Derivation of electron-density profiles in the lower ionosphere using radio absorption measurements at multiple frequencies

Abstract

A new method has been developed permitting the derivation, during disturbed ionospheric conditions, of the electron-density profiles in the lowermost ionosphere. On the basis of simultaneous measurement of ionospheric absorption on several frequencies, and an assumed model of the variation of electron collision frequency with height, the Sen-Wyller formulation of the magnetoionic theory is used to compute the profile best capable of producing the observed absorption values. The method is described, and some of its limitations are discussed. Its use is illustrated by means of representative electron-density profiles derived for the polar-cap absorption events of July 1961. These profiles show that the base of the layer varied in height from 30 to 50 km, and that the region of maximum absorption, for a frequency of 30 Mc/s, occurred systematically at about 60 km.