Estimating Near-Surface Vertical Heat Fluxes over Agricultural Areas Using Weather Sensors on Unmanned Aerial Vehicles

Near-surface heat fluxes are commonly estimated using the eddy covariance method via measurements from a flux tower; however, these towers are expensive and stationary, and therefore can only provide observations over a single land surface/cover type. Since surface features over agricultural areas can vary rapidly over space (i.e., crop type) and time (i.e., growth stage), heat flux estimates from a single eddy covariance tower may not truly represent an area. As a potential solution for obtaining flexible near-surface heat flux measurements, we propose the use of a small unmanned aerial vehicle (UAV) equipped with temperature, pressure, and relative humidity sensors to estimate sensible and latent heat fluxes over an active agricultural area in eastern Mississippi. The Bowen ratio method, which is a simple approach that requires only potential temperature and specific humidity, is applied to vertical soundings from the surface to 120 meters at 10-meter intervals. A number of flights were conducted at Mississippi State University’s R.R. Foil Plant Science Research Center during the early and late stages of the growing season with the purpose of obtaining heat flux estimates over different land surface/cover types. Results show that the UAV platform is able to provide reasonable heat and moisture flux estimates, and that the fluxes show substantial variability among different land cover types over a small spatial scale. Future work must be done to verify the heat flux estimates and investigate flight plans and sensor mounting options to maximize sensor precision.