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Using just a canopy height model to obtain lidar-level accuracy in 3D forest canopy shortwave transmissivity estimates
Agricultural and Forest Meteorology ( IF 6.2 ) Pub Date : 2023-05-20 , DOI: 10.1016/j.agrformet.2023.109429
Clare Webster, Richard Essery, Giulia Mazzotti, Tobias Jonas

This study presents a new model for calculating canopy shortwave radiation transmissivity from synthetic hemispheric images using only information contained within a canopy height model (CHM) – CanopyHeightModel2Radiation (C2R). The enhanced version calculates synthetic hemispherical images based on the geometric arrangement of the surrounding canopy while applying a statistical correction for canopy transmissivity using canopy thickness and tree species leaf area. The simple input data and statistical correction make this model suitable for estimating canopy transmissivity across large spatial extents typical of land surface models for which canopy transmissivity or radiation is a primary input variable. Performance of C2R-enhanced is assessed against hemispherical photographs, and compared to a basic version of C2R without transmissivity correction, and two versions of a Lidar2Radiation model (L2R-enhanced, L2R-basic) with either a basic representation of canopy structure or an enhanced representation including trunks and branches within tree crowns. The two enhanced models (L2R-enhanced and C2R-enhanced) perform best compared to hemispherical photographs, while the L2R-basic and C2R-basic models over- and underestimate canopy transmissivity, respectively. At 1-meter and 10-minute resolution, the two enhanced models perform similarly, but exact timing and location of transmissivity controlled by canopy structure is better represented in the physically explicit L2R-enhanced model. Across hourly and 25 × 25 m grid-averaged scales, both enhanced models achieve similar estimates of canopy transmissivity. Based on these results, it is recommended that the purely physically-based representation in the L2R-enhanced model is used when estimates of canopy transmissivity at high spatial and temporal (meter and minute) resolutions are necessary, while the computationally more efficient C2R-enhanced model is used when calculating canopy transmissivity within spatially aggregated grid cells, for example, as input into coarser-resolution land surface models. Incorporating C2R-enhanced into existing forest energy balance models creates exciting opportunities for investigating forest structure changes on forest hydrology and ecosystems across previously impossible spatial extents.



中文翻译:

仅使用冠层高度模型在 3D 森林冠层短波透射率估计中获得激光雷达级精度

本研究提出了一种新模型,用于从合成半球图像计算冠层短波辐射透射率,仅使用冠层高度模型 (CHM) 中包含的信息 - CanopyHeightModel2Radiation (C2R)。增强版根据周围树冠的几何排列计算合成半球图像,同时使用树冠厚度和树种叶面积对树冠透射率进行统计校正。简单的输入数据和统计校正使该模型适用于估算大空间范围内的冠层透射率,典型的陆地表面模型的冠层透射率或辐射是主要输入变量。C2R 增强的性能是根据半球形照片评估的,并与没有透射率校正的 C2R 基本版本以及 Lidar2Radiation 模型的两个版本(L2R 增强型、L2R 基本型)进行比较,它们具有树冠结构的基本表示或包括树冠内的树干和树枝的增强表示。与半球照片相比,两种增强模型(L2R 增强和 C2R 增强)表现最佳,而 L2R 基本模型和 C2R 基本模型分别高估和低估了冠层透射率。在 1 米和 10 分钟的分辨率下,两个增强模型的表现相似,但冠层结构控制的透射率的准确时间和位置在物理显式 L2R 增强模型中得到了更好的体现。在每小时和 25 × 25 m 网格平均尺度上,两种增强模型都实现了相似的冠层透射率估计。基于这些结果,建议当需要在高空间和时间(米和分钟)分辨率下估计冠层透射率时,使用 L2R 增强模型中纯粹基于物理的表示,而计算更有效的 C2R 增强模型模型在计算空间聚合网格单元内的冠层透射率时使用,例如,作为较粗分辨率陆地表面模型的输入。将 C2R 增强纳入现有的森林能量平衡模型,为调查森林水文和生态系统的森林结构变化跨越以前不可能的空间范围创造了令人兴奋的机会。当需要在高空间和时间(米和分钟)分辨率下估计冠层透射率时,建议使用 L2R 增强模型中纯粹基于物理的表示,而在计算时使用计算效率更高的 C2R 增强模型空间聚合网格单元内的冠层透射率,例如,作为较粗分辨率陆地表面模型的输入。将 C2R 增强纳入现有的森林能量平衡模型,为调查森林水文和生态系统的森林结构变化跨越以前不可能的空间范围创造了令人兴奋的机会。当需要在高空间和时间(米和分钟)分辨率下估计冠层透射率时,建议使用 L2R 增强模型中纯粹基于物理的表示,而在计算时使用计算效率更高的 C2R 增强模型空间聚合网格单元内的冠层透射率,例如,作为较粗分辨率陆地表面模型的输入。将 C2R 增强纳入现有的森林能量平衡模型,为调查森林水文和生态系统的森林结构变化跨越以前不可能的空间范围创造了令人兴奋的机会。作为较粗分辨率陆地表面模型的输入。将 C2R 增强纳入现有的森林能量平衡模型,为调查森林水文和生态系统的森林结构变化跨越以前不可能的空间范围创造了令人兴奋的机会。作为较粗分辨率陆地表面模型的输入。将 C2R 增强纳入现有的森林能量平衡模型,为调查森林水文和生态系统的森林结构变化跨越以前不可能的空间范围创造了令人兴奋的机会。

更新日期:2023-05-20
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