Study of through-the-earth communications (electromagnetic, speech intelligibility, trapped miner)
John R. Durkin · 1983
Through-the-earth electromagnetic communications has been studied both theoretically and through field tests to assess the expected performance of a communications link between individuals on the earth's surface and within a mine. Electromagnetic equations have been formulated to determine transmitted signal loss and were used to predict expected received signal level. The formation of vertical magnetic noise was studied theoretically and data was obtained at a number of mines and used to form noise regression models. A regression model was also formed for earth conductivity using through-the-earth transmission data. A computer model of a through-the-earth communications system was generated and used with the noise and conductivity models to predict expected performance of the intelligibility of the communications link. Recordings of through-the-earth communications were made and the intelligibility of the communications, as obtained by a human subject test panel, were compared with that predicted by the computer model. Various speech bandwidth compression techniques were studied to assess their potential in improving the effective range of the communications.