應用光達技術於人工林之經營與監測

人工林經營技術著重於以疏伐作業調整立木生長空間，而傳統疏伐作業中，係以定性與定量方式，訂定疏伐作業準則，而現地作業時如何配合林木經營策略，疏伐木如何選擇及如何有效監測疏伐效果，為疏伐作業之重要議題。本研究擬透過三維雷射掃瞄系統(光達)，探討如何以非破壞性方式，調查及監測樣區之立木三度空間資訊，及如何應用光達系統所萃取之資訊應用於人工林經營。本研究利用地面光達配合地面調查資料，以自動化方式獲取疏伐作業所需之林分性態值資料，包括樹高、胸高直徑、樹冠高、立木位置圖等資料，評估地面光達於人工林測計之可行性。結果顯示，透過地面光達系統確實可正確獲得立木資訊，對於永久監測樣區而言，利用光達系統之不同拍攝位置，可消除掃瞄的遮蔽效應，藉由高密度的點雲資料，立木位置測量的準確性，可控制1 m以上誤差低於11%，且可直接測量立木樹高與不同樹幹位置之直徑，而單位體積之點雲資料量不同，影響立木直徑推估之效度，當點雲資料量(2.84 points cm-2)比例，由100% 依比例降低時，以最大外切圓擬合法，所推估的立木位置座標，會隨著點雲不足而漸漸向外偏移，造成立木位置誤差。LiDAR系統所收集之光譜反射特徵，有助於利用點雲資料，進行枝葉分離之自動化分析，而透過地面光達所獲得之樹高與樹徑之3D資料，可進行非破壞性之區分材積估算並建立立木材積式。利用地面光達點雲資料，所推估之立木位置，可萃取與林木生長競爭之相關因子，進而推估林木競爭指數，探討立木生長競爭之相關議題。以立木光達點雲資料，推估立木不同高度直徑，其與實測值之平滑曲線接近，但當林木高度接近枝下高或樹冠基礎高時，會因林木枝葉的自我遮蔽，造成枝梢直徑推估之誤差。光達點雲資料之空間分布，所推估之樹冠高程模型，以樹冠高度之灰階值統計，藉由二值法所訂之閥值，可將林木與地表背景分離，獲取樹冠孔隙資料，其結果對於林冠孔隙可提供平面及垂直資訊，可供為孔隙之動態監測。藉由地面光達所建立之林木測計、立木競爭指標、林冠孔隙及與疏伐監測資訊，可更準確的量化疏伐效益及增加林木狀態變化之資訊，對於人工林經營可提高森林資源調查效率，及擴充森林資源監測資訊。

關鍵字

森林經營；疏伐作業；地面光達；三維雷射掃瞄；林分性態

並列摘要

The techniques of artificial forest management are focused on thinning operation and space adjusting, and the criteria of traditional thinning operation are based on quantitative and qualitative data. How to select thinning timbers and monitor the effects of thinning are the important subjects in artificial forest management. In this study, using 3D scanning Light Detection and Ranging (LiDAR) systems, which are the non-destructive methods, to investigate and monitor individual trees in artificial forest sample areas. Using ground-based LiDAR and traditional field survey data to obtain individual tree characteristic values which included tree height, diameter at breast height, canopy height, tree location map and evaluated the feasibility of ground-based LiDAR data in artificial forest areas. Results showed that the accurate information from the ground-based LiDAR system in permanent sampling plots, and different scanning stations could decrease occlusions. By using high density point cloud data, the error on the individual tree location that was over 1 meter could be controlled to less than 11% and the height and diameter at different height of the tree could also be measured directly by the LiDAR systems. Different number of point cloud affected the accuracy of diameter. When the ratio of point cloud fell below 100%(2.84 points cm-2), the coordinates of individual trees would shift from the accurate position on the circle fitting because of insufficient points. Results also showed that by the characteristics obtained from the LiDAR spectrum, the systems could automatically separate leaves, branches and stems and could also establish tree volume model non-destructively with tree height and DBH data obtained from ground-based LiDAR. The tree competition index could be estimated by the individual trees location, diameter at different height, tree distance and DBH. The diameter at different height could be estimated by the cloud data of LiDAR that were to approach with actual value; however, due to self-occlusion of the crown, errors may occur when estimating branch diameters. Using threshold value to classify gap fraction, results showed that were accurate. Therefore, the results could be used to analyze the horizontal and vertical canopy structure, it was beneficial for the monitoring of plot dynamics in forest areas. Ground-based LiDAR could be used to determine tree measurements, tree competition and canopy gap which solve the problems of quantification and spatial research and also help with the stimulation of thinning operations. Results of this study were beneficial to artificial forest management and improved the forest resource inventory methods.

並列關鍵字

Forest management ； Thinning operations ； Groud-based LiDAR technology ； 3D laser scanning ； Stand characteristics

參考文獻

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應用光達技術於人工林之經營與監測

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