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Journal Articles

Radiation monitoring using an unmanned helicopter in the evacuation zone around the Fukushima Daiichi Nuclear Power Plant

Sanada, Yukihisa; Kondo, Atsuya*; Sugita, Takeshi*; Nishizawa, Yukiyasu; Yuki, Yoichi*; Ikeda, Kazutaka*; Shoji, Yasunori*; Torii, Tatsuo

Exploration Geophysics, 45(1), p.3 - 7, 2014/11

 Times Cited Count:25 Percentile:71.34(Geochemistry & Geophysics)

The Great East Japan Earthquake on March 11, 2011 generated a series of large tsunami waves that resulted serious damage to the Fukushima Daiichi Nuclear Power Plant (NPP) and a large amount of radioactive materials were discharged from the NPP to the environment. In recent years, technologies for an unmanned helicopter have been developed and applied to various fields. In expectation of the application of the unmanned helicopter to airborne radiation monitoring, we had developed a radiation monitoring system. Then, we measured the radiation level by using unmanned helicopter in soil contaminated areas by radioactive cesium emitted from the NPP to evaluate ambient dose-rate distribution around the areas. Here, we reports on the measurement technique and the result.

Journal Articles

Three-dimensional magnetotelluric inversion using a heterogeneous smoothness-constrained least-squares method

Negi, Takeyuki*; Mizunaga, Hideki*; Asamori, Koichi; Umeda, Koji

Exploration Geophysics, 44(3), p.145 - 155, 2013/09

 Times Cited Count:1 Percentile:5.83(Geochemistry & Geophysics)

This paper presents a fast algorithm for electromagnetic inversion. The algorithm is distinct for the level of accuracy it attains when bypassing the sensitivity matrix update. A common sensitivity matrix for homogeneous half-space is used in all of the iterations. Instead of a fixed sensitivity matrix, the Laplace filter coefficients at each element are updated based on the spatial differences of resistivity calculated by a reconstructed structure derived from the former iteration. This substitution is expected not only to reduce the computation time required for large-scale inversions, such as those for three-dimensional surveys, but also to allow reconstruction for sharp boundaries in resistivity structures. This algorithm was applied to three-dimensional magnetotelluric inversion in order to confirm the effectiveness. This paper reports the results of several synthetic examples using different resistivity models and conditions.

Journal Articles

Seismic imaging for 3-D RVSP data using image point transform

Lee, C.*; Matsuoka, Toshiyuki; Ishigaki, Koichi; Tanoue, Masayoshi*; Yamaguchi, Shinji*; Tsuchiya, Terumitsu*; Matsuoka, Toshifumi*

Proceedings of 11th International Symposium on Recent Advances in Exploration Geophysics (RAEG 2007), p.69 - 71, 2007/04

Image Points are defined through geometry of sources, receivers and reflectors. IP (Image Point) transform is one type of Radon transform which change common shot section to IP domain (r-x). By the IP transform, reflection signals in time domain can be accumulated and enhanced in IP domain. We applied the IP transform to the field data of RVSP that had been carried out at the Mizunami Underground Research Laboratory (MIU) site. We could get the fault image around the MIU site using IP transform.

Journal Articles

Seismic imaging for 3-D VSP data using image point transform

Lee, C.*; Matsuoka, Toshiyuki; Ishigaki, Koichi; Tanoue, Masayoshi*; Narita, Norifumi*; Kojima, Masakazu*; Tsuchiya, Terumitsu*; Matsuoka, Toshifumi*

Proceedings of 10th International Symposium on Recent Advances in Exploration Geophysics (RAEG 2006), p.143 - 146, 2006/00

It is known that 3-D Vertical Seismic Profile (VSP) method has an advantage on imaging the fault and fracture zone near the borehole, especially steeply dipped structure. Cosma et al (2003) has developed the new technique named Image Point Transform (IP Transform) and applied to offset VSP data to improve the week reflection signals from the steeply dipped fracture. We test the applicability of this method to the 3-D Reverse VSP data of numerical simulation and develop the method of imaging named spectral operator of middle point of IP. In the results of applying to 3-D model of steeply dipped fracture, we know that this method is applicable to 3-D reverse VSP data and could get the good image of fracture reconstructed by spectral operator of middle point of IP.

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