GEODETIC REFERENCE SYSTEMS - GPS Satellite Surveying - page 15

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Historically speaking, the International Latitude Service (ILS) was created in
1895, shortly after polar motion had been verified observationally. It was the first
international group using globally distributed stations to monitor the reference frame.
This group evolved into the International Polar Motion Service (IPMS) in 1962. The
IERS was established in 1988 as a single international authority that henceforth uses
modern geodetic space techniques to establish and maintain the reference frames.
GPS increasingly contributes to the definition and maintenance of the terrestrial ref-
erence frame, largely due to the excellent cooperation of international research groups
and agencies with the IGS. The IGS began routine operation in 1994, providing GPS
orbits, tracking data, and offering other data products in support of geodetic and geo-
physical research.

2. 1.2 Tectonic Plate Motion

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The tectonic plate rotations can be approximated by spherical geophysical models
such as NNR-NUVELL1A (DeMets et al., 1994). This model is an improved version
of the original NUVEL-1 (Argus and Gordon, 1991). Table 2.1 lists the Cartesian
angular velocity components for each of the thirteen major plates. At the edges of
some of these plates, the motions can be as much as 5 cm per year. Denoting the
vector of rotation velocities by

Lin
—
* 1 ——
No
PgE

Ω z ] T and specifying the matrix R as

Ω = [ Ω x Ω y

0 −Ω z Ω y

Ω ≡

R ( ) Ω z 0 −Ω x (2.1)

−Ω Ω 0

y x

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TA BLE 2.1 The NNR-NUVEL1A Kinematic Plate Model

Ω

Plate Name Ω x (mas/y) Ω y (mas/y) Ω z (mas/y) (mas/y)

Africa 0.1837 − 0.6392 0.8090 1.047283

An tarctica − 0.1693 − 0.3508 0.7644 0.857922

Arabia 1.3789 − 0.1075 1.3943 1.963923

Australia 1.6169 1.0569 1.2957 2.325992

Caribbean − 0.0367 − 0.6982 0.3261 0.771473

Cocos − 2.1503 − 4.4563 2.2534 5.436930

Eurasia − 0.2023 − 0.4940 0.6503 0.841339

India 1.3758 0.0082 1.4005 1.407265

Nazca − 0.3160 − 1.7691 1.9820 2.675424

No rth America 0.0532 − 0.7423 − 0.0316 0.744874

Pacific − 0.3115 0.9983 − 2.0564 2.307036

So uth America − 0.2141 − 0.3125 − 0.1794 0.419141

Ph ilippines 2.0812 − 1.4768 − 1.9946 3.238944

Sources: McCarthy, 1996, p. 14, and Soler and Marshall (2002).
Note: The units were changed to milliarc seconds per year for easier visualization.