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Large‐amplitude ULF magnetic fields produced by a rapid transit system: Close‐range measurements
Author(s) -
Ho A. M.H.,
FraserSmith A. C.,
Villard O. G.
Publication year - 1979
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs014i006p01011
Subject(s) - amplitude , magnetic field , transit (satellite) , range (aeronautics) , physics , geodesy , geology , optics , materials science , public transport , quantum mechanics , political science , law , composite material
Measurements at a location close to the San Francisco Bay Area Rapid Transit (Bart) system show that Bart can produce ultra low frequency (ULF; frequencies less than 5 Hz) magnetic field fluctuations with amplitudes that are 2–3 orders of magnitude greater than the normal background level. The maximum increase in magnetic field fluctuations over the ambient background level occurs in the range 0.01–1 Hz, but significant increases occur at 0.001 and 10 Hz. Although it is generally accepted that moving trains cause magnetic field disturbances, it has not, until recently, been recognized that modern dc‐powered rapid transit systems are such powerful sources of ULF electromagnetic fields, and the existence of these sources in densely populated urban areas could have environmental implications.