| 講演要旨(和文) | | 現在,地下浅層部を探査する手法として,VLF-EM法が存在する.VLF-EM法は装置が小型軽量であるため,高効率な探査が可能であるという利点を有する.しかし,その一方で,ソースであるVLF局が不定期に停波するという欠点がある.そこで,VLF電波よりも安定性の高いJJY標準電波を用いることで,連続測定により広域探査が可能となり,測定結果の解釈の品質向上が期待される.JJY標準電波とは,電波時計用の周波数40kHz,60kHzとした超長波である. 本研究では,数値計算により,VLF帯の周波数を用いた計算結果と比較することでJJY標準電波を用いる手法の優位性を示した. また,空間フィルター処理によって地下の2次元擬似断面図を作成した.さらに,野外において,データ測定を行い,測定データを解析した. 解析結果より,JJY標準電波の安定性を検討することでJJY標準電波を用いる探査の有用性を検討した. |
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| | 講演要旨(英文) | | VLF-EM method has been used for detecting subsurface resistivity anomalies. However, because the source that has been used for the method is unstable, the VLF method is not so widespread. Since about a decade ago, JJY which is more stable than VLF has been used to broadcast the standard Japanese time, so that it would be more suitable for the exploration of underground structure. By using radio time-signal receivers, we can quickly record continuous time signals to estimate the resistivity distribution of subsurface ground wherever in Japan. In our study, we applied numerical experiments to reveal the characteristic of subsurface exploration using JJY. Using electromagnetic wave of 20 kHz as an existing VLF wave and 40 and 60 kHz as JJY standard electromagnetic waves, we evaluated the sensitivity in shallow subsurface resistivity anomalies using numerical method. We also evaluated the influence of angle between strike of an elongated resistivity anomalies and the propagation direction of radio waves. In addition, by applying the Fraser filter, when the model is simple, we obtain a rough resistivity profile of the underground according to magnetic field strength obtained by the numerical calculation. Moreover, we also confirmed that we receive the JJY electric wave for real data analysis. |
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