Performance of manpack electromagnetic location equipment in trapped miner location tests.
Proceedings of Thru-the-Earth Electromagnetics Workshop, August 15-17, 1973, Colorado School of Mines, Golden, Colorado. Geyer RG, ed., Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, Grant G0133023, 1973 Dec; :62-72
The use of radio signals for underground communications was considered as early as the mid-1920's  - . However, early experiments did not produce promising results with the type of equipment that was available then . With advancements in solid state technology many of the schemes considered impractical in the early days suddenly became practical. The properties of electromagnetic wave behavior in conducting media have been intensively studied by Wait  and others and can be utilized not only in communication with trapped miners, but also as a means of locating their position. This report deals with the development of portable electromagnetic equipment, powered by the miner's conventional lamp battery, which can be used to alert surface rescue personnel of the trapped miner's location. The Westinghouse Georesearch Laboratory (WGL) under BUMINES sponsorship initially approached the trapped miner location problem using seismic techniques. It was learned from this effort that two serious shortcomings of seismic techniques are (1) the extremely weak signals available on the surface from miner generated hammer blows, requiring long processing times at the surface receiver, and (2) the relatively slow procedure of deploying geophone arrays to sense the seismic uplink signals. By contrast, the electromagnetic techniques have proven much more practical from a deployment time standpoint and in most cases have also proven to be more accurate in determining location. Furthermore, these techniques have been successfully tested using a receiver in a helicopter for reconnaissance purposes. However, before any electromagnetic location technique can become fully operational, the miners themselves must be equipped with emergency transmitters to be carried with them on each work shift. Consequently, much emphasis has been placed on the development of extremely lightweight transmitting equipment. The performance of some of the electromagnetic location equipment developed by Westinghouse will be described in the following sections. Results of field tests conducted under "worst case" conditions have demonstrated the feasibility of using through-the-earth electromagnetic signals for detection and location of trapped miners equipped with manpack transmitters, Furthermore, the prototype receiving equipment is lightweight and easy to operate suggesting that unskilled personnel could be used in rescue search operations, Helicopter reconnaissance using a multichannel receiver and a towed loop and preamplifier provides a rapid means of determining the existence and general location of signals emanating from the mine, Signal reception at the mine portal provides another quick method of detecting the existence of signals, Precise location of EM sources over hilly terrain is sometimes hampered by profile ambiguities and secondary nulls.. Further research is needed to develop techniques for resolving these ambiguities in the field.
Mining-industry; Mining-equipment; Underground-mining; Radio-waves; Coal-mining; Electromagnetic-energy; Electromagnetic-fields; Electromagnetic-wave-transmission; Mine-disasters
Contract-H0220073; Contract H0232049
Proceedings of Thru-the-Earth Electromagnetics Workshop, August 15-17, 1973, Colorado School of Mines, Golden, Colorado
Westinghouse Georesearch Laboratory