Musgrave Province Airborne Electromagnetic Conductivity Grids

Airborne electromagnetic surveys undertaken in the Musgraves Province in South Australia Queensland, Australia. The surveys were flown between the 18th August 2016 and 14th October 2016.\n\nProject\n\nAs part of the Goyder Institutes Facilitating Long-Term Outback Water Solutions Stage 3 (G-FLOWS 3) two airborne electromagnetic (AEM) surveys were flown to assist in a regional groundwater resources assessment in an otherwise data poor area.\nAEM systems\nFor the AEM data acquisition, two different AEM surveys were planned with a relatively wide line spacing of 2km, wide enough to cover a large region, whilst being close enough to provide useful information about the variability of cover, including the location and geometry of the major palaeovalley systems known to be present in the area. Both surveys were flown with a line spacing of 2km in a north-south direction. The western survey was flown with the TEMPEST high moment (HM) system, and the eastern part with the SkyTEM312FAST system. Both systems are time domain AEM systems, one being of a fixed wing configuration (TEMPEST), the other being helicopter borne (SkyTEM). \nLineage: Inversion\n\nBoth the TEMPEST and SkyTEM data was inverted using the Aarhus Workbench processing and inversion software which uses the AarhusInv full non-linear inversion algorithm. A laterally constrained inversion (LCI) methodology. Lateral constraints, which are defined for adjacent soundings allow prior information to migrate along flight lines. This can enhance the connection of layer parameters between adjacent soundings. \n\nThe inversion of the SkyTEM data solved for the Z-component and the transmitter height, whereas the TEMPEST inversion solved for both the Z and the X component data along with the transmitter height and the position and pitch of the receiver bird.\n\nInversion model \n\nA smooth layer model was used for the inversion of these datasets. This type of model consists of a number of layers with fixed thicknesses, often increasing with depth. The amount the conductivity can vary from one layer to the next is defined by vertical constraints. A 30 layer model was used with the first thickness chosen to be 3m and logarithmically increasing layer thicknesses down to 300m, which was the depth of the last layer boundary. \n\nInterval conductivities\n\nConductivity-depth intervals in 10m intervals from the surface to 200m depth, were generated from the inversion results of the two AEM datasets. The intervals were gridded using kriging with a cell size of 400m. The two datasets where then merged together to form “seamless” grids.\n\nDepth of investigation\n\nThe depth of investigation (DOI) provides a depth to which the model is the most reliable, and model information below the DOI should be used with caution. The grids are blanked by the DOI.\n