Abstract Details

Details of the Abstract

Title of paper Reducing ocean wave and swell noise in continental shelf MT sites using remote magnetometers
List of authors Heinson, G., Constable, S., Kay, B., Boren, G., Perez, J., Thiel, S., Brand, K.
Affiliation(s) University of Adelaide Australia, Scripps Institution of Oceanography USA, University of Adelaide Australia, University of Adelaide Australia, Scripps Institution of Oceanography USA, CSIRO Australia, Bureau of Meteorology Australia
Summary Eleven marine MT stations have been acquired on the seafloor of Spencer Gulf in water depth 17-40 m, extending a land MT profile that crosses Eyre Peninsula in South Australia. The primary goal was to determine feasibility of collecting broadband to long-period MT (100 Hz to >1000 s) responses in depths < 200 m across the continental shelf. As a secondary geological objective, the Spencer Gulf transect was acquired to address continuity of resistivity anomalies imaged in land MT surveys across the Eyre Peninsula.

Water motion associated with ocean waves and swell corrupts MT data collected in depths < 200 m, by the conductive seawater moving in Earth’s magnetic field, and motion of the instrument itself. Instrument movement appears to be the bigger effect, since noise is larger in magnetic than electric fields. Unless the instrument motion is severe, noise is concentrated in a decade around typical wave and swell periods of 5–15 seconds.

To provide a robust estimate of the seafloor MT response in the wave-noise bandwidth, a hybrid MT response was obtained using seafloor electric fields with a nearby land magnetometer. At high-frequencies apparent resistivities are depressed due to the attenuation of the electric field in the water column, but at longer periods the hybrid MT asymptotes to an effective sea-surface MT response. As the water depth and seawater resistivity are known and reasonably 1D, the sea-surface hybrid impedances can be corrected to a seafloor response that is smoother and lower noise over the entire bandwidth.
Session Keyword 6.0 Marine and airbone EM
File upload 6.0_reducing_ocean_wave_and_s_heinson.pdf
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