| 講演要旨(和文) | | 繰り返し地中レーダ記録の走時変化量を解析することにより，単純断面や差分断面で特定できなかった水分率の変化を捉えることができる。解析を安定化させるために有効な改善方法を議論した。探索ウィンドウを走査方向にも移動させず，繰り返し記録間の探査位置補正をあらかじめ適用させる方法の改善効果を確かめた。探索元と探索先を入れ替えた探索結果を利用し，直接波周辺などの探索不能域を検出する手法の有効性を確認した。 |
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| | 講演要旨(英文) | | In theory, ground-penetrating radar (GPR) can detect the distribution of volumetric water content under the ground. However, the level of transition zone of water content in standard soil structures is difficult to be measured by using GPR. We evaluate time-shift analysis for time-lapse GPR records with different distribution of water content using FDTD numerical simulations. The reflection events from the transition zone of water content are sometimes difficult to detect on the survey sections of GPR also on the survey section subtracted from two time-lapse records. However, time-shift analysis can detect events caused by shift of the transition zone depth. Upper events of the transition zone move to in shallower travel time and lower events move to in deeper time when watertable moves to a shallower area. We discuss such characteristic phenomena in three analysis results applied for time-lapse records acquired in actual fields. Finally, we show methods to improve time-shift analysis using the result of opposite time differences and an initial modification record for the scanning direction. |
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