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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />

(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />

Interior<br />

JSS016 Oral Presentation 2339<br />

Inexpensive ocean bottom long-term geomagnetic observatory<br />

Prof. Valery Korepanov<br />

Laboratory for EM Investigations Lviv Center of Institute of Space Research IAGA<br />

Andriy Prystai, Yevhen Klymovych, Oleksandr Kuznetsov<br />

The need for long-term geomagnetic observatories at the ocean bottom is widely recognized by<br />

international scientific community in order to provide optimally sampled observations of geomagnetic<br />

field variations. Such a global coverage is necessary to improve the magnetic dynamo model as well as<br />

to monitor time-dependent processes in the Earths interior on global and regional scale. The<br />

technological problems of the realization of such a long-term geomagnetic observatory are analyzed. At<br />

the present state of the electronic components and microprocessor technique development the major<br />

difficulty presents not technological, but specific methodological aspects of the magnetic field<br />

measurement and data transmission. First the electromagnetic environment at deep sea is considered<br />

and expected spectral density of magnetic oscillations is estimated with the aim to determine necessary<br />

measurements resolution and sampling rate. Next the most important aspect magnetometer sensor<br />

orientation and calibration in automated mode without mowing parts is discussed. It is proposed to use<br />

the method of Euler angles determination of the randomly oriented coordinates frame o the station at<br />

the sea bed relatively to the reference Earths geomagnetic coordinates frame. It is shown that having<br />

the magnetometer data collected in this randomly oriented frame plus information about Z axis<br />

deviation from vertical position and the data from nearby geomagnetic observatory it is possible to<br />

calculate the corresponding Euler angles and to rotate virtually the randomly oriented sensitivity axes of<br />

the sea-bed magnetometer in order to reduce the data obtained in the random frame to the reference<br />

geomagnetic frame. Following the obtained recommendation an inexpensive autonomous sea-bed<br />

automatic magnetometer is constructed and successfully tested. The efficiency of the proposed<br />

methodology was experimentally confirmed. The peculiarities of the sea-bed magnetometer design<br />

destinated for the International Ocean Network and its performances are presented. This study was<br />

partially supported by the STCU Project -3165.<br />

Keywords: ocean bottom, geomagnetic observatory, orientation

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