Measurement of the Phase Constant for Rock Propagated Radio Signals

A method is described for determining the phase constant of the rock medium below the surface of the earth. The constant is deduced from the measured phase angle of the mutual impedance between two vertically polarized antennas placed in drill holes extending into the rock. Experiments were conducted at Cape Cod, Mass., using the method to determine the phase constant of the rock between two 1000-foot drill holes, separated by a distance of 6000 feet, at frequencies between 100 and 4200 Hz. Electrically short monopoles were used in the drill holes, with the overburden above the rock serving as a ground plane. Reference phase was derived from nearby Loran-C transmissions received at both the transmitting and receiving ends of the path. The measured phase constants at these frequencies indicate a large loss tangent for the medium. The bulk conductivity was thus deduced to be
1.1 \times 10^{-3}
mho/meter, and the measurements did not alone yield an estimate of the relative dielectric constant.