Mineral and groundwater exploration with the SkyTEM system

Abstract

The SkyTEM system is a helicopterborne TEM system (Sorensen and Auken, 2004) originally designed and developed for hydrogeophysical and environmental investigations. The aim was to develop an airborne system that would give the same resolution as conventional ground-based TEM soundings. To deliver both early and late time data of good quality, the SkyTEM system can presently be programmed to deliver the combination of moments that is optimal for the survey aims: low moments at ~12 kAm2 where low current and fast transmitter turnoff provide early time data with good near-surface resolution, and high moments at 120-220 kAm2 where a high current, more transmitter turns and lower base frequency provide late time data with good penetration. Repetition frequencies are chosen to optimally reject the power line frequency. In a sedimentary environment where small resistivity contrasts are significant, it is essential that the system produces data with high accuracy and that very early time gates are measured to provide good near-surface resolution. In its present configuration, the vertical resolution of the upper layers for the SkyTEM system is comparable to that of airborne frequency domain systems while the horizontal resolution is better due to less lateral filtering as the signal-to-noise ratio at early times is generally very good for TEM systems. The high moment provides good signal-to-noise ratio at late times. Because of its high lateral and vertical resolution, the SkyTEM system is increasingly used also in mineral prospecting where accurate definition of high conductivity anomalies is essential. The user-definable moments also makes it possible to include transmitter-off intervals so that background noise can be measured during flight. Before takeoff, a transmitter waveform calibration takes place.