Exploiting Uncrewed Aerial Systems for High Resolution Urban Heat Observations

Across the physical sciences, experiments in integrating and uncrewed aerial systems (UAS) are quickly advancing the ways in which researchers can collect field observations, and urban heat island (UHI) observation is no exception. The UHI is a physical phenomenon where elevated land surface and air temperatures are observed in cities and urbanized areas when compared to nearby areas of natural landcover. UHI’s are not confined to land surface and near-surface air temperature, rather it is a three-dimensional phenomenon from the land surface up to the free atmosphere. Cities have been observed to initiate convection and produce or enhance rainfall and lightning downwind, thus studying the vertical structure of the UHI is necessary to refine numerical weather prediction models. However, gathering vertical atmospheric observations in urban areas poses distinct challenges, making these measurements particularly difficult to obtain. Traditionally, in-situ UHI observations have been collected via established weather stations or intra-city traverses driven with automobile-mounted sensors. UHI studies based on weather station data are spatially limited to a single point and may miss local heterogeneities in the UHI, as well as being limited to surface air observations. Traverse-based UHI observations gathered via automobile-mounted sensors can solve the issue of limited intra-city spatial coverage, but these studies are still limited to surface air observations only. Some studies have made use of flux towers or sensors spaced vertically on skyscrapers, but these methods rely on installed vertical structures, are time consuming to deploy, and can be limited in their spatial coverage. Integrating UAS for UHI studies has the potential to greatly deepen our understanding of UHI vertical structure and diurnal cycle. By exploiting UAS capabilities for rapid and flexible deployment, UHI researchers can collect high density observations both at the surface and vertically through the urban canopy layer (UCL; from just above surface to building or tree height) and urban boundary layer (UBL; from top of the UCL to the free atmosphere). This study presents a proof-of-concept of novel methods for the deployment of UAS in urban areas, developed with the goal of producing spatially dense vertical profiles of temperature, pressure, and humidity to observe land-atmosphere interactions across differing natural and artificial landcover types in multiple locations throughout a city. The UAS used in this study was equipped with a novel low-cost atmospheric sensor system, as well as a radiometric thermal imager to observe the surface temperatures of the underlying landcover. Tested during the summer of 2023 in Augusta, Georgia, a medium city with a metro population of more than 615,000 people, eight different points were selected, informed via satellite visual imagery and thermal remote sensing, to observe locations with different landcover types and land surface temperatures. Results from this study suggest that landcover type influences near-surface air temperature and humidity levels, as well as vertical lapse rates in the UCL and lower UBL. Collecting measurements at many points throughout a diurnal cycle can greatly improve our understanding of urban microclimates and their effects on weather patterns. This proof-of-concept investigation demonstrates that these methods produce valuable data and can be scaled up for larger deployments with multiple UAS pilots to collect observations at multiple points simultaneously.