Measuring non-Kolmogorov turbulence

摘要

We have performed a series of experiments aiming at understanding the statistics of deep turbulence over cities. The experimental setup consisted of a Shack-Hartmann wavefront sensor and an imaging camera that simultaneously recorded wavefront-, and focal-plane data, respectively. At the same time, measurements of deep optical turbulence were performed at the urban area of interest using two large-aperture scintillometer systems to get an impression of the strength of C_n~2 above the rooftops of Ettlingen. Our focus is "urban" turbulence because we are interested in the usefulness of adaptive optics for free-space optical communications over urban areas. We discuss methods of determining departure from Kolmogorov turbulence. Our "last mile problem" is that urban turbulence can be significantly stronger, in the sense of flatter power spectrum, compared to the classic Kolmogorov turbulence. This could pose a significant challenge for adaptive optics systems.