ISSN:0048-6604    

DOI:10.1029/RS010i001p00001

年代:1975

数据来源: WILEY

摘要:

This paper deals with a review of theoretical and experimental work performed in the USSR on strong fluctuations of the intensity of light.

ISSN:0048-6604    

DOI:10.1029/RS010i001p00003

年代:1975

数据来源: WILEY

摘要:

In this paper we consider the equations governing the second‐ and fourth‐order coherence functions in random media. We first treat radiation propagating in a homogeneous and isotropic random medium in the limit of small wavelengths. We summarize the solutions that are available and report on some recent unpublished work. We next show how these equations may be generalized to include a nonhomogeneous background and the effects of anisotropy under acoustic conditions. The utility of the equations for considering free‐space propagation is also disc

ISSN:0048-6604    

DOI:10.1029/RS010i001p00015

年代:1975

数据来源: WILEY

摘要:

This paper concerns the wave equation for an irregular time‐dependent nondispersive medium contained in a slab, while a plane monochromatic primary wave passes through the latter in a perpendicular direction. The equation is reduced to an equivalent integral relation in which the influence of the medium in directions perpendicular to that of the incident wave is accounted for by an operational expression. The application of a corresponding forward‐scattering approximation, the reliability of which is discussed, enables the derivation of two alternative versions for the integral equation that refers to a mainly forward‐scattering medium. The second version contains as a factor the geometric optical approximation that is associated with a rectilinear propagation of the incident wave toward the point of observation. It is shown that the Neumann‐Liouville series for the solution of the two mentioned versions correspond, respectively, to the well‐known Born series (but including the time dependence of the slab medium) and to a series containing corrections to the above‐mentioned geometric opt

ISSN:0048-6604    

DOI:10.1029/RS010i001p00023

年代:1975

数据来源: WILEY

摘要:

In a previous paper, the characteristic functional of the wave function has been found to be the solution of a basic equation which has the same form as the original wave equation and is given in terms of the characteristic functional of the refractive index. In this paper, the theory is applied to the case of scalar wave propagation in a medium of randomly distributed particles, and the transport equation is derived by use of an analytical procedure. The renormalization of the medium and of the one‐particle scattering matrix is explicitly introduced, and is found to play an essential role for energy conservation. The Fourier transform of the resulting single Green's function (in the infinite medium) has a set of poles of infinite number. The transport equation is expressed by a series of residue values at the poles of the original and complex conjugate Green's functions, and has a wider range of applicability than that of the conventional transport equation. As a method of solving the transport equation, a set of eigenfunctions is introduced, and the solution is obtained in terms of the eigenfunction series. The diffusion function associated with each eigenfunction is also obtaine

ISSN:0048-6604    

DOI:10.1029/RS010i001p00029

年代:1975

数据来源: WILEY

摘要:

In this paper, integral and differential equations are derived for the correlation function of a wave in a random distribution of discrete scatterers. For stationary (nonmoving) scatterers, relatively simple integral and differential equations for the correlation functions are derived from Twersky's general formulations and their relationships with the radiative transfer theory are clarified. Small‐angle approximations of these differential equations are shown to be identical to the parabolic equations for the mutual coherence function in a turbulent medium. For moving scatterers, Twersky's formulation is modified to take into account the particle motion and the variation of the field in time. General integral and differential equations for spatial as well as temporal correlation function are obtained which include the effects of the constant velocity as well as the fluctuating velocity. Differential equations governing the temporal frequency spectra of the field as well as the specific intensity are derived showing the Doppler shift and the spectrum broadenin

ISSN:0048-6604    

DOI:10.1029/RS010i001p00045

年代:1975

数据来源: WILEY

摘要:

Although much progress has been made in the subject of propagation through random media recently, the average user of the results could be bewildered by the large number of governing parameters and conditions of validity of diverse scintillation statistics. Continuing from previous work summarizing a state of affairs of some years ago, we present some graphical representations of parameter regimes and discuss typical propagation links in nonionized media at optical and at radio wave frequencies, as well as microwave links through an ionized atmosphere. One useful graphical representation defines parameter regimes defined by a coordinate system that uses the number of mean free paths as one axis and the number of Fresnel radii as another. It is sketched for a medium defined by Kolmogorov turbulence laws in the inertial subrange.

ISSN:0048-6604    

DOI:10.1029/RS010i001p00053

年代:1975

数据来源: WILEY

摘要:

In this paper some general problems concerning the probability distribution of an optical signal propagated over a line‐of‐sight path are discussed. The basic physical models for the log‐normal and Rice‐Nakagami probability distributions are given, and various theoretical methods for finding the distribution are discussed, including application of the central‐limit theorem, calculating moments, finding the characteristic functional, and trial and error. The not‐well‐known fact that the log‐normal distribution is not uniquely determined by its moments is pointed out. A summary of the present theoretical and experimental work is given. In addition, some different methods of experimental analysis are suggested, including the use of hypothesis testing and goodness‐of‐fit tests. These methods should permit better presentation of information on probab

ISSN:0048-6604    

DOI:10.1029/RS010i001p00059

年代:1975

数据来源: WILEY

摘要:

The problem of measuring differential angle of arrival through two relatively small apertures of variable separation is considered. The motivation is to evaluate the practicality of a measurement program using such a quantity to observe atmospheric turbulence wave‐front distortion effects when one end of the link is moving and cannot be tracked precisely. (If precise tracking were possible, then measurement of the angular resolution with a single aperture could be used to characterize the propagation path.) Theoretical results for the mean‐square difference in angle of arrival are developed and numerical results are presented. Comparison of expected magnitude of effects with available measurement instrument precision indicates that the experiment should be possible, but will depend on our ability to achieve an rms single‐axis angle‐of‐arrival measurement precision of the order of 0.1 arc sec

ISSN:0048-6604    

DOI:10.1029/RS010i001p00071

年代:1975

数据来源: WILEY

摘要:

Numerical results are presented for the effect of the strength of turbulence on the temporal frequency spectrum of a focussed beam propagating in a random medium having a von Karman spectrum for the index of refraction fluctuations.We also present a new theory for the normalized covarianceBI(z, r) in the intensity fluctuations of a plane wave and find that forσ12≡ 1.23k07/6Cn2z11/6» 1,B1(z,R) ≃ (−11.2σ12R5/3) + (σ12)−2/5ƒ[R/(σ12)3/5]wherek0is the signal wave number,Cn2is the refractive index structure constant,zis the path length,R= (k0/2πz)1/2r, andf3(···) is a function given in section 3. Note that the first term is sharply peaked aboutR= 0 and corresponds to the rapid drop‐off inBI(R) observed experimentally. The second term varies very slowly withRand corresponds to the long tail ofBI(R) seen in experiments. Unlike other theories this theory is completely self‐contained, and does not involve the introduction of any arbitra

ISSN:0048-6604    

DOI:10.1029/RS010i001p00077

年代:1975

数据来源: WILEY