POLARIZATION OF AURORAL BACKSCATTER AT 50 MHZ

Auroral backscatter from the lower E region was studied using two 50 M Hz bistatic, continuous wave radar links which shared a common polarim etric receiver. The polarization parameters were defined in terms of t he polarization ellipse, which is described by the ellipticity angle c hi, orientation angle psi, and polarization ratio m. Spectral analysis was applied to the intensity measurements and its corresponding polar ization parameters. Observations of typical auroral spectral types 1, 2, and 3 indicated that the scattering of a linearly polarized inciden t wave produced an essentially linear and highly polarized scattered w ave. These results imply a small scattering volume and/or a small numb er of discrete scatterers located close to one another, ''scatterer'' referring to a volume where radar waves are scattered according to wea k coherent scattering theory, and also reaffirms that the scattering p rocess is a weak coherent one. These results are typical of most obser vations, but not all; an otherwise typical intensity spectrum may also exhibit variable polarization parameters with an appreciable reductio n in the polarization ratio and/or signals of significant ellipticity. These anomalous properties can be explained as scatter coming from a number of individual scattering volumes within the scattering region ( i.e., the effective radar viewing region), which are each influenced d ifferently by Faraday rotation to and from the scattering region.