Technical Papers - Airborne Electromagnetics

A special circumstance of airborne induced-polarisation measurements

Richard Smith, Fugro Airborne Surveys
2060 Walkley Road, Ottawa, Ontario, Canada, K1G 3P5 

Jan Klein, Cominco Ltd.
700-409 Granville St., Vancouver, B.C., Canada, V6T 1T1.

Abstract

Airborne induced-polarisation (IP) measurements can be obtained with standard time-domain airborne electromagnetic (EM) equipment, but only in the limited circumstances when the ground is sufficiently resistive that the normal EM response is small and when the polarisability of the ground is sufficiently large that the IP response can dominate the EM response. Further, the dispersion in conductivity must be within the bandwidth of the EM system. One example of what is hypothesised to be IP effects are the negative transients observed on a GEOTEM w survey in the high arctic of Canada. The dispersion in conductivity required to explain the data is very large, but is not inconsistent with some laboratory measurements. Whether the dispersion is caused by an electrolytic or dielectric polarisation is not clear from the limited ground follow-up, but in either case the polarisation can be considered to be induced by eddy currents associated with the EM response of the ground. If IP effects are the cause of the negative transients in the GEOTEM data, then the data can be used to estimate the polarisabilities in the area.

Presented at the Airborne Electromagnetic Workshop, Tuscon, AZ, September 13-16, 1993.

GEOPHYSICS, VOL. 61, NO. 1 (JANUARY-FEBRUARY 1996); P. 66-73, 13 FIGS.Manuscript received by the Editor February 28, 1994; revised manuscript received October 26, 1994. © 1996 Society of Exploration Geophysicists. All rights reserved.