A Fluid Dynamics Approach to Determine the Aerobiological Sampling Efficiency of Autonomous Unmanned Aerial Vehicles

Unmanned aerial vehicles (UAVs) are an important tool for studying the movement of microorganisms in the atmospheric boundary layer, which is tens to hundreds of meters above ground level (AGL). Knowledge of the aerobiological sampling efficiency of the UAVs is essential to estimating the actual atmospheric concentrations of microbes in a volume of air. We used experimental and mathematical approaches to study the sampling efficiency of autonomous UAVs equipped with eight microbe-sampling devices. Our experimental approach involved collecting fungi in the genus Fusarium with autonomous UAVs at the Kentland Farm in Blacksburg, VA. Results from four similar UAV sampling missions (flight speed of 25 ms-1 for 15 min at 100 m AGL) suggest that the depth and position of the sampling devices do not impact the collection of Fusarium. Our fluid dynamics approach involved developing a mathematical model of the fluid flow and particle (spore) motions to examine the affects of flight speed, size of the sampling device, particle (spore) size and drag force, and particle material density on aerobiological sampling efficiency. Results from the model suggest that all of these factors have a dramatic impact on the sampling efficiency of UAVs. Estimations of the actual concentration of an individual microbial species in the atmosphere by collecting with UAVs must use accurate estimates of sampling efficiency. This has important implications for the study of populations of microorganisms that may produce a wide range of spore types (and thus vary in shape, size, and density).