結合雙表面法與光達技術估計孟宗竹之葉面積

Abstract

本研究結合雙表面法與光達技術, 建立孟宗竹外罩表面積、樹冠碎形維度與全株葉面積三者之間的關係式, 除了印證雙表面法在估計植物葉面積的功效外, 還比較錐狀體法、拋物體法、雙橢球法、凸包法與樹冠解析法等五種植物外罩表面積的估算方法, 並進一步比較孟宗竹樹冠碎形維度與先前研究的差異。 結果顯示, 雙表面法如果搭配光達來估算樹冠碎形維度,孟宗竹全株葉面積無截距迴歸的決定係數可達 0.85。 外罩表面積的估算,以光達測量的凸包法表現最佳, 其次為人工測量的拋物體法。顯見雖然沒有光達測量, 透過人工的方式計算外罩表面積也有近似的成果。 孟宗竹葉平均碎形維度為 2.186, 接近先前研究的優勢木 2.2。未來如果不需要精確估算植物葉面積, 可考慮採用 2.2 的碎形維度數值。 本研究認為, 雙表面法確實可應用於推估植物的葉面積, 但其目標以單株植物或人工林純林為佳。 以光達輔助測量可得到較佳的結果, 但亦可使用相近植物種的碎形維度數值及人工測量植物外罩表面積來取代光達測量。

This study was aimed to combine two-surface method with LiDAR technology, and to construct an equation which included envelope surface, canopy fractal dimension and total leaf area of Moso bamboo ({sl Phyllostachys edulis}). Except of canopy fractal dimension, I also compared five methods of estimating bamboo envelope surface, which includes cone-shape method, paraboloid-shape method, double-ellipsoid-shape method, convex hull method and canopy analysis method. Results showed that, by combining two-surface method with LiDAR, the coefficient of determination in linear regression without the intercept term could reach up to 0.85. By correlating with total leaf area, convex hull method aided by LiDAR performed best in estimating envelope surface, seconded by paraboloid-shape method of manual measurement. This indicates estimating envelope surface by manual measurement could have similar performance with methods estimating by LiDAR. Mean fractal dimension of Moso bamboo was 2.186, close to the estimated 2.2 for dominant trees in previous studies. One could consider using 2.2 as fractal dimension for rough estimates of leaf area for moso bamboo in the future. I conclude two-surface method can be applied to estimate leaf area of plants and is especially suitable for single plants or monocultural plantations. Estimation aided by LiDAR should provide better results. However, the LiDAR measurement could be replaced by using fractal dimension estmates for similar plant species and manual measurements of envelope surface.