Performance of airborne electromagnetic (AEM) systems has changed dramatically since the first helicopter time-domain systems were employed in the early 2000s. These systems have experienced dramatic improvements in transmitter power and system noise reduction, such that signal-to-noise has improved to a level that inductively induced polarization (airborne IP) and superparamagnetic effects are detectable. Lowering base frequency below 25 Hz has been a goal to improve discrimination of very conductive targets and to explore under conductive cover. Although easy to achieve in ground EM surveys, noise caused by receiver motion on airborne platforms has prevented this barrier from being surpassed. Here we discuss the technological innovations that led to and survey results from an AEM system capable of operating at a base frequency of 15 Hz. The noise level increase we observe using 15 Hz over operating the same system at 30 Hz is largely identical to the theoretically expected amount caused by decrease in data available for stacking. We show results from an area with very conductive and thick cover to highlight the extended measurement time of the 15 Hz base frequency.

No abstract

SUMMARYRecent development and re-design of the Helitem helicopter time domain system have resulted in the release of the Helitem30C and Helitem35C systems, both of which employ MultiPulse™. We describe the Helitem30C system, which was designed for efficient operation and is applicable to the majority of TEM surveys. The Helitem35C was designed to increase sensitivity to both resistive and conductive targets (increased geologic bandwidth) while achieving maximum power (and depth). A redesigned receiver suspension system significantly reduces coil motion at low frequencies, allowing for 12.5/15 Hz operation with no increase in coil motion noise, important for exploring under cover. We show case histories using both systems to illustrate their performance.

Frequency domain electromagnetic (FDEM) systems are ideal candidates for geotechnical and environmental surveying because of their wide bandwidth, ability to reject power line noise and lightweight, compact design which allows for good flight control. A rigid system allows for in-phase measurements and discrimination of resistivity over a range of 5 orders of magnitude. Here, we review the application of the Resolve® FDEM system to mapping to assist in geotechnical projects, including planning a pipeline and a power-line corridor and construction of a pipeline where information of the very near-surface (<15m) was required. SAGEEP 2017 170 | Page Downloaded 04/22/17 to 132.239.1.231. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/

No abstract