Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Figure 2. Different platforms successfully used for FTG data acquisition by Bell Geospace. (a)
Marine acquisition aboard a ship, (b) Cessna Grand Caravan 208B, (c) Zeppelin NT Airship, and
(d) Basler BT67.
Bell Geospace now uses BT67 aircraft for airborne surveys (Figure 2). The BT67 is a reconditioned
fixed wing DC-3 aircraft that employs turbo prop engines and a suite of modern avionics that make it
ideally suited to airborne geophysical operations. An added benefit of having twin engines is that the
instrument can remain permanently installed between jobs for easier worldwide mobilisation. The
aircraft is larger than the Cessna Caravan and with its wider wingspan, is better suited for long
duration survey work. Increased stability in the air reduces the impact of turbulence on resultant data
and routinely yields final noise roof estimates of 5 to 6 Eo 2 km in final processed data, i.e., approaching
that of airship quality. However, the BT67 flies at average speeds of 105 knots (55 m/s) and so, the
final sampling rate, although better than that of the Cessna Caravan, is 55m. Nevertheless, the
improved stability and lower noise over the Cessna Grand Caravan (Table 1) routinely yields a
geological detectability of 2 to 3 Eo over 200 m wavelengths.
Table 1 summarises the noise performance achieved over time with 3 airborne platforms used by Bell
Geospace, demonstrating the continued improvement with FTG technology in terms of reducing noise
and improving geological detectability on airborne surveys since 2004. The benefits of a low noise
platform as exemplified by the airship and also with the BT67 aircraft are immense with increased
sensitivity to sub-surface geology producing repeatable subtle signature patterns in the data. BT67
fixed wing Air-FTG ® surveys permit geological features generating 2 to 3 Eo Tzz anomalies with
wavelengths of 200 m to be detectable.
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