東沙環礁測深光達精度驗證

Abstract

測深光達具有高效率獲取高密度測深資料之特性，適合在淺水及水質清澈處之環境作業。然而，其測深精度容易受到海面波浪及陡峭地形等因素之影響。本研究之目的即是對測深光達在東沙環礁區域施測之成果進行精度估計，為估計測深光達水深之精度，分別對內部及外部精度進行評估及探討。由內部精度可知測深資料彼此之間一致性，而外部精度則須藉由其他水深測量方式所得資料進行資料比對，最常與聲納測深資料比對。 本研究之內部精度評估方式包含三項，將兩條東西航向之檢核線與南北航向測線進行交叉測線檢測、相鄰航帶之重疊區之高程比對及將2x2m加密測區加入比較不同測點間距點位高程；外部精度引入單音束聲納測點與測深光達資料比對。內部精度成果顯示交叉航線檢測時檢核線A及檢核線B平均較差在5到7cm之間，標準偏差為23及23.1cm重疊航線檢測平均較差為5cm，標準偏差為30cm。外部精度成果則顯示在測深光達與聲納之間平均較差為30cm，在研究區之內潟湖區域有諸多礁體分布，地形起伏較大，相較於平坦區，此區較差及標準偏差皆大於平坦區。當坡度增加，對應的較差之RMSE曲線也呈正相關成長。

Airborne bathymetric LiDAR is capable of obtaining high density bathymetry data, especially when operates in shallow and clean water. However, the capability is affected by the turbidity of water and steepness of seabed. Evaluating the accuracy of airborne bathymetric LiDAR result of Dongsha atoll is the main objective of this research. In order to obtain the accuracy of height derived from bathymetric LiDAR, one can calculate and analyze the internal and external accuracy. Internal accuracy check includes cross-line check of cross-line comparing with other survey lines, overlap check between adjacent lines and comparing height discrepancy between different spot spacing points while in external check bathymetric LiDAR points compared with Single-beam points. Results show the mean difference and standard deviation is 6cm and 23cm in internal cross-line check, 2 cm and 30cm in internal overlap check, and 30cm between single beam and bathymetric LiDAR. Obviously, RMSE is proportional to slope after analyzing the terrain effect of height difference.