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Sea water is a dielectric, and we can approximate
.
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
with increasing salinitythis is associated with a rapid increase in conductivity.

Figure 1.2:
Fresnel coefficients in the form of H and V reflectance (that is, the H and V Fresnel coefficients squared).

Figure:
Fresnel coefficients in the form of RHCP and LHCP reflectance,
and
.

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 closereflectance 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 frequencieswhich 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: Ensemble averages. Surface waves
Up: Scattering fundamentals
Previous: Polarization effects
Giulio Ruffini Fores
19990703