Sigma Theta

 Sigma Theta is measured by our wind vane and is related to horizontal turbulence. Mathematically it is the standard deviation of the vane position. This calculation is tricky because the vane can swing in a circle (it uses polar coordinates).

We use Sigma Theta to estimate the potential for the atmosphere to spread a plume. The EPA provides guidance to calculate a common plume dispersion index (Pasquill Stability Class) from measurements of wind speed and sigma theta.