Precision heating strategy based dynamic heater path planning for frost protection in apple orchards

Frost is one of the severe weather events causing economic losses in agriculture. Traditionally, heating can be applied in an orchard during a frost event either using fixed heaters or mobile heaters to travel through. However, both traditional heating strategies have limited heating capacity. In this study, a precision heating strategy was proposed to prioritise applying heat to orchard canopies with high heating demands utilising multiple heaters. The precision heating experiment in a simulated orchard environment with dynamic multiple goal points was implemented by an improved A-Star path-planning algorithm, in which a path cost estimation method based on linear programming was presented to find the optimal paths for multiple heaters and a conflict-based search (CBS) method was used to generate collision-free paths. In addition, an estimation method for the heater number based on the precision heating strategy was proposed and the difference of the heater number between precision heating and traditional heating was compared. The simulated results show that the improved A-Star algorithm had higher search efficiency, resulting in 36.8% less total path cost and 98.7% less computational time than the control group. The comparison between precision heating and traditional heating indicates that the number of heaters used in the precision heating strategy decreased by 96.8% and 85.9% compared to the traditional fixed heating strategy and mobile heating strategy, respectively. Overall, this study provided a concept of high heat-demand priority precision heating and proved its superiority for frost protection.