International Gravity Formulae
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_{Adapted by DonEMitchell 09:57, 1 October 2012 (MDT) from http://geophysics.ou.edu/solid_earth/notes/potential/igf.htm}
International Gravity Formula(e)
 accounts for variation of gravity with distance from equator
 2 effects:
 rotation of Earth (centripetal acceleration):
 ,
where

 oblateness of Earth (caused by rotation)
Geodetic Reference System Formulae refer to theoretical estimates of the Earth's shape
 From these GRS formulae we obtain International Gravity Formulae (IGF)
 Several different formulae have been adopted over the years
 In these equations, is geographic latitude and is commonly referred to as theoretical gravity or normal gravity
 First internationally accepted IGF was 1930:
 γ = 9.78 (1 + 0.0052884 sin^{2} λ − 0.0000059 sin^{2} 2λ)
 This was found to be in error by about 13 mgals; with advent of satellite technology, much improved values were obtained.
 The Geodetic Reference System 1967 provided the 1967 IGF:
 γ = 9.78 (1 + 0.0053 sin^{2} λ − 0.0000058 sin^{2} 2λ)
 Most recently IAG developed Geodetic Reference System 1980, leading to World Geodetic System 1984 (WGS84); in closed form it is:
 γ = 9.7803267714 (1 + 0.00193185138639 sin^{2} λ / √ (1  0.00669437999013 sin^{2} λ) )
 The IGF value is subtracted from observed (absolute) gravity data. This corrects for the variation of gravity with latitude
See Also
 International Gravity Formula "Calculator" (XLS spreadsheet)
 International Gravity Formula