Geoscience Reference
In-Depth Information
According to the spatial-temporal attributes of the Earth that are being studied,
geodesy can be classified into geometric geodesy, physical geodesy, dynamic
geodesy, and integrated geodesy. Geometric geodesy adopts geometric methods
to study the shape and size of the Earth. It projects the terrestrial geodetic control
network onto the regular reference ellipsoid as the basis for calculating the geo-
metric positions of surface points. Physical geodesy is concerned with the external
gravity field of the Earth globally or regionally. It establishes the theory of the
Earth's shape by physical methods and deals with the geoidal undulation relative to
the Earth ellipsoid using measured data of gravity. Dynamic geodesy studies the
regional and global movement of the Earth and makes physical interpretations by
accurately measuring the time-varying positions of surface points and the gravity
field of the Earth. Integrated geodesy combines geometric and physical space and
deals with all geometric and physical observed quantities of geodesy in a uniform
mathematical model within the spatial-temporal reference system.
According to the technical means of carrying out the fundamental tasks, geodesy
can be divided into terrestrial geodesy (conventional geodesy, i.e., astro-geodesy),
space geodesy (satellite geodesy), and inertial geodesy. Terrestrial geodesy uses
optoelectronic instruments to carry out short-distance (usually shorter than 50 km)
terrestrial geometric survey (triangulateration, leveling, and astronomic surveying)
and gravity measurement to determine the horizontal positions and heights of
surface points and calculate the local gravity field parameters indirectly. By
observing extraterrestrial objects (artificial Earth satellites, quasar radio sources,
etc.), space geodesy realizes the positioning of surface points, including the relative
positioning and the absolute positioning, which is relative to the center of the Earth.
It uses the satellite gravity technique to obtain information on the global gravity
field. Inertial geodesy applies the principle of inertia of a moving object in mechan-
ics to carry out the relative positioning of surface points and measure the gravity
field parameters.
A modern geodetic technology system centered on space geodesy has already
been formed that can provide more accurate and abundant geodetic data than the
classical system. It has not only expanded the application area of geodesy in socio-
economic development but also improved its status as a basic discipline in
geoscience.
1.2 Applications of Geodesy
1.2.1 Applications of Geodesy in Topographic Mapping,
Engineering Construction, and Transportation
The important functions of geodetic control network in topographic mapping are
primarily:
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