Addressing the observational gap over heterogeneous land surfaces in the lower atmospheric boundary layer by multi-copter temperature and humidity profile measurements

Abstract

The effects of surface heterogeneity on the atmospheric boundary layer are still poorly understood and thus not appropriately parameterized in numerical weather prediction models. The complexity of types, shapes, and scales of heterogeneity poses also considerable challenges to any observational approach. The problem of heterogeneity is usually addressed by distributed single point measurements over the different surface types, but typically leave a considerable observational gap across the heterogeneity boundaries.

This study proposes the method of utilizing the Bebop2Met, a small multi-rotor drone equipped with a meteorological payload for temperature and humidity measurements, to bridge this gap. As a part of the international MOSAI (Models and Observations for Surface-Atmosphere Interaction) campaign, more than 400 individual temperature and humidity profiles were collected during three extensive operational periods in April, August, and December 2023, close to Lannemezan, France, at the foothills of the Pyrenees. The measurement strategy applied was to observe the thermodynamic properties of the lower atmosphere through repeated series of densely spaced vertical profiles along a line perpendicular to the transition from the smooth (grass/corn) to rough (forest) surface, to enhance the insight in the spatio-temporal variability over strongly heterogeneous surfaces.

The results show that the chosen measurement approach can provide valuable data sets that can clearly complement the classical mast based in-situ observations. The system is able to resolve small-scale structures near transitional boundaries. By an appropriate spatial and temporal interpolation of the individual profiles, measured at different positions and at different times, those structures can be properly visualized. Due to the limited number of observed and analyzed cases, in comparison to the varying meteorological conditions, remains the cause of these structures and there development unclear, the study can however be seen as a successful proof-of-concept.

The flexibility, affordability, and ease of access with a small drone make it appealing for both primary and complementary data collection for surface heterogeneity impacts and effects. Future studies could look into greater data collection periods, as well as utilizing multiple drones for greater spatial coverage and possibly adding another dimension for analyzing the structural development of these complex interactions between differing surface heterogeneities.