One can measure it directly by using a radar. Such is useful for probing both temporal and spatial features of optical turbulence, but is only useful for understanding one scale, and requires numerous assumptions to extend measurements both to larger and smaller scales. From this one may calculate a structure constant which can be related directly to the index of refraction structure constant, C n 2 . Such measurements have been made by balloons. For the Refractive Turbulence Project, we use temperature measurements on board an aircraft to determine the magnitude and extent of optical turbulence.
Aircraft have many distinct advantages in determining optical turbulence.
Large horizontal scales may also be probed using undercraft. Finally, temporal scales may be examined, to better understand the transient nature of strong optical turbulence regions. The Egrett is capable of long duration flights at 50,000 ft. Driven by the critical ABL need for accurate and statistically significant refractive turbulence measurements, three BAT probes were mounted on the Egrett. One probe under each wing symmetrically with the center line of the aircraft and a third probe at the top of the tail.