Exploitation of ionospheric Faraday rotation to perform radar astronomical polarization measurements

By carefully accounting for the effects of Faraday rotation, certain of the polarization properties of radar echoes from the moon at 25 MHz could be estimated even though only a single-fixed linearly polarized antenna was used. The combination of Faraday rotation and antenna response sinusoidally modulates the linear FM signals used. This "Faraday modulation" does not appreciably affect the range resolution (which was about
20 \mu
S) but strongly affects the proportions of the cross-polarized components of the echoes. The measured frequency and phase of the Faraday modulation on each echo allows the determination of the proportions and, hence, the separate estimation of the components. Because the data reduction primarily involved digital spectral analysis, the effects of the modulation are interpreted in terms appropriate to power spectral estimation. The techniques used, but not the results, are discussed here.