By Niek Fischer (the Netherlands)
The estimation of leaf chlorophyll using canopy spectra with combined radiative transfer modelling and vegetation indices has not been researched intensively. However, estimation of leaf chlorophyll using spaceborne sensors (Sentinel-2 & VENμS) could provide interesting applications in precision agriculture. The aim of this research was to estimate leaf chlorophyll content of a potato crop using radiative transfer modelling and vegetation indices on simulated bands of two spaceborne sensors and CropScan spectral measurements. The vegetation indices used were: NDVI, CVI and TCARI/OSAVI. Firstly a sensitivity analysis was performed using PROSAIL and the vegetation indices. Secondly, the models were improved where possible using: Best Band Combination and model constraint. Thirdly, simple regression was performed on the outcome of the PROSAIL models. Finally, these regressions were validated on spectral field measurements of a potato field. Important outcomes of this research are: 1) the model that performed most optimal was the PROSAIL model based on TCARI/OSAVI after a model constraint improvement limiting the range of possible leaf angles for potatoes. 2) A ratio index using Sentinel-2 bands at 705nm and 1375nm, resembling the NDWI, was found to also be able to perform leaf chlorophyll estimation from canopy spectra.