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Ultimate turbulence experiment: Simultaneous measurements of Cn2 near the ground using six devices and eight methods

Best Student Paper
: Yatcheva, Lydia; Barros, Rui; Segel, Max; Sprung, Detlev; Sucher, Erik; Eisele, Christian; Gladysz, Szymon


Stein, K.U. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optics in Atmospheric Propagation and Adaptive Systems XVIII : 22 September 2015, Toulouse, France
Bellingham, WA: SPIE, 2015 (Proceedings of SPIE 9641)
ISBN: 978-1-62841-851-4
Paper 964105, 8 pp.
Conference "Optics in Atmospheric Propagation and Adaptive Systems" <18, 2015, Toulouse>
Conference Paper
Fraunhofer IOSB ()
optical turbulence; refractive index structure constant

We have performed a series of experiments in order to simultaneously validate several devices and methods for measurement of the path-averaged refractive index structure constant ( 𝐶𝑛 2). The experiments were carried out along a horizontal urban path near the ground. Measuring turbulence in this layer is particularly important because of the prospect of using adaptive optics for free-space optical communications in an urban environment. On one hand, several commercial sensors were used: SLS20, a laser scintillometer from Scintec AG, BLS900, a largeaperture scintillometer, also from Scintec, and a 3D sonic anemometer from Thies GmbH. On the other hand, we measured turbulence strength with new approaches and devices developed in-house. Firstly, an LED array combined with a high-speed camera allowed for measurement of 𝐶𝑛 2 from raw- and differential image motion, and secondly a two-part system comprising a laser source, a Shack-Hartmann sensor and a PSF camera recoded turbulent modulation transfer functions, Zernike variances and angle-of-arrival structure functions, yielding three independent estimates of 𝐶𝑛 2. We compare the measured values yielded simultaneously by commercial and in-house developed devices and show very good agreement between 𝐶𝑛 2 values for all the methods. Limitations of each experimental method are also discussed.