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As a segment of a broader program to assess optical properties of the atmosphere in the vicinity of the tropopause, the refractive index structure constant was measured by an airborne anemometry method. This paper discusses details of the anemometer, its implementation as well as some results. The anemometry method emphasizes turbulence with horizonal scales lying between 6 meters and 60 meters. A subsequent overflight, to be reported elsewhere, of the 50 MHz radar at White Sands Missile Range indicates that the horizontally derived structure constants, Cn2, are comparable to the vertically derived structure constants obtained from radar. For some flights Cn2 appears to be log-normal at least in the asymptotic sense, i.e. only for small deviations from the mean. Large deviations are clearly sub log-normal and occur less frequently than would be the case were the structure constant a true log-normal variable. On other flights inhomogeneity was encountered in the sense of an exit form one air mass and entry into a second. This condition resulted in a bimodality of the statistics. On the whole, however, the entire data set collected in pat over the far east and in part of the western US also appears to be well approximated by an overall log-normal distribution in spite of the obvious inhomogeneity of the atmospheric masses encountered in the collection.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
