15.6: Geodetic and Geophysical Measurements and Observation of Fundamental Physical Phenomena

15.6 Geodetic and Geophysical Measurements and Observation of Fundamental Physical Phenomena

An accurate model of the shape of the Earth is a very important aspect of any terrestrial navigation system, as has already been discussed in Chapter 3. However, fluctuations in the rotational characteristics of the Earth also have an impact on the potential accuracy of terrestrial navigation systems, including those that use precision GPS data. Measurement of other changes to the behaviour of the Earth may be used to predict seismic events, such as earthquakes.

Many factors produce small fluctuations in the characteristics of the Earth's rotational parameters. The principal factors that induce these fluctuations are;

• continental drift;

• motion of the moon and its phases;

• movement of the subterranean magma in the Earth's core;

• tides;

• weather.

Chapter 13 and Appendix D considers the operation and use of the popular satellite-based navigation systems, which offer the potential for high-precision navigation for all types of vehicles and platforms. The basis of the technique is the constellation of satellites in geo-stationary orbits locked in a particular known position above the Earth. Consequently, errors in the estimated position of a navigation system's receiver will occur owing to the displacement of the constellation of satellites, resulting from the fluctuations of the Earth's rotational motion. Hence, changes in these characteristics of the motion of the Earth need to be measured and understood, so that an appropriate compensation technique can be applied.

One technique that is being investigated for the measurement and monitoring of the Earth's...