Dielectric anisotropy in ice Ih at 9.7 GHz

Dielectric anisotropy in ice Ih was investigated at 9.7 GHz with the waveguide method. The measurement of dielectric permittivity was made using single crystals collected from Mendenhall Glacier, Alaska. The result of the measurement shows that ϵ′‖c, the real part of dielectric permittivity parallel to the c axis, is larger than ϵ′⊥c the real part of dielectric permittivity perpendicular to the c axis. This tendency is similar to that at low frequencies in the region of the Debye relaxation dispersion. It can be proposed that ϵ′‖c>ϵ′⊥c in the HF, VHF and microwave frequency range. ϵ′‖c and ϵ′‖c depend slightly upon temperature but the dielectric anisotropy, ∆ϵ′=ϵ′‖c-ϵ′⊥c, is constant and becomes 0.037 (±0.007). Based on the present results, a simple caculation indicates that the maximum power reflection coefficient caused by the dielectric anisotropy is about −50 ∼ −80 dB, which is significantly larger than the power reflection coefficient observed in the ice sheet by radio-echo sounding, about −70 ∼ −80 dB. This leads to a conclusion that dielectric anisotropy is one of the dominant causes of internal reflections.