The dielectric properties of any material can be described by the complex relative dielectric constant (complex relative permittivity) and contains of the real part (moisture content) and the imaginary part (conductivity/loss tangent). For instance: Reflectivity of a smooth surface and the penetration capabilities of microwaves into the material are determined by these two quantities. The complex dielectric constant changes mainly due to variations in water content, salinity, temperature of the material as well as due to the observing wavelength and polarization of the electromagnetic wave. It relates to the interaction of weakly-charged material components, like bi-polar water molecules, with irradiation of electromagnetic waves. The interaction increases with amount and charge of the material components. The complex relative permittivity is also linked to the complex index of refraction as being its square. In order to describe the complex relative permittivity of pure and saline water the single-relaxation Debye and the double-Debye dielectric model can be used. As the movement of bi-polar material components is significantly reduced when the material is put under freezing conditions (temperatures below 0 °C), the permittivity falls to almost a constant. The real part of the relative permittivity of pure ice is almost constant, when ignoring a weak temperature dependence, and amounts to approx. 3.2. For heterogeneous (mixed) materials consisting of more than one component the equivalent dielectric constant is a function of the permittivity of the single components, their volume fractions, their distribution along space and the polarization and wavelength of the interacting electromagnetic wave.