Exploration of Model-Resolution Dependence of Forecasted Wind Hazards for Small Unmanned Aircraft System Operations

Use of Small Unmanned Aircraft Systems (sUAS) for commercial applications is growing. The use of sUAS for delivery, surveying of hard to reach areas in need of maintenance, public safety, and damage assessment from the air are examples of expanding utilization of this technology. An issue with these applications is sUAS are not generally approved for operation beyond the Line Of Sight (LOS) of the pilot, so an operator must still be close by in order to operate the aircraft. Once approval is granted to conduct flights Beyond Visual Line Of Sight (BVLOS), utilization of sUAS will grow rapidly. A factor that must be understood, especially when flying BVLOS, is hazards associated with sUAS flight, including weather hazards. One of the leading weather hazards is wind. In this study, nested simulations with horizontal grid spacing of 12 km, 4 km, 1.33 km, and 0.444 km were conducted to evaluate the impact changing resolution has on wind fields and, thus, on forecasting of sUAS wind hazards. These simulations were completed using the Weather Research and Forecast (WRF) model. The simulated area lies within the St. Lawrence and Mohawk River Valleys; the surrounding topographic features commonly generate small-scale wind patterns, creating excellent opportunities to explore dependence of winds on model resolution. Wind speeds of just 10-15 knots can have significant impacts, and thus modeling at a high resolution has potential of enhancing sUAS safety. In an attempt to preserve the expense of computational power, a grid spacing of 4 km appears satisfactory for resolving most hazardous wind features. The impact of upstream topographic influence seems to benefit from higher resolutions. Existence and resolution dependence of valley features such as the valley circulation, wind channeling, and countercurrents are also discussed. Understanding how valley circulations and wind channeling affect wind fields will enable broader sUAS utilization.