空載測深光達於毛細波及重力波水面偵測之初探
Other Title
The Preliminary Study of Airborne LiDAR Bathymetry on Capillary-Gravity Water Surface Detection
Journal
航測及遙測學刊
Journal Volume
16
Journal Issue
3
Start Page
181
End Page
192
ISSN
1021-8661
Date Issued
2012-08
Author(s)
孟稚開
Abstract
空載測深光達因其具備安全性與高效能的作業方式，使其成為執行淺海潮間帶三維地形圖資測繪有利的工具。然由於水體與水底材質分屬性質不同的介質體及反射體，為獲得正確的水底地形，須先掌握測深光達的正確雷射脈衝往返行經路徑，並從波形分析中分別偵測雷射脈衝碰觸水面及水底之時間點，此兩時間觀測量結合定位定向資料精度攸關水底三維地形測繪品質甚鉅。然而現階段對於水面模型幾何以及偵測水面時間點之相關研究仍顯薄弱，直接影響水底地形測繪品質的不確定性。本研究主要工作在瞭解及分析單一雷射脈衝至水面之交互作用；在水面模型方面考量水面局部變異顯著的毛細波及重力波。除了藉由改變系統掃描幾何與風速探討對水面回波波形在幾何與能量上之影響以外，亦歸結在不同系統掃描幾何及風速因素下較合宜且準確的波形時間偵測法。結果顯示中高風速下，以50%上升時間演算法為較佳偵測方式；而於低風速下，以較低掃描角可獲取較明顯起伏之能量值。
Airborne LiDAR Bathymetry has been proven as an ideal technique for safely and efficiently operating in both shallow water and tidal flat areas for 3-D topographic mapping tasks. Yet the crucial challenge for acquiring terrain of water bottom is to precisely capture the trajectory of laser pulse when travelling between different medium, in the air, water and at the water bottom. Therefore, the quality of mapping 3-D bottom terrain would depend on how well the waveform analysis on determining the timing hitting water surface and water bottom can be designated. The goal of this research is to focus on comprehending the reaction of laser pulse on water surface, mainly wind-induced capillary-gravity wave facets. In particular, laser scanning geometry and the wind factor that shape the waveform geometrically and radiometrically are analyzed and thus the better timing detection method can be advised. It is suggested that adopting 50% risetime point, among others, would render better timing detection results when operating under moderate to strong wind speeds. In addition, when provided with gentle wind speed, bathymetry scanned in a lower off-nadir angle would gain richer energy. Through this study, better understanding of laser-to-water interaction is realized. Last but not least, this work may contribute to highlighting the significance of water surface detection which current airborne LiDAR bathymetric systems overlook.
Subjects
空載測深光達
波形
毛細波及重力波
時間偵測法
Airborne LiDAR Bathymetry
Waveform
Capillary-Gravity Wave
Timing Detection Method
Type
journal article