利用多層模型於全波形光達分析樹冠結構;Multiple Layer Model for Tree Structure Analysis in Full Waveform LIDAR

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题名:	利用多層模型於全波形光達分析樹冠結構;Multiple Layer Model for Tree Structure Analysis in Full Waveform LIDAR
作者:	林漢威;Lin,Han-Wei
贡献者:	太空科學研究所
关键词:	樹冠結構;全波形光達;多層模型;Tree Structure;Multiple Layer Model;Full Waveform LIDAR
日期:	2012-08-28
上传时间:	2012-09-11 18:26:00 (UTC+8)
出版者:	國立中央大學
摘要:	空載雷射掃瞄系統(ALS)是一種主動式的遙測系統，利用紅外線對地表的反射與紀錄，能快速的獲得物表的三維點座標。全波形光達系統(Full waveform LIDAR systems)是一種新型的主動式遙測系統，和傳統光達系統相比，全波形光達系統可以克服許多弊端。以取樣頻率為例，全波形光達的取樣頻率可以到達1GHz。因為在取樣頻率上全波形光達比傳統光達要高上許多，因此全波形光達回波資料在描述待測物上遠比傳統光達來得詳細。　　一般來說，求取點雲位置的演算法有很多，但大多數的方法都是在回波中找出一到兩個點來做為點雲的位置，對樹冠的結構並未多加描述。由於全波形光達在回波資訊上的紀錄是非常的完整，因此可以試著由回波資訊來分析樹冠的結構。　　本篇論文使用多層模型來模擬樹冠的結構。在模型中套用了輻射傳輸方程式來協助我們了解每個時間點光線的路徑和消散程度。在實驗的過程中，層間的反射率、透射率以及層與層之間的寬度是本實驗的重點。　　實驗所使用的光達資料是國立中央大學校園內闊葉樹和針葉樹的空載全波形光達資料。由實驗分析可以得知，闊葉樹－樹冠分佈廣且疏，針葉樹－樹冠分佈小且密，這兩組特徵在回波資料的分析上可以有明確的表現。Airborne laser scanning (ALS) is an active remote sensing technique where a laser emits short infrared pulses towards the Earth's surface and the backscattered echo is recorded. Full waveform LIDAR systems are new technology. Comparing to traditional LIDAR instrument, full waveform LIDAR system can overcome many drawbacks of traditional multi-echo LIDAR data. It permits recording with typical 1 GHz frequency sampling the received signal for each transmitted laser pulse. Therefore, full waveform LIDAR data can demonstrate the vertical structure of target, since the density of waveform is much higher than traditional multi-echo LIDAR data.Generally, point cloud is selecting the specific point in the wave, such as peak point, 50% intensity etc. Because full waveform LIDAR can record the complete waveform of the backscattered signal echo, a lot of information is carried by the full waveform LIDAR data. It is not adequate to express the information only using one point. Therefore, in this research we hope to use the multiple layers model to simulate the target such as canopy. Here we adopt the radiation transfer equation to simulate the route of light. To simulate the composition of target thoroughly, adjusting width of every layer is necessary.The LIDAR data used for experiments are from area in National Central University. The experimental data is divided into coniferous tree and broadleaf tree. From the result, the method is effective in fitting the waveform data. The broadleaf tree canopies are wide and sparse, and coniferous tree canopies are small and dense. These two sets of characteristics are clear from the analysis of the echo data.
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