Numerical and laboratory investigations of electrical resistance tomography for environmental monitoring

© ASEG 2004Numerical and laboratory studies have been conducted to test the ability of Electrical Resistance Tomography ? a technique used to map the electrical resistivity of the subsurface ? to delineate contaminant plumes. Two-dimensional numerical models were created to investigate survey design and resolution. Optimal survey design consisted of both downhole and surface electrode sites. Resolution models revealed that while the bulk fluid flow could be outlined, small-scale fingering effects could not be delineated. Laboratory experiments were conducted in a narrow glass tank to validate theoretical models. A visual comparison of fluid flow with ERT images also showed that, while the bulk fluid flow could be seen in most instances, fine-scale effects were indeterminate.T. Dhu and G. Heinsonhttp://www.publish.csiro.au/nid/224/paper/EG04033.ht

The hydraulic and electrical fractal dimension of regolith

Tania Dhu, Graham Heinson & John Josep

Enhancement of airborne magnetic data using the variation method of fractal dimension estimation

Textural-based processing of airborne magnetic data is becoming a recognised tool for image enhancement. The variation method of fractal dimension (FD) estimation is a measure of texture that can resolve subtle textural contrasts as well as edge features that are otherwise difficult to discern. Application of the variation method to synthetic fractal datasets highlighted its ability to distinguish textural contrasts when using local estimates of FD. The variation method was also able to enhance thin linear anomalies, linear ramp anomalies and sinusoidal ramp anomalies contained in synthetic datasets. The variation method clearly resolved these features even in the presence of Gaussian noise. The results demonstrated that smaller window sizes will more effectively discriminate and enhance edges. Application of the variation method on the Ghanzi-Chobe aeromagnetic dataset highlighted features that were not resolved in the greyscale total magnetic intensity image. Comparison of the variation method with standard derivative-based enhancements showed that the variation method enhanced similar trends but with greater clarity. It also enhanced features that were not revealed by horizontal- and vertical-derivative images. Whilst the variation method needs to be applied to data from a wider variety of magnetic regimes, the results suggest that the technique can provide useful information not available from conventional enhancement processes.T. Dhu, M. Dentith and R.R. Hillishttp://trove.nla.gov.au/work/2419272

Viewing the regolith through different eyes: a new way of interpreting resistivity data

Tania Dhu, Graham Heinson & John Josep

Transport and Regional Services (DOTARS) in

The need for a new approach to understand and manage the risk posed by natural hazards in Australia has been acknowledged and emphasised by Australian Commonwealth and State governments. To this effect the Council of Australian Governments (COAG) commissioned a review of natural disaster relief arrangements in June 2001. The results of the review wer

The use of fractual dimension estimators for enhancing airborne magnetic data

Copyright © ASEG 1999Airborne magnetic data is routinely enhanced by amplitude based filters such as horizontal and vertical derivatives. Texture is defined as the spatial distribution of amplitudes over a region. Textural analysis provides a possible alternative method of data enhancement. This paper investigates the potential of using fractal dimension for quantifying texture and highlighting textural contrasts in airborne magnetic data. Profiles have been created by combining theoretical data with fractal dimensions (FD) of 1.1, 1.3 and 1.5. Estimates of FD using the semi-variogram and variation methods clearly distinguish between sections of the profiles with different theoretical FD. Fractal dimension estimates made on a real airborne magnetic profile, using the variation method, clearly define two regions of visible textural contrast. A series of other variations in the estimated FD suggests that the method is able to resolve subtle contrasts that are not easily detected visually. The semi-variogram method of FD estimation is not able to resolve the obvious textural contrasts in real data, a result that is perhaps due to the stochastic nature of this methodology. The variation method has been used to estimate FD on a series of airborne magnetic profiles. This profile data was then gridded to generate an image of FD that moderately improves structural resolution. Whilst more work needs to be carried out, it is obvious that estimates of FD do detect textural contrasts in both theoretical and real data, and that this information can be used to enhance aeromagnetic data

Geophysical exploration for iron ore in the Middleback Ranges, South Australia

Graham Bubner, Mike Dentith, Trevor Dhu & Richard Hilli

Climate risk assessment needs urgent improvement

Existing constraints in current climate risk assessments make them inappropriate to effectively assess the true exposure of society and businesses to climate-related risk. Using the key constraints to guide a conceptual framework, we identify four cross-cutting and inter-related critical paths for improvement