ETL 1110-1-184
01 Oct 1998
the Missouri and Ohio Rivers, and the Great Lakes Region.
Additional areas within the Midwest U.S. are still under
consideration. A map of the coverage area can be found at the
NAVCEN web site under the DGPS section.
(3) Availability and Reliability. The system was configured
to provide pseudorange corrections with a signal availability of
99.9 percent (in the designed coverage areas) assuming a healthy
and completed GPS constellation. To obtain this high
availability level, integrity monitors are located at each
broadcast site and the system is monitored 24 hours a day by
USCG. If a problem with a site is discovered, the user is
notified by a message within the information broadcast by that
site. Status for each site is also posted on the NAVCEN
Homepage. Because of the overlapping coverage of the broadcast
sites in most areas, the user should be able switch to another
broadcast site without any loss of accuracy.
(4) User Requirements and Equipment. To receive the
corrections generated by the reference station, the user needs to
have both a MSK Radiobeacon receiver with antenna and a L1 C/A
code GPS receiver with antenna. The GPS receiver must be capable
of receiving the Radio Technical Commission for Maritime Services
Special Committee 104 (RTCM SC-104) Type 9 messages and applying
these corrections to compute a "meter level" position. Some
receiver manufacturers have developed a combined MSK radiobeacon
and GPS receiver. The costs of radiobeacon receivers range from
0 to 00. For a combined radiobeacon/GPS receiver, prices
range from 00 to 00.
(5) Additional Information. Appendix A provides more
information on the USCG DGPS Radiobeacon system.
b. CORS System. The CORS Network is a group of GPS reference
stations providing pseudorange (C/A code) and carrier (L1/L2)
phase measurement data for DGPS post-processing applications.
This network is made up of USCG DGPS Radiobeacon sites, USACE
sites, National Oceanic and Atmospheric Administration (NOAA)
sites, U.S. Park Service sites, other Federal, State, and local
government sites and university sites. Future Federal Aviation
Administration (FAA) sites will also be included in the CORS
network. NGS maintains the CORS system. Data collected at a CORS
site is available for a 31-day period via the Internet at
www.ngs.noaa.gov/CORS/cors-data.html.
(1) General. The CORS system provides an extra reference
station for static positioning with GPS code or carrier phase
receivers. For geodetic surveys (using carrier phase), this
system provides an inexpensive way to tie a local network into
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