Advancing retrievals of surface reflectance and vegetation indices over forest ecosystems by combining imaging spectroscopy, digital object models, and 3D canopy modelling
Advancing retrievals of surface reflectance and vegetation indices over forest ecosystems by combining imaging spectroscopy, digital object models, and 3D canopy modelling
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DOI：
10.1016/j.rse.2017.09.040
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发表时间：
2018
影响因子：
13.5
通讯作者：
D. Fawcett;D. Fawcett;W. Verhoef;D. Schläpfer;F. Schneider;M. Schaepman;A. Damm;A. Damm
中科院分区：
文献类型：
--
作者：
D. Fawcett;D. Fawcett;W. Verhoef;D. Schläpfer;F. Schneider;M. Schaepman;A. Damm;A. Damm
成像光谱为基础的方法提供了独特的能力，检索窄带植被指数，可以经验相关的功能性状的植物。然而，在地形复杂的地区，照明效应影响从高空间分辨率的航空或卫星数据检索这样的指数。在像素级的辐照度组件是由大气成分，以及瞬时照明表面传感器的几何形状。一个准确的直接和漫射辐照度分量的像素级描述是必要的，以执行大气校正，最终导致改善表面反射率，因此产品。我们评估三种大气校正策略，不同的方法来模拟瞬时以及像素丰富的漫射和直接辐照度。我们使用基于物理的方法结合数字高程模型（DEM），高分辨率数字对象模型（DOM），或从离散各向异性辐射传输（DART）模型的3D建模输出。在瑞士Laegern试验场获得的这种顶部的冠层反射率，用于评估一组指数（归一化差异植被指数（NDVI），光化学反射指数（PRI），以及叶绿素和类胡萝卜素指数）检索改善。我们证明，DOM和DART为基础的方法，提高检索平坦的投射阴影≤71%相比，使用DEM。在茂密的森林地区，改善不太显着。剩余的关键问题与在极端照明条件下高估表面反射率有关。
Imaging spectroscopy based methods offer unique capabilities for retrieving narrow-band vegetation indices which can be empirically related to functional traits of plants. However, in areas with complex topography, illumination effects affect the retrieval of such indices from high spatial resolution airborne or satellite data. Irradiance components at the pixel level are determined by atmospheric composition, as well as instantaneous illumination-surface-sensor geometries. An accurate pixel-wise description of direct and diffuse irradiance components is necessary to perform atmospheric corrections, finally resulting in improved surface reflectances and hence products. We assess three atmospheric correction strategies, differing in their approaches to simulate instantaneous as well as pixel-wise abundances of diffuse and direct irradiance. We use physically-based approaches in combination with either digital elevation models (DEM), fine resolution digital object models (DOM), or 3D modelling output from the Discrete Anisotropic Radiative Transfer (DART) model. The such obtained top-of-canopy reflectances at the Laegern test-site in Switzerland, are used to assess retrieval improvement for a set of indices (Normalized Difference Vegetation Index (NDVI), Photochemical Reflectance Index (PRI), as well as chlorophyll and carotenoid indices). We demonstrate that both, the DOM and the DART based approach, improve the retrievals for flat cast-shadows by ≤71% compared to using a DEM. In dense forest areas, improvements are less significant. Remaining key issues are related to overestimating surface reflectance under extreme illumination conditions.