Structure Constant Of Atmospheric Turbulence Research Articles

Joint measurements of optical parameters by irradiance scintillation and angle-of-arrival fluctuations

AbstractA method for joint measuring the power law exponent and the structure constant of atmospheric turbulence is proposed and examined. The measurements are equivalent to solve the simultaneous equations formed by the irradiance scintillation index and the angle-of-arrival fluctuations variance, where the measured parameters are regarded as the unknowns. The measured error analysis is also presented. Based on our proposed method, the measured results accord with the daily trend of atmospheric turbulence.

Average intensity and spreading of an astigmatic sinh-Gaussian beam with small beam width propagating in atmospheric turbulence

Propagation properties of astigmatic sinh-Gaussian beams (ShGBs) with small beam width in turbulent atmosphere are investigated. Based on the extended Huygens–Fresnel integral, analytical formulae for the average intensity and the effective beam size of an astigmatic ShGB are derived in turbulent atmosphere. The average intensity distribution and the spreading properties of an astigmatic ShGB propagating in turbulent atmosphere are numerically demonstrated. The influences of the beam parameters and the structure constant of atmospheric turbulence on the propagation properties of astigmatic ShGBs are also discussed in detail. In particular, for sufficiently small beam width and sinh-part parameter as well as suitable astigmatism, we show that the average intensity pattern converts into a perfect dark-hollow profile from initial two-petal pattern when ShGBs with astigmatic aberration propagate through atmospheric turbulence.

Scintillations of LED sources in oceanic turbulence.

The scintillation index of light emitting diode (LED) sources is evaluated when such sources are employed in oceanic wireless optical communication (UWOC) links. In the formulation, LED source radiation is taken to be perfectly incoherent with a Gaussian field distribution. We have utilized the scintillation index solution of an incoherent source in atmospheric turbulence, together with our recently obtained expression that expresses the structure constant of atmospheric turbulence in terms of the oceanic turbulence and UWOC link parameters. Oceanic turbulence parameters of interest are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, and viscosity. UWOC link parameters are the LED source size, link length, and the wavelength. Scintillation index results are presented for various variations of the oceanic turbulence and UWOC link parameters.

Scintillation analysis of multiple-input single-output underwater optical links.

Multiple-input single-output (MISO) techniques are employed in underwater wireless optical communication (UWOC) links to mitigate the degrading effects of oceanic turbulence. In this paper, we consider a MISO UWOC system which consists of a laser beam array as transmitter and a point detector as receiver. Our aim is to find the scintillation index at the detector in order to quantify the system performance. For this purpose, the average intensity and the average of the square of the intensity are derived in underwater turbulence by using the extended Huygens-Fresnel principle. The scintillation index and the average bit-error-rate (⟨BER⟩) formulas presented in this paper depend on the oceanic turbulence parameters, such as the rate of dissipation of the mean-squared temperature, rate of dissipation of kinetic energy per unit mass of fluid, Kolmogorov microscale, and the ratio of temperature to salinity contributions to the refractive index spectrum, the link length, and the wavelength. Recently, we have derived an equivalent structure constant of atmospheric turbulence and expressed it in terms of the oceanic turbulence parameters [Appl. Opt.55, 1228 (2016)APOPAI0003-693510.1364/AO.55.001228]. In the formulation in this paper, this equivalent structure constant is utilized, which enables us to employ the existing similar formulation valid in atmospheric turbulence.

Fourth-order mutual coherence function in oceanic turbulence.

We have recently expressed the structure constant of atmospheric turbulence in terms of the oceanic turbulence parameters, which are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of the mean-squared temperature, wavelength, Kolmogorov microscale, and link length. In this paper, utilizing this recently found structure constant and the fourth-order mutual coherence function of atmospheric turbulence, we present the fourth-order mutual coherence function to be used in oceanic turbulence evaluations. Thus, the found fourth-order mutual coherence function of oceanic turbulence is evaluated for the special case of a point source located at the transmitter origin and at a single receiver point. The variations of this special case of the fourth-order mutual coherence function of oceanic turbulence against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of the mean-squared temperature, the wavelength, and the Kolmogorov microscale at various link lengths are presented.

Extension of the van Cittert–Zernike theorem for completely polarized incoherent electromagnetic beam propagating through non-Kolmogorov turbulence

Based on the 2 × 2 cross-spectral density matrix, the van Cittert–Zernike extended theorem is developed for the completely polarized incoherent beams propagation through the paraxial non-Kolmogorov turbulence. On the consequence of the extended theorem and the definition of general spectral degree of cross-polarization of a beam, we found that the spectral degree of cross-polarization of the resultant field is independent of the refractive index structure constant of atmospheric turbulence. We investigated the influences of the propagation distance and the distance of two detection points on the degree of coherence and the spectral degree of cross-polarization.

A Mixed Method for Measuring the Inner Scale of Atmospheric Turbulence

Abstract A new method for measuring the inner scale and structure constant of atmospheric turbulence is proposed and tested. It utilizes both phase and amplitude fluctuations of laser radiation propagating in the medium. The measured quantities are the intensity variance of a spherical wave and the transverse-displacement variance (wandering) of a narrow laser beam. The method is developed within the limits of geometrical optics. Experimental laboratory results are presented. Values of inner scale of a few millimetres are measured.

Atmospheric Velocity Spectral Width Measurements Using the Statistical Distribution of Pulsed CO2Lidar Return Signal Intensities

A pulsed CO2 lidar with coherent detection has been used to measure the correlation time of backscatter from an ensemble of atmospheric aerosol particles which are illuminated by the pulsed radiation. The correlation time of the backscatter of the return signal, which is directly related to the velocity spectral width, can be used to study the velocity structure constant of atmospheric turbulence and wind shear. Various techniques for correlation time measurement are discussed, and several measurement results are presented for the technique using the information contained in the statistical distribution of a set of lidar return signal intensities.