Low Frequency Geomagnetic Fluctuations (.04 to 25 Hz) on Land and on the Floor of Monterey Bay.
Abstract
A coil antenna consisting of approximately 6000 turns of copper wire was used 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 10(nT)-sq/Hz at 0.04 Hz to 0.000001(nT)-sq/Hz at 25 Hz, a monotonic decrease of about 6 dB/octave, except in the 8-20 Hz region where the Schuman 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 0.001(nT)-sq/Hz at 1 Hz and 0.000001(nT)-sq/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. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1980
- Accession Number
- ADA092399
Entities
People
- B. Bert Homan
- Gerald R. Mcdevitt
Organizations
- Naval Postgraduate School