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The dielectric properties of sea water

Sea water is a dielectric, and we can approximate $\mu\approx \mu_0$.
  
Figure: The effect of salinity on the dielectric constant at GPS frequencies (from expressions in [Ulaby et al., 1986]). Note the rapid increase in the imaginary part of $\epsilon $ with increasing salinity--this is associated with a rapid increase in conductivity.
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Figure 1.2: Fresnel coefficients  in the form of H and V reflectance (that is, the H and V Fresnel coefficients squared).
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Figure: Fresnel coefficients  in the form of RHCP and LHCP reflectance, $\vert{\cal R}_{RR}\vert^2$ and $\vert{\cal R}_{RL}\vert^2$ .
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If sea water were a perfect conductor, the incident field would generate surface charges and currents that would precisely cancel the fields in the interior of the surface. This is not the case, but it is pretty close--reflectance is more than 60 percent, for instance. Thus, the imaginary part of the dielectric constant, closely related to conductivity, makes the ocean behave like a pretty good mirror at microwave frequencies--which does not happen at optical frequencies. The Fresnel coefficients  are not unity, nonetheless, and therefore there is a Brewster angle for which the vertically polarized reflectance is a minimum.


next up previous contents index
Next: Ensemble averages. Surface waves Up: Scattering fundamentals Previous: Polarization effects
Giulio Ruffini Fores
1999-07-03