Cross-borehole electromagnetic probing to locate high-constrast anomalies
Journal Article
·
· Geophysics; (United States)
OSTI ID:5413164
Electromagnetic (EM) probing between boreholes is useful for locating high-contrast geophysical anomalies such as a tunnel. Theoretical and experimental studies of EM field interaction with a tunnel show that minima in the received signal can be used for locating the tunnel. The theoretical studies show that, as a transimitter and receiver are lowered in separate boreholes, the minima can be interpreted easily to yield both the lateral and vertical positions of the tunnel. The main mechanism of EM field interaction with the tunnel appears to be diffraction, and the spatial variation of the feld strength is affected by the tunnel shape. Frequencies from 10 to 70 MHz were studied to assess the usable frequencies. The field in the receiver borehole was an effective diagnostic when a half-wavelength in the surrounding medium was less than or equal to the diameter of the tunnel. EM probing at two test sites gave the locations of tunnels within 1 ft of the surveyed locations. 20 figures.
- Research Organization:
- Univ. of California, Livermore
- OSTI ID:
- 5413164
- Journal Information:
- Geophysics; (United States), Journal Name: Geophysics; (United States) Vol. 44:10; ISSN GPYSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
01 COAL, LIGNITE, AND PEAT
010404 -- Coal
Lignite
& Peat-- Gasification
42 ENGINEERING
422000 -- Engineering-- Mining & Underground Engineering-- (1980-)
58 GEOSCIENCES
580203* -- Geophysics-- Geophysical Survey Methods-- (1980-1989)
ACCURACY
BOREHOLES
CAVITIES
COAL GASIFICATION
COHERENT SCATTERING
COORDINATES
DIFFRACTION
DISTRIBUTION
ELECTRICAL SURVEYS
ELECTROMAGNETIC FIELDS
ELECTROMAGNETIC SURVEYS
FREQUENCY RANGE
GASIFICATION
GEOPHYSICAL SURVEYS
IN-SITU GASIFICATION
IN-SITU PROCESSING
LEVELS
MHZ RANGE
MHZ RANGE 01-100
MONITORING
PROCESSING
SCATTERING
SPATIAL DISTRIBUTION
SURVEYS
THERMOCHEMICAL PROCESSES
TUNNELS
UNDERGROUND
010404 -- Coal
Lignite
& Peat-- Gasification
42 ENGINEERING
422000 -- Engineering-- Mining & Underground Engineering-- (1980-)
58 GEOSCIENCES
580203* -- Geophysics-- Geophysical Survey Methods-- (1980-1989)
ACCURACY
BOREHOLES
CAVITIES
COAL GASIFICATION
COHERENT SCATTERING
COORDINATES
DIFFRACTION
DISTRIBUTION
ELECTRICAL SURVEYS
ELECTROMAGNETIC FIELDS
ELECTROMAGNETIC SURVEYS
FREQUENCY RANGE
GASIFICATION
GEOPHYSICAL SURVEYS
IN-SITU GASIFICATION
IN-SITU PROCESSING
LEVELS
MHZ RANGE
MHZ RANGE 01-100
MONITORING
PROCESSING
SCATTERING
SPATIAL DISTRIBUTION
SURVEYS
THERMOCHEMICAL PROCESSES
TUNNELS
UNDERGROUND