Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Abstract
Recent developments with Air-FTG ®
Colm A. Murphy 1
1 Bell Geospace Limited (cmurphy@bellgeo.com)
Air-FTG ® has enjoyed considerable success worldwide for the period since the Airborne Gravity 2004
Workshop on both mineral and petroleum exploration projects. Improved acquisition and data
processing procedures have been pivotal in its ability to produce fast and reliable results that allow the
end user to make cost effective decisions on their exploration programmes.
Noise level reduction has been achieved through installation aboard slower moving and more stable
platforms. Airships offer a platform that yielded a Tzz detectability of 1 to 1.5 Eo over 100 m spatial
wavelengths in 2006. The current platform of choice for Air-FTG ® technology is the fixed wing BT67
aircraft yielding 2 to 3 Eo over 200 m spatial wavelengths detectability for Tzz, which represents a
significant improvement from the 5 to 6 Eo over 400 m spatial wavelengths reported in 2004.
Concurrent with improvements to data acquisition, new data processing tools have been developed to
better extract geological signature patterns and suppress residual systematic noise. The concept of
Full Tensor Noise Reduction (FTNR) was introduced in 2006. FTNR exploits the properties of the full
tensor to isolate signal from noise in each of the Tensor components. The benefits are remarkable and
contribute enormously to the fast turnaround on Air-FTG ® survey programmes, often within days of
survey completion.
The benefits of the FTNR technique rest with data interpretation. The introduction of an invariant
analysis technique in 2007 allows the end user to quickly generate target anomaly and lineament
maps directly from processed data.
These improvements to Air-FTG ® technology have contributed to its acceptance as a viable
exploration tool by not only fast tracking identification of target geology but mapping their geological
setting in a timely manner.
Introduction
Air-FTG ® is a much used technology on both mineral and petroleum exploration projects around the
world. The successful deployment has seen the technology used for both green and brown field
exploration programmes as explorers expand their activities in the search for new resources. There
are many factors that impact the choice of system from technical to logistical, with Air-FTG ® proving to
be competitive because the system provides high resolution and high S/N data on a consistent basis
and is able to deliver workable products in a timely fashion, often within weeks upon end of
acquisition.
When first introduced, the technology attained a 5 Eo resolution over 400 to 500 m wavelengths
(Hammond and Murphy, 2003). Hatch (2004) confirmed these figures through his assessment of the
technology on survey work performed late 2003. This represented a significant achievement for such a
new technology. However, many improvements have been made since.
It was recognised early that to make significant in-roads to improving data quality, the technology
needed to be installed on a slower moving and more stable platform. Data quality would improve
because such a platform would induce less vertical accelerations caused by aircraft turbulence on the
instrument. The resultant effect was an improved data quality to 3 Eo over 300 m wavelengths
reported by Murphy et al. (2006). In addition, new software tools for QC and processing were
developed to take advantage of the improved data quality. The use of invariant analysis techniques
(Murphy and Brewster, 2007) permitted the end user to directly extract geological target and lineament
maps from Air-FTG ® data.
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