Electromagnetic scattering by low-density meteor trails

Abstract

Expressions for the scattering of electromagnetic radiation by a meteor trail have been derived for a simple model. A uniform line density of electrons is first considered, of sufficiently low density that the interaction between electrons can be neglected. Then, the model is extended to include the effect of ambipolar diffusion. Finally, the fast initial penetration of the particles before they are slowed down to thermal velocities is taken into account. Similar model assumptions have previously appeared in the literature, except that an effort has been made here to retain consistently the intrinsic three-dimensional geometry of the problem. The derivations are based on an idealized superposition of antenna patterns with a constant gain within the coverage and a sharp cut-off; the extension to an arbitrary pattern is simple, and the procedure is sketched. Various limiting cases are considered, with careful specification of the realm of validity of approximations. The familiar expressions emerge in the large wavelength limit for specular scattering. Non-specular scattering and intermediate orientations are also treated. A small wavelength limit is derived, and the transition wavelengths are explored in detail.