Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Figure 4. Terrain corrected Air-FTG ® data from a survey in eastern Canada. (a) Terrain corrected
Tzz, (b) survey location shown by the star, (c) rotation invariant tensor (I2) response, and (d) the
first vertical derivative of I2 demonstrating enhancement of the geological target response.
Murphy and Brewster (2007) demonstrate how the invariant tensor computation from the horizontal
component data can be used to extract anomalous signature patterns associated with geological
contact information (Figure 5). The example is from a Marine FTG ® survey acquired offshore Norway
in the Nordkapp Basin where salt bodies occur near sea-bed levels. Figure 5(b) shows the bathymetry
corrected Tzz response with the salt body imaged as a negative response. The invariant analysis
lineaments are shown in Figure 5(c) as interpreted anomalous contacts, and in Figure 5(d) plotted in
grey shade on a colour Tzz image. The lineaments are interpreted to image the edge of salt with the
outer rim locating the edge of the salt canopy and the inner rim defining a deeper edge of salt. An
area of overhang development is predicted to occur between these features.
The implementation of an invariant analysis technique to enhance FTG data facilitates a rapid and
efficient means of identifying geological targets and their structural setting. The methodology
presented works with all tensor components simultaneously. In our experience, to be successful for
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