Airborne Gravity 2010 - Geoscience Australia
Airborne Gravity 2010 - Geoscience Australia
Airborne Gravity 2010 - Geoscience Australia
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<strong>Airborne</strong> <strong>Gravity</strong> <strong>2010</strong><br />
Figure 1. Flight components of the Gedex HD-AGG installed in a Cessna 208.<br />
Instrument<br />
The gravity gradiometer instrument used by Gedex has been developed at the University of Maryland,<br />
and is described by Moody and Paik (2004, 2007). Fundamentally, it comprises pairs of angular<br />
accelerometers that share a common rotation axis, each of which employs an elongated test-mass<br />
(one of which is shown in Figure 2a). The two test-masses in each pair are oriented with their long<br />
axes mutually orthogonal and are supported within housings connected to each other, via bolting, to a<br />
central metering cube structure (Figure 2b). The assembled instrument is shown in Figure 2c. Angular<br />
acceleration of the instrument about the rotation axis of one of the test-mass pairs causes the two testmasses<br />
to rotate in the same direction (“common-mode” motion) with respect to the body of the<br />
instrument, while certain terms of the local gravity gradient tensor cause the two test-masses in each<br />
pair to rotate in opposite directions (“difference-mode” motion).<br />
Figure 2. (a) Angular accelerometer, (b) schematic diagram of sensor, and (c) the assembled<br />
prototype instrument.<br />
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