Moving Bicycle Measurements of Turbulent Flux

Turbulence distributions at pedestrian height (~2 m) remain rare. This is largely due to: a) weather observation station regulations, b) complex heterogeneity of Urban Canopy Layer (UCL), c) cost and d) technological limitations. This study explores the feasibility of using a bicycle-mounted sonic anemometer system, equipped with centimeter-level RTK-GPS, for high-frequency turbulence distribution observations. The analysis focuses on turbulence statistics obtained during repeat runs in an outdoor environment that is homogeneous and obstacle free as far as possible. Upon vector manipulations, average statistics showed strong agreement between mobile and stationary measurements for all measure components (u, v, w, T). Energy spectra showed better collapse with variance normalization (𝜎𝑖) over friction velocity (𝑢∗). This is likely because the Monin-Obukhov framework does not apply in the UCL. In the energy-containing range all observers demonstrated the same magnitude, indicating the mobile observers successfully captured this region. In the dissipation ranges the bicycle spectra showed consistently elevated energy levels across all components, with a strong dependence on bicycle velocity. Energy levels were elevated at all scales until wavelengths of 𝜆 ≈ 1 𝑚. From that point onward there is energy missing for the expected spectrum seen consistently at all speeds due to the motion of the bicycle. These results suggest that, although bicycle motion does affect the energy spectra, averaged turbulence statistics remain robust, supporting the use of low-cost mobile systems for fine-scale, spatially flexible turbulence measurements.