Solar Induced Fluorescence Retrieved from Avocado (Persea americanaMill.) Canopies Along the Season Correlates with Sugar Levels in the Developing Fruit

Solar Induced Fluorescence (SIF) emitted from the photosynthetic apparatus is related indirectly to biomass production. It can be remotely sensed from airborne platforms, yet, the spatial resolution from satellites, for example, is too low for commercial agricultural uses. We used a non-imager point spectroradiometer mounted on SIF-UAV (Unmanned Aerial Vehicle) system, and retrieved SIF at high spatial resolution, which is fitted for precision agriculture applications. In this study, we tracked the spatial variation of SIF along the season over a commercial avocado (P. americana Mill) orchard. The retrieved SIF signals were Krieg-interpolated to create a continuous SIF layer that allowed the estimation of SIF values for each tree in the orchard. We show that the SIF signal retrieved over the canopies in the main fruit development stage is highly correlated with the levels of sugars accumulated in the ripening avocado fruit. It established the foundations for high-spatial resolution detection of the natural variation of photosynthesis activity, which may lead to in-season adjustments of agronomic inputs using precision agriculture technologies.