b'Geophysics in the surveysNewsFigure 2.Top: The point located 100 second 1D and 5000 m 2D filtered free air gravity anomaly data (scale in mGal)left, and the AGQG2017 implied gravity anomaly upward continued/interpolated to the location of the point located data (scale in mGal) - right. Bottom: The difference between the point located 100 second 1D and 2750 m 2D filtered free air gravity anomaly data and the AGQG2017 implied gravity anomaly upward continued/interpolated to the location of the point located data. (scale in mGal)left, and the same but with existing terrestrial gravity data coverage overlayed as black marks - right.applied for gravimetry is summarised bywell above the topography. AGQG2017 wasconsidering that the ground data was Dr Jack McCubbine, InSAR Team Leader,calculated using an optimised combinationacquired on 11 km spacing compared to National Geodesy Section, Geoscienceof EGM2008, and terrestrial gravity data,airborne gravity acquired on 2 km line Australia, as thus: from a 2016 release of the Australianspacing (and after a 2500 m spatial filter National Gravity Database. A topographicapplied). The standard deviation of the We have compared filtered (generally to areconstruction technique is also applieddifferences is approximately 1.8 mGals.2.5 km resolution) free air airborne gravityto model short wavelength topographic anomaly data to the gravity anomalyeffects using a standard rock density ofReferenceimplied by the AGQG2017 geoid model.2670 kg/m3 (Featherstone etal., 2018). The This check verifies that the airborne derivedaccuracy of the model largely is limitedFeatherstone, W.E., McCubbine, J.C., gravity data match existing (ground) databy the terrestrial gravity spacing and theBrown, N.J., Claessens, S.J., Filmer, M.S. within the limitations of the existing dataassumed rock density to compensate forand J.F. Kirby, 2018. The first Australian coverage. The AGQG2017 geoid modelshort wavelength topographic effectsgravimetric quasigeoid model is effectively a 2 km grid of the Earthswhere the gravity data spacing is sparse. with location-specific uncertainty gravity potential and it can be transformedestimates. Journal of Geodesy 92(2): into a gravity anomaly map with someIn the example presented in Figures2a149-168. https://doi.org/10.1007/mathematical operations. Importantly,and 2b, AGQG2017 implied gravitys00190-017-1053-7the AGQG2017 implied gravity anomalyanomaly data has been upward corresponds to one that is external to allcontinued to the same height asMike Barlow gravitating massesakin to the airbornethe airborne gravity. The differenceGeoscience Australia gravimetry measurements which are madeis remarkably small, particularlyMike.Barlow@ga.gov.au15 PREVIEW APRIL 2022'