PreviousNext No Access18th International Conference on Ground Penetrating Radar, Golden, Colorado, 14–19 June 2020Borehole effects on direction finding of a planar interface with an array-type directional borehole radarAuthors: Satoshi EbiharaShyuhei KotaniKengo FujiwaraYuta KimuraTakaaki ShimomuraRyota UchimuraSatoshi EbiharaOsaka Electro-Communication University, JapanSearch for more papers by this author, Shyuhei KotaniOsaka Electro-Communication University, JapanSearch for more papers by this author, Kengo FujiwaraOsaka Electro-Communication University, JapanSearch for more papers by this author, Yuta KimuraOsaka Electro-Communication University, JapanSearch for more papers by this author, Takaaki ShimomuraOsaka Electro-Communication University, JapanSearch for more papers by this author, and Ryota UchimuraOsaka Electro-Communication University, JapanSearch for more papers by this authorhttps://doi.org/10.1190/gpr2020-090.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract We introduce the possible locations of the critical receiver position (CRP) to estimate the direction of arrival (DOA) with an array-type directional borehole radar. The circular dipole array antenna at the CRP in a borehole cannot estimate the DOA. Our method would be useful when we estimate the direction of a planar interface, such as a fault in the rock. We derive an analytical equation representing the possible CRP locations, considering the positions of the antennas and the planar interface geometrically. We output the numerical values of the possible CRP locations after estimating the dip angle of the planar interface in a radargram. We applied the proposed method to analyze reflected waves from a real-world fault in the rock. We confirmed that the actual CRP was inside the possible CRP locations. Making use of the CRP, we correctly estimated the direction of arrival of the reflected wave from a fault. Keywords: faults, estimation, electromagnetic, processing, numericalPermalink: https://doi.org/10.1190/gpr2020-090.1FiguresReferencesRelatedDetails 18th International Conference on Ground Penetrating Radar, Golden, Colorado, 14–19 June 2020ISSN (online):2159-6832Copyright: 2020 Pages: 455 publication data© 2020 Published in electronic format with permission by the Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 11 Nov 2020 CITATION INFORMATION Satoshi Ebihara, Shyuhei Kotani, Kengo Fujiwara, Yuta Kimura, Takaaki Shimomura, and Ryota Uchimura, (2020), "Borehole effects on direction finding of a planar interface with an array-type directional borehole radar," SEG Global Meeting Abstracts : 344-347. https://doi.org/10.1190/gpr2020-090.1 Plain-Language Summary KeywordsfaultsestimationelectromagneticprocessingnumericalPDF DownloadLoading ...

We consider the effects of oblique incidence of a wave on the creation of a 3-D image of a planar interface with an array-type directional borehole radar. In this study, we focus on the situation where the radar probe is close to the planar interface. In such circumstances, the reflected wave from the planar interface may be incident on the receiving array antenna at very steep elevation angles. As a result, borehole effects cause differences in the arrival times of the wave at the array elements, and consequently some errors emerge in imaging the planar interface. Observing the arrival time differences, we present an algorithm to compensate those errors in creating a 3-D image of a planar interface. Computer simulations predict that the errors may occur when the circular dipole array antenna is in an air-filled borehole in rock. Numerical simulations show that our proposed algorithm generates a 3-D image of an interface around an exact position, whereas conventional methods produce some spurious images opposite to the correct position (i.e., out of position by 180°). We then applied the proposed method to analyze reflected waves from a real-world fault in rock. A 3-D image of the fault could be successfully created, which was not possible using the conventional method.

In this paper, we propose a coaxial-fed dipole array antenna in a borehole with ferrite loading to achieve a thin directional borehole radar sonde (diameter of 54 mm). This radar works between about 20 and 150 MHz. When the dipole array, proposed previously, is used for the thin radar sonde, this antenna suffers from scattered waves from the centered conducting cylinder (CCC). This disturbs the estimation of the direction of arrival (DOA) below 100 MHz. To overcome the interference of the CCC, commercial ferrite cores were added to the CCC. A method-of-moment analysis showed that we may decrease the resonant frequency of the CCC to below 20 MHz, making use of the inductive characteristics of the ferrite cores. This widens the frequency bandwidth of the antenna. Field experiments in soil showed that the ferrite core-loaded CCC works reliably and confirmed that we can estimate the DOA between 20 and 150 MHz. Other measurements in rock which examined the power spectrum of a direct wave found that the ferrite cores widened the operating frequency bandwidth of the radar system.

This study demonstrates 3-D imaging of a fault using a thin (5.4 cm diameter) directional borehole radar sonde. In order to make the thin sonde, we needed to reduce interference between the centered conducting cylinder (CCC) and the antenna elements in the coaxial-fed circular dipole array in a borehole (CFCAB). Ferrite beads were loaded in the CCC for reduction of the interference. We conducted singlehole measurements with the thin sonde in an air-filled borehole. In this experiment, according to the power spectrum of a direct wave, we found that the ferrite loading decreased the resonant frequency of the CCC, widening the operating frequency bandwidth. The image constructed using the directional borehole radar agrees well with the information obtained from the boring core samples and observations in the gallery.

PreviousNext No AccessProceedings of the 11th SEGJ International Symposium, Yokohama, Japan, 18-21 November 2013Estimating 3-D Position of a Fault in Kamioka Mine with Directional Borehole RadarAuthors: Satoshi EbiharaYuta KimuraTakaaki ShimomuraRyota UchimuraSatoshi EbiharaOsaka Electro-Communication University, Search for more papers by this author, Yuta KimuraOsaka Electro-Communication University, Search for more papers by this author, Takaaki ShimomuraOsaka Electro-Communication University, Search for more papers by this author, and Ryota UchimuraOsaka Electro-Communication University, Search for more papers by this authorhttps://doi.org/10.1190/segj112013-028 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract This study demonstrates 3-D imaging of a fault using a thin (5.4 cm diameter) directional borehole radar sonde. In order to make the thin sonde, we needed to reduce interference between the centered conducting cylinder (CCC) and the antenna elements in the coaxial-fed circular dipole array in a borehole (CFCAB). Ferrite beads were loaded on the CCC for reduction of the interference. In order to determine permeability of the ferrite cores, we did experiments to measure an input impedance of a ferrite-loaded monopole antenna. Using the determined parameter of the ferrite, we design the CFCAB. We conducted single hole measurements with the thin sonde in an air-filled borehole. In this experiment, according to the power spectrum of a direct wave, we found that the ferrite loading decreased the resonant frequency of the CCC, widening the operating frequency bandwidth. The image constructed using the directional borehole radar agrees well with the information obtained from the boring core samples and observations in the gallery. Keywords: 3D, imaging, directional borehole radar, circular dipole array, MoM, permeabilityPermalink: https://doi.org/10.1190/segj112013-028FiguresReferencesRelatedDetails Proceedings of the 11th SEGJ International Symposium, Yokohama, Japan, 18-21 November 2013ISSN (online):2159-6832Copyright: 2013 Pages: 580 publication data© 2013 Published in electronic format with permission by the Society of Exploration Geophysicists of JapanPublisher:Society of Exploration Geophysicists HistoryPublished: 15 Jan 2014 CITATION INFORMATION Satoshi Ebihara, Yuta Kimura, Takaaki Shimomura, and Ryota Uchimura, (2013), "Estimating 3-D Position of a Fault in Kamioka Mine with Directional Borehole Radar," SEG Global Meeting Abstracts : 111-114. https://doi.org/10.1190/segj112013-028 Plain-Language Summary Keywords3Dimagingdirectional borehole radarcircular dipole arrayMoMpermeabilityPDF DownloadLoading ...