b'Bouguer corrections FeatureConclusionsEquations covering the application of both infinite horizontal slab and spherical cap Bouguer corrections have been presented\x08 These equations cover the complete range of scenarios for onshore and offshore locations, for observations made on and above the surface, and for both geoid and ellipsoid vertical datums\x08 This will enable people to choose to use either of these geometries for Bouguer corrections\x08 Recognising the increasing importance of airborne gravity methods, comparisons of the correction for Figure 7.Differences between spherical cap and infinite horizontal slabthe two geometries were provided for observations made Bouguer corrections for offshore locations for terrain clearances of 0 to 5000 m,at different surface clearances\x08 Images of the difference ocean depths of 0 to 5000 m, and an ellipsoid-geoid separation of 0 m. between the corrections for the two geometries were given when the ground surface has an elevation of approximatelyfor a range of ground clearances as a function of onshore 4150 m above the vertical datum\x08 For elevations greater thanground surface elevation and offshore water depth\x08 These this, the difference is negative indicating that the correction forimages highlighted two important characteristics of the two an infinite horizontal slab geometry is larger than the correctioncorrections, namely that (1) spherical cap Bouguer corrections for a spherical cap geometry\x08 It should be noted that thedecrease in amplitude with increasing ground clearance, and values quoted above are identical to those shown for the same(2) the difference between the two corrections changes sign scenario in figure 2 of LaFehr (1991)\x08 as a function of onshore ground elevation and offshore water depth\x08The behaviour described above can be summarised for any terrain clearance as follows: a zero difference for zero ground elevation, a positive difference for small to moderate elevations,Referencesand a negative difference at large values of surface elevation\x08Argast, Dominik, M\x08 Bacchin and R\x08 Tracey, 2009 An extension The final aspect of the image in Figure 6 to be examined is theof the closed-form solution for the gravity curvature (Bullard change parallel to the y-axis representing the differences for anyB) correction in the marine and airborne cases: ASEG single value of the ground elevation\x08 With the trivial exceptionExtended Abstracts 2009, 1-6, http://dx\x08doi\x08org/10\x081071/of the case of zero ground elevation, the amplitude of theASEG2009ab129, DOI 10\x081071/ASEG2009ab129\x08difference decreases with increasing terrain clearance\x08 Since theBullard, E\x08 C\x08, 1936\x08 Gravity measurements in East Africa: Phil. corrections for an infinite horizontal slab geometry do not varyTrans. Roy. Soc. London, 235, 757, 486-497\x08as the height of the observations above the surface increases,Hinze, W\x08 J\x08, C\x08 Aiken, J\x08 Brozena, B\x08 Coakley, D\x08 Dater, G\x08 this indicates that the corrections for an infinite horizontalFlanagan, R\x08 Forsberg, T\x08 Hildenbrand, R\x08 Kellar, J\x08 Kellogg, R\x08 slab geometry decrease in amplitude as the height of theKucks, X\x08 Li, A\x08 Mainville, R\x08 Morin, M\x08 Pilkington, D\x08 Plouff, observations above the surface increases\x08 D\x08 Ravat, D\x08 Roman, U\x08 F\x08 Jamie, M\x08 Veronneau, M\x08 Webring, Turning our attention to offshore locations, the differencesand D\x08 Winester, 2005, New standards for reducing gravity between the corrections for spherical cap and infinite horizontaldata: the North American gravity database: Geophysics, 70, slab geometries for a range of ocean depths and heightsJ25-J32\x08above the ocean surface are presented in figure 7\x08 It should beLaFehr, T\x08 R\x08, 1991\x08 An exact solution for the gravity curvature noted that the calculations were made for an ellipsoid-geoid(Bullard B) correction: Geophysics, 56, 1179-1184\x08separation of 0 m, or in other words, for the case when theMoritz, H\x08, 2000, Geodetic Reference System 1980: J. Geod., 74 vertical datum coincides with the ocean surface\x08 (1), 128-162, doi: 10\x081007/S001900050278\x08Tiesinga, E, P\x08 J\x08 Mohr, D\x08 B\x08 Newell, and B\x08 N\x08 Taylor, 2019\x08 The The trends of the changes as demonstrated by the form of the2018 CODATA Recommended Values of the Fundamental contour lines are the same as those in Figure 6, but the polarityPhysical Constants (Web Version 8\x080): Database developed by is the reverse\x08 Examining the changes parallel to the x-axisJ\x08 Baker, M\x08 Douma, and S\x08 Kotochigova, Available at http://for any given ocean clearance, the difference is zero for zerophysics\x08nist\x08gov/constants, National Institute of Standards water depth, negative at small to moderate water depths, andand Technology, Gaithersburg, MD 20899\x08positive over the deep ocean\x08 Looking at the changes parallelTracey, R\x08, M\x08 Bacchin, and P\x08 Wynne, 2007\x08 AAGD07: A new to the y-axis for any given water depth, the magnitude of theabsolute gravity datum for Australian gravity and new differences decreases with increasing ocean surface clearance\x08standards for the Australian National Gravity Database: As previously explained, this is a reflection of the decreasingExpanded Abstract, 19th ASEG/PESA International Geophysical amplitude of corrections for a spherical cap geometry as theConference & Exhibition, Perth, Western Australia, 1-3, http://terrain clearance increases\x08 library\x08seg\x08org/doi/abs/10\x081071/ASEG2007ab149APRIL 2021 PREVIEW 46'