Abstract
Accurate yield estimation is of utmost importance for the entire grape and wine production chain, yet it remains an extremely challenging process due to high spatial and temporal variability in vineyards. Recent research has focused on using image analysis for vineyard yield estimation, with one of the major obstacles being the high degree of occlusion of bunches by leaves. This work uses canopy features obtained from 2D images (canopy porosity and visible bunch area) as proxies for estimating the proportion of occluded bunches by leaves to enable automatic yield estimation on non-disturbed canopies. Data was collected from three grapevine varieties, and images were captured from 1 m segments at two phenological stages (veraison and full maturation) in non-defoliated and partially defoliated vines. Visible bunches (bunch exposure; BE) varied between 16 and 64 %. This percentage was estimated using a multiple regression model that includes canopy porosity and visible bunch area as predictors, yielding a R2 between 0.70 and 0.84 on a training set composed of 70 % of all data, showing an explanatory power 10 to 43 % higher than when using the predictors individually. A model based on the combined data set (all varieties and phenological stages) was selected for BE estimation, achieving a R2 = 0.80 on the validation set. This model did not show validation metrics differences when applied on data collected at veraison or full maturation, suggesting that BE can be accurately estimated at any stage. Bunch exposure was then used to estimate total bunch area (tBA), showing low errors (< 10 %) except for the variety Arinto, which presents specific morphological traits such as large leaves and bunches. Finally, yield estimation computed from estimated tBA presented a very low error (0.2 %) on the validation data set with pooled data. However, when performed on every single variety, the simplified approach of area-to-mass conversion was less accurate for the variety Syrah. The method demonstrated in this work is an important step towards a fully automated non-invasive yield estimation approach, as it offers a solution to estimate bunches that are not visible to imaging sensors.
Highlights
Accurate yield estimation is of utmost importance for many commercial crops
A similar trend is observed in Figure 4B between vBAp and bunch exposure (BE) but with variability that increases with the increase in the magnitude of BE
By knowing the fruit zone amplitude, which can potentially be estimated through image analysis, along with historical yield data, a promising strategy to estimate bunch by bunch occlusion could be computed, which should be added to the results presented by the approach described in this work
Summary
Accurate yield estimation is of utmost importance for many commercial crops. In viticulture, such information is helpful to address challenges of logistics at harvest, helping define workforce and machinery required, as well as cellar needs. Early yield forecasts can help planning bunch thinning to manage wine stock, grape prices and marketing strategies (Dunn and Martin, 2004). The information is extrapolated to the whole vineyard or plot, which can cause inaccurate estimates if sampling is not representative enough. It is a destructive and laborious technique (Dunn and Martin, 2004)
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