Gradients and turbulence
AcWaCo eliminates the effect of moving transversal temperature gradients by measuring the speed of sound along the laser beam path. The measurement is done with transducers located symmetrically on the opposite ends of the beam.
AcWaCo only derives the mean spatial air temperature. It does not measure spatial thermal gradients, nor does it need to know them. All the laser interferometer needs is the mean refractive index of air on the laser beam path, which can be calculated from the mean spatial air temperature.