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Polarization effects

The scattered signal, as we have seen, will in general have different polarization characteristics than the incident one. This is true even in very simple models such as reflection from a (non-perfectly conducting) flat surface (see [Beckmann et al., 1963], page 160):

\begin{displaymath}{ \sigma_0^\bot \over\sigma_0^\Vert } ={
(1+{\cal R}^\bot)\co...
...\cal R}^\Vert)\cos \theta_s -(1-{\cal R}^\Vert)\cos \theta} .
\end{displaymath} (1.35)

At grazing angles, it was already pointed out by [Katzberg et al., 1996] that the polarization of a GPS signal becomes linear . This is because the ocean surface is a partially conducting dielectric. Thus, with the exception of near-vertical specular incidence, depolarization is expected to occur even in a superscalar model (that is, assuming the surface is flat for polarization analysis purposes) . The same phenomenon occurs in scattering from the sea at optical frequencies.

Research on the polarization aspects of GNSS reflected signals and their possible geophysical content is an on-going active area of work. In [Katzberg et al., 1996] it is pointed out that it may be necessary or even desirable to measure the scattered power in both polarizations. More later?

Giulio Ruffini Fores