Roger Clifton

Roger Clifton
NT Geological Survey (retired)

Doctor of Philosophy
Occasional consultations. Willing to help anyone who wants to become skilled in this remarkably powerful depth method.

About

20
Publications
683
Reads
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33
Citations
Additional affiliations
April 1992 - December 2018
NT Geological Survey
Position
  • Geophysicist

Publications

Publications (20)
Article
Full-text available
Although spectral depth determination has played a role in magnetic interpretation for over four decades, automating the procedure has been inhibited by the need for manual intervention. This paper introduces the concept of a slope spectrum of an equivalent layer, to be used in an automated depth interpretation algorithm suitable for application to...
Article
Full-text available
A procedure for creating depth transects across the Northern Territory (Australia) has been established using magnetic spectral depths. Although these transects showed depths to layers, they failed to show depths in the upper few hundred metres. Because the magnetic depths had been derived on the basis of heterogeneity of the bodies, a method of fo...
Article
Full-text available
An existing method assumes that each TMI anomaly is due to an equivalent layer of random dipoles, so that the depth to each layer is obtained by inverting the slope of the power spectrum for depth, as if it were that of a single dipole. The deepest signals appear at the lowest frequencies. Since the noise is lowest there, only a few frequencies are...
Thesis
Full-text available
A formula has been derived to provide depth estimates from a greater length of the magnetic power spectrum than by using the classic Spector-Grant formula. Consequently, magnetic depths have been profiled at intervals of 5 km across the Northern Territory, giving depths of up to three bodies at each station. Shallower bodies can be located using...
Method
Full-text available
Automated magnetic depths are made possible with the introduction of a new formula that stands to supersede the Spector Grant formula for spectral depths. Good depths are obtained to the top of the dominant body in the sample grid, whether layered or not. Up to three layered bodies can be obtained from the same sample.
Article
Full-text available
A recently published method of automatically finding magnetic depths to magnetic layers is demonstrated, finding depths to significant details in the magnetic basement under Melville Island, Northern Territory. By using a method that simulates a magnetic basement as a series of layers of random dipoles, the depths to basement are satisfactorily ob...
Article
Full-text available
This paper describes a spectrum-based algorithmic procedure for rapid reconnaissance for compact bodies at depths of interest using magnetic line data. The established method of obtaining depth to source from power spectra requires an interpreter to subjectively select just a single slope along the power spectrum. However, many slopes along the spe...
Article
Full-text available
Previously essentially manual, the Spector-Grant method requires inspection of the power spectrum to assign a single slope characterising the depth to a large flat body. In effect, there is only one subjectively chosen point on the spectrum to apply the SG formula. Using animations, the (oral) presentation demonstrates a fresh derivation of the for...
Article
A full width image of the radiometrics of Australia is offered as a standard source for radiometric images of subset areas. High pass filtering each of the component grids has allowed colour transforms to be obtained for the whole continent that approximate the transforms that would be required to equalise each zoomed subset. Standard practice for...
Article
A method of searching aeromagnetic data for dipole-like bodies rediscovers most of the known ironstone-hosted gold mines on Tennant Creek, as well as many other dipole-like bodies, apparently ironstones. Surface ironstones and waste dumps mask the signal of an ironstone below, however many ironstones are detected at depths ranging down to 200 m, wi...
Article
Current airborne remotely sensed data can contribute to the characterisation of mine sites for monitoring and rehabilitation assessment. The spatial and spectral resolution required from airborne data depends on the issues to be addressed. For this paper we combine Compact Airborne Spectrographic Imager data with ground‐based reflectance measuremen...
Article
Full-text available
The country’s increasing collection of data sets and increasing resolution of instruments creates an opportunity to put the redundant data to work. The shape of the grid on fine scales may not be evident to the eye. However if a vector of shape components at each point is available, images and quantities may be extracted. This paper shows how to...
Article
Full-text available
Multichannel survey data imply a dataspace of a large number of dimensions. Often most of the dataspace is either empty of the factors of interest or their amplitude is lower than the local noise level. It is desirable to identify a subspace containing most of the factors of interest, allowing most of the noise to be discarded. The paper generalise...
Thesis
Full-text available
Airborne radiometric surveys routinely capture the gammaray field as a series of multichannel spectra. By taking the principal components of the intensity spectrum instead of the counts spectrum, the influence of potassium, uranium and thorium are concentrated into the first half dozen principal components. The spectral component of each of the thr...

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Projects

Projects (2)
Project
McA is old, contorted and magnetically complex, so it is a hard ask.