We propose a new technique for a joint inversion of apparent resistivity data from a vertical electrical sounding and peak-period of spectral ratio of horizontal microtremors to vertical one in order to infer resistivity and S-wave profiles simultaneously. Least-squares errors between the observed apparent resistivity and theoretical ones are minimized together with errors between the peak-periods of the horizontal-to-vertical spectrum of microtremors and theoretical ellipticity for fundamental-mode Rayleigh wave. We use a Simulated Annealing to minimize the misfit function defined by the summation of the two least-squared errors. First, we confirmed the performance of the method using synthetic data for a shallow soil model. The method reconstructs well the soil model, even though synthetic observed apparent resistivity data are incomplete. We, then, apply the method to actual observed data at a site in reclaimed area in Yokohama, Japan. The obtained profiles are in good agreements with results of geological and PS loggings. It is concluded that the proposed technique can be addressed as one of the easiest methods to infer shallow S-wave and resistivity profiles simultaneously.

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We can find many polygonal gravity anomalies in the gravity map series (1 : 200,000) published by Geological Survey of Japan, AIST. To analyze these gravity anomalies, the authors reviewed the computing equations based on the model bodies (vertical solid polygonal cylinder, polygonal cone, polygonal parabola, ellipsoid and error function shaped bodies). Some characteristics are described in the maps drawn by these computing equations.

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A helicopter-borne magnetic survey system was developed in use of a nose boom magnetic sensor, which enables safe and practical operation of low-altitude high-resolution survey even in mountainous regions of very steep topography and high elevation. The system consists mainly of airborne Cesium magnetometer, 3-axis fluxgate magnetometer, GPS receiver, navigation unit, data-acquisition PC, etc., incorporating with other equipment on the ground including base station magnetometer and reference station GPS receiver.
The nose boom magnetic sensor is situated rather near the helicopter body and cannot be free from its magnetic noise, though the boom itself is made non-magnetic. The 3-axis fluxgate magnetometer is the equipment to compensate aircraft's magnetic noise field. Theoretical consideration for passive magnetic compensation and the method of actual data processing for it are discussed. Then the software for magnetic compensation was developed and applied to the data of actual verification survey, and the procedure was proven to accomplish post-flight magnetic compensation properly.

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A way to apply the shortest path ray tracing (SPR) method to irregularly tetrahedralized velocity structure and its efficiency are described. SPR is the ray tracing method utilizing Dijkstra's shortest path algorithm in network graph theory. The tetrahedralization by Delaunay tessellation is one of the irregular parameterization of 3D velocity structure in travel time tomography. The irregular parameterization has great advantage of flexible expression of velocity structure though the computational costs in ray-tracing are relatively high. The hybrid ray tracing between SPR (for initialization) and pseudo-bending (for optimization) might be more economic. It has been known as the well proven scheme in the sense of the simplicity and robustness. Though SPR was originally developed under regular parameterization, it can easily be expanded to irregular parameterized structure without any theoretical modification. We propose a simple design of network for SPR that conforms the shape of tetrahedron. Generally, the cost and accuracy of SPR depends on the network design. In this paper, we have carried out a synthetic examination with a complex velocity model to assess the cost and accuracy of SPR with irregular network. Result reveals that the proposed ray tracing method is practically economic and accurate (almost the same accuracy as SPR under the regular cubic cell model). Further, it has potential to obtain more accuracy by lower costs due to the economical network integrated with flexible element size.

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In order to identify the underground objects, we often use a Ground Penetrating Radar (GPR) from the point of reducing cost and time. But it is not a few cases that the pavement situation prevents from underground prospecting.
From such background, we produced the prototype of the small GPR system to set into the drill head of the horizontal boring machine. And we are sure that it is highly possible to realize improving the limitation of exploration distance and resolution.
In this report, we described the goal specification required to such a small GPR, basic design of system and its performance. And we introduce the technical details concerned to the real time image processing algorithm for radar system which is mounted in the jacking drill head of a horizontal boring system.
The main functions of the image processing to use for a horizontal boring system are the followings.
1) Distance presumption : Presumes the distance between a drill head and pipe.
2) The piping direction distinction : Distinguishes the constructed direction of crossing pipe or parallel one.
3) Azimuth presumption : Presumes the azimuth of pipe against the moving axis.
As a result of experiments, it turned out that this algorithm was effective for the radar system of horizontal boring machine.

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The archaeology and history of Okinawa are receiving a great deal of public attention as the Okinawans attempt to define their cultural and political identity in the closing decade of the 20th century. In an attempt to explore some of the old ruins in the area of Futenma, an integrated geophysical survey had been conducted in the form of two and three dimensional geoelectrical resistivity, surface seismic wave and seismic reflection surveys. The interpretation results of geoelectric survey had identified three-layer structure, which consists of superficial low-resistivity layer that indicates filling of Shimajiri maaji followed by high-resistivity layer that indicates Ryukyu limestone, and low-resistivity layer that indicates Shimajiri mudstone group. Also clear-cut reflectors of seismic reflection lines with good continuity are identified. These reflectors considered to reveal the surface of Ryukyu limestone of archaeological remains. The result of the surface wave survey identified two-layer structure that consists of superficial layer of surface wave velocity (0.3 km/s) overlies a relatively high velocity layer (0.5 km/s). The low velocity layer is estimated to indicate filling of Shimajiri maaji, while the high velocity layer correlates Ryukyu limestone formation.
From the results it was predicted that subsurface structures of ruins influence the result of exploration even if their sizes are not large. Therefore, characteristic patterns due to a certain ruin structure can be distinguished, by making comparison with the excavation findings. The soil covering Ryukyu limestone is relatively thin; however, ruin structures naturally exist in the sedimentation soil above the limestone. It is highly probable that, as we trace back to older time, the land surface would be closer in shape to the upper surface of Ryukyu limestone. Furthermore, the survey results showed that Ryukyu limestone itself is considered to be divided into fresh zone and weathered zone, which possibly has been erroded and is providing channels for the ground water flow including a doline.
According to the results we obtained in this work, even though, geoelectrical resistivity technique is stand-alone for archaeological prospection, its integration with seismic methods, mainly Surface seismic wave, survey give successful results.

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Modern technology of prestack depth migration brings directly depth section from seismic data acquired in the time domain. However, practical methods of time to depth conversion from time structure interpretation survive because of its flexibility in handling velocity and cost performance.
One of the frequent problems in time-depth conversion is depth mistie at well markers. The more the well, the more complicated technique needs to be considered to solve the entire mistie. We introduce to solve the mistie issue in depth conversion by use of Geostatistics on to well check shot data, which guarantees to maintain the input data unchanged after spetial estimation.
In addition to utilization of Geostatistics for conversion velocity estimation, we introduce error estimation criterion to evaluate the estimated velocity for the conversion. This criterion is evaluated comparing velocity variation at well markers. After the estimation of 3D velocity from available check shot data using Kriging approach, we evaluate velocity error distributions by means of sequential Gaussian simulation methods and extract the reliable part of velocity from the criterion. This extracted velocity data and well velocity data are integrated for final depth conversion.
We estimate three realizations of velocity error distributions, which give us 3 realizations of final velocity models. The results of depth conversion by those 3 velocity models vary the depth structure within 170 meters or 7% variation at average depth of 3000 meters structure. This 7% variation can be considered as the structural uncertainty after depth conversion except for the well locations in this sturdy.

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Detection and evaluation of contaminated soil and ground water by GPR method was discussed. The electric properties of soil and contaminant and their mixed material are significant for GPR. Some models for mixed material including CRIM model were discussed. As an example, CRIM model was compared with the measured parameters using sampled core, and showed good agreement under low water content condition. Generally, if soil is contaminated by hydrocarbon contaminant such as DNAPL and LNAPL, the contaminant will replace the water in soil. Consequently, the conductivity of the soil will decrease, and the dielectric constant of the soil will also decrease. We think GPR detect the change of the dielectric constant of the soil and can detect the anomaly caused by the contamination. However, we should note that if there is chemical or bio-chemical reaction related to the contamination, the phenomena will be much more complex. Then we showed some examples of GPR profiles, which were applied to soil contamination and ground water problems. We showed that the change of ground water table by 5cm can be detected by GPR, which means GPR has a good possibility for detecting small anomaly due to contamination, if the phenomena happen in a short period, or if we can measure the time-lapse data. When the contamination is steady state, we can use the combination of profile and CMP measurements by GPR. CMP measurement will provide good information about the material that causes reflection in profile GPR measurement.

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Disposed materials and their buried conditions vary considerably in some landfills. Geophysical prospecting methods can be used to investigate the internal conditions of such landfills without excavating. Rainwater permeates through landfills and various components dissolve as ions in pore water from fills. Resistivity of landfill relates so closely to the electrochemical properties of fills and their pore water that the electrical resistivity prospecting is supposed one of the most effective methods for the landfill investigations.
In order to examine the above effectiveness, five landfill sites were selected on basis of the reclamation area and the classification of waste. Resistivity measurements were carried out there. The concrete subjects are; (1) Effects on disposed material and leachate to resistivity profiles; (2) Use of resistivity tomography for obtaining more precise profiles; (3) Use of resistivity monitoring for interpreting the properties of the landfill.
Resistivity profiles are related closely to conditions of fills. In addition, the profiles of resistivity tomography are better than those of another resistivity methods in the respects of their resolution and temporal stability. Resistivity monitoring is extremely useful for interpreting temporal changes in landfill properties.
The next targets are to study the possibilities of the resistivity measurements for a quantitative analysis of landfill stability and the identification of buried waste materials.

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We report the results from three geo-electrical surveys carried out in a hydrocarbon-contaminated site, a volatile organic compound-contaminated site and a waste disposal site, respectively. In these cases, polluted soil and waste deposits show the electrical properties unlike those estimated from the original source. We try to explain these phenomena from the geo-electrochemical change caused by geochemical and biochemical decomposition. We conclude that induced polarization (IP) method from which many geo-electrical information (resistivity and some IP parameters) is obtained is effective in the investigation of contaminated soil and wastes. Moreover, the time-differential tomography which observes a temporal change of geo-electrical properties is also useful in above investigations. We expect that these geo-electrical information will be applied to the wide field including not only detection of the contaminated soil, but also monitoring of pollutants in ground and evaluation of hydraulic parameters for behaviour prediction and repair design of pollutant in soil.

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The effectiveness of various electromagnetic geophysical exploration techniques for detecting near-surface soil contaminants is described in this paper. Field tests were carried out at an industrial site containing light nonaqueous phase liquid (LNAPL) in soil. Experiment results show that the combination of ground penetrating radar (GPR), electrical resistivity and electromagnetic (EM) exploration provide a means of mapping of subsurface contamination. The region where radar signal amplitude is decreased and high resistivity appears is illustrated over areas with LNAPL contamination under site specific circumstances. Electrical resistivity and EM exploration gave the similar resistivity distribution. A relationship between contaminant saturation and dielectric constant is established based on chemical analysis and modeling of mixed material. It is necessary to understand the geophysical properties of hydrocarbon contaminants for detecting them by geophysical techniques successfully.

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