Airborne Geophysics - the latest weapon in land management arsenal
Airborne Geophysics is increasingly being used to support land management decisions, as it provides a unique view of the structures that influence the movement of salt and water through the landscape. The data it provides fleshes out information obtained on the ground to give a comprehensive view of a landscape.
How Airborne Geophysics Works
Airborne Geophysics (AG) has long been a standard tool in the mineral exploration industry, used to probe geological and ore body signatures within the earth’s surface. More recently, this has been turned towards the natural resource management (NRM) arena, with four distinct, but often complementary airborne technologies providing information on the properties of the earth.
(i) Airborne Electromagnetics (AEM) – entails the transmission of an electromagnetic pulse from an airborne platform which interacts with materials in the ground. Secondary currents are generated with the strength and longevity of these currents indicative of the conductivity of the materials the primary pulse has interacted with. This conductivity is a function of the amount of water, salt, clay and void space in the material and the depth from which the signal is penetrating. This can be calibrated through on-ground investigations, primarily sampling via bore holes of the materials and waters in the sub-surface at strategic locations.
The ability to accurately deduce the 3-dimensional sub-surface nature of these responses and the strong correlation to either salt stores of saline groundwaters, created a new industry in airborne ‘salinity’ mapping.
In addition to mapping groundwater flow systems, salt loads and the extent of clays, AEM can also be used to detect such things as buried pipelines and UXOs (Un-Exploded Ordinances)!
(ii) Radiometrics – reveal the geochemistry of surface cover and can be used to infer deeply weathered profiles (potential salt stores), or be useful in better defining soil maps or land management units. It can also be used to detect man-made radioactivity or contaminants. It cannot, however, directly measure salinity at the surface.
(iii) Magnetics – measures the variable magnetism across and beneath the landscape and is useful for probing underground geological structures such as faults, rock bars or buried ancient stream channels (paleochannels). When combined with AEM, this can provide information on how groundwater moves beneath the landscape. It does not give good depth information, however.
(iv) Altimetry – is a useful by-product of the other techniques, as all rely on knowing precisely the position of the detecting equipment relative to the earth’s surface, so a Digital Elevation Model is readily generated. This allows detailed analysis of the catchment’s surface morphology.
South Australia Salinity Mapping and Management Support Project [SA SMMSP]
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Last updated: 30 August, 2012