Geoscience Reference
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processing, there are differences in the datum and system between large-scale GPS
networks. This has led to great difficulties in the practical application and made it
difficult for GPS networks to work effectively as a whole.
To make full use of China's large-scale GPS networks, one must first eliminate
the incompatibility of different networks and establish a unified systematic datum
and a uniform, durable, and highly precise national GPS geodetic control network
so as to establish a unified national geocentric coordinate system, improve accuracy
of the geoid, and provide a better service for national economy, national defense
construction, and geoscience studies. Hence, a unified adjustment to all the above-
mentioned GPS networks was carried out by SMBGSH, SBSM, and CEA. After
connection and data processing, the unified GPS network was named the “National
GPS Control Network 2000” (Yang et al. 2009). The whole network has 2,609
stations, which can meet the requirements of modern measurement techniques for
geocentric coordinates and lay a solid foundation for establishing China's new
generation geocentric coordinate system (China Geodetic Coordinate System 2000)
(see Chen et al. 2007a, b).
Continuously Operating Reference System
The Continuously Operating Reference System (CORS) is a major technique for
establishing regional three-dimensional geodetic datums. Thanks to the rapid
development of satellite positioning technology, information technology, and net-
work technology, CORS networks have appeared all over the world, including
global large-scale networks and regional small-scale networks. The classical hor-
izontal datum is defined and extended by the geodetic origin and horizontal control
network. Similarly, the three-dimensional coordinate datum is defined and
extended by CORS and GPS networks.
Basic Components of CORS
As the datum of the three-dimensional control network, CORS is the product of
sophisticated new technologies, such as satellite positioning technology, computer
network technology, digital communication technology, and so on. It is composed
of a datum station network, data processing center, data transmission system,
positioning and navigation data broadcast system, and user application system.
Every datum station is connected to the monitoring and analysis center through the
data transmission system, constituting a special purpose network.
The datum station network, made up of datum stations distributed evenly within
a certain scope, is used to collect observational data from GPS satellites, transmit
them to the data processing center, and provide services for monitoring the system
integrity.
The data processing center, as the control center of the system, is used to receive
data from every datum station and form multiple datum stations' differential
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