Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Conclusions
A Zeppelin airship is unique in its ability to provide a very low acceleration environment while also
closely adhering to a prescribed flight-path in a variety of wind conditions. Over a major test area, the
Air-FTG® data acquired on a Zeppelin NT airship possessed a noise level of 1.7 E RMS. The airship
flies at ¼ the speed of the standard fixed-wing implementation of the Air-FTG system and it was
shown that features with a wavelength of 100 m could be resolved in the data.
The technical limitation of deploying the airship into the high altitude and hot daytime temperatures of
South-Central Botswana was mitigated through a night-time flight program. An analysis of the
production data showed that for 28% of the time, the airship was unable to fly due to technical
problems, a figure that far exceeded the original estimates. During the duration of the survey program,
the airship was flown and moored fulltime in the harsh Kalahari Desert conditions. The downtime in a
future program would be reduced if the program was conducted in a more hospitable environment or if
hangar facilities are available. Additionally, if a later production model had been available, it would
likely have improved reliability over the pre-production prototype airship that was deployed.
The second largest impact on the day-to-day productivity of the airship system was weather downtime,
accounting for 14% of the project duration. Given the seasonal winds and violent storms during the
rainy season the observed level of weather downtime was not unexpected. As anticipated, weather
had very little impact during the relatively calm winter period. As with fixed-wing AGG operations, it is
important to identify the best weather window with cool temperatures and light winds and to favour this
period for airborne surveying. The availability of accurate real time weather radar images during future
surveys should increase the productivity levels over those observed. In the absence of such a service,
mobile vehicle mounted weather radar instruments could be deployed in the field to improve
productivity.
The high-quality airship gravity gradient data allowed kimberlite targets to be selected in the Jwaneng
area without the large number of false targets associated with an equivalent fixed-wing survey. This
greatly reduced the time and cost of the subsequent follow-up program. The high quality data acquired
reduced the risk of missing an economic body, and a new kimberlite was discovered over an area that
had been heavily prospected utilizing other techniques.
Acknowledgements
The authors would like to thank De Beers Group Services for permission to publish this paper and for
the invaluable assistance provided during the roll-out of the project by many individuals at Bell
Geospace and Zeppelin Luftshifftechnik.
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