Communications – electrical: acoustic wave systems and devices – Seismic prospecting
Patent
1978-05-11
1980-07-15
Buczinski, S. C.
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
181112, 181122, 367 47, 367 58, G01V 120
Patent
active
042131944
ABSTRACT:
A method of locating near-surface underground chambers, rooms, caves, pits, tubes, faults in surface rocks, and the like, using acoustic techniques is disclosed. For mapping large areas, a survey grid for transmitter transducer placement first is laid out over the area of interest.
A transmitting transducer is coupled to the bedrock at one of the grid sites, and acoustic waves are generated in the earth by operation thereof. Portable acoustic receiving means, including a receiving transducer, are used to detect acoustic waves from the transmitter at a plurality of receiving sites surrounding the transmitting station. Transmitted acoustic waves from the transmitting site received by the receiving transducer are converted to electrical signals by the receiving transducer and recorded for subsequent use. Following operation of the receiving means at each receiving site surrounding the transmitter transducer, the received signals are compared to determine any differences in their magnitudes. In competent rock, without the presence of subterranean discontinuities, substantially equal signals are received at receiving sites equally spaced from the transmitting site. If equal length acoustic paths are not employed, the different acoustic absorption due to the different-length paths must be considered in determining differences in received signal strength. This check for discontinuities is repeated with the transmitting transducer positioned at each of transmitting transducer sites of the survey grid until the entire area is mapped. At areas which indicate subterranean discontinuities the above-described process may be repeated to better identify the discontinuities. Now, however, shorter distances between the transmitting transducer and the receiving sites are employed, and operation preferably is at a higher operating frequency for increased resolution. Also, whereas pulse or continuous wave operation is used for the initial survey, now pulse operation preferably is employed for distinguishing between received longitudinal, transverse and surface waves which travel at different velocities within the rock and, thereby, are received at different times following pulse transmission operation of the transmitting transducer. Absorption of the different waves is dependent upon the medium through which the waves travel. Using pulse operation, this information too is available to the operator for use in analysis of the discontinuity encountered.
REFERENCES:
patent: 1743358 (1930-01-01), Koenigsberger
patent: 2331080 (1943-10-01), Petty
patent: 2693862 (1954-11-01), Rieber
patent: 3252131 (1966-05-01), Vogel
patent: 3292143 (1966-12-01), Russell
patent: 3362011 (1968-01-01), Zemanek, Jr.
patent: 3836952 (1974-09-01), Johnson
R. F. Doherty et al., Geophysical Prospecting, #19, pp. 430-458, 1971.
Smith Carl W.
Spurlock Eugene M.
Beckman Victor R.
Buczinski S. C.
SRI - International
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