地面光達系統可大量且快速獲取掃瞄物體的三維坐標值及反射強度值（合稱光達點雲），三維坐標值可應用於建物模型重建、防災與災害調查、隧道施測、水壩變形監控、建築古蹟維護等，反射強度值則可應用於光達點雲分類。反射強度值與物體表面的反射率有關，理論上可依光達方程式（lidar equation），改正反射強度值受距離及角度之影響，應用於分類辨識。實際上光達系統受限於硬體架構，必須修改反射強度值以簡化感應器之設計與方便資料儲存，故造成實測資料不符於光達方程式之理論預測，使得光達點雲分類精度不高。

本文以Optech ILRIS-3D 雷射掃描儀之地面光達系統為例，分別探討ILRIS-3D 所量測之二種反射強度值之資料特性：原始反射強度值（數值分佈0～25500）與灰階反射強度值（數值分佈0～255）。本文以一系列的實驗探討電池電量、陰影與距離對於反射強度值之影響。並進一步提出『動態同心圓法』以灰階反射強度值辨識物體分類。

Ground-based lidar system can rapidly gather highly detailed spatial information and intensity data of the scanned target. They have been applied successfully for building model reconstruction, disaster investigation, tunnel and dam monitoring, and architecture maintenance. Because the intensity data is related to the surface type of the scanned object, they can be used for point cloud classification by using lidar equation to correct for distance and angle effect. However, in order to accommodate the hardware design for the ease of data storage, the intensity data are usually altered by lidar system. As a result, the lidar equation can not be readily applied on the lidar data, hence a high classification accuracy is difficult to achieve.

In this study, two types of intensity data of an Optech ILRIS-3D system are examined, raw intensity (values range 0 ~ 25500) and gray-level intensity (values range 0 ~ 255). Experiments are conducted to examine the influence of battery voltage, shade cast on the scanned target, and distance on the intensity data. Finally, a new method, dynamic concentric method, is proposed to perform the point cloud classification based on gray-level intensity data.

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