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

grs67.gif

International Gravity Formula(e)

  • accounts for variation of gravity with distance from equator
  • 2 effects:
    • rotation of Earth (centripetal acceleration):
lp44.gif,

where

lp45.gif
  • oblateness of Earth (caused by rotation)
fig2.gif


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 sin2 λ − 0.0000059 sin2 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 sin2 λ − 0.0000058 sin2 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 sin2 λ / √ (1 - 0.00669437999013 sin2 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