An information theoretic Bayesian uncertainty analysis of AEM systems over Menindee Lake, Australia

Long-range, active-source airborne electromagnetic (AEM) systems for near-surface imaging fall into two categories: helicopter borne or fixed-wing aircraft borne. A multitude of factors such as flying height, transmitter loop area and current, source waveforms, aerodynamic stability and data stacking times contribute to the geological resolvability of the subsurface. A comprehensive comparison of the relative merits of each system considering all such factors is difficult, but test flights over known subsurface geology with downhole induction logs are extremely useful for resolution studies. Further, given the non-linear nature of the electromagnetic inverse problem, handling transmitter-receiver geometries in fixed-wing aircraft is especially challenging. As a consequence of this nonlinearity, inspecting the closeness of downhole conductivities to deterministic inversion results is not sufficient for studying resolvability. A more comprehensive picture is provided by examining the width of the depth-wise Bayesian posterior conductivity distributions for each kind of system. For this purpose, probabilistic inversions of data must be carried out -- with acquisition over the same geology, survey noise levels must be measured, and the same prior probabilities on conductivity must be used. With both synthetic models as well as real data from over the Menindee calibration range in New South Wales, Australia, we shed new light on the matter of AEM inverse model resolution. Specifically, we use a novel Bayesian inversion scheme which handles fixed-wing geometry attributes as generic nuisance parameters during Markov chain sampling. Our findings have useful implications in AEM system selection, as well as in the design of better deterministic AEM inversion algorithms. <b>Citation:</b> Anandaroop Ray, Yusen Ley-Cooper, Ross C Brodie, Richard Taylor, Neil Symington, Negin F Moghaddam, An information theoretic Bayesian uncertainty analysis of AEM systems over Menindee Lake, Australia, Geophysical Journal International, Volume 235, Issue 2, November 2023, Pages 1888–1911, <a href="https://doi.org/10.1093/gji/ggad337">https://doi.org/10.1093/gji/ggad337</a>

Airborne electromagnetics data return Template and User Guide

<div>Templates and User Guide to provide airborne geophysical data to non-technical people. The template includes a description of the project, survey method, how the data can be used, and what the data can show you. The template is internal use only</div><div>1. Airborne Electromagnetic Survey</div>

National Radioactive Waste Management Facility AEM Survey Logistics Report, AEM Data, and Laterally Constrained Inversion Results

<div>In July 2022 an airborne electromagnetic (AEM) survey was flown over and around the proposed site of the National Radioactive Waste Management Facility near the township of Kimba in South Australia. The survey was commissioned by the Australian Radioactive Waste Agency, and was project managed by Geoscience Australia. The survey has Geoscience Australia airborne survey project number P5008.</div><div><br></div><div>The survey was flown by Skytem Australia Pty Ltd using its SkyTEM312Fast AEM system. The survey was conducted on east-west lines at 500 m spacing, with a smaller central focus area of 100 m spaced lines, acquiring a total of 2,545 line kilometres of data. Skytem Australia Pty Ltd also processed the data.</div><div><br></div><div>This data package includes the acquisition and processing report, the final processed AEM data and the results of the 1D laterally constrained inversion of the data to conductivity-depth estimates that was carried out by the contractor.</div>

A decade-long between-system comparison of AEM conductivities at Menindee Lake using deterministic and stochastic inversion

<div>Airborne electromagnetic (AEM) surveying provides a rapid means of imaging shallow subsurface geology as represented by changes in electrical conductivity within the earth. Aircraft-borne systems fly at different heights and with different speeds, and the exciting transients for time-domain AEM systems provide different spectral content to image the earth with. Geoscience Australia</div><div>operates a test range over one of the Menindee lakes, in New South Wales, Australia, where different AEM systems have been flown over nearly a decade. Due to well studied geology and downhole induction data available in the area, this test range provides a useful proving ground for new AEM technology. For every test survey, certain lines within the range are repeatedly flown, and high-altitude lines are also acquired, such that robust data noise statistics can be established for all overflying AEM systems.</div><div><br></div><div>Test-range data and noise for various systems naturally allows us to compare AEM derived subsurface images of the test line. This study presents the results of both deterministic as well as Bayesian stochastic inversion over the same 13 km stretch of land, with six different systems flown between 2014-2023. While a deterministic inversion provides a first-pass image for comparing AEM systems, far more information is provided by the full posterior distribution of inverted conductivities, and in particular, the marginal quantiles of median and extremal conductivities over the entire image section. </div><div><br></div><div>Our findings indicate that there is generally good agreement with borehole logs, and the posterior conductivities for all systems agree well at the regional scale. The uncertainty (or the lack thereof) around ambiguous features in deterministic inversions is revealed through the stochastic inversions. Finally, we note that examination of water volumes in Menindee lakes do not show a simple relationship with inferred conductivity, indicating that unentangling environmental factors and system differences is a non-trivial matter. Presented at the 2024 Australian Society of Exploration Geophysicists (ASEG) Discover Symposium

AusAEM is the worlds largest airborne electromagnetic (AEM) survey undertaken

<div>Airborne electromagnetics surveys are at the forefront of addressing the challenge of exploration undercover. They have been essential in the regional mapping programmes to build Australia's resource potential inventory and provide information about the subsurface. In collaboration with state and territory geological surveys, Geoscience Australia (GA) leads a national initiative to acquire AEM data across Australia at 20 km line spacing, as a component of the Australian government Exploring for The Future (EFTF) program. Regional models of subsurface electrical conductivity show new undercover geological features that could host critical mineral deposits and groundwater resources. The models enable us to map potential alteration and structural zones and support environmental and land management studies. Several features observed in the AEM models have also provided insights into possible salt distribution analysed for its hydrogen storage potential. The AusAEM programme is rapidly covering areas with regional AEM transects at a scale never previously attempted. The programme's success leans on the high-resolution, non-invasive nature of the method and its ability to derive subsurface electrical conductivity in three dimensions – made possible by GA's implementation of modern high-performance computing algorithms. The programme is increasingly acquiring more AEM data, processing it, and working towards full national coverage.</div> This Abstract was submitted/presented to the 2023 Australian Exploration Geoscience Conference 13-18 Mar (https://2023.aegc.com.au/)

Warburton East, Warburton West, Great Victoria Desert, Kimberley Basin, Little Sandy Desert East and Little Sandy Desert West Gravity Surveys, 2018

<div>In 2018, Sander Geophysics Limited (SGL) conducted six fixed-wing high-resolution gravimetric surveys for Geoscience Australia and the Geological Survey of Western Australia. Over two hundred flights were flown to complete the planned 175,825 line kilometres, with five blocks acquired within 800 km to the northeast of Laverton and one block within 500 km to the west of Kununurra (Kimberley Basin block). The survey was flown with two aircraft utilising SGL’s airborne gravity system, Airborne Inertially Referenced Gravimeter (AIRGrav). </div><div> </div><div>The survey was funded by the Department of Mines, Industry Regulation and Safety (DMIRS) Western Australia, and managed by Geoscience Australia.</div><div><br></div><div>Survey Name: Warburton East, Warburton West, Great Victoria Desert, Kimberley Basin, Little Sandy Desert East and Little Sandy Desert West Gravity Surveys, 2018</div><div>State/Territory: Western Australia</div><div>Datasets Acquired: Airborne gravity, elevation</div><div>Geoscience Australia Project Numbers: P1312, P1313, P1315, P1316, P1317, P1318 (in the survey order above)</div><div> </div><div>Acquisition Start Date: 27 April 2018</div><div>Acquisition End Date: 04 October 2018</div><div>Flight line spacing: 2,500m</div><div>Flight line direction: East-West for Sandy Desert East and West, Kimberley Basin and Warburton East surveys, North-South for Warburton West and Great Victoria Desert surveys</div><div>Tie line spacing: 25,000 m</div><div>Tie line direction: Orthogonal to flight lines</div><div>Nominal terrain clearance: Smoother drape with nominal 160 m terrain clearance</div><div>Total distance flown: 175,825 km</div><div>Data projection: MGA51 or MGA52 using the GDA94 datum</div><div>Aircraft type: Fixed wing Cessna Grand Caravan 208B</div><div>Data Acquisition: Sander Geophysics Limited</div><div>Project Management: Geoscience Australia</div><div>Quality Control: Geoscience Australia</div><div>Dataset Ownership: Western Australia Department of Mines, Industry Regulation and Safety, and Geoscience Australia</div><div><br></div><div>Data package for the 6 sub surveys:</div><div>- Contractors Report (combined)</div><div>- Line data in XYZ and ASEG GDF format</div><div>- Read me files of datasets</div><div>- Quality control reports for each survey area</div><div>- Gridded data with details below</div><div><br></div><div>GRIDS</div><div>==============</div><div>Datum:      GDA94</div><div>Projection:   MGA 51 or MGA 52 </div><div>Grid cell size: 500m</div><div>Formats:     Grid Exchange File (.gxf) and ERMapper (.ers)</div><div><br></div><div>Name         Units       Description</div><div>--------------     ---------      ----------------------------------------------</div><div>GRVFAL5000M      µms-2      Free air gravity, 5000 m (#) full wavelength spatial filter</div><div>FVDFAL5000M      Eotvos      First vertical derivative of free air gravity, 5000 m (#) full wavelength spatial filter</div><div>GRVBGL5000M_267    µms-2      Full Bouguer gravity, 5000 m (#) full wavelength spatial filter, 2670 kg/m3 density</div><div>FVDBGL5000M_267    Eotvos      First vertical derivative of full Bouguer gravity, 5000 m (#) full wavelength spatial filter, 2670 kg/m3 density</div><div>GRVISO5000M_267    µms-2      Isostatic residual gravity, 5000 m (#) full wavelength spatial filter, 2670 kg/m3 density</div><div>FVDISO5000M_267    Eotvos      First vertical derivative of isostatic residual gravity, 5000 m (#) full wavelength spatial filter, 2670 kg/m3 density</div><div>TERRAIN        m        Laser terrain (above GDA94 Ellipsoid)</div><div>BAREEARTH       m        Bare earth terrain (above GDA94 Ellipsoid)</div><div>----------------------------------------------------------------------------------------------------------</div><div> </div><div># 5000 m wavelength filter employed for all projects other than Little Sandy Desert West where a 2500 m wavelength filter was employed instead. Read contractors report for more details</div><div><br></div><div>----------------------------------------------------------------------------------------------------------</div><div><br></div><div><br></div><div><br></div><div><br></div><div> </div><div><br></div>

P1291B Tanami-King Leopold WA Airborne Gravity Survey 2017

<div>The Tanami–King Leopold survey was part of a collaborative research project between Geoscience Australia (GA) and the Geological Survey of Western Australia. Gravity data was collected at 5 km wavelength resolution with the purpose to help characterise key undercover geological elements of the region. The project area extends approximately from the Balgo Hills region near the border with the Northern Territory through to Derby in the west. The survey was conducted by Thomson Aviation Pty Ltd with a GT-2A gravimeter and managed by GA. A total of 25,869.36 line km of data were acquired over an area of 58,040 km².</div><div> </div><div><strong>Survey details</strong></div><div>Survey Name: Tanami-King Leopold WA airborne gravity survey 2017</div><div>State/Territory: Western Australia (WA)</div><div>Datasets Acquired: Airborne gravity</div><div> Geoscience Australia Project Number: P1291B</div><div> Acquisition Start Date: June 16, 2017</div><div> Acquisition End Date: August 12, 2017</div><div> Flight line spacing: 2.5 km</div><div> Flight line direction: 180deg / NS</div><div> Tie line spacing: 25km</div><div> Tie line direction: 270 deg / EW</div><div>Total line kilometers: 25,869.36</div><div> Nominal terrain clearance (above ground level): 477 m</div><div> Aircraft type: GippsAero GA-8 Airvan</div><div>Data Acquisition: Thomson Aviation </div><div> Project Management: Geoscience Australia</div><div> Quality Control: CMG Operations Pty Ltd and Geoscience Australia</div><div> Dataset Ownership: GSWA and Geoscience Australia</div><div> </div><div><strong>Files included in this download</strong></div><div>This data package release contains the final survey deliverables received from the contractor Thomson Aviation. Quality control and data processing services were provided by CMG Operations Pty Ltd and peer reviewed by Dr Jack McCubbine (Geoscience Australia).</div><div> </div><div>The horizontal datum and projection for all the data are GDA94 and MGA52, respectively.</div><div> </div><div><strong>1.</strong> <strong><em>Point-located Data / line data</em></strong></div><div>ASCII column XYZ and ASEG-GDF2 format with accompanying description and definition files.</div><div><br></div><div> <strong><em>2.Grids</em></strong> </div><div> </div><div>Datum:      GDA94</div><div>Projection:  MGA52</div><div>Grid cell size: 500m</div><div>Format: ERMapper (.ers)</div><div>Gravity datum: AAGD07. </div><div> </div><div>There are 24 gridded data supplied in ERMapper (.ers) format. The grid cell size is 500 metres. The gravity datum used is AAGD07. </div><div><br></div><div> <strong>3. Reports</strong> </div><div> • Final survey logistic report delivered to Geoscience Australia by the survey contractor: <em>TNC-TANAMI-FINAL-REPORT.pdf</em></div><div>• QC report from the peer reviewer of the data package: <em>Tanami King Leopold QC report.pdf</em></div><div> </div><div>The data from this Tanami King Leopold survey can also be downloaded from the Geological Survey of Western Australia’s MAGIX platform at https://magix.dmirs.wa.gov.au and GeoVIEW.WA web mapping application at https://geoview.dmp.wa.gov.au/GeoView under reference number 71200. </div><div><br></div>