中文摘要
空載光達為生產數值高程模型(Digital Elevation Model, DEM)之主要來源。DEM經常運用於變形監測、防災規劃等等方面，因此DEM的精度品質可謂相當重要。其品質與空載光達測製之點雲資料為正相關。在空載光達掃瞄作業之飛航規劃階段，地形平緩地區之點雲密度的估計可以透過一些數學式即可運算而得。然而，在地形起伏較大的區域，點雲密度的估計一直都是一個挑戰。因此，本研究透過光達點雲模擬程式(Heidelberg LiDAR Operations Simulator, HELIOS)進行點雲密度模擬。模擬的地形模型採用由內政部提供之台灣20公尺網格數值地形模型資料。當點雲密度模擬於大範圍之測區進行模擬時，需花費大量的運算時間。由於飛航規劃階段需要在有限的時間之下完成，以避免影響後續掃瞄作業安排，因此模擬運算的時間需要縮短。本研究提出利用降低模擬程式中的雷射脈衝頻率以縮短運算時間，模擬之點雲密度會同時下降。故需要進行點雲密度值的補正。本研究將以八條航線以及規劃之飛航參數進行模擬，並且探討縮短運算時間所帶來之影響。最後將進行加快運算速度的效益探討。
關鍵字:空載光達、點雲密度、光達模擬、空載光達掃瞄飛航規劃

Abstract

Airborne Laser Scanning (ALS) is commonly used to generate the Digital Elevation Model (DEM). The important information such as deformation monitoring and disaster reduction planning can be derived from the DEM. The quality of DEM is positively correlated to the density of the point cloud. In flat terrain, the point density can be estimated by using the simple equation as compared to the complicated terrain, the estimation of the point density is much more complex through the equations. Therefore, this research is proposed to simulate point density through a laser scanning simulator, namely the Heidelberg LiDAR Operations Simulator (HELIOS). A 20-meter Taiwan DEM model of Taiwan was employed for HELIOS simulation. However, computation time becomes a critical issue when the ALS survey covers a large area, i.e., a large portion of Taiwan Island. In order to reduce the simulation time, the downsampling process was conducted by reducing the pulse frequency in HELIOS which was followed by compensating for the reduction factor. The results have demonstrated that different parameter settings of the scanning flight lines with different downsampling rate was used to explain the effect of downsampling process. Finally, the effect of the simulation time was tested.
KEYWORDS: Airborne Laser Scanning; simulation; HELIOS;ALS flight planning; point density

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