New advances in three dimensional transient electromagnetic inversion Page: 2 of 87
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
ABSTRACT
Inversion of transient electromagnetic (TEM) data sets to image the subsurface
three-dimensional (3-D) electrical conductivity and magnetic permeability properties can
be done directly in the time domain. The technique, first introduced by Wang et al.
(1994) for causal and diffusive electromagnetic fields and subsequently implemented by
Zhdanov and Portniaguine (1997) in the framework of iterative migration, is based upon
imaging methods originally developed for seismic wavefields (Claerbout, 1971;
Tarantola, 1984). In this paper we advance the original derivations of Wang et al. (1994)
and Zhdanov and Portniaguine (1997) to treat non-causal TEM fields, as well as correct a
flaw in the theory for treatment of magnetic field data. Our 3D imaging scheme is based
on a conjugate-gradient search for the minimum of an error functional involving EM
measurements governed by Maxwell's equations without displacement currents.
Treatment for magnetic field, voltage (time derivative of the magnetic field) and electric
field data are given. The functional can be computed by propagating the data errors back
into the model in reverse time along with a DC field, sourced by the integrated data errors
over the measurement time range. By correlating these fields, including the time-
integrated back-propagated fields, with the corresponding incident field and its initial
value at each image point, efficient computational forms for the gradients are developed.
The forms of the gradients allow for additional efficiencies when voltage and electric
field data are inverted. In such instances the combined data errors can be back-propagated
jointly, significantly reducing the computation time required to solve the inverse
problem. The inversion algorithm is applied to the long offset transient electromagnetic
measurement (LOTEM) configuration thereby demonstrating its capability in inverting2
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Newman, Gregory A. & Commer, Michael. New advances in three dimensional transient electromagnetic inversion, article, June 16, 2004; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc783504/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.