Concepts and development of educational materials for hands-on works in the open class is presented in this article. The open classrooms with hands-on works were held repeatedly for several years in Akita University. The materials and concepts are very important to be held an open classroom. Some educational materials for assembling a fundamental instrument were prepared with original design for open classrooms.
A development of the materials requires repeated trial assembling and robust design to assure stable operation of the instruments. The design of printed circuit boards and the order to a factory is very important process in the development of the materials. Being the person concerned with developing presents real phrases to explain everything in the open classroom. Kid participants get certain interest through finding a hand-made instrument in work or appearing interesting phenomenon after finishing their assembling work. High grade kids in junior school can be better candidates of application to the open classroom. Wide applications of the educational materials should be introduced to the participants because assembling the materials has tend to be occupy much part of the conventional open classroom.

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 The term of the “Geophysical Exploration” is a booklet name of this journal and it is known as a science and technology field, although the term doesn't appear in the school curriculum. Therefore, the activities to popularize this technology are important. The contents of “Geophysical Exploration” would help to resolve some social and technological educational problems, because of having a lot of applied science elements and familiar science.
 In this paper, I tried to survey of the educational potentiality from the content and the present circumstances on the viewpoint of the science education. This showed it had a disadvantageous situation, and it was recognized to connect with a social problem “Losing interest in science”. In the relations between this field and the school education, it was an effective means to advance a coordinated activity of the universities and companies. Considering the quality of academic and social contribution of it, the “Geophysical Exploration” was a suitable field to resolve for some problems. And the educational possibility was able to be shown, although a lot of problems in existence.

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 We can find many symmetrical gravity anomalies such as center linet symmetry in the gravity map series(1:200, 000) published by AIST. To analyze these gravity anomalies, the authors reviewed the computing equations based on the model bodies composed of variable density with center line symmetry(rectangular graben, terraced graben, parabolic graben, elliptical graben). Some characteristics are described in the maps drawn by these computing equations. The authors led out two methods to get bottom depth from the given value of gravity on center axis, and showed some examples applied these methods to model bodies.
 There is a difference among three depths of density's variations estimated from gravity anomalies observed on the ground- surface in taking account of three kind of vertical density variations. So we must analyze the underground structure from the gravity data in taking account of another data.

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 In conventional inversion schemes of magnetotelluric data by the linearized least-square method with a smooth constraint, a smoothing parameter, α contributes to all of the electrical resistivity blocks in the smooth constraint term evenly. Therefore, it is difficult to reconstruct a resistivity structure with sharp structural boundaries using the conventional inversion, although subsurface formations including both smooth and sharp structural changes are often targets of magnetotelluric surveys. In this paper, we propose a new two-dimensional inversion algorithm for magnetotelluric data to reconstruct the resistivity structure with both smooth resistivity variations and a sharp boundary. Our inversion scheme needs the location of sharp boundary as a priori information from the other geophysical surveys, such as seismic reflection method. A new hyper-parameter “β” between 0 and 1 is defined for expression of sharpness of the structural boundary. As β becomes 0 to 1, the resistivity variation across the assumed boundary becomes sharp to smooth. Two hyper-parameters are determined using the ABIC-minimizing scheme with a new simple way for searching optimized hyper-parameters efficiently. We applied both conventional and new sharp-boundary inversion to synthetic magnetotelluric data from two models. One model includes high and low resistivity anomalies, and another model consists of layers increasing their resistivity gradually. As a result of the synthetic tests, our sharp-boundary inversion reconstructed the resistivity structure with sharp boundary, if the location of sharp boundary is assigned at the proper position. Even if the sharp boundary is assigned within the smooth structure area wrongly, smooth model is obtained properly. After synthetic tests, we apply this sharp boundary inversion to field data obtained around the seafloor of the Nankai Trough using high-frequency ocean bottom electromagnetometer. The top of Philippine Sea plate, confirmed by a seismic reflection survey, is adopted as a location of sharp boundary in our inversion. As the result of our sharp-boundary inversion, the top of Philippine Sea plate is reconstructed as a sharp structural boundary. We conclude that our sharp-boundary inversion provides more realistic resistivity model compared with the smooth model by the conventional inversion.

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 In order to calculate the electric potential generated by a point current source that is placed at any position in a multilayered space, we have derived new theoretical formulas using the derivation process of recursive relations by Sato (2000). Individual coefficients of the formulas are described in the recursive equations based on upward and downward continuation processes. In the derivation of the recursive equations, we have considered the case where the point current source is placed at a layer boundary, which was not dealt with by Sato (2000).
 Moreover, we have modified the derived formulas to stabilize the exponential terms for numerical computation using the linear filter method. We also show that the well-known resistivity transform (function) is derived by using the new formulas and derivation process. As Ando (2006) indicated for the seafloor measurement in multilayered seawater part and sub-bottom structure, we have demonstrated that the resistivity transfer function for the whole system is equal to the parallel connection of two resistivity transfer functions for the seawater part and sub-bottom structure using our formulas.

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