Geoscience Reference
In-Depth Information
(a)
Figure 5.3.
(a) The geoid height anomaly: the height of
the geoid above (positive) or below (negative) the
spheroid in metres. Colour version Plate 6. (After Bowin,
C., Mass anomaly structure of the Earth,
Rev. Geophys
.,
38
, 355-87, 2000. Copyright 2000 American Geophysical
Union. Modified by permission of American Geophysical
Union.) (b) The averaged shape of the Earth, calculated
by assuming that the Earth is symmetrical about its
rotation axis (solid line), compared with a spheroid of
flattening 1/298.25 (dashed line). (From King-Hele
(1969).)
(b)
North
pole
+10
0
−
10
−
20
−
metres
30
30
−
Equator
metres
metres
−
30
−
20
−
10
metres
0
+10
South
pole
The oblate spheroid (discussed in the previous sectionprevious section)
approximates the geoid. This reference oblate spheroid, known as the
reference
spheroid
or
reference ellipsoid
,isamathematical figure whose surface is an
equipotential of the theoretical gravity field of a symmetrical spheroidal Earth
model with realistic radial variations in density, plus the centrifugal potential. The
