B.3  THE DEFINING PARAMETERS AND ASSOCIATED CONSTANTS

In geodetic considerations, three different surfaces or earth figures are normally

involved and used.  In addition to the earth s actual physical surface, the other two

include a geometric (or mathematical) reference surface, the ellipsoid, and an equi  

potential surface, the geoid.  

In determining the WGS 84 Ellipsoid and its associated defining parameters, the WGS 84

Development Committee decided to adopt the International Union of Geodesy and

Geophysics (IUGG) defined Geodetic Reference System (GRS) 1980 as its reference.

The WGS 84 Ellipsoid, as an integral component of the system for the earth s

geometric figure and theoretical gravity definition, is a geocentric, equipotential,

ellipsoid of revolution; Table B 1 lists the four defining parameters adopted from the

GRS 80

2

, except for one minor exception.  The WGS 84 defines C

2

 instead of J

2

 of

GRS 80.

Table B 1.  WGS 84 Ellipsoid Four Defining Parameters

Parameters

Notation

Magnitude

Accuracy (1s)

Semimajor Axis

a

6378137 m

 2 m

Normalized Second Degree Zonal

C

2,0

 484.16685 x 10

 6

 1.30 x 10

 9

  Harmonic Coefficient of the

  Gravitational Potential

Angular Velocity of the Earth

w

7292115 x 10

 11

 rad/s

 0.1500 x 10

 11

 rad/s

The Earth s Gravitational Constant

GM

39860065 x 10

8

 m

3

/s

2

 0.6 x 10

8

 m

3

/s

2

  (Mass of Earth s  Atmosphere

  Included)

Parameter Values for Special Applications

The Earth s Gravitational

CM'

3986001.5 x 10

8

 m

3

/s

2

 0.6 x 10

8

 m

3

/s

2

  Constant (Mass of Earth s

  Atmosphere Not Included)

Angular Velocity of the Earth

w

*

(7292115.8553 x 10

 11

 0.1500 x 10

 11

 rad/s

  (In a Processing Reference Frame)

+ 4.3 x 10

 15

 T

U

) rad/s

T

U

 = Julian Centuries From Epoch J2000.0

Other associated constants adopted and used in WGS 84 are given in Table B 2.

B 3