Farstad, Arnold J.

Thru-the-Earth-Electromagnetics Workshop (1973 : Colorado School of Mines)

The Location Group conversed in the Petroleum Room of the Green Center with the purpose of addressing the following list of topics in light of the Bureau of Mines' requirements for detecting and locating trapped miners by electromagnetic methods. These topics include: Noise, Sources, Antennas (transmit and receive), the Propagation Medium, Signal Processing, Optimum Frequency, Receivers, Pulse vs. CW Techniques, Passive Location Techniques, and Obstacles. Practical constraints such as equipment size, weight and power requirements, cost and intrinsic safety were kept in mind during these discussions. It was emphasized that in-mine equipment must be inexpensive, rugged, simple and lightweight. Otherwise, the mine operators probably would not buy it nor would the miners be able to effectively use it. Present techniques for experimentally detecting and locating trapped miners were discussed, along with techniques to improve their location accuracy. Analytical, numerical, and scale modelling methods were considered as a means of giving further insight into measurement, anomalies caused by terrain variations, conductivity contrasts, and obstacles. After discussion of these topics, conclusions were drawn and existing problem areas were identified. These problem areas were addressed in developing guidelines for future efforts. Following the discussion period, the Chairman gave a summary of the Location Group report and comments were solicited from the entire group. 2.0 GROUP DISCUSSION HIGHLIGHTS 2.1 Noise W. Bensema asked the group whether the noise data provided by NBS was adequate. It was determined that for location systems analysis, the most important form of noise data was the frequency spectra of vertical and horizontal magnetic fields on the surface, and the answer to his question was affirmative. Drs. Wait and Frischknecht pointed out the difficulty in accurately measuring the true vertical magnetic field since these measurements are heavily influenced by the loop setting and the local geology. Nevertheless, these measurements are important since the same perturbations would also affect a receiving loop oriented to receive the vertical magnetic field.

National Institute for Occupational Safety and Health