For the last five years, mining and exploration companies related to nonferrous metals have been expending the largest amount of exploration budget they have ever experienced, which has been led by the recent upward demand of metal resources caused by growth of BRICs including China as the influential countries to the world economy. This upward demand has been also derived by prospective growth in demand of lithium, nickel and cobalt, the principal materials of the secondary battery which is supposed to be prevailing in near future by an environmental preservation aspect.
 However, in recent days, metal exploration targets become to be located at deeper and at remoter areas, which makes our new discoveries of economical metal deposits more diffucult. Therefore, geophysics plays a more important role in metal exploration than ever before, and emergence of revolutionary and potent techniques and equipments are anticipated to detect the deeper mineralization and to survey over remote areas or inaccessible areas efficiently with high accuracy.
 There are three stages in metal exploration, that is to say, reconnaissance survey, regional survey and detailed survey. In the reconnaissance survey, magnetic and gravity methods are utilized in order to find the regional-scaled geological structure possibly related to mineralization event. In the regional survey, magnetics, gravity, DC resistivity/EM methods are applied to delineate prospective zones with mineralization and alteration. In the detailed survey, DC resistivity and EM methods are commonly applied in order to detect the anomalous zones in resistivity which are targets of drilling.
 With respect to the recent trend of geophysical technique R&D to fulfill the larger penetration depth, higher resolution, detectability and portability, airborne triaxial magnetometer and airborne triaxial magnetic gradiometer using SQUID are currently under development. FALCON is the commercial-based airborne gravity gradiometer and expected to provide enormous advantages in metal exploration. Several brand-new equipments with larger penetration depth have emerged in recent years. MIMDAS is capable of providing the data with one-order smaller noise level than the conventional IP equipments. B-field measurement in TEM survey is one of the most efficient way to increase the penetration depth using Fluxgate magnetometer, SQUID and integration circuit attached to the coil magnetometer in order to output the B-field by integrating the coil output. In 2006, JOGMEC completed SQUITEM, TEM data acquisition system using high temperature SQUID, and has been applying it to its own exploration activities.

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 In conventional marine controlled source electromagnetic (CSEM) survey, we need a vessel towing an electromagnetic (EM) transmitter near the seafloor using a long cable. However, in practice, we must tow cables at some height from seafloor because of rough topography (e.g, chimneys) around submarine massive sulphides (SMS). Therefore, it is difficult to get information about shallow sub-seafloor structure. In this research, we propose a new marine CSEM method to solve this problem using two autonomous underwater vehicles (AUV). Using this method, we could keep the diving two AUVs much closer to the seafloor than in the conventional marine CSEM, and we can effectively carry out the exploration of the SMS.
 In CSEM method, the behavior of electric and magnetic fields are determined by the arrangement of source dipoles against survey target. Therefore, it is important to consider where to place the transmitter and the receivers to the structure including low resistivity anomaly. In this study, we discussed the feasibility of our new two-AUV CSEM method employing a 2.5-D FEM forward program for solving EM propagation near the seafloor.
 Our analysis of electromagnetic field has revealed that the received electric and magnetic fields become weakened steeply as the offset from the transmitter to the receiver increases when the source dipole is placed near the SMS. We have also found that the change in the amplitude of electromagnetic anomalies decreases in proportion to the thickness of the SMS. Even in the contamination of noise, we found that it is possible to detect the electromagnetic field for about 200m offset. Our numerical calculations yield the following considerations: (1) the location of source dipole and the change in the amplitude of electromagnetic anomalies could be used to detect the rough horizontal extent of the SMS, and (2) the attenuation in the electromagnetic field could indicate the rough thickness of the SMS. Therefore, our study implies that the proposed two-AUV CSEM method would bring a way to detect the electromagnetic anomalies caused by the existence of the SMS.

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 The ocean bottom hydrothermal deposits are thought to be among the key mineral resources contribute to our future, and the urgent developments of submarine geophysical tools are strongly demanded. Electrical and electromagnetic methods are most commonly used for the onshore mineral explorations, but the technologies to apply to the ocean bottom survey are not yet developed. The main purpose of this research is to develop new ocean bottom EM technologies, and the time domain EM methods are decided to be the principal technology due to the flexibility of selecting transmitter-receiver offsets. The 3D numerical simulations and water tank analog model experiments were performed to define the practical problems for the EM technologies to apply to the ocean bottom. New magneto-impedance sensors for the ocean bottom are also developed, with high sensitivity (up to 1pT), and wide frequency range (DC-100kHz). Test surveys were performed at the shallow sea water of 32 m depth, and made practical problems clear for the ocean bottom measurements. Then more practical experiments were done at the Hakurei deposits, Ogasawara area by using ROV (Hyper dolphin) to test our newly developed system, with 2.5m square transmitting loop attached around the ROV, and MI magnetometer at the center of the bottom. Using this system, we could adequately distinguish the differences of the resistivities between the inside and outside of the ocean bottom mineral deposits. We are also measuring electrical properties of the core samples from the ocean bottom mineral deposits to analyze the EM results, and the differences between Okinawa and Ogasawara areas are clearly defined. High IP effects of the mineral samples are also recognized among the key properties of the samples. Although more high power transmission of the currents are required for the depth of investigation of up to 100m, we could clearly provide the effectiveness of the time domain EM technologies to apply to the ocean bottom mineral deposits.

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 The vertical cable seismic is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. This type of survey is generally called VCS (Vertical Cable Seismic). Because VCS is an efficient high-resolution 3D seismic survey method for a spatially-bounded area, we proposed the method for the hydrothermal deposit survey tool development program that the Ministry of Education, Culture, Sports, Science and Technology (MEXT) started in 2009. We are now developing a VCS system, including not only data acquisition hardware but data processing and analysis technique.
 Our first experiment of VCS surveys has been carried out in Lake Biwa, JAPAN in November 2009 for a feasibility study. Prestack depth migration is applied to the 3D VCS data to obtain a high quality 3D depth volume. Based on the results from the feasibility study, we have developed two autonomous recording VCS systems. After we carried out a trial experiment in the actual ocean at a water depth of about 400m and we carried out the second VCS survey at Iheya Knoll with a deep-towed source. In this survey, we could establish the procedures for the deployment/recovery of the system and could examine the locations and the fluctuations of the vertical cables at a water depth of around 1000m. The acquired VCS data clearly shows the reflections from the sub-seafloor. Through the experiment, we could confirm that our VCS system works well even in the severe circumstances around the locations of seafloor hydrothermal deposits. We have, however, also confirmed that the uncertainty in the locations of the source and of the hydrophones could lower the quality of subsurface image. It is, therefore, strongly necessary to develop a total survey system that assures a accurate positioning and a deployment techniques.
 We are planning two further field surveys in FY2011. One is a 3D survey with a boomer for a high-resolution surface source and the other one for an actual field survey in the Izena Cauldron an active hydrothermal area in the Okinawa Trough. Through these surveys, the VCS will become a practical exploration tool for the exploration of seafloor hydrothermal deposits.

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 A sonar, a kind of remote-sensing device with sonic wave in water, have been used in fishery for over 60 years. Sonars are essential devices to survey ocean bottom and generate the ocean bottom map. A synthetic aperture sonar has performance over several times higher than conventional sonar, so we expect the synthetic aperture sonar to be applied in surveying natural resources at ocean bottom.
 We developed a neutral buoyancy tow-fish as a stable platform equipped with synthetic aperture sonar for ocean resource survey. In the system, the synthetic aperture sonar sends wide sonic pulses and receives its echoes compensating the sonar motion, by changing the array directivity. The phase errors are minimized by the compensation. And we propose a calculating method to acquire a peak of amplitude in a sinc function from two sampled data near the peak. It enables a decimation of the recorded data after the pulse compression, keeping a resolution of sonar image and compensating a sonar motion. Synthetic aperture process can be done over 100 times faster with this methods than without it. The tow-fish is neutral buoyancy by using floats, and has a depressor that prevents mother ship's rock propagating to the tow-fish by the tow-line. An Ether line is within the ROV cable or the towline of the tow-fish. So the sonic signals are transferred to the mother ship immediately, and we can look ocean bottom on real time. Besides, the sonar conditions are checked and the sonar parameters are changed at any time. We named the surveying system Kyouryuu.
 The survey of 7 km² ocean bottom was conducted in the Wakamiko Caldera in Kagoshima Bay, October. In the survey, existence of more hydro-thermal vents than we previously confirmed was revealed. Filament-like reflections of sonar signals were detected in the east side of the 100-m sea mound. The images depicted rocks and rugged topography which are considered to be suitable for tubeworm habitation. At the caldera floor, topographic relief patterns apparently distinguishable from the surrounding muddy sediments were identified even in areas absent of the filament-like reflections. This indicates a possible change of hydrothermally active sites over the course of time.

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 Anomalies in dissolved manganese concentrations are useful for the discovery of new hydrothermal fields. Although in situ manganese analyzers have been developed and adapted for hydrothermal observation, they consume much power and are too large and heavy to be loaded onto small autonomous underwater vehicle (AUV) platforms. Therefore, we developed a miniaturized in situ manganese analyzer in which a new microflow trivalve pump replaces the peristaltic pump and diaphragm pump used in traditional analyzers. This trivalve pump has the advantages of not only a flow speed as high as that of a peristaltic pump but also power consumption as low as that of a diaphragm pump. We also developed a manifold unit to connect the trivalve pump to the selection valve for introduction of standard solutions. Our modifications resulted in a 90% reduction in size and weight relative to traditional in situ manganese analyzers, allowing the new analyzer to be loaded onto small AUV platforms. As a demonstration of the new analyzer's efficacy, we used it for long-term observation of manganese concentrations at the Wakamiko submarine crater in Kagoshima Bay. We detected temporal variation of manganese concentrations caused by temporal variation of hydrothermal fluid activity. We expect our new analyzer to be useful for exploration of hydrothermal fields by using small AUVs and for long-term environmental monitoring.

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