Effectiveness of the Reconstructed MODIS Typical-Angle Reflectances on Forest Biomass Estimation
Effectiveness of the Reconstructed MODIS Typical-Angle Reflectances on Forest Biomass Estimation
复制标题
DOI：
10.3390/rs14215475
复制
发表时间：
2022-10
期刊：
影响因子：
--
通讯作者：
Lei Cui;Mei Sun;Z. Jiao;Jongmin Park;Muge Agca;Hu Zhang;Long He;Yiqun Dai;Yadong Dong-
中科院分区：
文献类型：
--
作者：
Lei Cui;Mei Sun;Z. Jiao;Jongmin Park;Muge Agca;Hu Zhang;Long He;Yiqun Dai;Yadong Dong-
多角度的光学反射率测量，如那些从美国宇航局中分辨率成像光谱仪（MODIS）是敏感的森林三维结构，可能作为一个有用的代理估计森林结构变量，如地上生物量（AGB）-一个潜在的理论上承认，但很少探索。在本文中，我们研究了重建的MODIS典型角反射率的有效性，从热点，暗点，和最低点方向观察到的反射率，从理论和实践的角度来估计森林AGB。为了获得理论上的见解，我们首先测试了典型角度反射率的敏感性，森林AGB通过模拟使用4尺度双向反射分布函数（BRDF）模型。然后，我们建立了统计模型，以适应MODIS多角度观测和实地测量落叶阔叶林/混合温带森林AGB在美国东部的5个站点之间的关系，辅助半变异函数分析，以确定像素异质性的影响MODIS-AGB的关系。我们还确定了地形和季节对预测关系的影响。我们的研究结果表明，多角度反射与较少的可见阴影产生更好的AGB估计（热点：R2 = 0.63，RMSE = 54.28 Mg/ha;最低点：R2 = 0.55，RMSE = 59.95 Mg/ha;暗点：R2 = 0.46，RMSE = 65.66 Mg/ha）;近红外波段的典型角反射率对森林AGB最为敏感。我们还发现了强烈的敏感性估计精度的MODIS图像采集日期或季节。总的来说，我们的研究结果表明，目前的做法，利用单角度的MODIS数据可以是一个次优的战略AGB估计。我们提倡使用MODIS多角度反射率的光学遥感森林AGB或潜在的其他生态应用需要森林结构信息。
Multi-angle optical reflectance measurements such as those from the NASA moderate resolution imaging spectroradiometer (MODIS) are sensitive to forest 3D structures, potentially serving as a useful proxy to estimate forest structural variables such as aboveground biomass (AGB)—a potential theoretically recognized but rarely explored. In this paper, we examined the effectiveness of the reconstructed MODIS typical-angle reflectances—reflectances observed from the hotspot, darkspot, and nadir directions—for estimating forest AGB from both theoretical and practical perspectives. To gain theoretical insights, we first tested the sensitivities of typical-angle reflectances to forest AGB through simulations using the 4-scale bidirectional reflectance distribution function (BRDF) model. We then built statistical models to fit the relationship between MODIS multi-angle observations and field-measured deciduous-broadleaf/mixed-temperate forest AGB at five sites in the eastern USA, assisted by a semivariogram analysis to determine the effect of pixel heterogeneity on the MODIS–AGB relationship. We also determined the effects of terrain and season on the predictive relationships. Our results indicated that multi-angle reflectances with fewer visible shadows yielded better AGB estimates (hotspot: R2 = 0.63, RMSE = 54.28 Mg/ha; nadir: R2 = 0.55, RMSE = 59.95 Mg/ha; darkspot: R2 = 0.46, RMSE = 65.66 Mg/ha) after filtering out the effects of complex terrain and pixel heterogeneity; the MODIS typical-angle reflectances in the NIR band were the most sensitive to forest AGB. We also found strong sensitivities of estimated accuracies to MODIS image acquisition dates or season. Overall, our results suggest that the current practice of leveraging only single-angle MODIS data can be a suboptimal strategy for AGB estimation. We advocate the use of MODIS multi-angle reflectances for optical remote sensing of forest AGB or potentially other ecological applications requiring forest structure information.