A. Consortini

Inner-scale effect on irradiance variance measured for weak-to-strong atmospheric scintillation

Experimental results are described of measurements of irradiance fluctuations of laser radiation through atmospheric turbulence. Simultaneous measurements of irradiance fluctuations, inner scale, and structure parameter were made in conditions of homogeneous turbulence during a number of summer days, from very early in the morning, before sunrise, until approximately noon. During the measurements the turbulence strength varied continuously, spanning very low as well as intermediate and very high levels. We used the data collected in selected intervals, during which turbulence was stationary, to obtain plots of irradiance variance versus the structure parameter for fixed ranges of values of the inner scale. The results clearly show the effect of the inner scale. For a given value of the structure parameter larger inner scales result in larger values of irradiance variance in the regime of strong scintillation.

Investigation of Atmospheric Turbulence by Narrow Laser Beams

In order to determine the characteristic parameters of the atmospheric turbulence, the mutual dancing of two parallel narrow laser beams propagating through a turbulent atmosphere has been investigated theoretically and experimentally. The experiments have been carried out with a He-Ne laser on a 130-m path, one meter from the ground. The method allowed the determination of the variance of the refractive index fluctuations, as well as the values of scale of the turbulence in the vertical and horizontal planes.

Measuring inner scale of atmospheric turbulence by angle of arrival and scintillation

A new method for measuring inner scale of atmospheric turbulence based on simultaneous measurements of differential angle of arrival and intensity fluctuations of a wave propagating horizontally in a turbulent medium is presented. An experimental laboratory test of the method is also presented.

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.

Estimate method for outer scale of atmospheric turbulence

We developed a method for estimating the outer scale of atmospheric turbulence based on correlation functions of lateral displacements of thin beams propagating horizontally over short paths. A simple theory, based on the Von Karman model of turbulence and a suitable experiment for testing the method are presented.

Beam wandering of thin parallel beams through atmospheric turbulence

Abstract Wandering and correlation of wandering of two parallel laser beams after crossing atmospheric turbulence are theoretically and experimentally investigated. A general expression is given, valid for propagation through a thick layer of turbulence, which includes as a particular case that of a path completely filled with turbulence. Two different models of isotropic atmospheric turbulence are considered and numerical results are derived. The results of an experimental test through the atmosphere are also described.

Detector saturation effect on higher-order moments of intensity fluctuations in atmospheric laser propagation measurement

We investigate the influence of the detection-system saturation on the intensity-fluctuation statistics in measurements of optical scintillation induced by atmospheric turbulence. The statistical distribution of the intensity is assumed to be log normal. The values of the nth moments detected by the apparatus are shown to depend on the ratio between the saturation intensity of the detector and the mean intensity of the distribution to be measured.

Role of the outer scale of turbulence in atmospheric degradation of optical images

The atmospheric degradation of optical images is investigated by assuming the refractive-index structure function to be independent of the distance between two correlation points when such distance is larger than the outer scale (Von Karman model). It is found that, in most practical cases, the atmospheric turbulence puts a limit to the resolution as predicted by the 2/3-power law, however, only when the turbulence is sufficiently strong. The parameter distinguishing strong from weak turbulence turns out to be the limit value of the wave structure function Dw (∞) for infinite distance. Weak turbulence, with Dw (∞) ≲ 20, does not put a limit to the resolution of an optical system.

Choice of the Model of Atmospheric Turbulence

The concept of equivalent models of turbulence is introduced in order to investigate how the theoretical behavior of the structure function of an electromagnetic wave propagating in a given turbulent medium depends on the turbulence model. It is shown that equivalent models may give rise to substantially different structure functions of a wave parameter. On the other hand, the experimental structure function of the phase of a plane wave can be well fitted by the theoretical curves derived from different models, with suitable choices of the turbulence parameters appearing in the models. However, such models turn out not to be equivalent. When experimental data on the turbulence are not available, simultaneous measurements of the structure functions of more than one wave parameter are suggested, for the choice of the model.

Strong-scintillation-statistics deterioration due to detector saturation

The deterioration that is due to saturation of a revealing apparatus on high-order moments of intensity is investigated in the case of Furutsu’s distribution. This is a two-parameter distribution and seems suitable for describing intensity fluctuations that are due to atmospheric turbulence in the case of intermediate and strong scintillation. The effect of saturation was shown to depend on only one parameter, αDS, defined as the ratio between the saturation intensity of the system and the mean intensity to be measured, a result already found in the case of a log-normal distribution. An expression of the deteriorated moments is given in terms of αDS and of the two parameters of the distribution. The theoretical results are used to give a qualitative interpretation of measured moments after laser propagation along a 1800-m path above the city of Florence.