Measurement of the Ionospheric Faraday Effect by Radio Waves reflected from the Moon

Abstract

ROTATION of the plane of polarization (the Faraday effect) of radio echoes from the Moon has been used by Browne, Evans, Hargreaves and Murray¹ and by Evans² to determine the total electron content of the ionosphere. The method is based upon the fact that the plane of polarization of a linearly polarized wave during its double passage through the ionosphere is rotated by an amount: where ƒ is the frequency of the transmitted wave in c./s., B is the Earth's magnetic field in gauss at ionospheric levels, θ is the angle between the direction of propagation and the Earth's field, δ is the zenith angle of the path, N is the electron density per cm.³ and dh is an element of height in cm. The limits of integration correspond to the region in which the ionization is large enough to make an appreciable contribution to the rotation. The assumption is made that B is constant throughout this region and has a value of 0.5 gauss. The value of the constant in the above equation published by Browne, et al. ¹ appears to be in error by a factor of two, although the value given at a later date by Evans² is correct. The reason for the error is that the angular rotation was taken to be equal to the phase difference between the ordinary and extraordinary rays. The parameter of interest, however, is the displacement from its initial position of the resultant of two vectors, one of which has rotated clockwise and one counter-clockwise. This resultant is displaced (ϕ₁ − ϕ₂)/2 from its initial position, where ϕ₁ and ϕ₂ are the absolute values of the rotations of the two component vectors.