Scintillometers

Scintillometers consist of a transmitter–receiver pair for electromagnetic radiation separated from each other by a distance of E2 – E4 m. As the emitted radiation travels through the atmosphere, it is scattered by turbulent eddies of different density. At the receiver, the resulting high-frequency intensity fluctuations of the electromagnetic signal (scintillations) are recorded, from which the turbulent sensible and latent heat fluxes can be derived. Further, the wind component perpendicular to the path (crosswind) and, for a specific system configuration, the turbulent momentum flux can be determined from the correlation of the fluctuation time series between two parallel beams. The signal at the receiver represents an integrated effect of the conditions along the path; scintillometers, therefore, provide area-averaged values of fluxes and crosswind. This is of special relevance for applications like the validation of flux data from numerical weather prediction and climate models or from satellite retrievals, or for the estimation of regional-scale evaporation rates in agricultural management and hydrology. After a brief introduction to the theoretical background, the commercially available scintillometer types are characterized, and the conditions of their use are discussed.