The tau-p transform is a discretized Radon transform. The choice of discretization parameters is ... more The tau-p transform is a discretized Radon transform. The choice of discretization parameters is a very important part of performing the transform. Insufficient sampling in the tau direction leads to aliasing problems equivalent to those encountered in any one‐dimensional time series. A simple graphical method illustrates that too coarse sampling in the p direction results in reconstructions containing data duplicated incorrectly at different spatial positions. The spacing of these duplications is dependent on the temporal frequency of the data. Insufficient spatial sampling of the original seismic data causes events to plot at multiple p values in tau-p domain, again dependent on temporal frequency. Therefore, to velocity filter spatially aliased noise efficiently, multiple p values must be filtered. The use of appropriate filters in the p-f domain can substantially improve the noise rejection capabilities of velocity filters on spatially aliased noise while having little effect on...
Ground penetrating radar (GPR), of all the commonly practiced geophysical techniques, has the gre... more Ground penetrating radar (GPR), of all the commonly practiced geophysical techniques, has the greatest ability to provide clear high resolution images of shallow sub-surface structure. To date, however, the perceived unpredictability of its performance at different sites has limited its use. Factors which control the performance of GPR can be summarised by the radar range equation. The site dependence of GPR is a result of the wide variation between the wave attenuation rates of different geological materials and the variation in the reflectivities of the different targets. The attenuation rate of a material depends on its conductivity and dielectric constant while the reflectivity depends on the contrast of these properties between the target and host materials. Unfortunately, since conductivity varies with frequency, conductivities obtained by resistivity and other low frequency electromagnetic geophysical measurements are different to those at GPR frequencies. One way to obtain t...
Coal due to its low conductivity and high electromagnetic contrast with surrounding rocks is an a... more Coal due to its low conductivity and high electromagnetic contrast with surrounding rocks is an attractive medium for study by ground radar. Results of trials in Australian coal mines show that ground radar can be a useful tool for horizon control, locating old underground workings and mapping geological structure both from the surface and within mine roadways.
Recent research has shown that polarisation currents are significant in transient electromagnetic... more Recent research has shown that polarisation currents are significant in transient electromagnetic surveys, despite the high loss tangents of geological materials at the frequencies used. In a similar way, the presence of conductivity can significantly affect the results of Ground Penetrating Radar (GPR) surveys, despite the low loss tangents of rocks at radar frequencies. It has long been recognised that the effective range of GPR is strongly dependent on conductivity and that conductivity increases with frequency. However, the effect of conductivity on other aspects of GPR theory have often been overlooked to allow simpler lossless models to be used. In many instances lossless models are inadequate to describe observed behaviour. This paper shows examples of how conductivity, and in particular frequency-dependent conductivity, affects antenna radiation patterns, wavelet propagation and reflection, and illustrates how knowledge of these effects can be used to improve data acquisitio...
Fifth International Conferention on Ground Penetrating Radar, 1994
The properties of antennae change significantly when they are brought close to the ground surface... more The properties of antennae change significantly when they are brought close to the ground surface. Consequently the optimum design of ground penetrating radar (GPR) systems is strongly dependent on a detailed understanding of the interaction of the antenna and the neighbouring ground surface. The Numerical Electromagnetics Code (NEC) is a computer program for antenna modelling which uses integral equations to model wire-like objects and closed surfaces and can model loading and ground effects. NEC provides an attractive alternative to laboratory or field testing of antennas close to the ground surface as antenna configurations and ground conditions can be changed easily. It has the capability to detennine the electromagnetic field strength above and below the ground surface and in close proximity to the antennas where GPR measurements are made. The input impedance of the antenna can also be calculated.
The Arcolabs borehole radar system was developed to assist detailed orebody delineation particula... more The Arcolabs borehole radar system was developed to assist detailed orebody delineation particularly for mines extracting thin vein ore deposits. The probes are 32 mm and therefore fit in most common exploration and mining drillholes. The system has been successfully used at a number of mine sites to assist with ore delineation at a range of scales. Images from holes
ABSTRACT Broadband VHF borehole radars can be used by miners as tactical tools to map orebodies, ... more ABSTRACT Broadband VHF borehole radars can be used by miners as tactical tools to map orebodies, faults and other marker horizons; to identify hazards well in advance of mining and to stop unnecessary mine development or underdevelopment. In principle, fan scans and crosshole profiles of borehole pairs and triplets can be used to synthesize three-dimensional images interferometrically if their trajectories are accurately known, signal-to-noise ratios are adequate, the spatial sampling rate is sufficient and if the target space is sufficiently uncluttered to limit the formation of mirages during reconstruction. However automatic methods of projecting data into 3D image space make stringent demands upon rock homogeneity, translucence and the accuracy of borehole trajectories. These demands can be relaxed by kinematic mapping, using geologically plausible 3D primitives such as cylinders, planes and hollows. In this paper we show that a number of useful primitives derive from a common element - a hoop (with semi-circular shell cross-section) of finite radius, centered on the borehole. The parameters defining the hoop's plane, radius and thickness can be recovered sequentially from borehole radar data. Information about the location and shape of simply curved 3D reflectors can be recovered by finding common tangents to groups of kinematically derived rings.
Journal of Environmental and Engineering Geophysics, 2003
Broadband very high frequency (VHF) borehole radars (BHR) can be used as tactical tools to map or... more Broadband very high frequency (VHF) borehole radars (BHR) can be used as tactical tools to map orebodies, faults and marker horizons; to identify hazards well in advance of mining and to optimize mine development. In principle, radar profiles and cross-hole scans from fanned arrays of boreholes can be used to synthesize three-dimensional images interferometrically if: borehole trajectories are accurately known; signal-to-noise ratios are adequate; the spatial sampling rate is sufficient; target echoes are well correlated, and if the target space is sufficiently uncluttered to limit the formation of mirages during reconstruction. However, automatic methods of projecting data into three-dimensional image space make stringent demands upon rock homogeneity, translucence and the accuracy of borehole trajectories. These demands can be relaxed by reconstructing objects from parts of geologically plausible 3D primitives such as cylinders, planes and spheres. In this paper we show that a number of useful primitive...
Q is a measure of the energy stored to the energy dissipated in a propagating wave and can be est... more Q is a measure of the energy stored to the energy dissipated in a propagating wave and can be estimated from the ratio of attenuation and frequency. For seismic waves, Q has been found to be essentially independent of frequency. As a result, attenuation is an approximately linear function of frequency and the impulse response function of the earth. Hence, the distortion of a seismic pulse as it propagates can be described by a single parameter. Laboratory measurements show that the attenuation of radio waves in some geological materials can also be approximated by a linear function of frequency over the bandwidths of typical subsurface radar pulses. We define a new parameter Q* to describe the slope of this linear region. The impulse response of the transfer function for a given value of Q* differs from that of the same value of Q only in total amplitude. Thus the change of shape of a radar pulse as it travels through these materials can also be described by a single parameter. The ...
The frequency dependence of attenuation is typically far greater for subsurface radar waves than ... more The frequency dependence of attenuation is typically far greater for subsurface radar waves than for seismic waves. Since this frequency dependence causes the subsurface radar pulse shape to change as it propagates through the earth, conventional wavelet deconvolution techniques are often inadequate to reconstruct the earth’s reflectivity series. The application of a time‐variant filter that undoes the effect of frequency‐dependent attenuation can substantially improve the resolution of subsurface radar data. This filter is minimum‐phase with amplitude characteristics equal to the inverse of the attenuation function of the medium investigated. Preliminary tests on data from surveys over a water tank, an underground mine stope, and fractured granite suggest that good results can also be achieved by assuming attenuation is linearly proportional to frequency, similar to a constant Q model.
The tau-p transform is still a relatively new and novel seismic data processing technique. As wit... more The tau-p transform is still a relatively new and novel seismic data processing technique. As with other transforms used in digital seismic data processing, problems are encountered in choosing the appropriate discretization to avoid aliasing. A diagrammatic method of understanding the aliasing concept in tau-p domain is presented. Examples of the correctly applied tau-p transform velocity filters are presented and show the excellent capabilities of the technique. Convenient methods for enhancing events on the basis of their coherency are also made available by the transform. An example of one of these methods is presented along with a more novel application of enhancing events with characteristic travel times as well as moveouts.
The tau-p transform is a discretized Radon transform. The choice of discretization parameters is ... more The tau-p transform is a discretized Radon transform. The choice of discretization parameters is a very important part of performing the transform. Insufficient sampling in the tau direction leads to aliasing problems equivalent to those encountered in any one‐dimensional time series. A simple graphical method illustrates that too coarse sampling in the p direction results in reconstructions containing data duplicated incorrectly at different spatial positions. The spacing of these duplications is dependent on the temporal frequency of the data. Insufficient spatial sampling of the original seismic data causes events to plot at multiple p values in tau-p domain, again dependent on temporal frequency. Therefore, to velocity filter spatially aliased noise efficiently, multiple p values must be filtered. The use of appropriate filters in the p-f domain can substantially improve the noise rejection capabilities of velocity filters on spatially aliased noise while having little effect on...
Ground penetrating radar (GPR), of all the commonly practiced geophysical techniques, has the gre... more Ground penetrating radar (GPR), of all the commonly practiced geophysical techniques, has the greatest ability to provide clear high resolution images of shallow sub-surface structure. To date, however, the perceived unpredictability of its performance at different sites has limited its use. Factors which control the performance of GPR can be summarised by the radar range equation. The site dependence of GPR is a result of the wide variation between the wave attenuation rates of different geological materials and the variation in the reflectivities of the different targets. The attenuation rate of a material depends on its conductivity and dielectric constant while the reflectivity depends on the contrast of these properties between the target and host materials. Unfortunately, since conductivity varies with frequency, conductivities obtained by resistivity and other low frequency electromagnetic geophysical measurements are different to those at GPR frequencies. One way to obtain t...
Coal due to its low conductivity and high electromagnetic contrast with surrounding rocks is an a... more Coal due to its low conductivity and high electromagnetic contrast with surrounding rocks is an attractive medium for study by ground radar. Results of trials in Australian coal mines show that ground radar can be a useful tool for horizon control, locating old underground workings and mapping geological structure both from the surface and within mine roadways.
Recent research has shown that polarisation currents are significant in transient electromagnetic... more Recent research has shown that polarisation currents are significant in transient electromagnetic surveys, despite the high loss tangents of geological materials at the frequencies used. In a similar way, the presence of conductivity can significantly affect the results of Ground Penetrating Radar (GPR) surveys, despite the low loss tangents of rocks at radar frequencies. It has long been recognised that the effective range of GPR is strongly dependent on conductivity and that conductivity increases with frequency. However, the effect of conductivity on other aspects of GPR theory have often been overlooked to allow simpler lossless models to be used. In many instances lossless models are inadequate to describe observed behaviour. This paper shows examples of how conductivity, and in particular frequency-dependent conductivity, affects antenna radiation patterns, wavelet propagation and reflection, and illustrates how knowledge of these effects can be used to improve data acquisitio...
Fifth International Conferention on Ground Penetrating Radar, 1994
The properties of antennae change significantly when they are brought close to the ground surface... more The properties of antennae change significantly when they are brought close to the ground surface. Consequently the optimum design of ground penetrating radar (GPR) systems is strongly dependent on a detailed understanding of the interaction of the antenna and the neighbouring ground surface. The Numerical Electromagnetics Code (NEC) is a computer program for antenna modelling which uses integral equations to model wire-like objects and closed surfaces and can model loading and ground effects. NEC provides an attractive alternative to laboratory or field testing of antennas close to the ground surface as antenna configurations and ground conditions can be changed easily. It has the capability to detennine the electromagnetic field strength above and below the ground surface and in close proximity to the antennas where GPR measurements are made. The input impedance of the antenna can also be calculated.
The Arcolabs borehole radar system was developed to assist detailed orebody delineation particula... more The Arcolabs borehole radar system was developed to assist detailed orebody delineation particularly for mines extracting thin vein ore deposits. The probes are 32 mm and therefore fit in most common exploration and mining drillholes. The system has been successfully used at a number of mine sites to assist with ore delineation at a range of scales. Images from holes
ABSTRACT Broadband VHF borehole radars can be used by miners as tactical tools to map orebodies, ... more ABSTRACT Broadband VHF borehole radars can be used by miners as tactical tools to map orebodies, faults and other marker horizons; to identify hazards well in advance of mining and to stop unnecessary mine development or underdevelopment. In principle, fan scans and crosshole profiles of borehole pairs and triplets can be used to synthesize three-dimensional images interferometrically if their trajectories are accurately known, signal-to-noise ratios are adequate, the spatial sampling rate is sufficient and if the target space is sufficiently uncluttered to limit the formation of mirages during reconstruction. However automatic methods of projecting data into 3D image space make stringent demands upon rock homogeneity, translucence and the accuracy of borehole trajectories. These demands can be relaxed by kinematic mapping, using geologically plausible 3D primitives such as cylinders, planes and hollows. In this paper we show that a number of useful primitives derive from a common element - a hoop (with semi-circular shell cross-section) of finite radius, centered on the borehole. The parameters defining the hoop's plane, radius and thickness can be recovered sequentially from borehole radar data. Information about the location and shape of simply curved 3D reflectors can be recovered by finding common tangents to groups of kinematically derived rings.
Journal of Environmental and Engineering Geophysics, 2003
Broadband very high frequency (VHF) borehole radars (BHR) can be used as tactical tools to map or... more Broadband very high frequency (VHF) borehole radars (BHR) can be used as tactical tools to map orebodies, faults and marker horizons; to identify hazards well in advance of mining and to optimize mine development. In principle, radar profiles and cross-hole scans from fanned arrays of boreholes can be used to synthesize three-dimensional images interferometrically if: borehole trajectories are accurately known; signal-to-noise ratios are adequate; the spatial sampling rate is sufficient; target echoes are well correlated, and if the target space is sufficiently uncluttered to limit the formation of mirages during reconstruction. However, automatic methods of projecting data into three-dimensional image space make stringent demands upon rock homogeneity, translucence and the accuracy of borehole trajectories. These demands can be relaxed by reconstructing objects from parts of geologically plausible 3D primitives such as cylinders, planes and spheres. In this paper we show that a number of useful primitive...
Q is a measure of the energy stored to the energy dissipated in a propagating wave and can be est... more Q is a measure of the energy stored to the energy dissipated in a propagating wave and can be estimated from the ratio of attenuation and frequency. For seismic waves, Q has been found to be essentially independent of frequency. As a result, attenuation is an approximately linear function of frequency and the impulse response function of the earth. Hence, the distortion of a seismic pulse as it propagates can be described by a single parameter. Laboratory measurements show that the attenuation of radio waves in some geological materials can also be approximated by a linear function of frequency over the bandwidths of typical subsurface radar pulses. We define a new parameter Q* to describe the slope of this linear region. The impulse response of the transfer function for a given value of Q* differs from that of the same value of Q only in total amplitude. Thus the change of shape of a radar pulse as it travels through these materials can also be described by a single parameter. The ...
The frequency dependence of attenuation is typically far greater for subsurface radar waves than ... more The frequency dependence of attenuation is typically far greater for subsurface radar waves than for seismic waves. Since this frequency dependence causes the subsurface radar pulse shape to change as it propagates through the earth, conventional wavelet deconvolution techniques are often inadequate to reconstruct the earth’s reflectivity series. The application of a time‐variant filter that undoes the effect of frequency‐dependent attenuation can substantially improve the resolution of subsurface radar data. This filter is minimum‐phase with amplitude characteristics equal to the inverse of the attenuation function of the medium investigated. Preliminary tests on data from surveys over a water tank, an underground mine stope, and fractured granite suggest that good results can also be achieved by assuming attenuation is linearly proportional to frequency, similar to a constant Q model.
The tau-p transform is still a relatively new and novel seismic data processing technique. As wit... more The tau-p transform is still a relatively new and novel seismic data processing technique. As with other transforms used in digital seismic data processing, problems are encountered in choosing the appropriate discretization to avoid aliasing. A diagrammatic method of understanding the aliasing concept in tau-p domain is presented. Examples of the correctly applied tau-p transform velocity filters are presented and show the excellent capabilities of the technique. Convenient methods for enhancing events on the basis of their coherency are also made available by the transform. An example of one of these methods is presented along with a more novel application of enhancing events with characteristic travel times as well as moveouts.
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