A theory of ionospheric thermal radiation

Abstract

The ionosphere is considered as a dissipative medium in which the random thermal motions of the charged particles act as a source of thermal radiation. Attention has been focused on the electrons colliding with ions and neutral particles in the ionosphere. A method of analysis has been developed with the aid of the Maxwell and Langevin equations based on a linear, macroscopic, fluctuating electromagnetic field theory. The spectral density of the randomcurrent source function is derived in terms of the conductivity tensor of the ionosphere.The ionosphere is divided into a large number of incremental volume elements, each containing an ionized medium which represents an anisotropic elementary radiating system, characterized by the spectral density of the source function. The radiation characteristic of the radiating system observed at a point located outside of the source region is obtained with the aid of the potential functions which relate the thermal electromagnetic fields at the observation point to their source function. Based on the superposition principle, general expressions have been derived for w0, the thermal noise power generated per unit volume, per unit bandwidth, from any given source region Vs of the ionosphere, and for P0([function of (italic small f)], Vs), the available thermal noise per unit bandwidth at a receiving antenna. These expressions are valid for most regions of interest in the ionosphere where the electron collision process plays a major role in the thermal radiation and they are not limited in frequency range.