Westerhoff, R.S.; Herpe, M.; Rawlinson, Z.J.; Sahoo, T.R.; Kass, A. 2024 Hydrogeological mapping of the Aupōuri Peninsula, Northland: SkyTEM processing and resistivity models. Aqua Intel Aotearoa report 2024/01; (GNS Science consultancy report 2024/08). 117 p. https://doi.org/10.21420/ZEE1-VN08
Abstract
This report has been developed by Aqua Intel Aotearoa (a collaboration between the Regional Economic Development & Investment Unit [Kānoa] and GNS Science [GNS]) and Northland Regional Council (NRC) as part of the third phase of the investigations into water storage and aquifer mapping in Northland. The report describes the processing of airborne electromagnetic (AEM) geophysical surveying for aquifer characterisation in the Aupōuri Peninsula, Northland, utilising the SkyTEM AEM method. In October/November 2022, 6471 km of AEM data were collected over the Aupōuri Peninsula by SkyTEM Australia Pty Ltd and SkyTEM Denmark. This report details the steps taken to develop resistivity models for the survey area from these SkyTEM datasets, as well as the resultant resistivity models. Both automatic and manual data processing were carried out by GNS to remove electromagnetic noise from the SkyTEM low-moment and high-moment data. Part of the work was sub-contracted out to Aarhus University to provide quality control of the GNS processing. In addition, both parties checked the quality of one another’s data processing. Post-processing was undertaken by GNS to check for any remaining data artefacts, which were subsequently removed. Spatially constrained inversions were performed, creating both smooth and sharp resistivity models of the study area. The resistivity models provide a detailed three-dimensional resistivity picture of the subsurface. The resistivity models have a layer thickness of 2 m in the near-surface, with the layer thickness increasing to approximately 100 m at depths of 700 m. The standard Depth Of Investigation (DOI), a measure of confidence in the geophysical measurement at each point, varies from a worst case of 14 m (where only low moment data has been kept due to noise) to a best case of 800 m where all data are present and the inversion result is good. Over the entire survey, the mean DOI is 354 m (auths)
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