Dielectric properties of sea and sodium chloride ice at UHF and microwave frequencies

Sea ice differs from fresh water ice in physical behavior because of the entrapment of liquid inclusions of brine in the ice matrix. This difference is strongly evident in the dielectric properties of the two ice forms. Pure ice is a low-loss dielectric at frequencies above 107 Hz. Water, on the other hand, has its maximum loss at microwave frequencies. The liquid inclusions in sea ice, therefore, cause sea ice to be a lossy dielectric at microwave frequencies. The dielectric loss of sea ice at microwave frequencies is caused by two mechanisms, ionic conductivities and dipole rotations of the water molecules. The complex dielectric constant of sea ice was determined in the frequency range from 108 to 2.3×1010 Hz by measuring the changes in phase and amplitude when samples were placed in coaxial lines and waveguides. The measured values of the dielectric loss agree well with computations made using low-frequency conductivity, brine volume, and salinity as known parameters.