Route planning for multi-forest areas of helicopter plant protection operations based on vector modeling method and double-layer nested improved genetic algorithm

Forest pests and diseases have frequently caused huge economic losses in China. Helicopter spraying of pesticides has been one of the most important ways to pest control in modern forestry. Reasonable route planning is a high demand for helicopters during spraying operations in multiple forest areas. However, the current route planning still fully relies on manual experience, resulting in too many turnarounds, and large extra coverage areas. It is very necessary to optimize route planning for higher operational efficiency in an environmentally friendly way. In this study, an optimal helicopter route planning was developed for spraying pesticide operations in multiple forest areas. The routes were divided into two parts: intraregional application routes for individual forest areas and interregional dispatch routes between multiple forest areas. In the application routes, a Vector Modeling Method (VMM) was developed to reduce the number of turnarounds and extra coverage rate. A multiple objective genetic algorithm NSGA-II was used to find the Pareto optimal set, and then a manual decision was made on the application route plan. A Double-layer Nested improved Genetic Algorithm (DNiGA) was developed for the inter-regional dispatch route planning of multiple forests, in which the outer layer GA was used to solve the inter-regional scheduling routes, and the inner layer GA served as an operator to solve the adaptation of the outer layer GA. As such, the inter-regional optimal scheduling routes were derived suitable for the multiple forest areas. Taking Thunderbird R44 aircraft as an example, a multiple forest area environment was created to verify the model. Three spray widths of 10, 20, and 30 m were selected to plan the operating routes. The VMM and the popular Slice were used to plan the application routes. It was found that the number of turnarounds was significantly reduced less than that of Slice for all three spray widths. The extra coverage rate of the VMM was only 2.31% and 6.64% at the spraying width of 10 and 30 m, respectively, which were much lower than that of the Slice. Furthermore, the excess coverage rate differed from that of Slice (90°) by 0.26 percentage points at the spraying width of 20 m, but the number of turnarounds was reduced by 114 times. The DNiGA and the mainstream step-by-step IGA-GA were used to plan the inter-regional dispatch routes in multiple forests. The optimal lengths of 5 006.09, 4 644.97, and 5 295.47 m were achieved in the DNiGA inter-regional dispatch route for the spraying widths of 10, 20, and 30 m, respectively, which were 11.24%, 5.11%, and 6.59% shorter than that of IGA-GA, respectively. A spraying experiment with a helicopter was conducted near the Pigzui Mountain, Huai’an City, Jiangsu Province, China. It was found that the routes planning was here reduced the number of turnarounds by 4 times, the extra coverage rate by 27.8%, the application route length by 6.15%, and the dispatch route length by 16.41%, compared with the manual. Moreover, the consumption of helicopter fuel and pesticide decreased by 8.8% and 6.15%, respectively. The developed model can also be applicable to the helicopter route planning for plant protection operations in multiple forest areas, indicating a significant decrease in the number of turnarounds, the extra coverage rate, and the inter-regional dispatch route length for forestry spraying operations. The finding can be valuable to realize better plant protection operations in intelligent agriculture and forestry.