Continuously Operating Reference Stations
GPS positions are based on a series of calculations and averages.
Applying statistical principles, the more data that is used and
the more calculations that are made, the more confidence we can
have in the results. Continuously Operating Reference Stations
(CORS) are permanently located GPS receivers that operate on a
continual basis. They are continuously collecting satellite data
and using it to recalculate their positions. CORS generally use
higher quality GPS antennas, which allow for even more precise
calculations.
CORS and Post Processed Surveys
CORS can be implemented in both post processed and RTK surveying.
In post processed surveying, data from CORS can be used to generate
the corrections needed to accurately locate an otherwise unreferenced
position using the Online Positioning User Service (OPUS). The
GPS data a surveyor collected, along with some information about
the receiver used and how it was setup, can be sent over the internet
to the OPUS server, and a corrected location will be emailed to
you with in a few minute, depending on user load.
OPUS is run by the National Geodetic Survey (NGS). The data used
is collect for CORS which are members of one of two networks,
the National CORS network or the Cooperative CORS network. To
be part of these networks the satellite data collected by the
CORS must be made available to the general public free of charge,
as well as meet other operational and precision standards set
up by the NGS for the respective networks. The NGS operates websites
for each network which offer detailed information about the networks,
as well as links to the member CORS individual sites.
CORS and RTK Surveys
Many CORS are equipped with one or more communication links.
CORS that broadcast over UHF radio are making the corrections
available to the general public. Anyone with the right UHF radio
link on their receiver and within signal range should be able
to use the corrections for RTK surveys. CORS stations that are
using other methods for broadcasting the corrections may or may
not be available to the general public. In order to access the
corrections a user might need to be added to a user list or subscribe
to a pay service. The advantage of being able to access a CORS
for RTK surveys is that is eliminates the need to set up a reference
receiver for each survey.
Accessing a CORS
The first step in being able to use a CORS for RTK surveying
is locating one in the desired area. The NGS-CORS website has
a map of the currently networked CORS. Clicking on the desired
area of the map with bring up an enlarged view. Clicking on a
specific CORS bring up further enlarged view, as well as specific
information about the selected CORS, including information on
the organization that is operating the station. Information for
the majority of the stations also includes a link to the stations
website. Visiting the station’s website will usually produce
the name of a contact person for the CORS. The contact person
should be able to provide more information about the possibility
of accessing the CORS for RTK surveying.
Top of Page
Global Positioning Systems : Next >>
Other CORS Applications
