• journal_title：The Leading Edge
• Contributor：Richard S. Smith ; Li Zhen Cheng ; Michel Chouteau
• Publisher：Society of Exploration Geophysicists
• Date：2008-
• Format：text/html
• Language：en
• Identifier：10.1190/1.3011019
• journal_abbrev：The Leading Edge
• issn：1070-485X
• volume：27
• issue：11
• firstpage：1470
• section：Special section: Near-surface geophysics

The response measured by transient electromagnetic (TEM) systems is normally of a predictable sign. This is particularly true for coincident-loop ground TEM systems, where the response should in theory always be positive when the ground conductivity is a constant function of frequency and the quasi-static assumption is satisfied. In most cases, these are good assumptions, but, occasionally, coincident-loop negative transients are ob-served. These negatives can be explained if material in the ground has a conductivity that changes with frequency, or, equivalently, has nonzero polarizability.