Turbulence statistics in littoral area

Karin R. Weiss-Wrana

doi:10.1117/12.693496

28 September 2006 Turbulence statistics in littoral area

Karin R. Weiss-Wrana

Proceedings Volume 6364, Optics in Atmospheric Propagation and Adaptive Systems IX; 63640F (2006) https://doi.org/10.1117/12.693496
Event: SPIE Remote Sensing, 2006, Stockholm, Sweden

Abstract

FGAN-FOM carried out a long-term experiment to measure C_n² 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 C_n², 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 C_n² values. Turbulence over sea differs significantly from turbulence over land. The diurnal run of C_n² does not show generally the characteristic maximum at midday, C_n² values measured during night are not generally smaller than those measured at midday, and C_n² values measured in the daytime in summer are not generally larger than those measured in winter season. Since C_n² 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 C_n² as a function of ASTD for the measured meteorological parameters. The measurements indicate larger C_n² values than the calculations.

Citation Download Citation

Karin R. Weiss-Wrana "Turbulence statistics in littoral area", Proc. SPIE 6364, Optics in Atmospheric Propagation and Adaptive Systems IX, 63640F (28 September 2006); https://doi.org/10.1117/12.693496

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