A Low Power Optical Sensing System for Leaf Area Index (LAI) Measurement with Dynamically Adjustable Field of View

Leaf Area Index (LAI) is a crucial parameter for modeling and monitoring plant metabolism. LAI can be measured indirectly with passive optical instruments using a photodiode to measure the light transmitted through the canopy. While many such instruments have been developed, both commercially and in academia, one major limitation remains: the handling of heterogeneous canopies due to leaf clumping. To overcome this limitation, this work presents a novel system concept for continuous wireless LAI measurement with a dynamically adjustable field of view (FOV). The sensing system consists of (1) an imaging lens that collects the incoming light, (2) a programmable Liquid-Crystal Display (LCD), which acts as an optical shutter, (3) a diffuser, and (4) the AS7341 multispectral sensor. This work validates system functionality by proving the sensor's capability to distinguish between light of different colors originating from different azimuth and zenith directions. Dynamic FOV adjustment paves the way for better handling of canopy heterogeneity. The additional feature of measuring light in 8 different channels in the visible range and one in the NIR increases the competitiveness of this solution, enabling the distinction between green and woody components based on their transmission spectrum in the future.