International Gravity Formula

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:
- This was found to be in error by about 13 mgals; with advent of satellite technology, much improved values were obtained.
- The Geodetic Reference System1967 provided the 1967 IGF:
- Most recently IAG developed Geodetic Reference System 1980, leading to World Geodetic System 1984 (WGS84); in closed form it is:
The IGF value is subtracted from observed (absolute) gravity data. This corrects for the variation of gravity with latitude