Flexible microspectrometer for grape maturation monitoring in the vineyard

Optical spectroscopy is a well-suited technique for the nondestructive and real-time
maturation monitoring of fruits and vegetables. Although many commercial spectroscopy systems exist, including some for portable use in the field, a significant gap in
agricultural monitoring is the ability to continuously measure the condition of fruits in
the field over longer periods of time. To this end, we present here a fully integrated,
flexible microspectrometer consisting of multiple light sources and multiple broadband photodiodes for the spectral evaluation of grape maturation in the field. To
enable the microspectrometer design, a customized grape berry model generated
from the optical properties, primarily light scattering, of grape berries was developed.
The microspectrometer was fabricated using a scalable fabrication process based
on a spin-coated, flexible polyimide substrate. Experiments were conducted both in
a controlled laboratory environment as well as during the grape maturation period in
the vineyard and these demonstrated that the spectral properties of grapes at different maturation stages can be accurately measured. Using suitable chemometric
models, the amount of total soluble solids in °Br, which is the most important factor
for the maturation estimation of grapes, was determined from the microspectrometer
data.