Influence of turbulent fluctuations of refractive index on PSF

ABSTRACT Statistical properties of a turbulent flow have been investigated experimentally in a shock tube with a turbulence grid. The fluctuations of the refractive index were detected with the aid of a laser-schlieren technique. It was found that the structure function Dr n () has the form: Dr c br ar ar abc n ( ) (1 exp( )sin( )/( )), , ,=  being constants, in contrast with Kolmogorov's two-thirds law. These data were used in order to determine the PSF and MTF. Numerical results for the image of an object in a turbulent flow are also presented. Keywords : turbulent fluctuations, structure function, correlation function, PSF, MTF, formation of image. 1. INTRODUCTION We consider the formation of images during the propagation of an electromagnetic wave through a turbulent medium. As known, turbulence can effect considerably on the quality of the image. In order to solve the above-mentioned problem we must know the characteristics of turbulence and its influence on the propagation of electromagnetic waves. Turbulence has been investigated by many authors. The main question is to what degree turbulence is a universal phenomenon. As pointed out in a recent survey¹, there are statistical properties of small-scale flow field that occur in most turbulent flows. The large-scale eddy motions have qualitative similarities within particular types of turbulence. The propagation of electromagnetic waves through turbulence was investigated by Ishimaru². The author used the Kolmogorov's two-thirds law for the structure function. In contrast with this work, we used a different expression for the structure function which was found from our experimental data. Section 2 of this paper describes the experimental facility for the investigation of statistical properties of turbulent flow. Section 3 represents the expressions for the structure function and the correlation function of the turbulent fluctuations of the refractive index. The images of an object in a turbulent medium are given in Section 4.