Low frequency geomagnetic fluctuations (.04 to 25 Hz) on land and on the floor of Monterey Bay
McDevitt, Gerald R.
Homan, B. Bert
Moose, Paul H.
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A coil antenna consisting of approximately 6000 turns of copper wire was utilized to measure the horizontal component of fluctuations of the earth's magnetic field on the floor of Monterey Bay in water depth of approximately 50 meters. The results indicate that the power spectral density of the fluctuations varies from 10nT²/Hz at 0.04 Hz to 10ˉ⁶nT²/Hz at 25 Hz, a monotonic decrease of about 6 dB/ octave, except in the 8-20 Hz region where the Schumann resonances occur. While the sensitivity of the equipment was insufficient to measure the vertical component of the fluctuation we can put an upper limit of 10ˉ³nT²/Hz at 1 Hz and 10ˉ⁶(nT)²/Hz at 10 Hz on the magnitude of this component. The same sensor was also used to measure various components of the field fluctuations at a remote land' site (Chew's Ridge). In the frequency range observed the general shape of the spectra was similar to those obtained at sea. However, a strong azimuthal variation at certain frequencies was noted in the land data. The possibility that these directional signals are of man made origin cannot be excluded at this time.
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