The atmospheric structure constant, C2N, has been measured by use of three instruments, one optical and two thermal. The data show very good correlation (ρxy = 0.88), but are related by a consistent scale factor: CN (optical) = 0.34 × 10-8 cm-2/3 + 1.45CN (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)