Geometrical Characterization of Hazelnut Trees in an Intensive Orchard by an Unmanned Aerial Vehicle (UAV) for Precision Agriculture Applications

Abstract

Knowledge of tree size is of great importance for the precision management of a hazelnut orchard. In fact, it has been shown that site-specific crop management allows for the best possible management and efficiency of the use of inputs. Generally, measurements of tree parameters are carried out using manual techniques that are time-consuming, labor-intensive and not very precise. The aim of this study was to propose, evaluate and validate a simple and innovative procedure using images acquired by an unmanned aerial vehicle (UAV) for canopy characterization in an intensive hazelnut orchard. The parameters considered were the radius (Rc), the height of the canopy (hc), the height of the tree (htree) and of the trunk (htrunk). Two different methods were used for the assessment of the canopy volume using the UAV images. The performance of the method was evaluated by comparing manual and UAV data using the Pearson correlation coefficient and root mean square error (RMSE). High correlation values were obtained for Rc, hc and htree while a very low correlation was obtained for htrunk. The method proposed for the volume calculation was promising.

Assessment of the Midseason Crop Coefficient for the Evaluation of the Water Demand of Young, Grafted Hazelnut Trees in High-Density Orchards

“…Using the measurements of the canopy's average diameter D, the canopy height H, and the canopy volume obtained from the UAV survey [18,19], V u , the equations from ( 3) to (6) were applied to the hazelnut orchard for each plant density (Figure S1). The mean value for the midseason (June, July, and August) of the coefficients K c,Tr , evaluated using the coefficients tested for olive orchards [7] are reported in the first row of Table 1.…”

“…Due to these missing data, in this study, assuming a similarity in the water sensibility behaviors of hazelnut and walnut orchards [32], the F r value of walnuts reported in Table 2 of [15] was used (F r = 0.90). The values of the mean tree height measured using the UAV surveys [18,19] were used for the evaluation of K cb full using Equation (13). The density coefficient K d was calculated using the measurements of LAI conducted during the midseason and applied to Equation (15) (Figure S3).…”

“…The DJI (Shenzhen, China) Phantom 4 (P4) multispectral unmanned aerial vehicle UAV was used to assess the tree canopy and ground cover characteristics according to [18,19].…”

“…Moreover, ground cover was obtained as the ratio between the average canopy crosssectional area and the ground area for each plant, equal to 16 m 2 , 8 m 2 , and 4 m 2 , respectively, from the highest to the lowest tree density plantation. The average canopy cross-sectional areas were calculated as reported by [19].…”

“…In Equation (7), the canopy volume V 0 was substituted with the volume V c, evaluated using the procedure described by [18,19]. Briefly, volume V c was calculated considering the shape of the canopy obtained from the 3D point cloud reconstruction using a UAV survey.…”