多音束測深機音鼓的側旋與測深精度的探討研究

Abstract

當我們在對水下地形進行測繪時，測量到邊界區域的時候會有很多的斜坡地帶，像是湖泊的邊坡、淺海海岸邊坡和一些工程上的堤防等等，施測時船無法到達這些邊界地區的水線位置，用音鼓正打的方式就沒辦法對於這些斜坡地帶作測量，所以必須把測深機音鼓側旋一個角度，使外側音束和水面平行來對邊界地區作測量。正打區和側打區資料經處理後必須要可以接合，但是在做資料整合時會有正打和側打資料不吻合的問題；為了解決這樣的問題，就應對於音鼓側旋的測深精度做探討。 從分析結果可以知道在多音束音鼓側打時橫搖角的偏差所引起的誤差效應，是會使所測得的邊坡地形變緩或變陡；縱搖角的偏差則是會使邊坡的測深誤差在最外面兩側的音束會最大，垂直入射坡面的音束所產生的測深誤差最小；而當有航偏角的偏差量時，在音鼓正下方之音束之誤差都會為零；且越向岸線指向的音束的誤差量越大，會使坡度變得越緩。 要使多音束測深系統利用音鼓側旋45度能精準的測量出邊坡地形，必須要先解決一連串的問題，並遵照我們認為可以將誤差效應減到最低的施測方法來進行野外工作。所以可以從資料結果知道若Seabat9001型測深機的音束以60度的入射角為門檻時，旋轉音鼓以得到邊坡延伸到岸邊位置的地形值，其邊坡的坡度的下限為30度；在施測時如果邊坡走向不是很平直，航線的彎曲容易造成指向上的測深誤差效應加大，故我們不應該任意的調整施測船隻的航向；且測量時若離岸距離適當則航偏角的誤差效應主要會來自於轉彎所造成的航偏角延遲的誤差量。

When we are conducting underwater topography survey, in the bank region with steep slopes, in which cannot be measured by a down-looking multi-beam transducer. As a result it generally rotates the transducer such that the outermost beams can reach the surface of the slope. After survey, measurement collected by a down-looking multi-beam transducer will be merged the measurement collected by a tilted transducer, but experience indicated these two acts of data did not fit together while doing data processing. This study is the purpose to analyze the accuracy of soundings measured by a tilted multi-beam transducer. Results indicate that roll offset angle shall cause the slope at inaccurate gradient, and the pitch offset angle brings a slope of concave / convex slopeness the error shall appears most in the outermost beams that approach toward coastline, and gives gentle slope. In order to make sure that we can have high accurate slope topography by using a multi-beam transducer rotated 45 degree to the slope, this study thus provide the guidelines which may reduce the error to its minimal. When using Seabat 9001 multi-beam system, a 45degree tilted transducer can only be applied to the slope more than 30degrees. In addition, survey track shall not follow the coastline of “S” shape, because it will create error measurement significantly. Finally, survey track shall close to coastline as near as possible to reduce the effect caused by yaw offset.