Introduction - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 18

3. To measure the shape of the Earth and the fine structure of the Earth's external
gravity field and its time-varying changes, and to interpret the observational
results from a geophysical point of view.

These assignments will be accomplished along with development of relevant
geosciences with the support of modern science and technology. Geodesy will be
one of the frontier subjects in promoting the development of the geosciences.

Space Geodesy Will Dominate Future Developments in the Discipline

The dominant position of space geodesy in the future development of geodesy has
already been determined by its wide application prospects and enormous potential.
In terms of conventional mapping and general engineering control, GPS positioning
techniques have basically replaced terrestrial measurement techniques using
devices like theodolites and rangefinders. The former demonstrates superiority to
the latter in accuracy, fieldwork efficiency, saving of workforce, and financial
resources. In terms of the scientific objective of geodesy, the monitoring and
research of various kinds of geodynamic and geophysical phenomena and processes
will be the major assignments. These require geodetic techniques to realize this
scientific objective on both the space and time scales; namely, to reach a sufficiently
high spatial and temporal sampling rate. On the space scale, the objective is the
ability to position on a regional and global scale more accurately and to determine
the global gravity field with higher accuracy and resolution. On the time scale, the
objective is the ability to monitor from crustal deformation by sudden earthquakes
to long-term slow movements of plates; and, in populated seismic zones with
intense tectonic movements, the ability to monitor successively and automatically.
The monitoring accuracy for displacement is required to reach 10 8 to 10 9

(equivalent to 1 mm); the measurement of gravity anomaly is required to reach

an accuracy of 1-3 mGal (1 mGal

10 5 m/s 2 ) with a resolution of less than
30 km. Concerning the current situation of science and technology, these require-
ments are only practicable with the vigorous development of space geodesy,
primarily satellite geodesy.
The space geodetic techniques currently applied or developed mainly comprise
the following: satellite positioning systems such as GPS, SLR, satellite altimetry,
radio source VLBI,

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satellite gradiometry, and satellite-satellite tracking

measurement.

Satellite Navigation and Positioning Techniques Have Expanded
the Application Area of Geodesy

GPS techniques can provide static and dynamic objects with reasonably priced,
highly efficient, continuous, and precise positioning and illustration of the state of
motion. As an extensively applied technique, GPS has greatly extended the