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Vertical spatial sensitivity and exploration depth of low-induction-number electromagnetic-induction instruments

Vadose Zone Journal

By:
, , and
DOI: 10.2136/vzj2006.0120

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Abstract

Vertical spatial sensitivity and effective depth of exploration (d e) of low-induction-number (LIN) instruments over a layered soil were evaluated using a complete numerical solution to Maxwell's equations. Previous studies using approximate mathematical solutions predicted a vertical spatial sensitivity for instruments operating under LIN conditions that, for a given transmitter-receiver coil separation (s), coil orientation, and transmitter frequency, should depend solely on depth below the land surface. When not operating under LIN conditions, vertical spatial sensitivity and de also depend on apparent soil electrical conductivity (??a) and therefore the induction number (??). In this new evaluation, we determined the range of ??a and ?? values for which the LIN conditions hold and how de changes when they do not. Two-layer soil models were simulated with both horizontal (HCP) and vertical (VCP) coplanar coil orientations. Soil layers were given electrical conductivity values ranging from 0.1 to 200 mS m-1. As expected, de decreased as ??a increased. Only the least electrically conductive soil produced the de expected when operating under LIN conditions. For the VCP orientation, this was 1.6s, decreasing to 0.8s in the most electrically conductive soil. For the HCP orientation, de decreased from 0.76s to 0.51s. Differences between this and previous studies are attributed to inadequate representation of skin-depth effect and scattering at interfaces between layers. When using LIN instruments to identify depth to water tables, interfaces between soil layers, and variations in salt or moisture content, it is important to consider the dependence of de on ??a. ?? Soil Science Society of America.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Vertical spatial sensitivity and exploration depth of low-induction-number electromagnetic-induction instruments
Series title:
Vadose Zone Journal
DOI:
10.2136/vzj2006.0120
Volume
6
Issue:
1
Year Published:
2007
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Vadose Zone Journal
First page:
158
Last page:
167