imaging geometry, in accordance with tow fish on the imaging direction of rotation can be divided into reverse and forward slope side slope side, when the rotation angle, when appropriate, will be able to show a good side-scan sonar image, but when the rotation angle difference between the two but when too large, improper easily lead to uneven distribution of the strength of the image, on the slope of the landscape it is difficult to identify the problem, drag the rotation angle of larger fish, so the sound beam reverse side of the slope toward the water surface firing in imaging, reflecting forward image slope side is also more recognizable on the forward side of the slope difference. In addition, in order to make the slope image mapping, drag to rotate the direction of the fish to make video recording more clearly, but also likely to cause error image on positioning, not directly match the multibeam terrain, this study swash fight the imaging geometry, calculate tow fish is pointing downward position, adjust the actual position of the tow fish space through projection plane way to obtain sound reflection point and elevation values on a slope in the cross-sectional every ping sent sound waves, calculate the reflection point fish and drag the distance from the projected point and re-exported into a new coordinate system, so we can match the depth and data together with the side-scan sonar images, results not only in the image not only get to read on the slopes landform image data, terrain information can be read simultaneously. In this paper, this method is applied to hydroelectric facilities on the slope of the Sun Moon Lake, through this way to draw water inlet and outlet fence and embankment dam image, and analyze their results.