Comparison of radar probing and nonlinear sonar probing through rock salt.
| Main Author: | |
|---|---|
| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1984.
|
| Subjects: | |
| Online Access: | Link to ProQuest Copy Link to OAKTrust copy |
| Abstract: | Detection of geologic discontinuities ahead of the mining process has been attempted by both electromagnetic and acoustic methods. Rock salt is an ideal medium for the propagation of electromagnetic waves. However, in cases where the salt contains small amounts of water ((TURN) 0.1%), the effectiveness of the electromagnetic method is reduced. To overcome the problem of "wet" salt, acoustic probing has been used. Small amounts of water saturation do not effect the results of acoustic probing. However, the beamwidth of the sound generated by traditional linear acoustics is too wide to allow unique targe identification. Nonlinear acoustics provides a method of obtaining a narrow, acoustic beamwidth in rock salt from a small transducer. To test this hypothesis, a nonlinear-sonar system was constructed at Texas A&M University. Using this system, rock salt was driven by two high-intensity pulses (1 kW each) having primary frequencies of 90 and 114 kHz. Since the pulses are collinear, the salt acts as a parametric array generating a 24 kHz difference-frequency acoustic beam. The Nonlinear Sonar System (NLS) was field tested at Morton Salt's Kleer Mine in Grand Saline, Texas. These results were then compared to the results of an electromagnetic probing system (Foxtrot). The Foxtrot system is a high-resolution, pulsed-radar system. Both systems recorded data which was found to be consistent with the following geologic model. A slab of salt 12.5 m thick, backed on both sides by air, sliced by two thin anhydrite layers: one 2.7 m below the measurement surface, and the other 7.1 m below this surface. The attenuation of 100 kHz sound, which was found to be 0.83 (+OR-) 0.17 dB/m, was used to calculate the beamwidth resulting from the nonlinear acoustic source. The beamwidth was found to be 12.3(DEGREES), as compared to the 45(DEGREES) beamwidth which is generated using linear probing at the same frequency. Thus, the results indicate that nonlinear acoustic probing can be used to map ahead of a mined zone with accuracy comparable to that obtainable from high-resolution, electromagnetic methods. |
|---|---|
| Item Description: | "Major subject: Geophysics." Typescript (photocopy). Vita. |
| Physical Description: | xii, 98 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 85-87). |