Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Airborne gravimetry and gravity gradiometry at
Fugro Airborne Surveys
Summary
Mark Dransfield 1 , Tiaan Le Roux 2 , and Darren Burrows 3
1 Fugro Airborne Geophysics Pty Ltd (mdransfield@fugroairborne.com.au)
2 Fugro Airborne Surveys
3 Fugro Airborne Surveys
Gravity data provide valuable information used in geotechnical, groundwater, mineral and petroleum
exploration, and geodesy applications. The different length scales of interest, increasing in the
preceding list, place different requirements on the gravity acquisition systems. Geographic conditions
are also an important variable since gravity observations may be desired on land, at sea, or from the
air. Airborne observations are particularly relevant over lakes, rivers, shallow or deep seas, swamps,
deserts, jungles or mountains. A variety of gravity survey technologies are required to satisfy this
broad range of applications and conditions. Fugro provides gravity services that include processing
and interpretation, on land, at sea and from the air, utilising both gravimeters and gravity gradiometers.
This paper reviews some advances over the last 6 years in airborne exploration applications.
Recent development efforts in airborne gravimetry (AirG) have focused primarily on ‘fit for purpose
solutions’, with an emphasis on operational effectiveness and acquiring data of consistent quality
utilizing the GT-1A instrument technology. Post acquisition improvements include statistical noise
reduction techniques, specialized data processing methods that apply when acquiring data at tighter
line spacing, and 3D regional-scale inversions.
In airborne gravity gradiometer (AGG) surveying, there has been a similar continuing effort on noise
reduction techniques with Fugro’s proprietary FALCON technology. Noise levels have nearly halved
since 2004 and the routine incorporation of regional gravity data has increased the bandwidth of the
processed gravity data. New deployment options have increased the practical range of applications for
FALCON AGG technology. The successful development of a digital AGG has made it possible to
deliver cost-effective helicopter-borne gravity gradiometry, providing increased sensitivity and spatial
resolution. In addition, joint gravity, magnetic and electromagnetic surveys have been demonstrated
from both helicopter and fixed-wing aircraft. The heli-FALCON system is credited with the discovery of
new kimberlites in the Ekati diamond field. Successful fixed-wing survey campaigns have now been
flown in twin-engine aircraft, important for safety reasons in some circumstances. The use of FALCON
AGG systems in oil and gas applications has greatly expanded including wide line-spaced surveys for
regional exploration.
Introduction
Airborne measurements of the gravity field can be made using both gravimeters and gravity
gradiometers. The former are limited to providing gravity information at wavelengths above about 5 km
making them more useful in regional studies at basin scale; the latter provide dramatically better
sensitivity at short wavelengths, making gradiometers the preferred technology for mineral exploration
and high resolution oil and gas exploration.
The first airborne gravity gradiometer survey in October 1999 was reported by van Leeuwen (2000)
and results from many surveys have been reported since. Dransfield (2007) has reviewed early
results. The performance of the GT-1A has been reported by Gabell et al. (2004), Ameglio (2005), and
Studinger et al. (2008).
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