b'Geophysics in the SurveysNewsNorthern Territory Geological Survey: New gravity grid of theNorthern TerritoryThe Northern Territory Geological SurveyEast Tennant and South West McArthur Matthew Hutchens (NTGS) has released a new Territory-wideBarkly surveys are also available forSenior Geophysicist, NTGS gravity grid (Figure 1). The new griddownload and can be viewed on email@example.com the recently released EastGeophysical Image Web Server.Tennant and South West McArthurBarkly gravity surveys, both funded under Geoscience Australias Exploring for the Future programme. NTGS also contributed funding to extend the South West McArthurBarkly gravity survey under the Northern Territory Governments Resourcing the Territory 201822 initiative. These surveys infilled existing 4 km-spaced data to 2 km. Figure 2 illustrates the finer scale of features visible in the new grid over the East Tennant area.DataData for the new grid was sourced from government and industry surveys. The grid was generated using only ground gravity observations as opposed to previous versions that included the West Arnhem airborne gravity survey. A total of 218 155 gravity observations within the Territory were incorporated into the new grid. This represents an increase of 20 718 ground observations compared to the previous (2018) Territory wide grid, including 5855 observations from the new East Tennant and South West McArthurBarkly surveys.Gridding methodologyGridding was performed using Generic Mapping Tools (GMT) software, which grids data using splines under tension (Smith and Wessel 1990). The entire Northern Territory was gridded at a constant cell size of 250 m. A tension value of zero was used to generate a smooth surface that closely matches the gravity observation values.Available productsA suite of grids including Bouguer Anomaly, 1st order residual of Bouguer Anomaly, and 1st vertical derivative of Bouguer Anomaly, as well as a printable map are available through the NTGS Geoscience Exploration and Mining Information System (https://geoscience.nt.gov.au/gemis). Images in ECW format are also available to view and downloadFigure 1.New Bouguer Anomaly grid of the Northern Territory. The East Tennant (ET) and South West though the NTGS Geophysical ImageMcArthurBarkly (SWMB) survey boundaries are also shown. The grid is displayed with histogram Web Server (http://geoscience.nt.gov. equalised pseudocolour mapping, sun shading from the northeast and sun highlights from the northwest. au/giws). Individual surveys includingThe projection is GDA94 geodetic.OCTOBER 2020 PREVIEW 24'