Technical Papers - Airborne Electromagnetics

A Comparison of Data from Airborne, Semi-Airborne and Ground Electromagnetic Systems

Richard S. Smith, A. Peter Annan, Fugro Airborne Surveys, and Patrick McGowan, Geophysical Consultant.

Abstract

The region around a small conductive massive sulfide body near Sudbury, Ontario, Canada, was used as a test site to compare airborne and ground electromagnetic (EM) systems with a new experimental EM system that uses a ground-based transmitter and an airborne receiver. 

In this test survey, the semi-airborne data were acquired with the transmitter loop used for the ground survey and the receiver normally used for the airborne system. At the time the data were acquired, there was no synchronisation between the semi-airborne receiver and the ground transmitter. However, subsequent digital processing of the full waveform data allowed the zero-time position to be defined. The data could then be stacked and windowed.

The ratio of the peak signal to the late-time noise level for the airborne data is about 25:1, the semi-airborne data shows signal-to-noise ratios of 500:1, while the signal-to-noise ratio for the ground data has a ratio of 50 000:1. This particular conductor is very close to the ground transmitter and receiver, so the signal-to-noise ratio for the ground system is very high. Numerical modeling shows that the marked advantage of the ground sys-tem is reduced when the conductor is deeper. However, the semi-airborne system will generally show signal-to-noise intermediate between the airborne and ground systems. 

From an operational perspective, the semi-airborne system has features of both the ground and airborne systems. Like the ground system, it is necessary to lay a transmitter loop on the ground; but because an aircraft is used, the semi-airborne receiver can cover the survey area much more quickly.

GEOPHYSICS, VOL. 66, NO. 5 (SEPTEMBER-OCTOBER 2001); P. 1379-1385, 12 FIGS., 1 TABLE.

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