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Enhancing Grape Brix Prediction in Precision Viticulture: A Benchmarking Study of Predictive Models using Hyperspectral Proximal Sensors
1 , 1, 2 , 1, 2 , 3 , 3, 4 , 2 , 2 , * 1, 2
1  Department of Geosciences, Environment and Spatial Planning, Faculty of Sciences of the University of Porto, Rua do Campo Alegre, S/N, 4169-007, Porto-Portugal
2  INESC TEC - Institute for Systems and Computer Engineering, Technology and Science, Campus da Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, S/N, 4200-465, Porto-Portugal
3  Associação para o Desenvolvimento da Viticultura Duriense, Edifício Centro de Excelência da Vinha e do Vinho Parque de Ciência e Tecnologia de Vila Real, Régia Douro Park, Portugal
4  CoLAB Vines&Wines – National Collaborative Laboratory for the Portuguese Wine Sector, Edifício Centro de Excelência da Vinha e do Vinho Parque de Ciência e Tecnologia de Vila Real, Régia Douro Park, Portugal
Academic Editor: Gianni Bellocchi


Sustainable and efficient agricultural production is a growing priority in modern society. Viticulture, an important agricultural and food sector, also faces this challenge. Precision Viticulture (PV) has gained prominence as it aims to foster high-quality, efficient, and environmentally sustainable practices. The Soluble Solids Content (SSC) is essential for assessing grape ripeness and quality in the winemaking process. Conventional methods for determining SSC values (expressed in ºBrix) are invasive, expensive and labour-intensive, necessitating sample preparation, making large-scale analysis impractical. In response to these limitations, this study presents an innovative approach within the field of Precision Viticulture. It focuses on the non-invasive prediction of SSC using low-cost Proximal Hyperspectral Optical Sensors. These sensors rely on spectral reflectance measurements in the range of 340-850 nm. The study was conducted in a commercial vineyard in the Demarcated Douro Region, Cima-Corgo sub-region, Portugal, over six weeks during ripening. 169 grape berries from Touriga Nacional vines were analyzed under three irrigation regimes (no irrigation, 30% ETc, and 60% ETc). After organizing and preprocessing the data, machine learning algorithms, namely Partial Least Squares Regression (PLS), Random Forest (RF), and Generalized Linear Model (GLM), were applied to predict SSC values. These models' performance was thoroughly evaluated using cross-validation techniques. The performance of different models was evaluated showing significant differences, according to the metrics used (R2, RMSE and MAPE). The RF model demonstrated effectiveness and precision. A high R² value of 0.9312, coupled with low RMSE (0.9199 ºBrix) and MAPE (3.88%), signifies a strong fit to the data and accurate predictive capabilities. The results of this benchmarking study on predictive models of SSC provide valuable insights into the performance of various models, aiding winegrowers and winemakers in decision-making.

Keywords: grapes berries; machine learning; point-of-measurement; sugar content; Vitis vinifera