Electrical ground impedance measurements in Alaskan permafrost regions

Investigation was conducted to establish the techniques leading to construction of an electrical conductivity map of Alaska in the V/L/MF frequency band for use in planning of navigational aids. Results about ground conductivity in North America were available from geophysical studies near Fairbanks, from sites along the Alaska pipeline and in several areas of the Canadian Arctic; at these locations ground and/or airborne conductivity measurements were made by measuring the wavetilt and/or the surface impedance of radio groundwaves. Several difficulties were encountered in using ground conductivity data of high quality to construct a conductivity map of Alaska. They are: the results showed that the ground conductivity in permafrost areas of North America is very heterogeneous, so that it is not directly apparent how to assign an effective conductivity value to a path of practical length (approximately 100 km). The geological and permafrost conditions vary much in Alaska, so that measurements at a location are representative of a small area only, leaving large areas of Alaska open to question. Theoretical evaluations of the seasonal changes in ground conductivity and their effect on radiowave propagation and electrical grounding are also discussed.