Comparison of Near-Surface Turbulence Spectral Shapes over Built and Open Terrain Using Commercial Drones as Portable Probes

Monitoring atmospheric turbulence data of the near-surface sublayer presents a difficult challenge on complex and heterogeneous terrain such as mixed land areas where weather facilities are not always available. This study uses tilt data derived from the flight logs of two hovering unmanned aerial vehicles (UAVS) as portable probes (DJI Mavic 2 and DJI Mavic 3 Classic) to compare the turbulence spectral characteristics of two adjacent contrasting surfaces; a built open courtyard and an open grass field. Turbulence spectra were divided into three ranges: E1 (0.05–0.2 Hz), E2 (0.2–1 Hz), and E3 (1–5 Hz). A 30 s moving mean and welch methods were used to filter out noise to ensure that the resulting spectra only showed the small tilts that were derived to show atmospheric turbulence. Normalization was applied to compare spectral shapes. Comparisons were made within platform (M2 vs. M2, M3 vs. M3). Observations show that spectral shapes generally agree. Contrasts were systematic within the energy bands and were not global. The study concludes on the notion that the unobstructed surfaces produce stronger fluctuations at the largest scales, whereas the built environments intensify turbulence at smaller scales.