A new technique for probing length scales in clear air

When light is transmitted through the atmosphere, it can scatter off turbulent vortex filaments in the air that have different densities and indices of refraction. These filaments, or eddies, are distributed through a turbulent air flow and their scale size represents the boundary between an energy cascade down size scales that ends in viscous energy dissipation. We are measuring with high spatial and temporal precision spatial and temporal correlation functions that reveal the turbulence dynamics and inner scale in conditions of single scattering. In essence, we can "see" the shadows of individual turbulent vortices. These measurements are made over short path lengths in conditions of known Reynold's number and average temperature. By changing the characteristics of the air flow in a volume, different length scales can be associated with different conditions. This creates a "fingerprint" that characterizes the turbulence.