Towards sensible heat flux measurements with fast-response fine-wire platinum resistance thermometers on small multicopter uncrewed aerial systems

Abstract. This study demonstrates the feasibility of measuring temperature variance and sensible heat flux with self-calibrated fine-wire platinum resistance thermometers (FWPRT) on multicopter drones. The sensors are especially designed for light-weight, fast response-times and to be carried on miniature drones for turbulence measurements. A significant improvement was found in vertical profiling of temperature gradients compared to slower solid-state sensors, demonstrating reduced hysteresis between ascent and descent phases and accurate representation of strong gradients. More than 100 single flights with the sensors attached to drones of the SWUF-3D fleet were carried out in vicinity to a meteorological mast array at the WiValdi wind energy research park in Northern Germany. The comparison to sonic anemometers shows that mean temperature and temperature variance can be accurately measured within the background flow variability. The same applies for sensible heat flux, which was measured for the first time with multicopter UAS and the eddy covariance method. Sensible heat flux is a crucial parameter to understand the energy balance of the atmospheric boundary layer. An uncertainty of 50 W m^-2 was determined with the constraint that only low wind speed conditions could be used to allow vertical wind speed measurements with the current algorithm. The results indicate that the temperature sensors are suited for sensible heat flux measurements, but further improvements are necessary with regard to vertical wind speed estimates to decrease the overall uncertainty.