The 2D coastal effect on marine time domain electromagnetic measurements using broadside dBz/dt of an electrical transmitter dipole

Goldman, M.; Levi, E.; Tezkan, B.; Yogeshwar, Pritam

doi:10.1190/1.3525276

Cited by 19 publications

(5 citation statements)

References 7 publications

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“…For near‐seafloor surveys in shallow water, commercially available land EM systems can be adapted for marine use [e.g., Müller et al ., ; Goldman et al ., ], but in deep water (where, for example, gas hydrate is found), customized equipment must be developed. Deep‐water bottom‐towed electric and magnetic field systems have been developed and used effectively [ Cheesman et al ., ; Yuan and Edwards , ; Evans , ; Schwalenberg et al ., ; Schwalenberg and Engels , ].…”

Section: Introductionmentioning

confidence: 99%

Vulcan: A deep‐towed CSEM receiver

Constable

Kannberg

Weitemeyer³

2016

Geochem Geophys Geosyst

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We have developed a three‐axis electric field receiver designed to be towed behind a marine electromagnetic transmitter for the purpose of mapping the electrical resistivity in the upper 1000 m of seafloor geology. By careful adjustment of buoyancy and the use of real‐time monitoring of depth and altitude, we are able to deep‐tow multiple receivers on arrays up to 1200 m long within 50 m of the seafloor, thereby obtaining good coupling to geology. The rigid body of the receiver is designed to reduce noise associated with lateral motion of flexible antennas during towing, and allows the measurement of the vertical electric field component, which modeling shows to be particularly sensitive to near‐seafloor resistivity variations. The positions and orientations of the receivers are continuously measured, and realistic estimates of positioning errors can be used to build an error model for the data. During a test in the San Diego Trough, offshore California, inversions of the data were able to fit amplitude and phase of horizontal electric fields at three frequencies on three receivers to about 1% in amplitude and 1° in phase and vertical fields to about 5% in amplitude and 5° in phase. The geological target of the tests was a known cold seep and methane vent in 1000 m water depth, which inversions show to be associated with a 1 km wide resistor at a depth between 50 and 150 m below seafloor. Given the high resistivity (30 Ωm) and position within the gas hydrate stability field, we interpret this to be massive methane hydrate.

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Section: Introductionmentioning

confidence: 99%

Vulcan: A deep‐towed CSEM receiver

Constable

Kannberg

Weitemeyer³

2016

Geochem Geophys Geosyst

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“…Offshore measurements by Goldman et al . () and Levi et al . () prove the extension of the aquifer under the Mediterranean Sea in this region.…”

Section: Introduction and The Long‐offset Transient Electromagnetic Mmentioning

confidence: 88%

“…The area from the cities of Ashdod in the south to Bat Yam in the north, the so-called Palmahin disturbance, has to be highlighted: Here, resistivity values show constant high values, which argues against lateral seawater intrusion. Offshore measurements by Goldman et al (2011) and Levi et al (2018) prove the extension of the aquifer under the Mediterranean Sea in this region. For this survey, the authors used a grounded dipole emitting TE and TM mode and recorded the vertical magnetic field at a short offset (e.g.…”

Section: Figurementioning

confidence: 99%

On the exploration of a marine aquifer offshore Israel by long‐offset transient electromagnetics

Lippert

Tezkan

2019

Geophysical Prospecting

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The existence of aquifers extending from land beneath the sea floor up to a distance of several kilometres has been observed and examined all over the world. The coastal aquifer of Israel is a heavily used groundwater reservoir which has to be constantly monitored to ensure the drinking water supply. Former land‐based electromagnetic measurements show that it is, in several places, blocked to seawater intrusion and is consequently a candidate for submarine extension. Multicomponent long‐offset transient electromagnetic measurements were carried out offshore on the coast of Israel. We deployed a 400‐m‐long grounded dipole as transmitter and several electric and magnetic receivers on the sea floor up to a distance of 4.8 km from the coast. Altogether, we deployed 8 transmitter positions and received data sets at 14 receiver stations onshore and offshore, with offsets of mostly 400 and 800 m. In this paper, we present the survey and 1D Occam and Marquardt inversions of the offshore horizontal electric components in the broadside and inline configuration. In addition, the vertical magnetic component in the broadside position is also considered. Only single inversions, both single offset and single component, were used to detect the aquifer under sea sediments. We prove the submarine existence of the Israeli coastal aquifer up to a distance to the coast of approximately 3.2 to 3.6 km using all measured long‐offset transient electromagnetic components. In addition, we present modelling studies with synthetic data derived from a subsurface model adjusted to our survey area with very shallow water from 10 to 50 m. As part of the planning before the survey, a parameter study of the expected subsurface, the examination of the airwave phenomenon and the justification for our 1D inversion strategy are shown. More detailed eigen parameter analyses are added to explain the measured data.

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“…Goldman et al . () investigated the 2D coastal effect on time‐domain marine electromagnetic measurements when utilizing transient electromagnetic method to detect fresh sub‐seafloor groundwater bodies. Using a 3D FE time‐domain modelling algorithm, Um et al .…”

Section: Introductionmentioning

confidence: 99%

“…Topography problems in time-domain CSEM are also seldom discussed. Goldman et al (2011) investigated the 2D coastal effect on time-domain marine electromagnetic measurements when utilizing transient electromagnetic method to detect fresh sub-seafloor groundwater bodies. Using a 3D FE time-domain modelling algorithm, Um et al (2012b) analysed effects of a subtle multidimensional seafloor topography on short offset electric-field measurements near a vertical electric dipole (VED).…”

Section: Introductionmentioning

confidence: 99%

Effects of the sea floor topography on the 1D inversion of time‐domain marine controlled source electromagnetic data

Cai

Tezkan

2018

Geophysical Prospecting

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Time‐domain marine controlled source electromagnetic methods have been used successfully for the detection of resistive targets such as hydrocarbons, gas hydrate, or marine groundwater aquifers. As the application of time‐domain marine controlled source electromagnetic methods increases, surveys in areas with a strong seabed topography are inevitable. In these cases, an important question is whether bathymetry information should be included in the interpretation of the measured electromagnetic field or not. Since multi‐dimensional inversion is still not common in time‐domain marine controlled source electromagnetic methods, bathymetry effects on the 1D inversion of single‐offset and multi‐offset joint inversions of time‐domain controlled source electromagnetic methods data are investigated. We firstly used an adaptive finite element algorithm to calculate the time‐domain controlled source electromagnetic methods responses of 2D resistivity models with seafloor topography. Then, 1D inversions are applied on the synthetic data derived from marine resistivity models, including the topography in order to study the possible topography effects on the 1D interpretation. To evaluate the effects of topography with various steepness, the slope angle of the seabed topography is varied in the synthetic modelling studies for deep water (air interaction is absent or very weak) and shallow water (air interaction is dominant), respectively. Several different patterns of measuring configurations are considered, such as the systems adopting nodal receivers and the bottom‐towed system. According to the modelling results for deep water when air interaction is absent, the 2D topography can distort the measured electric field. The distortion of the data increases gradually with the enlarging of the topography's slope angle. In our test, depending on the configuration, the seabed topography does not affect the 1D interpretation significantly if the slope angle is less or around 10°. However, if the slope angle increases to 30° or more, it is possible that significant artificial layers occur in inversion results and lead to a wrong interpretation. In a shallow water environment with seabed topography, where the air interaction dominates, it is possible to uncover the true subsurface resistivity structure if the water depth for the 1D inversion is properly chosen. In our synthetic modelling, this scheme can always present a satisfactory data fit in the 1D inversion if only one offset is used in the inversion process. However, the determination of the optimal water depth for a multi‐offset joint inversion is challenging due to the various air interaction for different offsets.

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The 2D coastal effect on marine time domain electromagnetic measurements using broadside dBz/dt of an electrical transmitter dipole

Cited by 19 publications

References 7 publications

Vulcan: A deep‐towed CSEM receiver

Vulcan: A deep‐towed CSEM receiver

On the exploration of a marine aquifer offshore Israel by long‐offset transient electromagnetics

Effects of the sea floor topography on the 1D inversion of time‐domain marine controlled source electromagnetic data

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