Leaf motion for flow characterization: generalizing visual anemometry

The Beaufort scale exemplifies qualitative assessment of fluid flow through observations of its interaction with surrounding objects. However, translating these dynamics into quantitative measurements remains a challenge due to structure-specific calibration requirements. This is particularly true for complex structures like trees, where the dynamic response is highly sensitive to individual components (branch architecture, leaf density, water content). Consequently, current methods require reference anemometers for flow characterization from observed structural motion. This study presents a physics-based approach to model the fluid-structure interaction between the impinging wind and the observed leaf motion. We reveal a relationship governing leaf motion across a diverse dataset encompassing twelve tree species, exhibiting variations in age, size, and health. The identified relationship enables flow prediction with a single characteristic length scale, obviating species-specific anemometer calibration within the validated measurement range.