基於水下數值高程模型對於偵測河川環境、獲取河床底質資訊以及量測水工模型有重要價值。本研究使用近景攝影測量以及光達技術獲取水下數值高程模型，並發展出修正折射影響之改正方法。本研究分為兩大主體，其一為近景攝影測量實驗，藉由真實數值高程模型與水下數值高程模型之系統偏差，建立改正回歸式修正水下高程。另一主體為光達技術，以Snell’s Law為基礎建立水下模型改正方法。實驗中以覆蓋Ottawa標準沙之碗狀模型體為建模對象，其直徑為15cm，高度為3cm。藉由比較無水環境中建立出的數值模型(參考真值)以及由5公分開始依序增加5 cm至25cm水深建立之數值模型，比較不同水深下數值高程模型的變化，可得其RMSE與平均值的變化量。本研究所提出之改正方法均有助於快速改正各水深之數值高程模型，結果精度在數值攝影測量實驗中，RMSE數值均小於 1.5 mm， 而在光達技術實驗中，RMSE 均小於4.0 mm。

Acquiring underwater Digital Elevation Model (DEM) plays a relevant role in sediment environment process observation, the structure of river-bed and the hydraulic model elevation measurements. This research has generated the underwater DEM from close-range photogrammetry and Light detection and ranging (Lidar) techniques with green-wavelength Terrestrial Laser Scanner (TLS) and reports a correction procedure for light refraction effects to estimate underwater topography.
In this research, we developed a reliable and stable method to correct the water refraction effect by regression method. We also developed the algorithm based on Snell’s Law to correct the water refraction effect in TLS point clouds. A bowl-shaped model with the diameter of 15 cm and the height of 3 cm covered by the Ottawa standard soil was submerged into the water depths from 5 cm to 25 cm for accuracy assessment of our methods. The results show that the corrected DEM has a RMSE value less than 1.5 mm for photogrammetry technique and a RMSE value less than 4.0 mm for lidar technique, respectively.

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