Electrical Properties of Frozen Ground at VHF near Point Barrow, Alaska

Electrical properties of frozen ground were measured using radio frequency interferometry (RFI) in the very high frequency (VHF) radiowave band. Ice-rich organic silts and sandy gravel of variable ice content were investigated during early April of both 1979 and 1980. Frequencies between 10 and 150 MHz were used but best results were obtained at VHF between 40 and 100 MHz. Surface impedance and magnetic-induction techniques were also used to obtain a separate control on vertical inhomogeneity. Soil samples were tested for organic and water content. The dielectric constants determined for the ice-rich organic silts ranged from 4.0 to 5.5 while the sands and gravels were about 5.1. Dielectric loss was due to dc conduction and was very low for the silts but significant for the sandy gravel. The higher values for the sandy gravel were most likely due to higher concentrations of salt that are reported to exist in the old beach ridges in this region. All the RFI measurements are believed to be indicative of only the first few meters of the ground although the radiowaves could penetrate to tens of meters. Inconsistencies from year to year show that the RFI method at VHF may often be too dependent upon the idealizations of the theoretical model upon which it is based.