Wireless Channel and Electromagnetic Environments for Through-the-earth (TTE) Communications in an Underground Coal Mine

Through-the-earth (TTE) communication systems are useful for post-disaster emergency communications due to their likelihood of surviving a mine disaster. The wireless channel and electromagnetic environment (EME) are two primary factors that affect the performance of a TTE system and have not been well understood. This paper reports measurements made in an active coal mine to characterize the wireless channel and EME of a TTE system operating at frequencies up to 25 KHz. TTE transmissions were successfully demonstrated in a mine location with a depth of 567m (1860 ft) by using ground rods installed on the surface and existing roof bolts in the underground mine as electrodes. The results show that the EME in the mine is dominated by the 60-Hz signal and its harmonics for both the surface and the underground environments. The signal attenuation caused by the channel increases for frequencies greater than 90 Hz. This paper provides a measured data set pertaining to realistic EMEs and channels that an E-field TTE system operator or system designer can reference when implementing similar technologies in a mining environment.