Geophysical surveys

In March 2005 NUFG contracted the DPI to map the distribution of saline soils across the site. DPI completed the survey using a four wheel drive motorcycle fitted with electromagnetic instruments.  

Electromagnetic surveys measure the apparent electrical conductance of soil. Since high salinity soils are more conductive than low salinity soils maps of electrical conductance can be used to illustrate the distribution of salinity across an area.  

Two EM-38 units were used, (one in horizontal dipole mode and one in vertical mode) together with an EM-31.  The different instruments and different orientations allow interrogation of salinity at different depths in the soil.  

Each instrument has a transmitting coil and a receiving coil. The transmitting coil generates an electromagnetic field that penetrates the land surface.  This in turn generates a secondary field in conductive material that is sensed by the receiving coil. The two coils fitted to a motorcycle can pass quickly over the land measuring the apparent electrical conductivity and salinity of the upper soil layers.                

In addition to the electromagnetic survey radiometric readings were also recorded along with variations in micro-relief. Radiometric maps measure minor differences in soil radiation resulting from variations in soil mineralogy. Such maps are often useful in assessing soil texture across a site.  

The next step in this assessment process is to manipulate the field data via computer imaging techniques and to interpret the results. 

Images from the Kamarooka geophysical survey

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Geophysical Survey of New Treatment Site

(immediately east of main treatment site)

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EM-31 survey depicting SW-NE orientation of saline land across the new treatment area

 

EM-38 (horizontal) survey depicting SW-NE orientation of saline land across the new treatment area EM-38 (Vertical) survey depicting SW-NE orientation of saline land across the new treatment area

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Radiometric image illustrating potassium response from new treatment area

 

Radiometric image illustrating thorium response from new treatment area

Radiometric image illustrating Uranium response from new treatment area i

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Radiometric image illustrating total radiometric count response from new treatment area