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The NTGS Brunette Downs Gravity Survey, 2021, is a survey funded by the Northern Territory (NTGS) and managed by Geoscience Australia (GA). Atlas Geophysics was commissioned by GA to conduct the survey. The survey was conducted as part of NTGS’s Resourcing the Territory initiative and was given a survey ID of 202180. The survey is a roughly east-west rectangular shape covering approximately 57,000 square kilometres. It consists of a 2km by 2km grid across the entire survey area, in some areas omitting existing 4km by 4km gravity stations, and several areas of infill at 1km by 1km and 500m by 500m. The survey covers approximately 57,000 square kilometres, to the north and east of Tennant Creek to the border with Queensland. This survey acts as infill for other surveys: 200980 “Barkly”, 201580 “Northern Wiso Basin” and 201701 “Southern Nicholson”, which were acquired in regional 4km x 4km grid configurations. The data package consist of 17,312 gravity stations as a point located dataset, a series of grids in GDA94 Geodetic at 500m equivalent cells size, and the Operations Report.

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A collection of NetCDF files containing ground gravity point data that is organised by survey. The files are derived from the Australian National Gravity Database (ANGD), and formatted in such a way as to provide highly efficient, analysis ready data. The data covers the onshore Australian continent, and dates from 1947 until June 2019. Surveys acquired after June 2019 are not included in this collection, but are available via the Data & Publication search or the Geophysical Archiving and Data Delivery System (GADDS).

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Presentation slides and speaking notes are provided for a presentation that was given online on Wednesday 7th October 2020, 11:00 to 12:00 AEDT time (UTC +11). The presentation coincided with the release of two products; (1) a new web page for the Australian Fundamental Gravity Network (AFGN), and (2) the 2019 Australian National Gravity Grids (eCat Record 133023). Not mentioned as a separate item, the presentation drew heavily on material in the Explanatory Notes for the gravity grids (eCat Record 144233) which was also released on this day. The presentation was pitched at the level of a general audience. It commenced with an introduction to gravity, and how it changes from one place to another in step with different geological units. The subjects of 2-dimensional digital grids and how coloured images are derived from them were then covered as a prelude to later material. The speakers then described first of the two main topics - the Australian Fundamental Gravity Network (AFGN) and its importance when producing the 2019 Australian National Gravity Grids. The AFGN is a series of gravity benchmarks that allow gravity surveys to be linked to the Australian Absolute Gravity Datum 2007 (AAGD07). This makes it possible for the many separate gravity data sets that have been acquired in Australia to be combined into a seamless whole. Gravity data from 1308 ground surveys and 14 blocks of airborne gravity and airborne gravity gradiometry have been combined with offshore gravity data from satellite altimetry to form the 2019 Australian National Gravity Grids. This marks the first time that airborne data have been incorporated into the national gravity grids. It is also the first time that the offshore data have been fully processed alongside the onshore data. Grids of three types of gravity anomalies were produced; Free Air Anomaly (FAA), Complete Bouguer Anomaly (CBA), and De-trended Global Isostatic Residual (DGIR). During the presentation, various comparisons were made illustrating the improvements made with the 2019 grids in comparison with the previous 2016 grids and the benefits of incorporating airborne data into the grids. The gravity grids were produced to assist those involved in geological mapping and exploration, and it is hoped that the new grids will inspire users to revisit their geological interpretations and to aid explorers to identify new opportunities and to more efficiently focus their efforts on prospective ground. The presentation was recorded, and the recording of the presentation is available on demand on the Geoscience Australia YouTube Channel at https://youtu.be/3CyqrqBM0xg. Introductions were made by Marina Costelloe. The event was controlled by Chris Nelson, and the recording was edited by Douglas Warouw. Note that there are some minor differences between the presentation material given here and the presentation seen in the video recording. These changes were made in the interest of clarity and include the removal of “animation” effects and the provision of some additional text. Speaker Biography for Richard Lane; Richard joined Geoscience Australia in 2001 after a career as a mineral and petroleum geophysicist with CRA Exploration / Rio Tinto and as the Program Leader responsible for the development of the TEMPEST AEM system in CRC AMET. As a Senior Geophysicist in the Geophysical Acquisition and Processing Section, he has been evaluating the role of airborne gravity and airborne gravity gradiometry on a national scale. He is an ASEG Gold Medal recipient, a Society of Exploration Geophysicists Honorary Lecturer, and a Distinguished Geoscience Australia Lecturer. Speaker Biography for Phillip Wynne; Phillip has been with GA for over twenty years. In that time, he has been involved in all aspects of regional gravity surveys. He currently oversees gravity surveys conducted by GA and Australian States and Territories and manages the Australian Fundamental Gravity Network.