DEPARTMENT OF TRANSPORTATION

Downloaded (8/20/94) from the U. S. Coast Guard

NAVIGATION INFORMATION SERVICE BULLETIN BOARD

703-313-5910

Department of Transportation

U. S. 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.

____________________________________________________________

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 accuracies

required for the different phases of 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 relied 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

(HHA) 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

continental 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:

+---------------------------------------------------+

|----------+------------+---------+-----------------|

|----------+------------+---------+-----------------|

|WWV |Minutes |STATUS |2.5, 5, 10, 15 |

|----------+------------+---------+-----------------|

| | 43 & 44 |FORECASTS|15 MHz |

|----------+------------+---------+-----------------|

|----------+------------+---------+-----------------|

|----------+------------+---------+-----------------|

|DMA |Published & |STATUS |(301) 227-3126 |

|----------+------------+---------+-----------------|

|DMA |24 hours |STATUS |(301) 227-3351 |

|MARINERS | | |(301) 227 4360 |

| | |INFO CALL|(301) 227-3296 |

|----------+------------+---------+-----------------|

+---------------------------------------------------+

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

DATED: March 23, 1994