Development of a New Electromagnetic Tool for Evaluating the Ground Environment

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Applications of the electromagnetic methods to investigations of the soil pollution and the near surface buried objects are expected. These situations demand signifficant improvements in exploration technology. For the electromagnetic method, the improvements of sensor are especially important elements.High-temperature SQUID sensor is ideal for geophysical exploration both in its sensitivity and its measuring frequency band, and the basic character of high-temperature SQUID sensor was examined. As a result it was developed that the frequency characteristics are flat from DC to 100kHz and the system noise level is within 0.85 pT, and the SQUID sensor gives reliable measurements in Frequency Domain Electromagnetic Method, although leaves scope for improvement.Then, the magnetometers using a GMR sensor and a MI sensor are contrived, and their characteristics and performance for application to the electromagnetic method were examined. As a result, their linearity and sensitivity are good enough for practical electromagnetic sounding use. These new magnetometers can be practically applied as receivers in the electromagnetic method with minor modifying to the magnetometers and some improvements to its signal processing technology.These small sensors should enable the logging tools to downsize, and the borehole electromagnetic techniques could be improved suitable for the near surface exploration.These estimate the prospecting ability of the borehole electromagnetic method, 3-D electromagnetic responses were calculated using integral equation method, especially, Tx-Rx configurations of single borehole and borehole-to-borehole were examined.These outcomes could contribute to develop new possibilities in the electromagnetic methods.