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首页> 外文期刊>Agricultural and Forest Meteorology >Estimation of leaf area index in eucalypt forest using digital photography.
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Estimation of leaf area index in eucalypt forest using digital photography.

机译：使用数码摄影估算桉树林的叶面积指数。

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摘要

We tested whether leaf area index (L) in eucalypt vegetation could be accurately estimated from gap fraction measurements made using both fisheye and non-fisheye digital photography. We compared methods that measure the gap fraction at a single zenith angle (0 degrees or 57 degrees ), with fisheye photography that measures the gap fraction at multiple zenith angles. We applied these methods in an unthinned stand of the broadleaf tree species Eucalyptus marginata that had an initial L of 3. We removed one-third of the trees and reapplied the methods, and then removed another one-third of the trees and applied the methods a third time. L from the photographic methods was compared to L obtained from destructive sampling and allometry. We found that L was accurately estimated from non-fisheye images taken at the zenith, providing that the total gap fraction was divided into large, between-crown gaps and smaller, within-crown gaps, prior to using the Beer-Lambert law to estimate L. This rapid and simple method corrected for foliage clumping and provided estimates of crown porosity, crown cover, foliage cover and the foliage clumping index at the zenith, but required an assumption about the light extinction coefficient at the zenith. Fisheye photography also provided good estimates of L but only if the images were corrected for the gamma function of the digital camera, and the combined Chen-Cihlar and Lang-Xiang method of correcting for foliage clumping was used. The clumping index derived from fisheye images was insensitive to thinning but the calculated foliage projection coefficient was. Methods of obtaining and analysing gap fraction and gap size distributions from fisheye photography need further improvement to separate the effects of foliage clumping and leaf angle distribution..
机译：我们测试了是否可以通过使用鱼眼镜头和非鱼眼镜头数码摄影进行的间隙分数测量来准确估计桉树植被的叶面积指数（L）。我们比较了在单个天顶角（0度或57度）下测量间隙比例的方法与在多个天顶角测量间隙比例的鱼眼摄影方法。我们将这些方法应用在初始L值为3的阔叶树种桉树未稀疏林中。我们移除了三分之一的树木并重新应用该方法，然后再移除了三分之一的树木并应用了这些方法第三次。将来自摄影方法的L与通过破坏性采样和异速测量获得的L进行比较。我们发现，在使用比尔-兰伯特定律进行估计之前，只要将总间隙分数分为大的，冠间的间隙和较小的，冠内的间隙，就可以从在天顶拍摄的非鱼眼镜头图像准确地估算出L。 L.这种快速，简单的方法校正了叶丛的结实，并提供了天顶孔隙度，树冠覆盖率，叶面覆盖率和天顶处的叶丛聚集指数的估计值，但需要对天顶处的消光系数进行假设。鱼眼镜头摄影还可以提供很好的L估计值，但前提是必须针对数码相机的伽马功能对图像进行校正，并且使用Chen-Cihlar和Lang-Xiang组合的校正叶丛的方法。从鱼眼图像得出的聚集指数对稀疏不敏感，但计算出的叶子投影系数却不敏感。从鱼眼摄影获得和分析间隙分数和间隙尺寸分布的方法需要进一步改进，以分离叶子结块和叶片角度分布的影响。

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