ELF ground design and installation

Methods used for designing safe, durable, economical, and low resistance grounds for the three Michigan extremely low frequency (ELF) antennas are described. Antenna location criteria include high resistivity for antenna efficiency, while low ground system resistance requires low resistivity, at least in the near-surface layers. These incompatible criteria increase the difficulty of finding suitable ground areas in the vicinity of the antenna ends. This process begins with maps, aerial pictures, and aerial resistivity surveys. Low resistivity areas not due to cultural artifacts are further investigated with surface surveys consisting of Schlumberger expansions and seismic profiles. When the earth resistivity from the Schlumberger data and the till depth from the seismic profile are suitable for well locations, a borehole may be drilled and logged to confirm the earth characteristics. Use of this data is illustrated in a design example. Some installation details are included.