为了低成本和方便地评估植被冠层结构和底层照明,已经开发了几种智能手机应用程序。像标准的半球形摄影,这些应用程序中的大多数都需要用户做出有关图像处理的决定,对测量的可重复性提出了挑战。在这里,我报告了CanopyCapture的测试,在没有用户任何输入的情况下即时估计冠层间隙百分比的应用程序,并具有直观的调平机制的附加优点。
将CanopyCapture的间隙分数估计值与LAI-2200C冠层分析仪计算的间隙分数值进行比较,在新西兰的两个对比鲜明的常绿温带森林中:一个均匀的南部山毛榉(Nothofagus)林和一个古老的罗汉果/阔叶森林。使用广角适配器重复进行这些比较,以将智能手机相机的视野从45°增强到65°。我还问CanopyCapture的结果是否取决于天空条件(晴天与阴天)和使用的智能手机类型。
CanopyCapture输出与LAI-2200C计算的间隙分数显着相关(R2=0.39),并且使用广角适配器将该值提升到0.56。然而,在均匀的Nothofagus林分中,CanopyCapture的产量与LAI-2200C的产量没有显着相关,其中冠层结构的空间变化较小。尽管与LAI-2200C相比,对间隙分数的变化不那么敏感,尽管如此,CanopyCapture还是能够检测到所研究的两个森林之间平均间隙分数的差异。完整冠层下的CanopyCapture结果没有受到天空条件的显著影响,但是在晴朗的天气中,直射光从树干上的反射会导致对破碎的树冠和缝隙下方的缝隙分数的略微高估。不均匀或零散的云层也可能导致大型顶篷开口下方的错误读数。三种不同型号的智能手机给出了不同的结果。
CanopyCapture为比较多个林分/森林中的平均冠层间隙分数提供了快速且可重复的代理,前提是使用大样本量。建议在阴天下进行测量,涉及多个运营商的研究将需要标准化智能手机,以确保结果的可比性。虽然广角适配器可以提高性能,CanopyCapture的低灵敏度可防止对林下各个植物的光环境进行高分辨率比较。
Several smartphone applications have been developed for the purpose of low-cost and convenient assessments of vegetation canopy structure and understorey illumination. Like standard hemispherical photography, most of these applications require user decisions about image processing, posing challenges for repeatability of measurements. Here I report a test of CanopyCapture, an application that instantaneously estimates percentage canopy gap fraction without any input from the user, and has the added advantage of an intuitive levelling mechanism.
Gap fraction estimates by CanopyCapture were compared with gap fraction values computed by the LAI-2200C Canopy Analyzer, in two contrasting evergreen temperate forests in New Zealand: an even-aged southern beech (Nothofagus) stand and an old-growth podocarp/broadleaf forest. These comparisons were repeated using a wide-angle adapter to enhance the smartphone camera\'s field of view from 45 to 65°. I also asked if CanopyCapture results depended on sky condition (sunny vs. overcast) and on the type of smartphone used.
CanopyCapture output was significantly correlated with gap fraction computed by the LAI-2200C (R2 = 0.39), and use of the wide-angle adapter lifted this value to 0.56. However, CanopyCapture output was not significantly correlated with LAI-2200C output in the even-aged Nothofagus stand, where there was less spatial variation in canopy structure. Despite being much less sensitive to variation in gap fraction than the LAI-2200C, CanopyCapture was nevertheless able to detect differences in average gap fraction between the two forests studied. CanopyCapture results beneath intact canopies were not significantly affected by sky condition, but reflection of direct light off tree trunks in sunny weather caused slight overestimation of gap fraction beneath broken canopies and gaps. Uneven or patchy cloud cover can also cause erroneous readings beneath large canopy openings. Three different models of smartphone gave different results.
CanopyCapture offers a rapid and repeatable proxy for comparisons of average canopy gap fraction in multiple stands/forests, provided large sample sizes are used. Measurement under even overcast skies is recommended, and studies involving multiple operators will need to standardize smartphones to ensure comparability of results. Although wide-angle adapters can improve performance, CanopyCapture\'s low sensitivity prevents high-resolution comparisons of the light environments of individual understorey plants within a stand.