Characterizing inertial and convective optical turbulence by detrended fluctuation analysis

Gustavo Funes, Eduardo Figueroa, Damían Gulich, Luciano Zunino, DARIO GABRIEL PEREZ

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

5 Scopus citations

Abstract

Atmospheric turbulence is usually simulated at the laboratory by generating convective free flows with hot surfaces, or heaters. It is tacitly assumed that propagation experiments in this environment are comparable to those usually found outdoors. Nevertheless, it is unclear under which conditions the analogy between convective and isotropic turbulence is valid; that is, obeying Kolmogorov isotropic models. For instance, near-ground-level turbulence often is driven by shear ratchets deviating from established inertial models. In this case, a value for the structure constant can be obtained but it would be unable to distinguish between both classes of turbulence. We have performed a conceptually simple experiment of laser beam propagation through two types of artificial turbulence: isotropic turbulence generated by a turbulator [Proc. SPIE 8535, 853508 (2012)], and convective turbulence by controlling the temperature of electric heaters. In both cases, a thin laser beam propagates across the turbulent path, and its wandering is registered by a position sensor detector. The strength of the optical turbulence, in terms of the structure constant, is obtained from the wandering variance. It is expressed as a function of the temperature difference between cold and hot sources in each setup. We compare the time series behaviour for each turbulence with increasing turbulence strength by estimating the Hurst exponent, H, through detrended fluctuation analysis (DFA). Refractive index fluctuations are inherently fractal; this characteristic is reflected in their spectra power-law dependence-in the inertial range. This fractal behaviour is inherited by time series of optical quantities, such as the wandering, by the occurrence of long-range correlations. By analyzing the wandering time series with this technique, we are able to correlate the turbulence strength to the value of the Hurt exponent. Ultimately, we characterize both types of turbulence.

Original languageEnglish
Title of host publicationRemote Sensing of Clouds and the Atmosphere XVIII; and Optics in Atmospheric Propagation and Adaptive Systems XVI
DOIs
StatePublished - 25 Nov 2013
EventRemote Sensing of Clouds and the Atmosphere XVIII; and Optics in Atmospheric Propagation and Adaptive Systems XVI - Dresden, Germany
Duration: 23 Sep 201326 Sep 2013

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume8890
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferenceRemote Sensing of Clouds and the Atmosphere XVIII; and Optics in Atmospheric Propagation and Adaptive Systems XVI
CountryGermany
CityDresden
Period23/09/1326/09/13

Keywords

  • angle-of-arrival
  • beam wandering
  • Hurst exponent
  • multifractal detrended fluctuation analysis
  • non-Kolmogorov turbulence

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