Differential Global Positioning System (DGPS)

[Federal Register Volume 64, Number 100 (Tuesday, May 25, 1999)]
[Notices]
[Pages 28234-28236]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-13238]


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DEPARTMENT OF TRANSPORTATION

Coast Guard
[USCG-1999-5592]


Differential Global Positioning System (DGPS)

AGENCY: Coast Guard, DOT.

ACTION: Notice.

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SUMMARY: The Coast Guard announces that it has determined that the 
Maritime Differential Global Positioning System (DGPS) Service has 
achieved Full Operational Capability (FOC). The network now meets the 
high standards for accuracy, integrity, reliability, availability, and 
coverage required for the Harbor Entrance and Approach phase of 
maritime navigation. In addition, the Coast Guard announces that it is 
beginning expansion of DGPS into the continental U.S. as the Nationwide 
DGPS (NDGPS). The NDGPS will have the same signal characteristics as 
the Maritime DGPS Service. However, until it is fully operational, it 
may not meet the same coverage, availability, and reliability 
specifications. This notice describes the two systems, and explains how 
users can identify which system is providing the signal they are using.

DATES: The Maritime DGPS Service was certified FOC on March 15, 1999.

ADDRESSES: The Docket Management Facility maintains the public docket 
for this notice. It is available for inspection or copying in room PL-
401 on the Plaza Level of the Nassif Building at the Docket Management 
Facility, US Department of Transportation, 400 Seventh Street SW, 
Washington DC 20590-0001. Hours are between 9 a.m. and 5 p.m., Monday 
through Friday, except Federal holidays. The telephone number is 202-
366-9329. You may also access this docket on the Internet at https://
dms.dot.gov.

FOR FURTHER INFORMATION CONTACT:
    For questions on this notice, contact LT Terry Johns, Office of 
Aids to Navigation, Radio Aids Division (G-OPN-3), Coast Guard, 
telephone 202-267-6538. You can obtain a copy of this notice by calling 
the Coast Guard's Navigation Information Center at (703) 313-5900, via 
email nisws@smtp.navcen.uscg.mil or on the Internet at https://
www.navcen.uscg.mil.
    For questions on viewing the docket, contact Chief, Dockets, 
Department of Transportation, telephone 202-366-9329.

For questions or copies of documents mentioned in this Notice:

    1. Federal Radionavigation Plan (FRP). Contact the National 
Technical Information Service, Springfield, VA 22161 or on the Internet 
at https://www.navcen.uscg.mil.
    2. BROADCAST STANDARD FOR THE USCG DGPS NAVIGATION SERVICE, 
COMDTINST M16577.1. Available on the Internet at https://
www.navcen.uscg.mil or contact LT Terry Johns, telephone 202-267-6538, 
as listed above in this preamble.
    3. International Telecommunications Union (ITU) document ITU-R 
M.823. Write to ITU, General Secretariat, Place des Nations, CH-1211 
Geneva, Switzerland or on the Internet at https://www.itu.ch.
    4. International Maritime Organization's International 
Electrotechnical Committee (IEC) documents IEC-61108-1 and IEC-61108-4. 
Write to IEC, 3 rue de Verembe' PO Box 131, CH-1211 Geneva, Switzerland 
or on the Internet at https://www.iec.ch.

SUPPLEMENTARY INFORMATION:

Determinations

    On January 30, 1996, the Coast Guard determined that the Maritime 
DGPS Service met Initial Operational Capability (IOC) and was declared 
operational. This notice announces that the Coast Guard has determined 
that the Maritime DGPS Service achieved FOC on March 15, 1999. All 
Maritime DGPS Service broadcast sites are operational,

[[Page 28235]]

providing better than 10-meter (95 percent) horizontal navigational 
accuracy with integrity. Also, the Coast Guard has verified the system 
coverage areas, and installed beacon transmitters and antenna systems 
necessary to meet advertised availability and reliability standards.
    In addition to the real-time DGPS correction broadcast by the 
Maritime DGPS Service, each site has been integrated into the 
Continuously Operating Reference Stations (CORS) network operated by 
the Department of Commerce. The full GPS signal is archived and made 
available publicly for all post-processing GPS applications at the 
following Internet address--https://www.ngs.noaa.gov/CORS/cors-
data.html.
    This notice also announces that the Coast Guard is beginning 
expansion of DGPS into the continental U.S. as the Nationwide DGPS 
(NDGPS). Eight NDGPS sites in: Appleton, WA; Whitney, NB; Savannah, GA; 
Penobscot, ME; Chico, CA; Hartsville, TN; Clark, SD; and Driver, VA 
have been installed and another eight NDGPS sites should be installed 
by the end of 1999. By December 31, 2002, the NDGPS is expected to 
provide single coverage for the continental U.S. and portions of 
Alaska.
    Until the NDGPS achieves full operational capability, it may not 
meet the same coverage, availability and reliability specifications as 
the Maritime DGPS Service; however where healthy NDGPS signals are 
available, they will meet the same accuracy and integrity 
specifications as the Maritime DGPS Service.

Background and Purpose

    a. Definitions. The following terms used in this notice are 
defined. Further explanation may be found in the Federal 
Radionavigation Plan. The FRP is jointly developed by the Department of 
Defense and the Department of Transportation as the official source of 
radionavigation policy and planning for the Federal Government.
    Accuracy of an estimated or measured position of a craft at a given 
time is the degree of conformance of that position with the true 
position of the craft at that time.
    Availability is the percentage of time that the services of the 
system are usable by the navigator.
    Coverage provided by a radionavigation system is that surface area 
in which the signal strengths are adequate to permit the navigator to 
determine a position to a specified level of accuracy.
    Full Operational Capability (FOC) was established for the Maritime 
DGPS Service when the signals were capable of providing the accuracy, 
integrity, reliability, availability, and coverage defined in the FRP. 
For the NDGPS, FOC has not yet been defined.
    Initial Operational Capability (IOC) was established for the 
Maritime DGPS Service when the signals were capable of being received 
at selected portions of the nation's coastline and major inland rivers 
with full integrity, and accuracy as specified by the FRP. For the 
NDGPS, IOC has not yet been defined.
    Integrity is the ability of a system to provide timely warnings to 
users when the system should not be used for navigation.
    Reliability is a function of the frequency with which failures 
occur within the system.
    b. System Description. The FRP contains information concerning 
navigational accuracy required for different phases of navigation, 
descriptions of radionavigation systems, and plans for government 
operated radionavigation systems. One of the systems described in the 
FRP is the Global Positioning System (GPS). This space-based 
radionavigation system is available worldwide. The Standard Positioning 
Service (SPS) is the standard specified level of positioning and timing 
accuracy which provides a predictable positioning accuracy of 100 
meters (95 percent) horizontally and time transfer accuracy to 
Universal Time Coordinated (UTC) within 340 nanoseconds (95 percent). 
Delays and adjustment factors such as propagation anomalies, errors in 
geodesy, or other factors, affect GPS accuracy.
    The FRP defines the degree of accuracy required for the Ocean and 
Coastal phases of maritime navigation. GPS has met these standards for 
some time. However, unaugmented GPS provides only 100-meter accuracy 
(95 percent) horizontal. This performance does not meet the more 
precise accuracy requirements defined for the U.S. Harbor Entrance and 
Approach phase of maritime navigation by the FRP. Additionally, other 
Coast Guard missions such as Vessel Traffic Services and positioning 
aids to navigation require higher levels of accuracy than unaugmented 
GPS can provide. In addition, the unaugmented GPS service may be 
inadequate for many proposed land-based applications.
    GPS augmentations are designed to provide integrity and to improve 
position accuracy. The Coast Guard Maritime DGPS Service augments GPS 
by using a system of DGPS broadcast sites to provide pseudo-range 
corrections and integrity checks for users within the advertised 
coverage area of each site. Each site is surveyed to establish its 
precise location. Using this known location, the station calculates a 
pseudo-range correction for each satellite in view. The user receives 
GPS signals from the satellites and DGPS corrections from the DGPS 
broadcast site. Those corrections are automatically applied to the 
individual satellite pseudo-ranges in DGPS user equipment. The 
resulting calculated position accuracy is better than 10 meters (95 
percent) horizontal, and may be more accurate depending on factors 
including user equipment capabilities, positioning process, and the 
user's distance from the DGPS broadcast site. Positioning accuracy near 
the site can be as good as one-half meter, but degrades up to one meter 
for every 150 kilometers from the DGPS broadcast site. Given this 
degradation, users are encouraged to identify and use the nearest 
healthy DGPS site to receive the most accurate corrections.
    In addition to providing a highly accurate navigational signal, the 
Maritime DGPS Service also provides a continuous integrity check on GPS 
satellite health. Due to the design of the ground segment of GPS, a 
satellite can be transmitting an unhealthy signal for 2 to 6 hours 
before it can be detected and corrected by the Master Control Station 
or before users can be warned not to use the signal. However, the 
equipment at a DGPS broadcast site can detect a malfunctioning 
satellite and inform users. Through its use of continuous, real-time 
messages, the Maritime DGPS Service can often extend the use of 
unhealthy GPS satellites by providing accurate corrections, or by 
directing the navigator to ignore erroneous GPS signals.
    The Federal Government has completed the establishment of the 
Maritime DGPS Service and is beginning the expansion of that service to 
create the NDGPS. The Coast Guard currently operates the Maritime DGPS 
Service, which includes coastal areas of the continental U.S., the 
Great Lakes, Puerto Rico, portions of Alaska and Hawaii, and portions 
of the Mississippi River Basin. The Federal Railroad Administration is 
sponsoring the NDGPS, and the Coast Guard is responsible for the 
establishment, operation, management, and future improvements of the 
service. The NDGPS is planned to provide dual signal coverage for the 
continental U.S. and the major transportation corridor in Alaska, from 
Anchorage to Fairbanks, with single signal coverage planned for the 
interior of Alaska. The NDGPS will

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provide the required enabling technology for the Federal Railroad 
Administration's Positive Train Control initiative, and will benefit 
the Federal Highway Administration's Intelligent Transportation 
Systems, precision farming, weather forecasting, survey, and other 
applications. NDGPS sites may be identified by one or more of the 
methods described in paragraph c.1-3 of this notice.
    c. System Identification/Notifications: Occasionally, Maritime and 
Nationwide DGPS signals may not meet the established service 
requirements of accuracy, integrity and coverage. When such a condition 
occurs, one or more of the following notifications are made:
    (1) Through Coast Guard Broadcast Notice to Mariners for those 
sites with maritime coverage. The processes to notify terrestrial 
(NDGPS) users have not been defined. Until such time as the process for 
those notices is developed, concerned users are encouraged to use the 
resources in (2).
    (2) By the Navigation Information Center at (703) 313-5900 or 
https://www.navcen.uscg.mil.
    (3) By a type 16 informational message transmitted by the site.
    (4) By automatic transmission of ``DO NOT USE'' values, or 
Unmonitored/Unhealthy health codes embedded in the standardized GPS 
correction messages.
    d. Equipment. The following equipment is capable of receiving and 
applying broadcast station DGPS correction messages:
    1. A GPS receiver that has the ability to accept differential 
correction messages that comply with the BROADCAST STANDARD FOR THE 
USCG DGPS NAVIGATION SERVICE, COMDTINST M16577.1.
    2. A differential beacon receiver designed to receive differential 
correction messages that comply with the BROADCAST STANDARD FOR THE 
USCG DGPS NAVIGATION SERVICE, COMDTINST M16577.1.
    These two pieces of equipment are often integrated into a single 
unit. Users should note that the quality of equipment selected will 
have an effect on their ability to receive the differential 
transmissions, and on the final navigational accuracy achieved after 
these corrections are applied in the GPS receiver. Appropriate 
authority will promulgate specific standards.
    Further international maritime DGPS signal standards are contained 
in the International Telecommunications Union document: ITU-R M.823. 
Maritime GPS/DGPS receiver specifications and minimum performance 
standards are prepared by the International Maritime Organization's 
International Electrotechnical Committee. The GPS receiver 
specifications are contained in IEC-61108-1; the maritime DGPS receiver 
specifications are still under development, the draft specifications 
are contained in document IEC-61108-4.

    Dated: May 14, 1999.

Ernest R. Riutta,
Rear Admiral, U.S. Coast Guard, Assistant Commandant for Operations.
[FR Doc. 99-13238 Filed 5-24-99; 8:45 am]
BILLING CODE 4910-15-P