( Global Positioning System )
2nd Mate Isidro E. Estremadura
GPS employs 24 spacecraft in 20,200
km circular orbits inclined at 55
degrees. These spacecraft are placed
in 6 orbit planes with four
operational satellites in each plane.
All launches have been successful
except for one launch failure in 1981.
The full 24-satellite constellation was
completed on March 9, 1994.
The Global Positioning
Baseline 24 satellite constellation in medium earth orbit
Global coverage, 24 hours a day, all weather conditions
Satellites broadcast precise time and orbit information on
L-band radio frequencies
Two types of service:
• Standard (free of direct user fees)
• Precise (U.S. and Allied military)
• Ground control
• User equipment
GPS satellites provide service to civilian and
military users. The civilian service is
freely available to all users on a
continuous, worldwide basis. The military
service is available to U.S. and allied
armed forces as well as approved
Standard Positioning Service
The Standard Positioning Service (SPS) is
defined in the standard specified level of
positioning and timing accuracy that is
available, without restrictions, to any user
on a continuous worldwide basis. The
accuracy of this service will be established
by the DOD and DOT based on U. S.
security interests. SPS provides a
predictable positioning accuracy of 100
meters (95 percent) horizontally and 156
meters (95 percent) vertically and time
transfer accuracy to UTC within 340
nanoseconds (95 percent).
Precise Positioning Service
Precise Positioning Service (PPS) as the
most accurate direct positioning, velocity,
and timing information continuously
available, worldwide, from the basic GPS.
This service is limited to users specifically
authorized by the U.S. P(Y)-code capable
military user equipment provides a
predictable positioning accuracy of at least
22 meters (95 percent) horizontally and
27.7 meters (95 percent) vertically and
time transfer accuracy to UTC within 200
nanoseconds (95 percent) (DoD and DoT
circle the earth
twice a day in a
very precise orbit
GPS receivers take
Essentially, the GPS receiver
compares the time a signal
was transmitted by a satellite
with the time it was received.
The time difference tells the
GPS receiver how far away the
• Now, with distance measurements
from a few more satellites, the
receiver can determine the user's
position and display it on the
• With four or more satellites in
view, the receiver can determine
the user's 3D position (latitude,
longitude and altitude).
The Space Segment
consists of a
way signals that
give the current
The User Segment
The user segment
consists of the GPS
signals from the
GPS satellites and
calculate the user’s
position and time.
The control segment consists of
worldwide monitor and control
stations that maintain the satellites
in their proper orbits through
occasional command maneuvers, and
adjust the satellite clocks. It tracks
the GPS satellites, uploads updated
navigational data, and maintains
health and status of the satellite
A full size model of the Earth observation satellite ERS 2
L1 (1575.42 MHz): Mix of Navigation Message,
coarse-acquisition (C/A) code and encrypted
precision P(Y) code, plus the new L1C on future
Block III satellites.
L2 (1227.60 MHz): P(Y) code, plus the new L2C
code on the Block IIR-M and newer satellites.
L3 (1381.05 MHz): Used by the Nuclear
Detonation (NUDET) Detection System Payload
(NDS) to signal detection of nuclear detonations
and other high-energy infrared events. Used to
enforce nuclear test ban treaties.
Cont’d Satellite frequencies
L4 (1379.913 MHz): Being studied for
additional ionospheric correction.
L5 (1176.45 MHz): Proposed for use as a
civilian safety-of-life (SoL) signal . This
frequency falls into an internationally
protected range for aeronautical
navigation, promising little or no
interference under all circumstances. The
first Block IIF satellite that would provide
this signal is set to be launched in 2009.
Other Satellite System
Galileo – a GNSS developed and constructed by
the European Union and other partner countries,
and planned to be operational by 2014.
Beidou – People's Republic of China's
experimental regional system.
COMPASS – A proposed global satellite
positioning system by the People's Republic of
GLONASS – Russia's GNSS which is being
completed in partnership with India.
IRNSS – India's regional navigation system
covering Asia and the Indian Ocean only (distinct
from India's participation in GLONASS).
QZSS – Japanese proposed regional system
covering Japan only.
Facts about the GPS satellites
(also called NAVSTAR )
The first GPS satellite was launched in
A full constellation of 24 satellites was
achieved in 1994.
Each satellite is built to last about 10
years. Replacements are constantly being
built and launched into orbit.
A GPS satellite weighs approximately
2,000 pounds and is about 17 feet across
with the solar panels extended.
Transmitter power is only 50 watts or less.
GPS satellite launches began in
1978, and a second-generation
set of satellites ("Block II") was
launched beginning in 1989.
Today's GPS constellation
consists of at least 24 Block II
satellites. The system became
fully operational in 1995.
A GPS receiver "knows" the location of the
satellites, because that information is
included in satellite transmissions. By
estimating how far away a satellite is, the
receiver also "knows" it is located
somewhere on the surface of an imaginary
sphere centered at the satellite. It then
determines the sizes of several spheres,
one for each satellite. The receiver is
located where these spheres intersect.
Sources of GPS signal errors
1. Signal Multipath
2. Ionospheric and Tropospheric
3. Receiver Clock error
4. Orbital Error
This occurs when
the GPS signal
is reflected off
objects such as
tall buildings or
it reaches the
Ionosphere and troposphere delays
as it passes
Receiver clock error
is not as
Also known as
Primary Function: Positioning, navigation,
timing and velocity information worldwide
Primary Contractors: Block II/IIA, Rockwell
International (Boeing North American); Block IIR,
Lockheed Martin; Block IIR-M, Lockheed Martin;
Block IIF, Boeing North American
Power Plant: Solar panels generating 800
watts; Block IIF panels generate 2450 watts
Weight: Block IIA, 3,670 pounds (1,816
kilograms); Block IIR/M, 4,480 pounds (2,217
kilograms); Block IIF, 3,758 pounds (1,705
Height: Block IIA, 136 inches (3.4 meters);
Block IIR, 70 inches (1.7 meters); Block IIF, 98
inches (2.4 meters)
Width (includes wingspan): Block IIA, 208.6
inches (5.3 meters); Block IIR, 449 inches (11.4
meters); Block IIF, approximately 116 feet (35.5
Design life: Block II/IIA, 7.5 years; Block IIR,
10 years; Block IIR-M (modernized) 8.57 years;
Block IIF, 11 years
Date of First Launch: 1978
Launch vehicle: Delta II; EELV for Block IIF
Date Constellation Operational: April 1995 (at
full operational capacity)
GPS Accuracy by Land
The accuracy of a position determined
with GPS depends on the type of receiver.
Most hand-held GPS units have about 10-
20 meter accuracy. Other types of
receivers use a method called Differential
GPS (DGPS) to obtain much higher
accuracy. DGPS requires an additional
receiver fixed at a known location nearby.
Observations made by the stationary
receiver are used to correct positions
recorded by the roving units, producing an
accuracy greater than 1 meter.
What is GMDSS?
The Global Maritime Distress and Safety
System (GMDSS) is the international radio
safety system mandated by the
International Maritime Organization (IMO)
for ships at sea.
The GMDSS was implemented on February 1,
1999 through amendments to the Safety of
Life At Sea (SOLAS) Convention.
The primary purpose of GMDSS is to
automate and improve emergency
communications for the world's shipping
GMDSS was developed to SAVE LIVES by modernizing and
enhancing the current radio communications system. By
utilizing satellite and digital selective calling technology,
GMDSS provides a more effective distress alerting system.
It improves the current system by:
1. increasing the probability that an alert will be sent when a
vessel is in distress;
2. increasing the likelihood that the alert will be received;
3. increasing the ability to locate survivors;
4. improving rescue communications and coordination; and
5. providing mariners with vital maritime safety information.
1. transmitting ship-to-shore Distress Alerts;
2. receiving shore-to-ship Distress Alerts;
3. transmitting and receiving ship-to-ship Distress
4. transmitting and receiving search and rescue co-
5. transmitting and receiving on-scene
6. transmitting and receiving locating signals;
7. receiving maritime safety information;
8. transmitting and receiving general
9. transmitting and receiving bridge-to-bridge
The GMDSS applies to vessels subject to
the SOLAS Convention - that is:
Commercial vessels of 300 Gross
Registered Tons (GRT) and above,
engaged on international voyages.
The GMDSS became mandatory for such
vessels as of February 1, 1999.
GMDSS ships are required to carry the following minimum
A VHF radio installation capable of transmitting DSC on channel
70, and radiotelephony on channels 16, 13 and 6.
One SART if under 500 GRT, 2 SARTs if over 500 GRT.
Two portable VHF transceivers for use in survival craft if under
500 GRT, three if over 500 GRT.
A NAVTEX receiver, if the ship is engaged on voyages in any area
where a NAVTEX service is provided.
An Inmarsat EGC receiver, if the ship is engaged on voyages in
any area of Inmarsat coverage where MSI services are not
provided by NAVTEX or HF NBDP.
A 406 MHz or 1.6 GHz EPIRB
Digital Selective Calling (DSC)
Emergency Position Indicating
Radio beacon (EPIRB)
Search And Rescue Transponder
Maritime Safety Information
GMDSS Sea Areas - International
Digital Selective Calling (DSC)
The traditional marine radio (VHF/MF/HF)
has been enhanced with the addition of a
feature known as DSC. This feature
enables vessels to automatically maintain
the required watch on distress and calling
channels instead of the current aural
listening watch. A DSC receiver will only
respond to the vessel’s unique Maritime
Mobile Service Identity number (MMSI#),
similar to a telephone number, or to an
"All Ships" DSC call within range. Once
contact has been made by DSC, follow-up
communications take place by voice on
VHF with DSC
VHF channel 70
(156.525 MHz) is
dedicated to DSC
are prohibited on
MF/HF with DSC
An MF radio
receiving on the
2187.5 kHz using
DSC and 2182
GMDSS makes use
of the COSPAS-
detection of 406
Cospas-Sarsat is a
designed to provide
distress alert and
location data to assist
search and rescue
using spacecraft and
ground facilities to
detect and locate the
signals of distress
beacons operating on
406 Megahertz (MHz).
are fully automatic
and receive safety
coastal regions up
to 300 nautical
518 kHz – MSI broadcast in
490 kHz – MSI broadcast in in
local languages (non English)
Survival Craft Radio Equipment
Although SARTs are
primarily designed to
be used in lifeboats or
liferafts, they can be
deployed on board a
ship, or even in the
SARTs are powered by
which are designed to
provide up to 96
hours of operation.
Call - SafetyNET
for areas outside
MF/HF Radio Equipment
HF Narrow Band
can be used
where service is
available as an
Search And Rescue
SARTs operate in
the 9 GHz marine
radar band, and
by a searching
respond with a
signal which is
displayed as a
series of dots on a
Portable VHF transceivers
These units are
designed to allow
vessels and survivors
in liferafts. They
operate on the VHF
marine band in voice
mode. DSC capability
is not fitted.
What is ECDIS?
The Electronic Chart Display and
Information systems (ECDIS) are
extremely efficient mean of
navigation, which significantly reduce
the workload of the officers on
watch, thus allowing them to devote
more time to the observation of the
surroundings and to the navigation
of the ship.
An Electronic Chart Display and
Information System (ECDIS) is a
computer-based navigation information
system that complies with International
Maritime Organization (IMO) regulations
and can be used as an alternative to paper
navigational chart. IMO refers to similar
systems not meeting the regulations as
Electric Chart Systems (ECS).
Timeline of ECDIS
Mandatory for large international
The new standard was adopted in
June 2009 during the 86th session of
International Maritime Safety
Expected entry into force will be on
January 1, 2011.
ECDIS (as defined by
Publications S-52 and
S-57) is an approved
chart and information
system, which is
accepted as complying
with the conventional
paper charts required
by Regulation V/20 of
the 1974 IMO SOLAS
Application of ECDIS
ECDIS provides continuous
position and navigational safety
information. The system
generates audible and/or visual
alarms when the vessel is in
proximity to navigational
Electronic chart data
Vector charts are the chart databases
for ECDIS, with standardized
content, structure and format, issued
for use with ECDIS on the authority
of government authorized
Raster navigational charts are raster charts
that conform to IHO specifications and are
produced by converting paper charts to
digital image by scanner. The image is
similar to digital camera pictures, which
could be zoomed in for more detailed
information as it does in ENC. IHO Special
Publication S-61 provides guidelines for
the production of raster data. IMO
Resolution MSC.86(70) permits ECDIS
equipment to operate in a Raster Chart
Display System (RCDS) mode in the
absence of ENC.
ECDIS provides continuous position
and navigational safety information.
The system generates audible and/or
visual alarms when the vessel is in
proximity to navigational hazards.
What is AIS?
Automatic identification system (AIS) are
designed to be capable of providing
information about the ship to other ships
and to coastal authorities automatically.
The Automatic Identification System (AIS) is
a short range coastal tracking system used
on ships and by Vessel Traffic Service (VTS)
for identifying and locating vessels by
electronically exchanging data with other
nearby ships and VTS stations.
AIS main objectives are:
- to improve maritime safety
- to protect the maritime environment
AIS operates in the VHF frequency band.
Regulations for carriage of AIS
Regulation 19 of SOLAS Chapter V -
Carriage requirements for shipborne
navigational systems and equipment -
sets out navigational equipment to be
carried on board ships, according to ship
type. In 2000, IMO adopted a new
requirement (as part of a revised new
chapter V) for all ships to carry automatic
identification system (AIS) capable of
providing information about the ship to
other ships and to coastal authorities
The regulation requires AIS to be
fitted aboard all ships of 300 gross
tonnage and upwards engaged on
international voyages, cargo ships of
500 gross tonnage and upwards not
engaged on international voyages
and all passenger ships irrespective
of size. The requirement became
effective for all ships by 31
The regulation requires that AIS shall:
provide information - including the ship's
identity, type, position, course, speed,
navigational status and other safety-
related information - automatically to
appropriately equipped shore stations,
other ships and aircraft;
receive automatically such information
from similarly fitted ships; · monitor and
exchange data with shore-based facilities.
The regulation applies to ships built on or
after 1 July 2002 and to ships engaged on
international voyages constructed before 1
July 2002, according to the following
passenger ships, not later than 1 July 2003;
tankers, not later than the first survey for
safety equipment on or after 1 July 2003;
ships, other than passenger ships and
tankers, of 50,000 gross tonnage and
upwards, not later than 1 July 2004.
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