Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Figure 1. The base of salt in green and the 3D density distribution of the starting model used to
test a joint inversion of gravity gradients T XY and T UV .
We simulated T XY and T UV , the curvature gravity gradient components that are directly measured by
the FALCON airborne gravity gradiometer system (Lee, 2001; Dransfield, 2007). Although we only
display the T XY responses, a joint inversion of T XY and T UV was performed to make changes to the
base of salt so that the calculated gradients matched “observed” gradients. Figure 2b demonstrates
the inverted results, which are almost identical to the true model. We have a seismic section in this
test and its location is shown as the NW-SE diagonal line in the bottom-left map of Figure 2b. Figure 3
illustrates the cross-section along this diagonal profile. In practice, a seismic section can be used to
constrain and calibrate our 3D inversion. The algorithms converge fast: it takes 10 iterations
(13 minutes) to complete this joint inversion of T XY and T UV on a desktop computer (Dell Precision
T3400 Workstation with 64-bit Intel® CoreTM 2 Duo E8500 processor, 3.16 GHz and 8 GB RAM). The
modeled and observed responses are very close (the RMS misfit is smaller than 0.1 eötvös). To test
the effects of noise, we added random noise with a standard deviation of 3 eötvös to T XY and T UV .
This inversion run was terminated at the 18th iteration when the RMS misfit between observed and
computed responses is smaller than 3 eötvös. The resulting model and responses are shown in Figure
2c. It is close to the true model and this demonstrates that our joint inversion algorithm is robust.
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