Quantitative assessment of banana canopy porosity based on a three-dimensional canopy model and its impact on spray droplet penetration within the canopy from Unmanned Aerial Vehicle Spraying Systems

Abstract

Precision agriculture using Unmanned Aircraft Spraying Systems (UASS) enables targeted pesticide delivery. However, structural changes in the banana canopy during growth complicate pesticide application, particularly in achieving uniform coverage of the lower canopy. This study investigates the impact of canopy porosity and UASS flight height on droplet penetration. The study focused on three growth stages (BBCH-35, BBCH-49, and BBCH-63) of banana plants. Using 3D reconstruction techniques, including LiDAR scanning and point cloud voxel processing, volumetric and optical porosity within the specified area were extracted for each stage. The mean volumetric porosity of the banana canopy was found to be 78.72 %, while the mean optical porosity was 4.16 %. In the lower canopy, the mean volumetric porosity was 73.33 %, and the mean optical porosity was 13.68 %. Additionally, the relationship between volumetric porosity and optical porosity of the banana canopy was fitted using a Boltzmann sigmoid function, achieving a Coefficient of Determination (R²) value of 0.708. Unmanned Aerial Vehicle (UAV) tests revealed that UASS spraying at a height of 4m achieved the optimal balance between deposition, deposition uniformity, and ground loss ratio. Additionally, a BP neural network model demonstrated a strong correlation between canopy porosity and lower-layer droplet penetration during the BBCH-63 stage, with an R² value of 0.883. The study found lower UASS flight heights optimal for banana plants and highlighted canopy porosity's role in enhancing droplet penetration, especially in later growth stages, providing insights for improving spraying efficiency.

Plant phenotyping relevance

3D LiDAR再構成と点群ボクセル処理により、バナナ樹冠の孔隙率という構造形質を定量抽出しており、植物表現型取得手法が研究の中心である。

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