The atmospheric structure constant, <i>C</i><sup>2</sup><sub><i>N</i></sub>, has been measured by use of three instruments, one optical and two thermal. The data show very good correlation (ρ<sub>xy</sub> = 0.88), but are related by a consistent scale factor: <i>C</i><sub><i>N</i></sub> (optical) = 0.34 × 10<sup>-8</sup> cm<sup>-2/3</sup> + 1.45C<sub><i>N</i></sub> (thermal). Several effects are discussed that may explain these results.
J. E. Pearson, "Comparison of scintillometer and microthermometer measurements of C2N," J. Opt. Soc. Am. 65, 938-941 (1975)