Year: 1978
Type: report
Abstract: This dissertation is concerned with the measurement of the relationship between the natural fluctuations of the earth's magnetic field and the voltages they produce in the surface of the earth. This relationship is approximately defined by the electromagnetic impedance of the surface of the earth for normally incident plane waves. Measurements of the impedance have been used as a method of geophysical survey called magnetotellurics. Because the electrical resistivities of different types of ground differ by several orders of magnitude this method has met with moderate success in spite of the fact that the estimates of the impedance have not been very precisely reproducible. The design, construction, and operation of a 3 axis dc SQUID magnetometer suitable for field measurements are described. Repeated magnetotelluric surveys with this instrument showed that the reduced intrinsic noise of the magnetometer did not significantly improve the reproducibility of the estimates of the impedance. It is demonstrated that the discrepancies between the surveys are consistent with the noise bias errors of the least squares linear regression technique that was used to estimate the impedance rather than with the errors inherent in the approximations made in the consideration of the physical problem.
DOI: 10.2172/6418767
Author: T.D. Gamble
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W75943232