In this study, we investigate the fractal properties of optical turbulence profiles. Through rescaled range analysis, optical turbulence profiles roughly exhibit three different regimes. The effects of stratifications are the underlying mechanism contributing to this phenomenon. The results of detrended fluctuation analysis and multifractal detrended fluctuation analysis indicate that optical turbulence profiles have multifractal structure.
The long-term measurement of atmospheric aerosol is constructed via such equipment as visibility meter, optical particle counter, solar radiometer, automatic weather station, aerosol laser radar and aerosol scattering absorption coefficient measurer and so on during the year of 2010 and 2017 in the coastal areas of Guangzhou, China to study the optical parameter characteristics of atmospheric aerosol and establish the aerosol optical parameter mode in such areas. The effects of temperature and humidity on aerosol concentration, extinction and absorption coefficient are analyzed and the statistical characteristics of atmospheric temperature and humidity, visibility, extinction profiles and other parameters in different months are tallied, preliminarily establishing the atmospheric aerosol optical parameter pattern in Guangzhou coastal areas.
By using wave optics numerical simulation, the scintillation of pseudo-partially coherent Gaussian beam propagating in atmospheric turbulence is investigated. The effects of partial coherence on scintillation index are analyzed as a function of the correlation length of beam source. The reduction of the aperture averaging scintillation index, on-axis and off-axis scintillation are shown for a horizontal propagation path. The aperture averaging factor of pseudo-partially coherent beam is
compared with that of fully-coherent beam. And how the pseudo-partially coherent Gaussian beam behaves like partially coherent Gaussian Schell-model beam is also discussed. It was found that the on-axis scintillation index and off-axis scintillation index of pseudo-partially coherent beam can be reduced greatly by decreasing the coherence degree of beam source. The results of aperture averaging scintillation index also revealed the advantage of using pseudo-partially coherent beam compared to fully coherent beam. However, the aperture averaging factor of a pseudo-partially coherent beam is smaller than that of the fully coherent beam at the same receiving aperture diameter. This implies that the aperture averaging effect of scintillation index may be weakened by reducing the coherence degree of beam source. This work may
provide a basis for the utilization of pseudo-partially coherent beam in free-space optical communications.
This paper designs a style of particle counter which may measure the aerodynamic size and the
scattering intensity of two scattering angles of the aerosol particles. The scattering intensity can also be
calculated from the size and the refractive index according to the Mie theory. When the aerodynamic size is
equal to the optics size approximatively, we can inverse the refractive index of individual aerosol particles by
combining the relative results of the measurements.
This paper presents a speckle image restoration algorithm using wavelet transform. Based on the wavelet theory, a new gauss PSF accurate estimation is put forward. Firstly, wavelet with varied scales is transformed, after which the local maxima of the modulus of the wavelet are computed respectively. Secondly, on the basis of the relation deduced among the local maxima of the modulus of the wavelet at different scales, Lipschitz exponent and variance, the variance of a Gaussian point spread function is computed. According to Fried theory, the Fried parameter can be deduced from the variance. From the Fried parameter we could estimate the optical transfer function of the turbulence. Row action projection Method is applied to restore the image through atmosphere over a distance of 1 km. Primary results are obtained.
The intermittency in optical scintillation was theoretically studied and experimentally observed by laser propagation through the turbulent atmosphere over sea surface. It is found that the intermittent characteristics of the atmospheric turbulence repeat itself in optical irradiance fluctuations, then a method of the singularity measurement analysis was introduced and the intermittency index was presented to quantitatively evaluate the intermittency strength. Experiment results show that the intermittency index in laser scintillation is around 0.1 and varies a little compared with the significant variation of the turbulence strength, which had been approximately estimated at two orders of magnitude in a whole day.
The dependence of the intermittency on the wavelength was further studied and the relationship was obtained using a multi-wavelength scintillometer. Generally, the intermittency indices display some differences at the different optical wavelengths, especially in strong turbulence. However, the wavelength dependence is not so notable that the intermittency indices are assumed to be equal within less than 10%, even the maximum error is no more than 20%. Moreover, some statistical results of the intermittency strength are also obtained from a long-term plan of laser propagating in coastal surroundings.
The spot dancing of the focused laser beam in the turbulent atmosphere was studied using a two dimensional position sensitive photomultiplier tube (PSPMT). The centroid position of the laser spot was evaluated by means of current-dividing center-of-gravity detection. The system has advantage over detector array system in spatial resolution and over the imaging system in dynamic range and sampling rate. Laser propagation experiments were carried out over 1000m path above the sea level and the fluctuations of laser intensity were measured simultaneously. The frequency spectra were calculated by fast Fourier tansform and the standard deviation of the spot dancing were analyzed.
Laser scintillation in the atmosphere exhibits fractal behavior. Two fractal characteristic parameters, the fractal dimension and the Hurst coefficient, are analyzed and compared with two traditional parameters, the scintillation index and the scaling exponent of the power spectrum. Results show that the scintillation is a kind of non-stationary process with long-run dependence; under the saturated scintillation conditions, the values of the two-fractal parameters are mostly smaller than those under weak scintillation conditions. According to the statistical behavior of the fractal parameters, it is possible to find new ways to deal with some problems concerning the scintillation saturation.