Aerial imagery or on-ground detection? An economic analysis for vineyard crops

Aerial and on-ground vegetation characterization technologies are continuously evolving. An experiment was conducted in a vineyard field in order to test the economic feasibility of applying fertilizers site specifically based on different mapping systems. The capacity of UAV missions and on-ground systems has been compared using depth cameras or LiDAR systems respectively in order to provide the necessary vineyard volume maps for specific applications like fertilization. Aerial imagery was obtained using a UAV equipped with a high-resolution RGB camera, and a digital surface model was reconstructed using photogrammetry procedures. On-ground crop reconstruction was performed using LiDAR-based measurements taken with an RTK-GNSS along the crop rows. Furthermore, a Kinect v2 sensor was also used as a low cost depth camera. All systems were tested in a commercial field, under sunlight conditions. Every technique provided a 3D dense point cloud from which volume was calculated. The results showed that volume values were always consistent and similar between the studied systems. The on-ground techniques provided the best details of the plants. However, the cost of acquisition was always higher than that of aerial imagery. Concerning the fertiliser application it should be noted that, the changes in shape and size of plants obtained within the vineyard indicate that continuous adjustment of the applied dose would be required to optimize the performed application. When using site-specific spraying based on the created maps, the dose was reduced by up to 80% of the total dosage used with a conventional application. A detailed analysis of savings indicates differences between the systems. The use of aerial imagery techniques resulted in positive net returns, whereas the on-ground technologies needed a faster time of acquisition in order of them to be profitable. Regarding efficacy, no significant differences between applications based on the constructed maps were found. This important reduction in fertilizer application could be followed by an equivalent reduction in plant protection products (e.g., fungicides). Thus, the use of some 3D characterization technologies has shown to be profitable at the current stage of development while also reducing the inputs and the environmental impact of agricultural tasks.