Effect of the Illumination Angle on NDVI Data Composed of Mixed Surface Values Obtained over Vertical-Shoot-Positioned Vineyards

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