Accurate quantification of the spatial variation of canopy size is crucial for vineyard management in the context of Precision Viticulture. Biophysical parameters associated with canopy size, such as Leaf Area Index (LAI), can be estimated from Vegetation Indices (VI) such as the Normalized Difference Vegetation Index (NDVI), but in Vertical-Shoot-Positioned (VSP) vineyards, common satellite, or aerial imagery with moderate-resolution capture information at nadir of pixels whose values are a mix of canopy, sunlit soil, and shaded soil fractions and their respective spectral signatures. VI values for each fraction are considerably different. On a VSP vineyard, the illumination direction for each specific row orientation depends on the relative position of sun and earth. Respective proportions of shaded and sunlit soil fractions change as a function of solar elevation and azimuth, but canopy fraction is independent of these variations. The focus of this study is the interaction of illumination direction with canopy orientation, and the corresponding effect on integrated NDVI. The results confirm that factors that intervene in determining the direction of illumination on a VSP will alter the integrated NDVI value. Shading induced considerable changes in the NDVI proportions affecting the final integrated NDVI value. However, the effect of shading decreases as the row orientation approaches the solar path. Therefore, models of biophysical parameters using moderate-resolution imagery should consider corrections for variations caused by factors affecting the angle of illumination to provide more general solutions that may enable canopy data to be obtained from mixed, integrated vine NDVI.

中文翻译：

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照明角度对垂直射影定位葡萄园获得的混合表面值组成的NDVI数据的影响

在精确葡萄栽培的背景下，准确量化冠层大小的空间变化对于葡萄园管理至关重要。与冠层大小相关的生物物理参数（例如叶面积指数（LAI））可以通过植被指数（VI）（例如归一化植被指数（NDVI））进行估算，但是在垂直射影定位（VSP）葡萄园中，通常是卫星，或具有中等分辨率的航空影像，在像素最低点捕获信息，这些像素的值是冠层，阳光照射的土壤和阴影土壤部分及其各自的光谱特征的混合。每个分数的VI值有很大不同。在VSP葡萄园上，每个特定行方向的照明方向取决于太阳和地球的相对位置。阴影和阳光照射的土壤部分的比例随太阳高度和方位角的变化而变化，但冠层部分不受这些变化的影响。这项研究的重点是照明方向与树冠方向的相互作用，以及对集成NDVI的相应影响。结果证实，干扰确定VSP上照明方向的因素将改变积分NDVI值。阴影会导致NDVI比例发生显着变化，从而影响最终的综合NDVI值。但是，随着行方向接近太阳路径，阴影效果会降低。所以，