Mapping an outdoor odor plume using a mobile chemical sensor

Insects are remarkably adept at tracking wind-borne odor plumes, and understanding their algorithms is of great interest to roboticists. At short distances, walking flies make decisions based on odor statistics such as whiff lengths and encounter frequencies. Experiments in wind tunnels show that these statistics are correlated with distance from the source, and may therefore offer information to flying insects. To test the feasibility of this hypothesis, we measured odor plume statistics driven by natural wind on an open landscape in the Black Rock Desert, Nevada, by traversing a space of 90m2 for 5 hours using a mobile chemical sensor. Stationary wind sensors were arranged around the source to measure the ambient wind speed and direction. Our analysis shows that for higher wind speeds, whiff durations decrease and encounter frequency increases at greater distances from the source. But these trends disappear for lower wind speeds when the wind direction was more variable, suggesting that in real world scenarios plume encounter statistics offer limited information. The statistical relationships we found can be used to develop data-driven plume simulators with realistic dynamics, as well as inform plume tracking algorithms for flying agents such as drones.