Use of the Planar Fit Method in Tilt and Distortion Analysis of the Mean Flow

The Planar Fit Method (PFM) is being used more and more to perform turbulent fluxes calculations in a coordinate system that minimizes the vertical component of wind velocity. It can be applied only after having gathered sonic anemometer data over a long time during which the anemometer position did not change. This implies that PFM has never been used in real time. Coordinate transformations are proposed to convert into a single, time-independent coordinate system the velocity components measured by a set of anemometers with time-dependent tilt fluctuations. By applying the PFM to each anemometer data set it is then possible to check the flow planarity, to detect flow distortions and to compare the mean streamlines tilt with the terrain slope. Tilt and orientation of each plane become in fact a characteristic of the measurement point, independent from the anemometer that has been or that will be deployed. The use of PFM in real time applications becomes therefore feasible, after a preliminary long period of measurements aimed at locating the planes.