Gravity field of the earth - Physical Geodesy - page 83

Table 2.2. GRS 1980 derived constants

Parameter and value Description

Geometrical constants
b = 6 356 752 . 3141 m semiminor axis of the ellipsoid

E = 521 854 . 0097 m linear eccentricity

c = 6 399 593 . 6259 m polar radius of curvature

e 2 =0 . 006 694 380 022 90 first eccentricity squared

e 2 =0 . 006 739 496 775 48 second eccentricity squared

f =0 . 003 352 810 681 18 flattening

1 /f = 298 . 257 222 101 reciprocal flattening

Physical constants
U 0 = 62 636 860 . 850 m 2 s − 2 normal potential at the ellipsoid

J 4 = − 0 . 000 002 370 912 22 spherical-harmonic coecient

J 6 =0 . 000 000 006 083 47 spherical-harmonic coecient

J 8 = − 0 . 000 000 000 014 27 spherical-harmonic coecient

m = ω 2 a 2 b/ ( GM ) m

=0 . 003 449 786 003 08

=9 . 780 326 7715 m s − 2 γ a normal gravity at the equator

=9 . 832 186 3685 m s − 2

γ b

normal gravity at the pole

The WGS 84 is a right-handed, earth-fixed orthogonal coordinate system.
The origin and axes are defined in the following way:

• Origin: earth's center of mass.

• Z -axis: the direction of the IERS Reference Pole (IRP); this direction

corresponds to the direction of the BIH Conventional Terrestrial Pole
(CTP) (epoch 1984.0). In other terms, the Z -axis is, by convention,
identical to the mean position of the earth's rotational axis.

• X -axis: intersection of the IERS Reference Meridian (IRM) and the

plane passing through the origin and normal to the Z -axis; the IRM is
coincident with the BIH Zero Meridian (epoch 1984.0); in other terms,
the X -axis is associated with the mean Greenwich meridian.

• Y -axis: this axis completes a right-handed, earth-centered-earth-fixed

(ECEF) orthogonal coordinate system.

The WGS 84 origin also serves as the geometric center of the WGS 84 ellip-
soid and the Z -axis serves as the rotational axis of this ellipsoid of revolution.
This completes the definition of the WGS 84 as given in National Imagery
and Mapping Agency (2000). Note that the definition of the WGS 84 CTRS
has not changed in any fundamental way.