Electricity: measuring and testing – Of geophysical surface or subsurface in situ – With radiant energy or nonconductive-type transmitter
Patent
1992-03-09
1994-06-21
Strecker, Gerard R.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
With radiant energy or nonconductive-type transmitter
324337, 324338, 342 22, G01V 312, G01V 330, G01S 1388
Patent
active
053231147
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an underground radar tomography and an apparatus therefor, in which an electromagnetic wave is sent into the ground, the amplitude and propagation time of a transmitted wave, a reflected wave or a diffracted wave of the electromagnetic wave are measured, and signal processing is performed on the result of measurement to thereby obtain the distribution of strata and geologic features in the ground as sectional information, and particularly relates to the detection of a very weak signal attenuated by the propagation of the signal through the underground.
2. Background Art
For the investigation of a rock bed, it is necessary to estimate detailed information about the existence, distribution shape or the like, of dislocations, crushed belts, cracks, etc. In the tomographic arts it is possible to analyze a stratum structure in section and display it graphically. An underground tomography using an electromagnetic wave is expected to be effective in resolution, non-destructivity, etc.
Conventional underground tomographic arts using an electromagnetic wave are briefly classified into a continuous-wave amplitude detection method and an underground radar tomography. They both are designed to perform operational processing upon the obtained data and display a stratum structure as a sectional. They are different in the way to obtain the basic data in the following ways.
(1) Continuous-Wave Amplitude Detection Method
This method is a method in which a continuous-wave-like electromagnetic wave is propagated in the ground, and the attenuation of the transmitted wave of the electromagnetic wave is measured to thereby obtain the distribution of an attenuation factor of a rock bed to estimate the state of the rock bed. This method is disclosed, for example, in the literature by D. L. Larger and R. J. Lytle, "Determining a subsurface electromagnetic Profile from high-frequency measurements by applying reconstruction-technique algorithm," Radio Science, vol. 12, No. 2, p. 249, Mar.-Apr. 1977.
This system is based on the same principle of a medical X-ray tomography. In the case of underground investigation, however, there is a defect that it is impossible to obtain enough accuracy because measured points are limited and only amplitude information is used. In addition, the attenuation of an electromagnetic wave in the ground is so large that it is impossible to obtain enough strength of a received signal, and the range to be investigated is very much limited.
(2) Underground Radar Tomography
A so-called underground radar tomography is a system in which a pulse-like electromagnetic wave is transmitted into the ground, and the strength and propagation time of the reflected wave, transmitted wave or diffracted wave of the electromagnetic wave are measured. For example, such a system is disclosed in the literatures by Masaki Nagata and Toshihiko Sakayama, "Utilization of Electromagnetic Wave Prospect in Rock-Bed Investigation", Extended Abstracts of '86 Study Meeting, Japan Society of Engineering Geology, p. 95, 1986, and by Hideo Otomo, "Present Situation of Geotomographic Technique", Physical Prospect, vol. 39, no. 6, Dec. 1986.
Recently this system has been observed because it uses information about the characteristics of attenuation and propagation time in the ground so that it can estimate the detailed structure of strata. The system however uses a pulse-like electromagnetic wave, and therefore the signal is apt to be attenuated in the soil so that the reception signal strength becomes so weak that the range which can be investigated at a time is limited. In addition, in the current state, it is difficult to increase transmission power because of the limitation in devices and the deterioration in electromagnetic environment. Particularly in a place of a thick stratum of soil such as Kanto Loam Layer in Japan, the soil contains much water so as to cause large attenuation of electromagnetic wave so that the practical limitation on the range to be investigated
REFERENCES:
patent: 3521154 (1970-07-01), Maricelli
patent: 4045724 (1977-08-01), Shuck et al.
patent: 4114155 (1978-09-01), Raab
patent: 4161687 (1979-07-01), Lytle et al.
patent: 4326129 (1982-04-01), Neufeld
patent: 4742305 (1988-05-01), Stolarczyk
patent: 4994747 (1991-02-01), Stolarczyk
"A Computational Study of Reconstruction Algorithms for Diffraction Tomography: Interpolation Versus Filtered Back-propagation" by S. X. Pan and Avinash C. Kak from IEEE Transactions on Acoustics, Speech, & Signal Processing, vol. ASSP-31, No. 5., Oct. 1983.
"Pulse Time-Delay Method for Geophysical Tomography" by Brad L. Carlson and Constantine A. Balanis from IEEE Transactions on Geoscience and Remote Sensing, vol. 26, No. 5, Sep. 1988.
Komine Isamu
Nagamune Akio
Tezuka Koichi
Meller Michael N.
NKK Corporation
Strecker Gerard R.
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