Wall induced turbulence distortions of optical measurements

Ove K. S. Gustafsson; Markus Henriksson; Lars Sjöqvist

doi:10.1117/12.830606

30 September 2009 Wall induced turbulence distortions of optical measurements

Ove K. S. Gustafsson, Markus Henriksson, Lars Sjöqvist

Proceedings Volume 7482, Electro-Optical Remote Sensing, Photonic Technologies, and Applications III; 74820E (2009) https://doi.org/10.1117/12.830606
Event: SPIE Security + Defence, 2009, Berlin, Germany

Abstract

Optical measurements and tests of optical instruments are often performed through an opened window or from the roof of an elevated building. This can also be a common situation for free-space optical (FSO) communication systems. Wind friction in combination with solar heating of the wall and the ground will create increased turbulence in a boundary layer close to the wall. For an outgoing laser beam this thin region of strong turbulence causes beam wander, beam broadening and beam break-up. For imaging and detection systems angle of arrival fluctuations and image blurring may result. In an attempt to estimate the strength of the atmospheric turbulence in the layer at the wall the refractive index structure constant (C_n²) was measured with an ultra sonic anemometer as a function of distance from the wall. The measurements were performed at the lower part of a window that was open just enough to give space for the anemometer. The window was placed 10 m above ground in a 12 m high building, with brick wall below the window and wooden panel above the window. Measurements of the turbulence as a function of distance from the wall were performed during different times of the day to study the influence of sun heating of the wall. The measured average C_n² shows an exponentially decreasing function of distance from the wall. The exponential decay of C_n² depends on the time of the day. The highest measured value of C_n² was approximately 3x10^-11 m^-2/3 near the wall. The influence of wall turbulence is discussed with respect to its influence on laser beam propagation.

Citation Download Citation

Ove K. S. Gustafsson, Markus Henriksson, and Lars Sjöqvist "Wall induced turbulence distortions of optical measurements", Proc. SPIE 7482, Electro-Optical Remote Sensing, Photonic Technologies, and Applications III, 74820E (30 September 2009); https://doi.org/10.1117/12.830606

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