The Scattering of Electromagnetic Waves by Turbulent Atmospheric Fluctuations

The statistical theory of turbulence is applied to the problem of density fluctuations in the troposphere and the ionosphere. For suitable wavelengths, for which the so-called similarity region (Kolmogoroff spectrum) of the spectrum of turbulence is relevant, a closed formula can be given for the scattering cross section. It contains as only parameter the turbulent power dissipation $S$,and its angular dependence is given by ${\left(sin\frac{1}{2}\theta \right)}^{\frac{13}{3}}$, $\theta$ being the scattering angle. The values of $S$ required to explain ionospheric scattering are in excellent agreement with values found from investigations of meteor trails. Tropospheric data cannot be fitted with the assumptions of dry-air turbulence alone. The inference is that humidity fluctuations play an essential part in tropospheric scattering. A preliminary study of these latter fluctuations gives satisfactory results. Further investigations (and experimental data) are needed, however, to work out a quantitative theory.