Physical constraints on visual anemometry from vegetation displacement statistics

Visual anemometry (VA) leverages observations of fluid-structure interactions to infer incident flow characteristics. Recent work has demonstrated the concept of VA using both data-driven and physical modelling approaches applied to natural vegetation. These methods have not yet achieved generalization across plant species and require site-specific calibration. We conducted a laboratory study of VA in an open circuit wind tunnel using overhead imagery of three plant species to assess the utility of structure displacement fields for wind speed inference. Both the wind and vegetation speeds exhibited a two-parameter Weibull distribution. A sigmoid shape was found to describe the relationship between the scale factors—one of two parameters—of the wind and vegetation distributions, indicating three regions of distinct structural response. At intermediate wind speeds, the scale factors are proportional, thereby enabling VA. The remaining two regions are uncorrelated and reveal a fundamental constraint. The physical basis for these regimes will be presented, along with additional parametric relationships that can be exploited to generalize inference of the wind speed, direction, and eventually physical properties of the observed structures.