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Surface magnetic field noise measurements at Geneva Mine.

Authors
Adams-JW; Bensema-WD; Tomoeda-N
Source
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, Contract No. H0133005, :1-35
NIOSHTIC No.
10001388
Abstract
Measurements of surface magnetic field noise were made at various locations over the Geneva Coal Mine near Price, Utah, on June 12, 1973. The locations selected were on the surface over emergency locator beacons underground at depths between 350 meters (1150 ft.) and 488 meters (1600 ft.). The surface terrain where these measurements were made was mountainous, and access was difficult. There were no power lines within several miles, and the weather was clear; therefore, the magnetic noise levels were about as low as will normally occur. Results of measurements of distant atmospherics indicate rather sharp cutoff frequencies below which broadband, impulsive noise is attenuated. The mechanism of propagation for this noise above the daytime cutoff frequency of 3500 Hz and the nighttime cutoff frequency of 1700 Hz is deduced to be a waveguide formed by the D or E layers of ionosphere as an upper plane and the earth as a lower plane. The measurement systems used are similar to those used earlier. The technique is to record broadband, analog signals, digitize the data, and use a fast-Fourier transform to obtain spectral plots. This technique is novel in that it can measure simultaneously all magnetic field energy within a limited portion of the spectrum for a limited time, and, after processing, reproduce the events occurring in that time interval in great detail.
Keywords
Mining-industry; Electromagnetic-energy; Electromagnetic-fields; Electromagnetic-interference; Electromagnetic-radiation; Statistical-analysis; Underground-mining; Radio-waves
Publication Date
19740601
Document Type
CP; Final Contract Report
Funding Type
Contract
Fiscal Year
1974
NTIS Accession No.
COM-741-1688
NTIS Price
A04
Identifying No.
OFR-36-75; Contract-H0133005
NIOSH Division
PRC
Source Name
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, Contract No. H0133005
State
UT; PA; CO
Performing Organization
National Bureau of Standards
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