# Dictionary:Latitude correction

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1. A correction to gravity data because of (a) variation in centrifugal force resulting from the Earth’s rotation, as the distance to the Earth’s axis varies with latitude ${\displaystyle \phi }$, and (b) variation of the Earth’s radius because of polar flattening. The Geodetic Reference System 1967 (GRS67) gives

${\displaystyle {\textrm {g}}=978031.846(1+0.005278895~{\sin }^{2}\phi +0.000023462~{\sin }^{4}\phi )~{\textrm {mGal}}.}$

The latitude correction amounts to

${\displaystyle 1.3049~{\sin }^{2}\phi ~{\textrm {mGal/mile}}=0.8108~{\sin }^{2}\phi ~{\textrm {mGal/km}}.}$

2. A gyrocompass correction for the rotation of the horizontal north vector as a function of latitude. (The horizontal north vector is tangent to the Earth and hence the rotation is the result of Earth curvature.)

3. The north-south correction to magnetic data to remove the Earth’s normal field.