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28 September 2006 Turbulence statistics in littoral area
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FGAN-FOM carried out a long-term experiment to measure Cn2 over sea in littoral area in moderate climate, Central Europe. A Boundary Layer Scintillometer was installed along a 1.7 km path crossing a bay of the Baltic Sea (Eckernfoerder Bucht) at a height of 4.7 m above water level. Meteorological parameters were measured simultaneously. One of the main parameters, which effects Cn2, is the temperature difference between air and ground. In general a larger temperature difference causes stronger turbulence. Over sea, the air-sea temperature difference, ASTD, is generally smaller than the air-ground temperature difference over land, which implicates smaller Cn2 values. Turbulence over sea differs significantly from turbulence over land. The diurnal run of Cn2 does not show generally the characteristic maximum at midday, Cn2 values measured during night are not generally smaller than those measured at midday, and Cn2 values measured in the daytime in summer are not generally larger than those measured in winter season. Since Cn2 usually changes with environmental conditions, its influence on the effectiveness of electro-optical systems can normally only be expressed in a statistical way. We worked out a statistical database for atmospheric turbulence over sea accordingly to our turbulence statistics over land. The cumulative frequency of occurrence was calculated for a period of one month for a two-hour time interval during daytime and during night. Even though the meteorological conditions in Central Europe show a large variability, the cumulative frequencies of occurrence derived for 2003 and 2004 indicate the same seasonal devolution. We applied the LWKD model of the Defence Research and Development, DRDC Valcartier, Canada, to calculate Cn2 as a function of ASTD for the measured meteorological parameters. The measurements indicate larger Cn2 values than the calculations.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Karin R. Weiss-Wrana "Turbulence statistics in littoral area", Proc. SPIE 6364, Optics in Atmospheric Propagation and Adaptive Systems IX, 63640F (28 September 2006);

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