Radio Astronomy Polarization Measurements

Various polarization measuring schemes are discussed in terms of the Stokes parameters. The methods are separated into three groups according to the number of components isolated by the antenna system. The dispersion resulting from the frequency dependence of the Faraday effect is considered, and the interpretation of polarization data in terms of these effects is discussed. Some results are that one polarization determination will allow limits to be placed on the axial ratio and polarization percentage at the source, and on the ray path integral of longitudinal magnetic field times electron density. A graphical presentation of Hatanaka's dispersion theory permits this to be done very quickly. With suitable assumptions, measurements at two frequencies or with two bandwidths will fix the three quantities. Radio astronomy polarization observations are surveyed. The ionosphere, solar corona, and Crab Nebula are considered briefly in the light of possible Faraday effects. Mayer, McCullough, and Sloanaker's 3.15-cm observations on the Crab Nebula and the optical results are used to analyze lower frequency attempts to find polarized radiation from this object.