Portability of leaf chlorophyll empirical estimators obtained at Sentinel-2 spectral resolution

Future ESA Sentinel-2 (S2) constellation is expected to represent a breakthrough for the exploitation of earth observation data in precision agriculture applications. The present work addresses the comparison of the sensitivity of leaf chlorophyll estimators vegetation indices (VI), obtainable from Sentinel-2 spectral bands, and of their portability with different crops/soil/illumination conditions. The comparison is addressed by the analysis of a large synthetic dataset, obtained using the PROSPECT-SAILH model in the direct mode, considering different crops canopies in the 1-4 LAI (Leaf Area Index) range with different soil backgrounds and different illumination geometry. Considered broad-band indices (i.e. indices obtained only from visible and NIR bands) included the classical NDVI index and some indices incorporating green reflectance proposed al leaf chlorophyll density estimators (Green NDVI, Green SR or CI and CVI), whereas narrow-band indices (i.e. indices requiring narrow bands in the red-edge) included VI specifically proposed as leaf chlorophyll estimators at the canopy scale (i.e. TCI/OSAVI, REP and MTCI). Results indicate that the MTCI and TCI/OSAVI indices, obtainable at 20 m spatial resolution from future S2 data, are the best leaf chlorophyll estimators respectively for planophile and erectophile crops canopies and that the CVI index, obtainable at 10 m, is the second best estimator for both planophile and erectophile crops canopies.