Universität zu Köln

Haroon, Amir ORCID: 0000-0001-5138-6730, Swidinsky, Andrei, Hoelz, Sebastian, Jegen, Marion and Tezkan, Buelent (2020). Step-on versus step-off signals in time-domain controlled source electromagnetic methods using a grounded electric dipole. Geophys. Prospect., 68 (9). S. 2825 - 2845. HOBOKEN: WILEY. ISSN 1365-2478

Full text not available from this repository.

Abstract

The time-domain controlled source electromagnetic method is a geophysical prospecting tool applied to image the subsurface resistivity distribution on land and in the marine environment. In its most general set-up, a square-wave current is fed into a grounded horizontal electric dipole, and several electric and magnetic field receivers at defined offsets to the imposed current measure the electromagnetic response of the Earth. In the marine environment, the application often uses only inline electric field receivers that, for a 50% duty-cycle current waveform, include both step-on and step-off signals. Here, forward and inverse 1D modelling is used to demonstrate limited sensitivity towards shallow resistive layers in the step-off electric field when transmitter and receivers are surrounded by conductive seawater. This observation is explained by a masking effect of the direct current signal that flows through the seawater and primarily affects step-off data. During a step-off measurement, this direct current is orders of magnitude larger than the inductive response at early and intermediate times, limiting the step-off sensitivity towards shallow resistive layers in the seafloor. Step-on data measure the resistive layer at times preceding the arrival of the direct current signal leading to higher sensitivity compared to step-off data. Such dichotomous behaviour between step-on and step-off data is less obvious in onshore experiments due to the lack of a strong overlying conductive zone and corresponding masking effect from direct current flow. Supported by synthetic 1D inversion studies, we conclude that time-domain controlled source electromagnetic measurements on land should apply both step-on and step-off data in a combined inversion approach to maximize signal-to-noise ratios and utilize the sensitivity characteristics of each signal. In an isotropic marine environment, step-off electric fields have inferior sensitivity towards shallow resistive layers compared to step-on data, resulting in an increase of non-uniqueness when interpreting step-off data in a single or combined inversion.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Haroon, Amir UNSPECIFIED orcid.org/0000-0001-5138-6730 UNSPECIFIED Swidinsky, Andrei UNSPECIFIED UNSPECIFIED UNSPECIFIED Hoelz, Sebastian UNSPECIFIED UNSPECIFIED UNSPECIFIED Jegen, Marion UNSPECIFIED UNSPECIFIED UNSPECIFIED Tezkan, Buelent UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-322452
DOI:	10.1111/1365-2478.13016
Journal or Publication Title:	Geophys. Prospect.
Volume:	68
Number:	9
Page Range:	S. 2825 - 2845
Date:	2020
Publisher:	WILEY
Place of Publication:	HOBOKEN
ISSN:	1365-2478
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language GAS HYDRATE; HIKURANGI MARGIN; JOINT INVERSION; METHANE SEEPS; OPOUAWE BANK; MUD VOLCANO; LONG-OFFSET; MARINE; EXPLORATION; SOUNDINGS Multiple languages Geochemistry & Geophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/32245