Logn-term, Absolute Measurement of the 3 Componets of Geomagnetic Field and Establishment of Fixed Geomagnetic Stations at the Sea Floor

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Main results we have obtained through this study can be summatized as follows: (1) A small 3-component fluxgate magnetometer(OBM-S5) was developed. As this meter is deiven by a battery installed separately from the sensor housing is is not affected by the magnetization battery and can continue measurement for a longer time.(2) Another Fluxgate magnetometer (OBM-C3) whose sensor was installed about I m above the electronics was developed in order to remove the magnetic effect from the electronics components completely. (3) A proton magnetometer for sea floor use (OBP) was developed to be used for calibration of the fluxgate magnetometer. (4) An electric field recorde for the sea floor (OBE) was developed.Using the equipments mentiones above a dea floor experiment was conductod in the area of the Izu-Bonin ridge alon the parallel 33゜N from August to October 1986 (about 75 days). In the next year from July to October (78 days) another sea floor experiment was conducted in the area a little south of the last area along the parallel 31゜N Through these experiments is was proven that thr fluxgate magnetometer could be calibrated with the aid of a proton marnetometer installed nearby. This result will ensure the plausibility of making absolute measurements of 3-component magnetic field at the seq floor. Another importani result of our study is the installation of thw Ocean Bottom Observation Station in the Sagami Bay from October to November 1987. This station made of non-magnetic concrete, equipped with an acoustic transponder, works as a permanent oceam bottom platrofm reaccessible at any timw. In November the Oceam Bottom Platform was visited by a manned submersible of the Japan Matine Scienece and Technoloby Center and it was confirmed that the platform setteld in a good condition.