Measurement of the scattering matrix with an intervening ionosphere

With the advent of radar scattering from the moon and earth satellites, it is interesting to examine the effect of the interposition of a magneto-ionic medium (the ionosphere) between the observer and the scatterer upon measurements of the scattering matrix. The integrated electron density of the ionosphere is of the order of 1013 electrons per centimeter squared, with diurnal variations of a factor of two. A typical value of the geomagnetic field is Vs gauss. For radar frequencies, the Faraday effect may be considered as a rotation of the plane of polarization without absorption. At 200 megacycles, the rotation is about ¿ each way. It varies as the inverse square of the frequency. For simplicity, the discussion is restricted to back-scattering; no new essential features appear in the general case. The scattering matrix of interest is, of course, that which would be present in the absence of the ionosphere, not that due to the composite system of scatterer plus ionosphere. The complication is that it can be observed only with the effect of the Faraday rotation superimposed.