scintillometers

A scintillometer is an optical instrument used to measure atmospheric turbulence by detecting scintillation, or fluctuations in light intensity, caused by variations in air refractive index along a beam path. The measurements provide a path-averaged measure of turbulence strength, commonly expressed through the refractive-index structure parameter Cn^2, which relates to temperature and humidity fluctuations in the boundary layer. With additional meteorological data and theoretical flux relations, scintillometers can be used to estimate surface turbulent fluxes such as sensible heat flux.

There are two main types. Large-aperture scintillometers (LAS) use a substantial receiver aperture and long optical paths—typically hundreds of meters to a few kilometers—to yield robust estimates of path-averaged Cn^2 and related turbulence quantities. Small-aperture scintillometers (SAS) employ smaller apertures and shorter paths, providing measurements over shorter distances and with relatively simpler hardware. Both configurations require a stable light source, a receiver, and data processing to extract scintillation statistics from the intensity fluctuations.

Principle and use: as the beam traverses the atmosphere, refractive-index fluctuations cause focusing and defocusing, leading to intensity fluctuations at the detector. Analysis of these fluctuations yields Cn^2, which, together with wind speed, temperature, and humidity data, is used within Monin-Obukhov similarity theory or bulk methods to estimate surface fluxes.

Applications include boundary-layer research, weather and climate studies, hydrology and agriculture, and wind-energy site assessment. Limitations include the need for an unobstructed line of sight, vulnerability to clouds and heavy aerosols, and the necessity of site-specific calibration and supporting meteorological data.