Land and Water Link

December 2004

X-ray specs to spot salinity

Airborne geophysics, dubbed the ‘ultrasound of the earth’, is being enlisted in the fight against Australia’s salinity woes.

This technology, used for decades by the mining industry to help locate ore hidden beneath Australia’s thick mantle of soils and weathered rock, now adds to the land manager’s arsenal, providing a new layer of information about the makeup of the underground structures that impede or enhance the movement of salt and water. (See How Airborne Geophysics Works.)

With salinity affecting more than 2.6 million hectares and costing upwards of $500 million a year in environmental and agricultural degradation, the Federal Government has invested heavily in making airborne geophysics data available to support natural resource planning and salinity management.

CSIRO Land and Water has been intimately involved in the practical application of the technology as part of the South Australia Salinity Mapping and Management Support Project (SA-SMMSP), funded by the National Action Plan for Salinity and Water Quality. This $3.8m project, undertaken across five South Australian sites representing a range of landscapes and issues, had the dual aim of proving the technology in the natural resource management arena as well as gaining improved information for salinity management.

Overseeing this multi-agency project, Dr Glen Walker’s role was to ensure the data obtained could be practically used for land planning processes or salinity mitigation works. ‘The Catchment Management bodies we consulted came back with a whole heap of ways it could be used, and some we hadn’t even planned on’, he says.

This study helped build confidence that the technology could support regional salinity management plans, prompting data from an earlier airborne geophysics survey in northern Victoria to be incorporated into one of the Heartlands projects.

CSIRO Land and Water’s Dr Pauline English was conducting on-ground hydrogeological studies in the Honeysuckle Creek Catchment, drilling to obtain groundwater information, when airborne geophysics data was offered to compliment her investigations. ‘I found it very stimulating,’ she recalls, ‘intellectually, and scientifically, especially to help direct us where we were going to drill.’

While the data can provide a detailed image that may relate to an area’s salinity, Dr English reminds us that it must be married to ground investigations and existing knowledge, pointing out that, thus far, ‘excellent hydrogeological and salinity research can be conducted using conventional techniques in the absence of airborne geophysics, but not vice versa’.

A point echoed by Dr Walker, who noted that a major finding of SA-SMMSP was that airborne geophysics is most useful and cost-effective when there is a definable target to explore and a sizeable amount of existing data.

Such discoveries are adding to the knowledge base around the technology, suggesting that the information it produces will offer more to management in future. Dr English says its quite detailed spatial information would increase confidence in land planning and engineering works. ‘If you were going to put a pumping scheme in, or define an irrigation zone, this provides explicit data which should reduce the effort’, she muses.

Dr Walker is confident that ‘as this technology is used more often, both software and interpretation will improve, as will the current restrictive pricing.

‘In a number of the areas studied, airborne geophysics has added to what we already knew about the landscapes, ‘and in some cases,’ Dr Walker adds, ‘changed the way we thought those landscapes worked’.

Further information:

CSIRO contact:

Dr Glen Walker
+61-8-8303 8743

By Cris Kennedy

How Airborne Geophysics works

Airborne Geophysics’ four distinct, but often complementary airborne technologies provide information on the properties of the earth.

1. Airborne Electromagnetics (AEM) – an electromagnetic pulse transmitted from an airborne platform generates currents as it interacts with materials in the ground. The strength and longevity of these currents indicate the conductivity of the materials underground (water, salt, clay, etc) and the depth from which the signal is penetrating – this data is calibrated with information from the ground, allowing construction of 3-dimensional maps of subsurface conductivity.
   
2. Radiometrics – reveals the geochemistry of surface cover and can be used to detect deeply weathered profiles (potential salt stores), or be useful in better defining soil maps or land management units.
   
3. Magnetics – probes underground geological structures such as faults, rock bars or buried ancient stream channels (palaeochannels). When combined with AEM, can provide information on how groundwater moves beneath the landscape.
   
4. Altimetry – generates a Digital Elevation Model, which allows detailed analysis of the catchment’s surface morphology.