Scintillation at two optical frequencies

Stellar scintillation data were obtained on a single night at a variety of zenith distances and azimuths, usinga photon-counting photometer recording at 100 Hz simultaneously at wavelengths of 0.475, m and 0.870 Am.Orientable apertures of 42-cm diam separated by 1 m were used to establish the average upper atmospherewind direction and velocity. Dispersion in the earth's atmosphere separate the average optical paths at thetwo wavelengths, permitting a reconstruction of the spatial cross-correlation function for scintillations, independentof assumptions about differential fluid motions. Although there is clear evidence of a complicatedvelocity field, scintillation power was predominantly produced by levels at pressures of 130 ± 30 mbar. Thedata are not grossly inconsistent with layers of isotropic Kolmogorov turbulence, but there is some evidencefor deviation from the Kolmogorov spectral index and/or anisotropy.