Sea-surface observations of the magnetic signals of ocean swells

Lilley, F. E. M.; Hitchman, Adrian; Milligan, Peter; Pedersen, T.

doi:10.1111/j.1365-246x.2004.02420.x

Cited by 25 publications

(17 citation statements)

References 19 publications

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“…( 9) Sea-surface measurements as reported in Lilley et al (2004) combined with forecast knowledge of the ocean swell at the time confirm that to within the errors involved, actual observed signals are consistent with this theory. An example of the signal from Lilley et al (2004) is shown in Figure 2.…”

Section: Motional Inductionsupporting

confidence: 70%

“…The point is made in Lilley et al (2004) that often the ocean swell signal will be a sharp spectral peak, for a stationary magnetometer. The present paper examines how a moving aircraft sees a different frequency, and how this frequency translates into an apparent spatial wavelength if it is preserved in data that are then plotted in map form.…”

Section: Introductionmentioning

confidence: 99%

“…An example of the signal from Lilley et al (2004) is shown in Figure 2. The data in this figure were observed by a floating magnetometer in water depths in the range 2000 to 3000 m, thus satisfying the deep-water requirements of the Weaver theory.…”

Section: Motional Inductionmentioning

confidence: 99%

“…More widely, the topic of electromagnetic induction in the ocean is reviewed by Larsen (1973) and Palshin (1996). Recently, Lilley et al (2004) observed the magnetic signals of ocean swells with a magnetometer released from a ship to float freely on the surface of the ocean for several days. The signal observed was consistent with knowledge of the swell characteristics at that time, combined with the theory of Weaver (1997).…”

Section: Introductionmentioning

confidence: 99%

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Apparent Aeromagnetic Wavelengths of the Magnetic Signals of Ocean Swell

Lilley¹,

Weitemeyer²

2004

Exploration Geophysics

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Ocean swells have a magnetic signal, caused by the motional induction of seawater moving in the steady main magnetic field of Earth. These signals may be sensed by a low-flying aircraft, carrying out aeromagnetic measurements over the ocean. The apparent spatial wavelength that such signals will have, when observed data are plotted out for geological purposes, can vary greatly. It will depend particularly on the relative speeds and directions of travel of the observing aircraft and the ocean swells. The apparent wavelength of the ocean swell magnetic signal cannot be less than the actual ocean swell wavelength. Generally, it is greater, and it can range up to infinity in value. For observations over continental shelves, the situation is complicated by the dependence of the swell phase-velocity on water depth, by which the swell speed generally slows as land is approached.

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Section: Motional Inductionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Section: Motional Inductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Apparent Aeromagnetic Wavelengths of the Magnetic Signals of Ocean Swell

Lilley¹,

Weitemeyer²

2004

Exploration Geophysics

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“…The wave heights and periods of ocean swells are usually several metres and around 13 s. These ocean swells can generate magnetic signals up to 5 nT [26]. Typical tide flow can induce a magnetic field of 20-30 nT.…”

Section: Introductionmentioning

confidence: 99%

Space–time behaviour of magnetic anomalies induced by tsunami waves in open ocean

Wang

Liu

2013

Proc. R. Soc. A.

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The magnetic anomaly induced by an inhomogeneous velocity field under tsunami waves in open ocean is investigated. With asymptotical analysis, an explicit series solution of the kinematic dynamo problem is established for weak dispersive water waves. The magnetic field induced by typical tsunami models, including single wave and N -wave, can be directly obtained using the proposed series solution. The characteristics of the magnetic field induced by two realistic tsunami events are investigated. By analysis, the magnetic magnitude induced by a 1 m high tsunami is estimated as of the order of 10 nT at the sea surface, which depends on the wave parameters as well as the Earth's magnetic field. The space and time behaviour of the magnetic field shows fair similarity with the field data at Easter Island during the 2010 Chile tsunami.

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Experimental Study of Marine Magnetotelluric in Southern Huanghai

Wei

Deng

Wen

et al. 2009

Chinese J of Geophysics

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In the southern Huanghai (Yellow Sea), seismic exploration for oil and gas in pre‐Tertiary strata encounters some difficulties, such as poor geological conditions at depth, screened seismic waves, and serious attenuation of seismic energy, so that the reflective signals from the Mesozoic and Paleozoic systems cannot be recognized. To solve this issue by other approach, an experiment of seafloor magnetotelluric (MT) sounding was carried out in this region in May 2006. This work has deployed 3 measurement sites on the Wulian slope and Jiaozhou sag in the basin and obtained good data. In this article, we present the difference of data processing between the marine MT and routine MT soundings, and analyze the influence of marine electromagnetic noise on the MT observation on seafloor. We propose correction methods for the horizontal attitude and orientation of the instrument as well as removal of marine noise. Using these and other regular methods, we have performed data processing and inversion, and a comprehensive analysis of geology and physical properties. The result shows that there are residual Paleozoic strata below the seafloor in the southern Huanghai. This is of great significance for prospect assessment of oil and gas in the pre‐Tertiary system in this region. The experiment also demonstrates that the marine MT technology can play an important role in exploration of relict basins of Paleozoic time.

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Sea-surface observations of the magnetic signals of ocean swells

Cited by 25 publications

References 19 publications

Apparent Aeromagnetic Wavelengths of the Magnetic Signals of Ocean Swell

Apparent Aeromagnetic Wavelengths of the Magnetic Signals of Ocean Swell

Space–time behaviour of magnetic anomalies induced by tsunami waves in open ocean

Experimental Study of Marine Magnetotelluric in Southern Huanghai

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