Experimental estimation of the spatial statistics of turbulence-induced index of refraction fluctuations in the upper atmosphere

We present results from an experiment to estimate the parameters of homogeneous, isotropic optical turbulence in the upper atmosphere. The balloon-borne experiment made high-resolution temperature measurements at seven points on a hexagonal grid for altitudes from 12,000 to 18,000 m. From the temperature data, we obtained index of refraction fluctuations that can be used to compute a samplebased estimate for a parameterized description of the spatial autocorrelation of the turbulence. The three parameters of interest were a proportionality constant PC, the power-law parameter α, and the outer scale L0. The results obtained for PCare within the expected range and agree well with independent measurements made from a standard rising thermosonde measurement made approximately simultaneously with the data collection. Values for α were in the range 1.52 ≤ α ≤ 1.73 were observed, which are significantly less than the power law used in the Kolmogorov and von Karman models, α = 1.833. Values observed for L0were in the range 5 ≤ L0≤ 190 m. Evidence that α may be consistently less than that used in the Kolmogorov and von Karman models likely has the most significant implications for systems that must work in or through the tropopause. © 2003 Optical Society of America