用无人机多角度影像量化地物反射率各向异性，揭示观测几何对辐射一致性的影响。
Multi-Angular Reflectance Anisotropy Observed from UAV Multispectral Imagery
- 通过SFM优化相机参数，从多视角影像中联合提取反射率与观测几何参数。
- 红边和近红外波段反射率在不同观测角下波动达119%-137%，存在显著各向异性。
- 适合从事遥感定标、植被监测或低空影像分析的研究者参考。
由于低空飞行和广角成像，无人机多光谱影像天然包含多角度观测，可能引入由几何引起的辐射变异。本研究提出一种面向几何的多角度观测提取流程，从双向反射分布函数（BRDF）角度量化观测几何的影响。具体而言，利用结构光束法（SFM）精化相机内外参，并将正射影像上标注的均质区域重投影到多个不同视角的原始子图像上，实现同一地物在不同观测方向下的多波段反射率与观测几何参数的联合提取。进一步采用波段级极坐标可视化分析（VZA, RAA）域。在草地目标上的结果表明，十个波段均呈现明显的反射率各向异性，其中红边与近红外波段最大与最小反射率差异达119%-137%，说明观测几何对辐射一致性有不可忽视的影响。
原文摘要 · Abstract (English)
UAV multispectral imagery naturally contains multi-angular observations due to low flight altitude and wide field-of-view imaging, which may introduce geometry-driven radiometric variability. This study proposes a geometry-aware multi-angular observation extraction workflow to quantify observation-geometry effects from a BRDF perspective. Specifically, camera intrinsics and extrinsics are refined via structure-from-motion (SFM), and homogeneous regions annotated on an orthomosaic are reprojected onto multiple raw sub-images acquired from different viewpoints. This enables joint extraction of multi-band reflectance and observation geometry parameters for the same ground targets under varying viewing directions. The extracted observations are further analyzed using band-wise polar visualization in the (VZA, RAA) domain. Results on a grassland target show clear reflectance anisotropy across ten bands, with red-edge and nearinfrared bands exhibiting 119-137% variability between maximum and minimum reflectance, indicating non-negligible observation-geometry effects on radiometric consistency.
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