The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGAT... more The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGATEM surveys, allows for the extraction of passive EM signals also present, but not normally processed. These include (1) powerline responses, (2) responses in the very low frequency (VLF) range due to radio transmissions and (3) natural-source audio-frequency magnetic (AFMAG) and VLF responses in the frequency range 25 Hz–25 kHz extracted from individual atmospheric electrical discharges (sferics). The latter approach manages to extract good signal in the audio-frequency magnetotelluric (AMT) dead band (1–5 kHz) for one of the discussed data sets. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the vertical-to-horizontal magnetic field ratio (tipper) data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain’s topography. The extraction and modelling of passive EM responses is demonstrated on two data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures similar to those in the corresponding active-source EM data. VLF and AFMAG responses derived from South American MEGATEM data show a strong correlation to topography. These data were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows ... more The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows for the extraction of passive EM responses, inadvertently recorded during AEM surveys. These include powerline responses in data sets acquired in the vicinity of strong powerlines, VLF responses in data sets recorded with sufficiently high sampling frequencies and potentially AFMAG responses in the frequency range 25-600 Hz. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the tipper data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain's topography. The extraction of passive EM responses is demonstrated on a number of data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures not evident in the corresponding active-source EM data. VLF responses derived from South American MEGATEM and North American HELITEM data show a strong correlation to topography. The former were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows fo... more The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows for the reprocessing of the acquired EM data, including square-wave processing. During the latter, the recorded EM response to the actual half-sine waveform is replaced by the EM response to a square-wave, derived via deconvolution/convolution in the frequency domain. This makes the onand early-time information more accessible for data modelling, including 1D inversions and conductivity-depth transformations. Square-wave EM data can also be corrected for survey height, transmitter-receiver offset and transmitter attitude. That correction allows for the interpretation of early-time EM response grids, which generally offer better spatial resolution than derived conductivitydepth slices. The advantages of square-wave processing are demonstrated on a MEGATEM data set acquired in 2013 in South America. With survey terrain clearance ranging from 100-1600 m, due to the rugged topography, early-time grids of elevation-corrected squarewave data outlined the shallow conductivity structure, whereas early-time grids of the original half-sine data mostly reflected the variable system elevation. Further, derived conductivity-depth sections of the square-wave data show more lateral continuity than the sections derived from the original half-sine data. These results show that the early-time information of square-wave is more accessible than in the original data, facilitating interpretation of shallow conductivity structures.
The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGAT... more The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGATEM surveys, allows for the extraction of passive EM signals also present, but not normally processed. These include (1) powerline responses, (2) responses in the very low frequency (VLF) range due to radio transmissions and (3) natural-source audio-frequency magnetic (AFMAG) and VLF responses in the frequency range 25 Hz–25 kHz extracted from individual atmospheric electrical discharges (sferics). The latter approach manages to extract good signal in the audio-frequency magnetotelluric (AMT) dead band (1–5 kHz) for one of the discussed data sets. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the vertical-to-horizontal magnetic field ratio (tipper) data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain’s topography. The extraction and modelling of passive EM responses is demonstrated on two data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures similar to those in the corresponding active-source EM data. VLF and AFMAG responses derived from South American MEGATEM data show a strong correlation to topography. These data were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
Current work is focussing on further optimisation of the data acquisition, processing and interpr... more Current work is focussing on further optimisation of the data acquisition, processing and interpretation workflows to ensure fit-for-purpose, long-lived information is delivered to the business. This includes revisiting and reprocessing legacy 3D datasets to harness advances in processing algorithms.
The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows fo... more The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows for the reprocessing of the acquired EM data, including square-wave processing. During the latter, the recorded EM response to the actual half-sine waveform is replaced by the EM response to a square-wave, derived via deconvolution/convolution in the frequency domain. This makes the onand early-time information more accessible for data modelling, including 1D inversions and conductivity-depth transformations. Square-wave EM data can also be corrected for survey height, transmitter-receiver offset and transmitter attitude. That correction allows for the interpretation of early-time EM response grids, which generally offer better spatial resolution than derived conductivitydepth slices. The advantages of square-wave processing are demonstrated on a MEGATEM data set acquired in 2013 in South America. With survey terrain clearance ranging from 100-1600 m, due to the rugged topography, early-time grids of elevation-corrected squarewave data outlined the shallow conductivity structure, whereas early-time grids of the original half-sine data mostly reflected the variable system elevation. Further, derived conductivity-depth sections of the square-wave data show more lateral continuity than the sections derived from the original half-sine data. These results show that the early-time information of square-wave is more accessible than in the original data, facilitating interpretation of shallow conductivity structures.
The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows ... more The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows for the extraction of passive EM responses, inadvertently recorded during AEM surveys. These include powerline responses in data sets acquired in the vicinity of strong powerlines, VLF responses in data sets recorded with sufficiently high sampling frequencies and potentially AFMAG responses in the frequency range 25-600 Hz. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the tipper data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain's topography. The extraction of passive EM responses is demonstrated on a number of data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures not evident in the corresponding active-source EM data. VLF responses derived from South American MEGATEM and North American HELITEM data show a strong correlation to topography. The former were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
Summary IP, DC Resistivity and MT data have been acquired using three-dimensional arrays at the G... more Summary IP, DC Resistivity and MT data have been acquired using three-dimensional arrays at the Green Dam Prospect, located approximately 120 km east-northeast of Kalgoorlie. The 3D acquisition has enabled data interpretation using both two and three-dimensional inversion methods, leading to increased confidence in results and an improved understanding of the variation in mineralization along strike. The results in the case study will show the IP data clearly map the dominant disseminated Ni- Cu-PGM sulphide mineralization. The data have also mapped the semi-massive to massive Ni-Cu-PGM sulphides and clearly show a high degree of correlation with previously acquired moving loop TEM (MLTEM) and downhole TEM (DHTEM) data.
We have used numerical modelling to improve understanding of seismic reflection in basalt covered... more We have used numerical modelling to improve understanding of seismic reflection in basalt covered regions. Our models are based on hydrocarbon prospects in the Denison Trough (Queensland, Australia). Reflectivity modelling has been used to assess the influence on reflection events, of a range of model and source parameters. Models that include a single near-surface basalt layer generally result in relatively noise-free reflection signals, provided the basalt is reasonably attenuative. Reflection quality is poorest for models with buried high-velocity basalts, or for multi-layered basalts interspersed with lower-velocity material. Such models result in strong reverberatory noise, apparently propagating between the surface and basalt, or within the multi-layered basalts. In these situations, reflection strength is significantly improved if the source can be positioned below the basalt. Finite-difference modelling permits analysis of models incorporating lateral variations in basalt ge...
The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGAT... more The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGATEM surveys, allows for the extraction of passive EM signals also present, but not normally processed. These include (1) powerline responses, (2) responses in the very low frequency (VLF) range due to radio transmissions and (3) natural-source audio-frequency magnetic (AFMAG) and VLF responses in the frequency range 25 Hz–25 kHz extracted from individual atmospheric electrical discharges (sferics). The latter approach manages to extract good signal in the audio-frequency magnetotelluric (AMT) dead band (1–5 kHz) for one of the discussed data sets. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the vertical-to-horizontal magnetic field ratio (tipper) data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain’s topography. The extraction and modelling of passive EM responses is demonstrated on two data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures similar to those in the corresponding active-source EM data. VLF and AFMAG responses derived from South American MEGATEM data show a strong correlation to topography. These data were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows ... more The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows for the extraction of passive EM responses, inadvertently recorded during AEM surveys. These include powerline responses in data sets acquired in the vicinity of strong powerlines, VLF responses in data sets recorded with sufficiently high sampling frequencies and potentially AFMAG responses in the frequency range 25-600 Hz. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the tipper data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain's topography. The extraction of passive EM responses is demonstrated on a number of data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures not evident in the corresponding active-source EM data. VLF responses derived from South American MEGATEM and North American HELITEM data show a strong correlation to topography. The former were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows fo... more The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows for the reprocessing of the acquired EM data, including square-wave processing. During the latter, the recorded EM response to the actual half-sine waveform is replaced by the EM response to a square-wave, derived via deconvolution/convolution in the frequency domain. This makes the onand early-time information more accessible for data modelling, including 1D inversions and conductivity-depth transformations. Square-wave EM data can also be corrected for survey height, transmitter-receiver offset and transmitter attitude. That correction allows for the interpretation of early-time EM response grids, which generally offer better spatial resolution than derived conductivitydepth slices. The advantages of square-wave processing are demonstrated on a MEGATEM data set acquired in 2013 in South America. With survey terrain clearance ranging from 100-1600 m, due to the rugged topography, early-time grids of elevation-corrected squarewave data outlined the shallow conductivity structure, whereas early-time grids of the original half-sine data mostly reflected the variable system elevation. Further, derived conductivity-depth sections of the square-wave data show more lateral continuity than the sections derived from the original half-sine data. These results show that the early-time information of square-wave is more accessible than in the original data, facilitating interpretation of shallow conductivity structures.
The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGAT... more The recording of raw or streamed airborne electromagnetic (AEM) data, as done by CGG during MEGATEM surveys, allows for the extraction of passive EM signals also present, but not normally processed. These include (1) powerline responses, (2) responses in the very low frequency (VLF) range due to radio transmissions and (3) natural-source audio-frequency magnetic (AFMAG) and VLF responses in the frequency range 25 Hz–25 kHz extracted from individual atmospheric electrical discharges (sferics). The latter approach manages to extract good signal in the audio-frequency magnetotelluric (AMT) dead band (1–5 kHz) for one of the discussed data sets. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the vertical-to-horizontal magnetic field ratio (tipper) data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain’s topography. The extraction and modelling of passive EM responses is demonstrated on two data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures similar to those in the corresponding active-source EM data. VLF and AFMAG responses derived from South American MEGATEM data show a strong correlation to topography. These data were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
Current work is focussing on further optimisation of the data acquisition, processing and interpr... more Current work is focussing on further optimisation of the data acquisition, processing and interpretation workflows to ensure fit-for-purpose, long-lived information is delivered to the business. This includes revisiting and reprocessing legacy 3D datasets to harness advances in processing algorithms.
The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows fo... more The recording of raw or streamed EM survey data, as done by CGG during MEGATEM surveys, allows for the reprocessing of the acquired EM data, including square-wave processing. During the latter, the recorded EM response to the actual half-sine waveform is replaced by the EM response to a square-wave, derived via deconvolution/convolution in the frequency domain. This makes the onand early-time information more accessible for data modelling, including 1D inversions and conductivity-depth transformations. Square-wave EM data can also be corrected for survey height, transmitter-receiver offset and transmitter attitude. That correction allows for the interpretation of early-time EM response grids, which generally offer better spatial resolution than derived conductivitydepth slices. The advantages of square-wave processing are demonstrated on a MEGATEM data set acquired in 2013 in South America. With survey terrain clearance ranging from 100-1600 m, due to the rugged topography, early-time grids of elevation-corrected squarewave data outlined the shallow conductivity structure, whereas early-time grids of the original half-sine data mostly reflected the variable system elevation. Further, derived conductivity-depth sections of the square-wave data show more lateral continuity than the sections derived from the original half-sine data. These results show that the early-time information of square-wave is more accessible than in the original data, facilitating interpretation of shallow conductivity structures.
The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows ... more The recording of raw or streamed data, as done by CGG during MEGATEM and HELITEM surveys, allows for the extraction of passive EM responses, inadvertently recorded during AEM surveys. These include powerline responses in data sets acquired in the vicinity of strong powerlines, VLF responses in data sets recorded with sufficiently high sampling frequencies and potentially AFMAG responses in the frequency range 25-600 Hz. The recording of the three-component AEM data allows for the vector processing of these passive EM responses, including the derivation and modelling of the tipper data. Conductivity information can be derived from the tipper data with an apparent conductivity transformation and, more rigorously, with 2D and 3D inversions that take into account the terrain's topography. The extraction of passive EM responses is demonstrated on a number of data sets. A powerline apparent-conductivity grid derived from a MEGATEM survey near Timmins, Canada indicates conductivity structures not evident in the corresponding active-source EM data. VLF responses derived from South American MEGATEM and North American HELITEM data show a strong correlation to topography. The former were successfully modelled with 2D and 3D inversions, and the derived shallow conductivity structures confirm and complement the information extracted from the active-source EM data.
Summary IP, DC Resistivity and MT data have been acquired using three-dimensional arrays at the G... more Summary IP, DC Resistivity and MT data have been acquired using three-dimensional arrays at the Green Dam Prospect, located approximately 120 km east-northeast of Kalgoorlie. The 3D acquisition has enabled data interpretation using both two and three-dimensional inversion methods, leading to increased confidence in results and an improved understanding of the variation in mineralization along strike. The results in the case study will show the IP data clearly map the dominant disseminated Ni- Cu-PGM sulphide mineralization. The data have also mapped the semi-massive to massive Ni-Cu-PGM sulphides and clearly show a high degree of correlation with previously acquired moving loop TEM (MLTEM) and downhole TEM (DHTEM) data.
We have used numerical modelling to improve understanding of seismic reflection in basalt covered... more We have used numerical modelling to improve understanding of seismic reflection in basalt covered regions. Our models are based on hydrocarbon prospects in the Denison Trough (Queensland, Australia). Reflectivity modelling has been used to assess the influence on reflection events, of a range of model and source parameters. Models that include a single near-surface basalt layer generally result in relatively noise-free reflection signals, provided the basalt is reasonably attenuative. Reflection quality is poorest for models with buried high-velocity basalts, or for multi-layered basalts interspersed with lower-velocity material. Such models result in strong reverberatory noise, apparently propagating between the surface and basalt, or within the multi-layered basalts. In these situations, reflection strength is significantly improved if the source can be positioned below the basalt. Finite-difference modelling permits analysis of models incorporating lateral variations in basalt ge...
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