An Empirical Model of Angle-of-Arrival Variance for a Gaussian Wave Propagation through Non-Kolmogorov Turbulence

This paper proposes an empirical model of the angle-of-arrival (AOA) variance for a Gaussian wave propagating through the weak non-Kolmogorov turbulence. The proposed model is approximately expressed as the linear weighted average between the AOA variances of the plane and spherical waves. The Monte Carlo method is applied to validate the proposed model. The numerical simulations indicate that, under the geometrical optics approximation, the AOA variance for a Gaussian wave is insensitive to the change of the diffraction parameter and can be closely approximated by a simple linear relationship in the refraction parameter. These two properties ensure the validity of the empirical model.

О рассеянии света двухслойными эллипсоидами с несофокусными границами

New approaches to calculate the optical properties of small nonspherical layered particles whose layer boundaries are nonconfocal concentric coaxial ellipsoids are considered. A simple analytical approximation is suggested and substantiated for the case when the size of similar layer particles is much less than the wavelength of the incident radiation. It is found that this approximation provides the results with the accuracy of about 0.003 when the diffraction parameter x < 0.1. An approach to calculate the optical properties of nonconfocal ellipsoids by using a substitute of the nonconfocal boundaries with the confocal ones with keeping the layer volumes constant is justified. It is shown that for dielectric particles such an approach has the accuracy of a few percent for x < 1 and about 20% for x < 5. It is noted that both approximations are easily expanded on the case of multilayered nonconfocal ellipsoids.

WWM Extended to Account for Wave Diffraction on a Current Over a Rapidly Varying Topography

The WWM (wind wave model) is extended to account for wave refraction-diffraction for wind waves propagating over a rapidly varying seabed in the presence of current. The wave diffraction effect is introduced into the wave action balance equation through the correction of wavenumber and propagation velocities using a diffraction corrected parameter. The approximation is based on the mild-slope equation for wave refraction-diffraction with current effect on a rapidly varying sea bottom. The relative importance of additional terms that influence the corrected diffraction parameter in the presence of currents was first introduced. The comparison of numerical results with other numerical models and experiments show that the validity of the model for describing wave propagating over a rapidly varying bottom with current effect is satisfactory. The implementation of this phase-decoupled refraction-diffraction approximation in WWM shows capability of the present model can be used in most practical engineering situations.

ATTENUATION OF LASER-GENERATED ACOUSTIC SIGNALS IN LIQUIDS

The dependence of the optoacoustic wave amplitude in liquids on propagation distance was investigated for various values of the diffraction parameter. The results of the theoretical model are discussed and the computed results are compared to the experimental data obtained from optoacoustic waves generated in water and in n-heptane by means of a hybride CO 2 laser, for rigid and free boundary conditions of the liquid. The coefficients for amplitude attenuation based solely on diffraction, i.e. diffraction attenuation coefficient, are evaluated, as are the total attenuation coefficients. A simple method to correct experimental diffraction data obtained with non-ideal liquids is proposed.