Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
New methods, specific to satellite gravity data, are required, for example, for computing Bouguer
anomalies. Furthermore, in ice-covered areas, no terrain corrections have so far been applied and the
computed anomalies do not take into account for the reduced density associated with ice sheets.
Satellite gravity data resolution and lithospheric studies
The resolving power of satellite gravity is an issue that needs to be addressed and must be quantified
to ascertain the degree to which the satellite data resolves lithospheric structures. This can be
achieved by comparing the satellite data to gravity and gradients predicted from existing 3D density
models (Figure 1). Another test of the resolution of satellite-derived data is to compare it with the
gravity field predicted from independently determined density models based on petrological and
thermodynamic approaches.
Figure 1. A vertical cross-section through a 3D density model from the South-Central Chilean
subduction zone at 37.4° S (Tašárová, 2004).
The model in Figure 1 is constrained with geological and seismological information (e.g., seismicity
shown in red circles). The red curve in the upper panel shows the gravity response calculated from the
model that was matched to a detailed dataset of surface gravity measurements (not shown). The
crosses show gravity anomalies from the combined satellite and ground gravity field model EIGEN-
GL04C (Förste et al., 2008). This comparison indicates that the satellite data are sufficiently accurate
to resolve major structures associated with the subduction zone.
Gravity gradients and invariants
Gravity gradients and invariants have better resolution of shallow subsurface density structures. An
initial public release of gravity gradient data from the GOCE mission was announced on the 9th of
June 2010 by the the European Space Agency (ESA)
(http://www.esa.int/SPECIALS/GOCE/SEMB1EPK2AG_0.html). Up until this time, the only available
data were simulated gravity gradients such as those shown in Figure 2. It remains to be determined
whether the gradient data provided by GOCE will have sufficient resolution for direct application to
lithospheric studies. The GOCE gradient data will be measured at 250 km elevation and will require
downward continuation to the surface. Given that noise in the data contribute towards making
downward continuation an unstable process, the applicability of GOCE data to lithospheric studies still
needs to be examined. As a preliminary approach, gradients can be calculated from existing forward
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