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

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 ( \u1d436\u1d45b 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 \u1d436\u1d45b 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 \u1d436\u1d45b 2. We compare the measured values yielded simultaneously by commercial and in-house developed devices and show very good agreement between \u1d436\u1d45b 2 values for all the methods. Limitations of each experimental method are also discussed