Announcement of Global Positioning System (GPS) Initial Operational Capability (IOC) and Its Impact on Vessel Carriage Requirement Regulations

DEPARTMENT OF TRANSPORTATION

Coast Guard

[CGD 94-006]

Announcement of Global Positioning System (GPS) Initial

Operational Capability (IOC) and Its Impact on Vessel Carriage

Requirement Regulations

agency: Coast Guard, DOT.

action: Notice.

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Summary: The Department of Defense has notified the Department of

Transportation that the Global Positioning System (GPS) has reached its

Initial Operational Capability (IOC). A GPS receiver now meets the

carriage requirements for electronic position fixing devices under 33

CFR 164.41 (a)(2).

dates: Effective December 8, 1993, the Coast Guard will accept a GPS

receiver as an electronic position fixing device satisfying the

requirements of 33 CFR 164.41.

addresses: If so indicated, documents referenced in this preamble are

available for inspection or copying at the office of the Executive

Secretary, Marine Safety Council (G-LRA/3406), U.S. Coast Guard

Headquarters, 2100 Second Street SW, Washington, DC 20593-0001 between

8 a.m. and 3 p.m., Monday through Friday, except Federal holidays. The

telephone number is (202) 267-1477.

for further information contact: LCDR Jean Butler, Chief, Radio Aids

Applications and Developments Branch, Radionavigation Division, Office

of Navigation Safety and Waterway Services, USCG Headquarters,

Washington, DC 20593-0001, telephone 202-267-0298. A copy of this

notice may be obtained by calling the Coast Guard's toll-free Boating

Safety Hotline, 1-800-368-5647. In Washington, DC, call 267-0780.

Background

The Federal Radionavigation Plan (FRP), jointly prepared by the

Department of Defense (DOD) and Department of Transportation (DOT) on a

biennial basis, contains further information concerning navigation,

radionavigation system descriptions, and plans for government operated

radionavigation systems. It is available to the public through the

National Technical Information Service (NTIS).

GPS is a DOD-developed, worldwide, satellite-based radionavigation

system that will be the primary radionavigation system well into the

next century. When fully operational, the GPS will be composed of 24

satellites in six orbital planes. The spacing of the satellites in

orbit will be arranged so that a minimum of five satellites will be in

view to users worldwide. Full Operational Capability will be achieved

when 24 operational, production model satellites (Block II or newer)

are operating in their assigned orbits and when the constellation has

successfully completed testing for operational military functionality.

This is not expected to occur until 1995. GPS Initial Operational

Capability (IOC) has been met and means that 24 GPS satellites (any

model) are operating in their assigned orbits, are available for

navigation, and provide the SPS levels of service as defined in the

FRP. Any planned disruption of the GPS in peacetime will be subject to

a minimum 48-hour advance notice provided by the DOD to the Coast Guard

GPS Information Center (GPSIC). A disruption is defined as periods in

which the GPS is not capable of providing Standard Positioning Service

as defined in the FRP. Unplanned system outages resulting from system

malfunctions or unscheduled maintenance will be announced by the GPSIC

as they become known.

GPS provides two levels of service: Standard Positioning Service

(SPS) and Precise Positioning Service (PPS). SPS is the standard level

of positioning, velocity, and timing accuracy that is available to any

user on a continuous worldwide basis. The horizontal positioning

accuracy of this service is 100 meters (2 distance root mean squared

(drms), 95% probability) and 300 meters with 99.99% probability. PPS

will be limited to authorized U.S. and allied Federal government and

military users and to those civil users who can satisfy U.S.

requirements. These requirements are: the use must be in the U.S.

national interest; the user must meet specific GPS security

requirements; and a reasonable alternative to the use of PPS must not

be available. Unauthorized users will be denied access to PPS through

encryption of the signals. PPS military user equipment will provide

horizontal positioning accuracy of 21 meters (2 drms). The SPS is

affected by a process called Selective Availability (SA), which

degrades the basic accuracy of the SPS through adjustment and

encryption of some of the signals and data.

One of the shortcomings of GPS for civil navigation use is its

problem meeting integrity requirements. Integrity is the ability of a

system to provide timely warnings to users when the system should not

be railed upon for navigation. According to DOD's concept of operation,

GPS satellites are monitored more than 95 percent of the time by a

network of five monitoring stations spread around the world. The

information collected by the monitoring stations is processed by the

GPS Master Control Station (MCS) and used to periodically update the

navigation message, including the satellite health message, transmitted

by each satellite. The health message is transmitted as part of the GPS

navigation message for reception by both PPS and SPS users.

Additionally, satellite operating parameters such as navigation data

errors, signal availability failures, and certain types of satellite

clock failures are monitored internally within the satellite. If such

internal failures are detected, users are notified within six seconds.

Other failures detectable only by the control segment may take from 15

minutes to several hours before users are notified of a problem. This

is unsatisfactory for many modes and phases of navigation, and, from

the maritime perspective, it is particularly deficient for the harbor

and harbor approach (HHS) phase of navigation. The integrity required

for HHA navigation will be provided through augmentation of the GPS SPS

by the Coast Guard's Differential GPS (DGPS) service, now being

implemented.

As with Loran-C and Transit (the Navy Navigation Satellite System),

the GPS should not be used by itself in or near restricted waters. As

described above, the accuracy of the system is not monitored

continuously and it may take 2-6 hours to be aware of a problem or fix

a problem with a satellite. Additionally, mariners need to be aware of

the real accuracy of the system. GPS receivers may produce a latitude

and longitude position that appears accurate to several decimal places,

which may mislead a mariner to believe the system is really that

accurate. GPS SPS will only give an accuracy to within 100 meters, with

95% probability. That means that the mariner can be anywhere within a

100 meter radius of the position indicated by the receiver. It also

means that 5% of the time, the actual position could be greater than

100 meters from the indicated location. Mariners must constantly be

aware of this and navigate with due caution, using all means available,

most importantly in more restricted locations such as harbor and harbor

approach areas.

The FRP outlines navigation accuracies required for the different

phases of navigation. While the Ocean and Coastal phases have been

satisfied for some time, the harbor and harbor-approach phase

requirements have been unattainable with existing systems.

Additionally, a similar need for higher accuracy exists for other Coast

Guard missions such as positioning aids to navigation and Vessel

Traffic Services. DGPS is a solution to all of these needs.

DGPS improves upon GPS signals by using a local reference receiver

to correct errors in the standard GPS signals. An ``all in view'' GPS

receiver is located at a site which has been geodetically surveyed. The

receiver monitors all visible satellites and measures the pseudorange

to each satellite. Since the satellite signal contains information on

the precise satellite orbits and the reference receiver knows its

position, the true range to each satellite can be calculated. By

comparing the calculated true range and the measured pseudorange, a

correction term can be determined for each satellite. These corrections

are then broadcast to the user over the communications network, and can

be received by the user with a DGPS receiver. The Coast Guard will be

using selected marine radiobeacons to transmit the corrections to

users. The corrections are then applied to the pseudorange measurements

within the user's receiver, achieving a position accurate within 10

meters, with 95% probability. One advantage of DGPS is that it will

provide radionavigation accuracy that is not possible with existing

systems. It will also reduce the integrity check of satellites from

hours to seconds, and will even allow for use of satellites considered

unhealthy. By knowing its position, the reference station can detect

immediately when a satellite may be sending erroneous data. DGPS

accuracies cannot be achieved with either the GPS Standard Positioning

Service, with Selective Availability on or off, or Precise Positioning

Service. The Coast Guard will also implement an integrity monitoring

system which will verify the accuracy of the corrections that it

transmits on the selected radiobeacon. The Coast Guard's DGPS Service

will be implemented for harbor and harbor approach areas of the

continential U.S., Great Lakes, Puerto Rico, and most of Hawaii and

Alaska by 1996.

Information Availability

Operational status and other information about GPS is available to

worldwide users of GPS through the Coast Guard's GPS Information Center

(GPSIC). The GPSIC sends GPS operational status information to civil

users through Operational Advisory Broadcasts (OAB). These broadcasts

contain the following general categories of GPS performance data:

Current constellation status, Recent (past) outages, Scheduled (future)

outages, and Almanac data. The OAB is disseminated or made available

through the following media:

GPSIC Computer Bulletin Board System (BBS)

GPSIC 24-Hour Status Recording

WWV/WWVH worldwide high-frequency radio broadcasts

U.S. Coast Guard Marine Information Broadcasts (MIB)

DMAHTC Broadcast Warnings

DMAHTC Weekly Notice to Mariners

DMA Navigation Information Network (NAVINFONET)

NAVTEX Data Broadcast

Through a duty watchstander and an electronic bulletin board

service (BBS), both available 24 hours per day, GPSIC also makes the

following information available:

--Operational status of GPS as provided by DOD

--Precise GPS orbit data from the National Geodetic Survey

--Technical information on GPS

--Operational status and information on other Coast Guard operated

radionavigation systems

--Instructions on the access and use of GPSIC services

The U.S. Air Force Second Space Operations Squadron (2SOPS), which

operates the GPS Master Control Station (MCS) in Colorado Springs, CO,

provides the following GPS information for the GPSIC:

Notice Advisories to NAVSTAR Users (NANU) are near real-time

operational status capability reports. NANUs are issued to notify users

of future, current, or past satellite outages, system adjustments, or

any condition which might adversely affect users. NANUs are generated

by 2SOPs as events occur. GPS Status Messages contain general

information that is downloaded daily from the Air Force's (2SOPS)

electronic bulletin board. The message contains information about the

satellite orbit (plane/slot), clocks, and current or recent NANUs.

Status Messages are generated by 2SOPS once a day Monday through

Friday, except on Federal holidays.

Almanacs contain the orbital information and clock data of all the

satellites. The almanac for all satellites can be obtained from

downloading the continuously transmitted data stream from any

satellite.

In addition to receiving information from the MCS, the GPSIC works

with representatives of the National Geodetic Survey (NGS) to offer NGS

computed precise GPS orbit data to the public via the GPSIC bulletin

board. This data is called precise ephemeris data. Precise ephemeris

data describes the orbit of each satellite as observed by numerous

ground stations. It is useful in making a refined determination of

where the satellites were at some time in the past. The time lag for

this information is about eight days.

The BBS is an electronic version of a bulletin board, where

information is made available in easy to access lists and files. Any

user with a computer and modem can dial the BBS and browse through the

information or copy files into their own computer for further use. The

BBS is menu-driven and has an extensive set of on-line help utilities.

If necessary, users can also page the GPSIC watchstander to request

personal assistance. The BBS is free and open to all. However, users

will have to pay their own connection charges (long distance telephone

or public data network costs). First-time callers are asked to register

on-line (provide their names, addresses, etc.) before proceeding to the

BBS main menu. Through the BBS, a wide range of information is

available 24 hours a day. BBS information is updated whenever the other

GPSIC sources are. Users may call the BBS via either telephone or

SprintNet (a public data network). Ordinary telephone is the easiest

for most people, but SprintNet offers a high speed error-free

alternative for those (especially international callers) who may have

difficulty in getting a good data connection over the voice phone

lines. To contact the BBS, call: (tel) 703-313-5910. Modem speeds of

300 to 14,400 bps and most common U.S. or international protocols are

supported. Communications parameters should be set to: 8 data bits, No

parity, 1 stop bit (8N1), asynchronous comms, full duplex. We have

eight phone lines at this number and two auxiliary numbers to

accommodate modems which may be incompatible with the ones on 313-5910.

The BBS SprintNet number is: 31102021323 (or abbreviate to 202 1328 if

accessing SprintNet via telephone to one of their modems.) For

SprintNet access, users must set up their own accounts with Sprint or a

similar public data network which has a ``gateway'' to SprintNet. For

more information, call: (800) 736-1130 (U.S.) or (913) 541-6876)

(international).

Users who need further information or assistance may call the GPSIC

watchstander at 703-313-5900, or write to Commanding Officer, USCG

Omega Navigation System Center, 7323 Telegraph Road, Alexandria, VA

22310-3998.

In addition to the GPSIC watchstander and BBS already described,

users can access the GPS OAB information from the services described

below:

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Service Availability Info type Contact No./Freq

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GPS/Omega voice 24 hours a day... Status forecasts (703) 313-5905.

tape recording. historic.

WWV.............. Minutes; 14 & 15. Status forecasts 2.5, 5, 10, 15

and 20 MHz.

WWVH............. Minutes; 43 & 44. Status forecasts 2.5, 5, 10 and

15 MHz.

USCG MIB......... When broadcast... Status forecasts VHF-FM, med freq

& high freq.

DMA broadcast When broadcast... Status forecast ................

warnings. outages.

DMA weekly notice Published & Status forecast (301) 227-3126.

to mariners. mailed weekly. outages.

DMA Navinfonet 24 hours a day... Status forecasts (301) 227-3351

automated notice historic 300 baud, (301)

to mariners almanacs. 227-5925 1200

system. baud, (301) 227

4360 2400 baud.

For more info (301 227-3296.

call.

Navtex data When broadcast; 4- Status forecast 518 KHz.

broadcast. 6 time/day. outages.

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(Authority 33 USC 1231, 46 USC 2103, 3703, 49 CFR 1.46)

Dated: March 15, 1994.

R.C. Houle,

Captain, U.S. Coast Guard, Acting Chief, Office of Navigation Safety

and Waterway Services.

[FR Doc. 94-6813 Filed 3-22-94; 8:45 am]

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