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Navigational Aids
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Animal Navigation
Finding the way to wintering sites thousands of milesaway is easy for animals -- they just put the coordinates
into their GPS systems and follow the turn-by-turn
directions. No problem.
Actually, the methods animals use to navigate their
migration routes are even more amazing than an animal
that could program a GPS device. Some of their
navigation methods are so weird we don't really
understand them.
http://animals.howstuffworks.com/animal-facts/animal-migration4.htm
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Here, we report the first study of post-release movement patterns in translocated
adult crocodiles, and the first application of satellite telemetry to a crocodilian.
Three large male Crocodylus porosus (3.14.5 m) were captured in northern
Australia and translocated by helicopter for 56, 99 and 411 km of coastline, the lastacross Cape York Peninsula from the west coast to the east coast.
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All crocodiles spent time around their release
site before returning rapidly and apparently
purposefully to their capture locations. The
animal that circumnavigated Cape YorkPeninsula to return to its capture site, travelled
more than 400 km in 20 days, which is the
longest homeward travel yet reported for a
crocodilian. Such impressive homing ability is
significant because translocation has
sometimes been used to manage potentiallydangerous C. porosus close to human
settlement. It is clear that large male estuarine
crocodiles can exhibit strong site fidelity, have
remarkable navigational skills, and may move
long distances following a coastline. These long
journeys included impressive daily movementsof1030 km, often consecutively.
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The sun - This seems pretty simple. You can judge
roughly what direction you're heading in by wherethe sun is. But factor in the time of day, time of
year and cloud cover, and you're left with a pretty
tricky navigation system. Yet starlings and ants
navigate this way. Some birds can even travel at
night using the sun -- theories suggest they take a
"reading" from where the sun sets and use that to
set their course.
Weather - Wind conditions are often used assupplementary navigation aid by birds. When
deprived of other cues, such as the sun or stars,birds chose to fly downwind in an experiment.
When the birds could see the sun and stars, they
flew in the right direction regardless of wind
direction.
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Landmarks - This is another pretty
basic navigation system. Fly towardthose mountains, head to the left a little
when you see the ocean, and make a
nest in the first nice-looking tree you can
find. Whales traveling in the Pacific
Ocean near the North American west
coast use this method -- their landmark
is hard to miss, because it's the entire
continent of North America. They keep it
on their left on the way south, and to
their right when they head north.
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Scent - Once an animal is in the general
area, scent can pinpoint specificlocations. Scent won't get an animal
from Saskatchewan to Mexico, but it
probably helps salmon find their exact
spawning ground, for instance. The scent
of rain might shape wildebeest
migrations.
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Magnetic field - The earth has a magnetic field that's usually undetectableto humans who aren't holding a compass. Some animal species do have the
ability to detect the magnetic field, however, and they use it to make their
migrations. Bats and sea turtles use magnetic information to find their way
Sea Turtles
Baby loggerhead sea turtles are able to find
their way along an 8,000-mile migration route
the first time they ever see it. Scientists took
some turtles off course, but they were able to
find their way back with little difficulty.
Believing that some magnetic orienteering was
going on, the next experiment subjected the
turtles to a variety of magnetic fields that
differed from the earth's natural field. These
turtles went off course. Exposure to a magnet
that mimicked the earth's field set them right
again -- proof that the turtles can detect the
earth's magnetic field and use it to navigate
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Last summer, 16-year-old Andrea Axtell read a riveting article in the papers:
A family had wandered aimlessly in an Arizona desert after their car broke
down. Family members said they felt as if they'd wandered in circles for
hours before help arrived. That detail ignited Andrea's interest. "Without acompass or specific landmarks, do people who get lost end up walking in
circles?" she wondered. "And if they do, why?"
These simple questions fueled Andrea's 10th-grade science project. Hungry
for answers, she hit the library to conduct background research. Among
many facts, she discovered that several body organs control direction andmovement. For example:
* Eyes allow people to see their route.
* Structures in the middle ear affect a person's sense of balance.
* The brain controls whether a person's right side or left side is dominant,
or exerts more control. "Studies of runners' strides show that the dominant
foot pushes off with a greater thrust, which pushes the runner slightly right
or left," she explains.
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How does being blindfolded affect a person's ability to walk straight? What
factors seem to affect the direction a blindfolded person takes?
AWINNING PROJECT
Andrea's project led her to an intriguing conclusion: People who are lost and
can't see a defined path or final destination do in fact tend to walk in circles.
But Andrea never expected to walk off with a prize at the 2003 Intel
International Science and Engineering Fair. "I just hoped my project would dowell in our school fair," she says.
It just goes to show, says Andrea: "A winning project doesn't have to be save-
the-world science. Just pick something that fascinates you."
http://findarticles.com/p/articles/mi_m1590/is_2_60/ai_112168970/?tag=content;col1
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Prior to the introduction of the compass, position, destination, and direction at
sea was primarily determined by the sighting of landmarks, supplemented with
the observation of the position of celestial bodies. Ancient mariners often kept
within sight of land. The invention of the compass enabled the determination of
heading when the sky was overcast or foggy. And, when the sun or other known
celestial bodies could be observed, it enabled the calculation of latitude. This
enabled mariners to navigate safely far from land, increasing sea trade, and
contributing to the Age of Discovery
Cantino planisphere 1502, earliest surviving chart showing the explorations of Columbus to Central America, Corte-Real to
Newfoundland, Gama to India and Cabral to Brazil. Tordesillas line depicted, Biblioteca Estense, Modena
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Navigation
is the process of reading, and controlling the movement of acraft or vehicle from one place to another. It is also the term
of art used for the specialized knowledge used by navigators
to perform navigation tasks. The word navigate is derived
from the Latin "navigate", which is the command "sail". More
literally however, the word "Navi" in Sanskrit means 'boat'
and "Gathi" means 'direction'. All navigational techniques
involve locating the navigator's position compared to known
locations or patterns.
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Modern NavigationalMethods:
Dead reckoning or DR, in which one advances a prior position using the ship's
course and speed. The new position is called a DR position. It is generally acceptedthat only course and speed determine the DR position. Correcting the DR position
for leeway, current effects, and steering error result in an estimated position or EP.
An inertial navigator develops an extremely accurate EP.
is the process of estimating one's current
position based upon a previously
determined position, or fix, andadvancing that position based upon
known or estimated speeds over elapsed
time, and course. While traditional
methods of dead reckoning are no longer
considered primary means of navigation,
modern inertial navigation systems,which also depend upon dead reckoning,
are very widely used.
A disadvantage of dead reckoning is that since new positions are
calculated solely from previous positions, the errors of the process are
cumulative, so the error in the position fix grows with time.
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Pilotage involves navigating in restricted waters with frequent determination
of position relative to geographic and hydrographic features.
is the use of fixed visual references on the ground or sea by means of sight or radar
to guide oneself to a destination, sometimes with the help of a map or nautical
chart. People use pilotage for activities such as guiding vessels and aircraft, hiking
and Scuba diving. When visual references are not available, it is necessary to use an
alternative method of navigation such as dead reckoning (typically with a compass),
radio navigation, and satellite navigation (such as GPS).
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Celestial navigation involves reducing celestial measurements to lines of position using
tables, spherical trigonometry, and almanacs.
also known as astronavigation, is a position fixing technique that has steadily evolved overseveral thousand years to help sailors cross featureless oceans without having to rely on
estimated calculations, or dead reckoning, to enable them to know their position on the
ocean. Celestial navigation uses "sights," or angular measurements taken between a visible
celestial body (the sun, the moon, a planet or a star) and the visible horizon. The angle
measured between the sun and the visible horizon is most commonly used. Skilled
navigators can additionally use the moon, a planet or one of 57 navigational stars whose
coordinates are tabulated in the Nautical Almanac and Air Almanacs.
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An example illustrating the concept behind the intercept method for determining
ones position is shown to the right. (Two other common methods for determining
ones position using celestial navigation are the longitude by chronometer and ex-
meridian methods.) In the image to the right, the two circles on the map representlines of position for the Sun and Moon at 1200 GMT on October 29, 2005. At this
time, a navigator on a ship at sea measured the Moon to be 56 degrees above the
horizon using a sextant. Ten minutes later, the Sun was observed to be 40 degrees
above the horizon. Lines of position were then calculated and plotted for each of
these observations. Since both the Sun and Moon were observed at their respective
angles from the same location, the navigator would have to be located at one of thetwo locations where the circles cross.
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While celestial navigation is becoming increasingly redundant with the advent of
inexpensive and highly accurate satellite navigation receivers (GPS), it was used
extensively in aviation until 1960s, and marine navigation until quite recently. But since
a prudent mariner never relies on any sole means of fixing his position, many national
maritime authorities still require deck officers to show knowledge of celestial
navigation in examinations, primarily as a back up for electronic navigation. One of the
most common current usages of celestial navigation aboard large merchant vessels is
for compass calibration and error checking at sea when no terrestrial references are
available.
The U.S. Air Force and U.S. Navy continued instructing military aviators on its use until
1997, because:
it can be used independently of ground aids
has global coverage
cannot be jammed (although it can be obscured by clouds)
does not give off any signals that could be detected by an enemy
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The US Naval Academy announced that it was discontinuing its course on celestial
navigation, considered to be one of its most demanding courses, from the formal
curriculum in the spring of 1998 stating that a sex
tant is acc
urate
to a three
-mile
(5km) radius, while a satellite-linked computercan pinpoint a ship within 60 feet (18
m). Presently, midshipmen continue to learn to use the sextant, but instead of
performing a tedious 22-step mathematical calculation to plot a ship's course,
midshipmen feed the raw data into a computer.
Likewise, celestial navigation was used in commercial aviation up until the early part of
the jet age; it was only phased out in the 1960s with the advent of inertial navigation
systems.
Celestial navigation continues to be taught to cadets during their training in the British
Merchant Navy and remains as a requirement for their certificate of competency.
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Celestial navigation trainer
Celestial navigation trainers combine a simple flight simulator with a planetarium in order
to train aircraft crews in celestial navigation.
An early example is the Link Celestial Navigation Trainer, used of the Second World War.
Housed in a 45 feet (14 m) high building, it featured a cockpit which accommodated a
whole bomber crew (pilot, navigator and bomber). The cockpit offered a full array of
instruments which the pilot used to fly the simulated aeroplane. Fixed to a dome above
the cockpit was an arrangement of lights, some collimated, simulating constellations from
which the navigator determined the plane's position. The dome's movement simulatedthe changing positions of the stars with the passage of time and the movement of the
plane around the earth. The navigator also received simulated radio signals from various
positions on the ground.
Below the cockpit moved "terrain plates" large, movable aerial photographs of the land
below, which gave the crew the impression of flight and enabled the bomber to practiselining up bombing targets.
A team of operators sat at a control booth on the ground below the machine, from which
they could simulate weather conditions such as wind or cloud. This team also tracked the
aeroplane's position by moving a "crab" (a marker) on a paper map.
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Because in the current era UMi lies nearly in
a direct line with the axis of the Earth's
rotation "above" the North Pole the north
celestial pole Polaris stands almostmotionless on the sky, and all the stars of the
Northern sky appear to rotate around it.
Therefore, it makes an excellent fixed point
from which to draw measurements for celestial
navigation and for astrometry. In more recent
history it was referenced in NathanielBowditch's 1802 book, The American Practical
Navigator, where it is listed as one of the
navigational stars. At present, Polaris is 0.7
away from the pole of rotation (1.4 times the
Moon disc) and hence revolves around the
pole in a small circle 1 in diameter. Onlytwice during every sidereal day does Polaris
accurately define the true north azimuth; the
rest of the time it is only an approximation and
must be corrected using tables or a rough rule
of thumb.
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A compass is a navigational instrument for determining direction relative to the
Earth's magnetic poles. It consists of a magnetized pointer (usually marked on the
North end) free to align itself with Earth's magnetic field. The compass greatlyimproved the safety and efficiency of travel, especially ocean travel. A compass can
be used to calculate heading, used with a sextant to calculate latitude, and with a
marine chronometer to calculate longitude. It thus provides a much improved
navigational capability that has only been recently supplanted by modern devices
such as the Global Positioning System (GPS).
A compass is any magnetically sensitive device capable of indicating the direction of
the magnetic north of a planet's magnetosphere. The face of the compass generally
highlights the cardinal points of north, south, east and west. Often, compasses are
built as a stand alone sealed instrument with a magnetized bar or needle turning
freely upon a pivot, or moving in a fluid, thus able to point in a northerly and
southerly direction. The compass was invented in ancient China sometime before
the 2nd century, and was used for navigation by the 11th century. The dry compass
was invented in medieval Europe around 1300. This was supplanted in the early
20th century by the liquid-filled magnetic compass.
http://en.wikipedia.org/wiki/Compass
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China
The earliest Chinese compasses were probably not designed for navigation,
but rather to order and harmonize their environments and buildings in
accordance with the geomantic principles of feng shui. These early
compasses were made using lodestone, a special form of the mineral
magnetite that aligns itself with the Earths magnetic field.
The earliest Chinese literature reference to magnetism lies in the 4th century BC
writings of Wang Xu (): "The lodestone attracts iron.The first mention of the attraction of a needle by a magnet is a Chinese work
composed between 70 and 80 AD (Lunheng ch. 47): "A lodestone attracts a needle.
The earliest reference to a specific magnetic direction finder device is recorded in
a Song Dynasty book dated to 1040-44. There is a description of an iron "south-
pointing fish" floating in a bowl of water, aligning itself to the south.
The first incontestable reference to a magnetized needle in Chinese literature
appears in 1088.
The earliest recorded actual use of a magnetized needle for navigational purposes
is found in Zhu Yu's book Pingzhou Table Talks
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The use of a magnetic compass as a direction finder occurred sometime before 1044,
but incontestable evidence for the use of the compass as a navigational device did not
appear until 1119.
Diagram of a Ming Dynasty
mariner's compass
Navigational sailor's compass rose.Pivoting compass needle in a 14th
century copy of Epistola de
magnete of Peter Peregrinus
(1269)
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Later developments
Dry compass
Early modern dry compass suspended by a gimbal
(1570)
The dry mariner's compass was invented in Europe
around 1300. The dry mariner's compass consists of
three elements: A freely pivoting needle on a pin
enclosed in a little box with a glass cover and a wind
rose, whereby "the wind rose or compass card is
attached to a magnetized needle in such a manner
that when placed on a pivot in a box fastened in line
with the keel of the ship the card would turn as the
ship changed direction, indicating always what
course the ship was on".Early modern dry compass suspended by a
gimbal (1570)
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A bearing compass is a magnetic compass mounted
in such a way that it allows the taking of bearings of
objects by aligning them with the lubber line of the
bearing compass. A surveyor's compass is aspecialized compass made to accurately measure
heading of landmarks and measure horizontal
angles to help with map making. These were
already in common use by the early 18th century
and are described in the 1728 Cyclopaedia. The
bearing compass was steadily reduced in size andweight to increase portability, resulting in a model
that could be carried and operated in one hand.
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Liquid compass
The liquid compass is a design in which the magnetized needle or card is damped by
fluid to protect against excessive swing or wobble, improving readability while reducingwear. A rudimentary working model of a liquid compass was introduced by Sir Edmund
Halley at a meeting of the Royal Society in 1690. However, as early liquid compasses
were fairly cumbersome and heavy, and subject to damage, their main advantage was
aboard ship. Protected in a binnacle and normally gimbal-mounted, the liquid inside the
compass housing effectively damped shock and vibration, while eliminating excessive
swing and grounding of the card caused by the pitch and roll of the vessel.
A flush mount compass on a boat
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Liquid compasses were next adapted for aircraft. In 1909, Captain F.O.
Creagh-Osborne, Superintendent of Compasses at the British Admiralty,
introduced his Creagh-Osborne aircraft compass, which used a mixture of
alcohol and distilled water to damp the compass card. After the success of
this invention, Capt. Creagh-Osborne adapted his design to a much smaller
pocket model for individual use by officers of artillery or infantry, receiving
a patent in 1915.
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Thumb compass is a type of compass commonly usedin orienteering, a sport in which map reading and terrain
association are paramount. Consequently, most thumbcompasses have minimal or no degree markings at all, and
are normally used only to orient the map to magnetic north.
Thumb compasses are also often transparent so that an
orienteer can hold a map in the hand with the compass and
see the map through the compass.
Thumb compasses attach to one's thumb using a small
elastic band.
Placing an even greater emphasis on speed over accuracy,
the wrist compass lacks even a baseplate, consisting solely
of a needle capsule strapped to the carpometacarpal joint
at the base of the thumb; the thumb serves the function of
a baseplate when taking and sighting bearings. It is often
used for city and park race orienteering.
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Using the Compass
The compass consists of a magnetized metal needle that floats on a pivot
point. The needle orients to the magnetic field lines of the earth. The basicorienteering compass is composed of the following parts:
Base plate
Straight edge and ruler
Direction of travel arrow
Compass housing with 360 degree markings
North labelIndex line
Orienting arrow
Magnetic needle (north end is red)
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What is North
No, this is not a silly question, there are
two types of north.
True North: (also known as Geographic
North or Map North - marked as H on a
topographic map) is the geographic
north pole where all longitude lines
meet. All maps are laid out with true
north directly at the top. Unfortunately
for the wilderness traveler, true north is
not at the same point on the earth as the
magnetic north Pole which is where your
compass points.
In 2001, the North Magnetic Pole was determined by the Geological Survey of
Canada to lie near Ellesmere Island in northern Canada at 81.3N 110.8W. It
was estimated to be at 82.7N 114.4W in 2005. In 2009, it was moving
toward Russia at almost 40 miles (64 km) per year due to magnetic changes in
the Earth's core.
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LatitudeThe latitude of a place on the earth's surface is the angular distance north or
south of the equator. Latitude is usually expressed in degrees (marked with )
ranging from 0 at the Equator to 90 at the North and South poles. The
latitude of the North Pole is 90 N, and the latitude of the South Pole is 90 S.
Historically, mariners calculated latitude in the Northern Hemisphere by
sighting the North Star Polaris with a sextant and sight reduction tables to take
out error for height of eye and atmospheric refraction. Generally, the height of
Polaris in degrees of arc above the horizon is the latitude of the observer.
LongitudeSimilar to latitude, the longitude of a place on the earth's surface is the angular
distance east or west of the prime meridian or Greenwich meridian. Longitude
is usually expressed in degrees (marked with ) ranging from 0 at the
Greenwich meridian to 180 east and west. Sydney, Australia, for example, has a
longitude of about 151 east. New York City has a longitude of about 74 west.
For most of history, mariners struggled to determine precise longitude. The
problem was solved with the invention of the marine chronometer. Longitude
can be calculated if the precise time of a sighting is known.
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Philippines is located within the latitude and longitude of 13 00 N, 122 00 E.
Philippine Islands are located in the northern hemisphere.
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1. South Geographic Pole
2. South Magnetic Pole (2007)
3. South Geomagnetic Pole[when?]
4. South Pole of Inaccessibility
The South Pole, also known as the Geographic
South Pole or Terrestrial South Pole, is one of
the two points where the Earth's axis of
rotation intersects its surface. It is thesouthernmost point on the surface of the Earth
and lies on the opposite side of the Earth from
the North Pole. Situated on the continent of
Antarctica, it is the site of the United States
Amundsen-Scott South Pole Station, which was
established in 1956 and has been permanentlystaffed since that year. The Geographic South
Pole should not be confused with the South
Magnetic Pole.
Its southern hemisphere counterpart is the South Magnetic Pole. Because the
Earth's magnetic field is not exactly symmetrical, the North and South
Magnetic Poles are not antipodal: a line drawn from one to the other does not
pass through the centre of the Earth; it actually misses by about 530 km (329.3
mi).
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GeographicSouth Pole is marked by a smallsign and a stake in the ice pack, which are
repositioned each year on New Year's Day tocompensate for the movement of the ice. The sign
records the respective dates that Roald Amundsen
and Robert F. Scott reached the Pole, followed by a
short quotation from each man and gives the
elevation as 2,835 m (9,301 ft)
CeremonialSouthPole is an area set asidefor photo opportunities at the South Pole Station.
It is located a short distance from the GeographicSouth Pole, and consists of a metallic sphere on a
plinth, surrounded by the flags of the Antarctic
Treaty signatory states
The Geographic South Pole
The Ceremonial South Pole
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Magnetic North: Think of the earth as a giant magnet (it is actually). The shape of the
earth's magnetic field is roughly the same shape as the field of a bar magnet. However,
the earth's magnetic field is inclined at about 11 from the axis of rotation of the earth,
so this means that the earth's magnetic pole doesn't correspond to the Geographic
North Pole and because the earth's core is molten, the magnetic field is always shifting
slightly. The red end of your compass needle is magnetized and wherever you are, the
earth's magnetic field causes the needle to rotate until it lies in the same direction as the
earth's magnetic field. This is magnetic north (marked as MN on a topographic map).
Figure 6.7 shows the magnetic lines for the United States (as of 1985). If you locate
yourself at any point in the U.S., your compass will orient itself parallel to the lines of
magnetic force in that area.
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Magnetic North vs. True North
Once you've set your bearing, you're on the right track to finding your way. But there's
still another wrinkle. Magnetic north isn't the same as true north -- it's close, but nocigar. Magnetic north is always moving, and we call this margin of error declination.
Declination is an angle that measures the difference between true north and magnetic
north. The angle varies depending on where you are on the planet. This is why it's
important to always use a current map when you're in unfamiliar territory, especially
when you're trekking long distances. With short distances, the declination may only be
100 feet (30 meters) or so. But when you're trekking long distances, the margin of error
could be several miles (or kilometers). Your map will tell you the declination. When you
make your navigation calculations, you add or subtract that angle from the compass
bearing numbers. Some compasses only require you to make that adjustment once for
your entire trip -- check your compass instructions for more about setting the
declination.
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What's yourMap Declination?
The first thing you need to know is where you are in relation to magnetic north.
You can find this information by looking on your map legend. If you look at themap of North America in Figure 6.8 you will see the line roughly marking 0
declination. If you are on the line where the declination is 0 degrees, then you
don't have to worry about any of this, since magnetic north and map north are
equivalent. (Wouldn't it be nice if all your trips were on the 0 degree of
declination line?) If you are to the right of that line, your compass will point
toward the line (to the left) and hence the declination is to the west. If you are
to the left of the line, your compass will point toward the line (to the right) and
hence the declination is to the east.
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The Compass Phone
In early 2008, Nokia unveiled the first
compass phone. This cell phone
features a built-in compass designedfor pedestrian navigation. The
compass aligns the phone's built-in
GPS maps with magnetic north.
Integrating the compass with the GPS
means that the phone will always
show the map in the correctorientation, no matter how the user is
holding the phone
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Navigational-Aid Basics
Unlike the roads and highways that we drive on, thewaterways we go boating on do not have road signs
that tell us our location, the route or distance to a
destination, or of hazards along the way. Instead, the
waterways have AIDS TO NAVIGATION (or ATONs),
which are all of those man-made objects used by
mariners to determine position or a safe course.
These aids also assist mariners in making a safe landfall,
mark isolated dangers, enable pilots to follow channels,
and provide a continuous chain of charted marks for
precise piloting in coastal waters. The U.S. Aids to
Navigation System is intended for use with nauticalcharts, which provide valuable information regarding
water depths, hazards, and other features that you will
not find in an atlas or road map.
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The term "aids to navigation" includes buoys, day beacons, lights, lightships, radio
beacons, fog signals, marks and other devices used to provide "street" signs on the
water. Aids To Navigation include all the visible, audible and electronic symbols that
are established by government and private authorities for piloting purposesTypes of Aids to Navigation
The term "aids to navigation" encompasses a wide range of floating and
fixed objects (fixed meaning attached to the bottom or shore), and
consist primarily of:
Buoys - floating objects that are anchored to the bottom. Theirdistinctive shapes and colors indicate their purpose and how to navigate
around them.
Beacons -Which are structures that are permanently fixed to the sea-
bed or land. They range from structures such as light houses, to single-
pile poles. Most beacons have lateral or non-lateral aids attached to
them. Lighted beacons are called "LIGHTS", unlighted beacons are"DAYBEACONS".
Both Buoys and Beacons may have lights attached, and may have a
sound making device such as a gong, bell or horn. Both Buoys and
Beacons may be called "marks".
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Types of BuoysLateral Marks
Used generally to mark the sides of well-defined, navigablechannels.
They are positioned in accordance with a Conventional Direction
of Buoyage. They indicate the Port and Starboard hand sides of
the route to be followed. They are colored Red (Port Hand
Marks) and Green (Starboard Hand Marks).
http://www.trinityhouse.co.uk/interactive/buoys.pdf
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CardinalMarksUsed in conjunction with the compass to indicate the direction from the mark in which
the deepest navigable water lies, to draw attention to a
bend, junction or fork in a channel, or to mark the end of a shoal. The mariner will be
safe if they pass North of a North mark, South of a South mark, East of an East mark and
West of a West mark.
Cardinal Marks are also used for permanent wreck marking whereby North, East, South
and West Cardinal buoys are placed around the wreck. In the case of a new wreck, any
one of the Cardinal buoys may be duplicated and fixed with a Radar Beacon (RACON).
Cardinal Marks
From left to right: North Cardinal,
East Cardinal, South Cardinal,and West Cardinal Class Two buoys
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Isolate
d Danger
M
arks
Used to mark small, isolated dangers with navigable
water around the
buoy. Typically used to mark hazards such as an
underwater shoal or rock.
They are coloured Black and Red.
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Safe WaterMarks
May be used mid-channel, as a centreline or at
the point where land is reached. These buoys (as
the name suggests) indicate the presence of safe,
navigable water all around the buoy. They may
also indicate the best point of passage under a
fixed bridge. These buoys are coloured Red andWhite.
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SpecialMarks
Not primarily intended to assist navigation but are used
to indicate a special area or feature, the nature of which
is apparent by referring to a chart or Notice to Mariners.
Special Marks are used in the marking of cables and
pipelines, including outfall pipes and recreation zones.
They are colored yellow.
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Emergency Wreck BuoysThese buoys provide a clear and unambiguous
means of marking new wrecks. This buoy is used as
a temporary response, typically for the first 24 - 72hours. This buoy is coloured in an equal number of
blue and yellow vertical stripes and is fitted with an
alternating blue and yellow
flashing light.
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Buoys and markers
Buoys and markers are water traffic signs that provide offering direction and information.They also help identify danger areas and restricted zones.
Learn to identify the different types of buoys and markers and what they mean see the
illustration below.
Mile/channel markers are installed on the main channel of the Colorado River on lakes
Buchanan and Travis. The river channel is not marked on other Highland Lakes.Mile/channel markers are placed about one mile apart and are sequentially numbered
starting at the dam. Facing upstream, green markers are on the left and have odd numbers,
while red markers are on the right and have even numbers.
Its a violation of state law to moor or attach a vessel to any buoy or marker. Its also illegal
to move, remove, displace, tamper with, damage or destroy any buoy or marker.
Hazard buoys on LCRA lakes are installed and maintained by LCRA. Regulatory buoys onthe Highland Lakes must have a permit from LCRA. For information, contact LCRA.
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Sound Buoys
Bell
GongWhistle
H
orn
88
5
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Combination Buoys
Any buoy in which a light and a sound signal are
combined
Examples include:
Lighted bell
Lighted gong
Lighted whistle
Lighted horn
4
5
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beacon is an intentionally conspicuousdevice designed to attract attention to a
specific location.
Beacons can also be combined with
semaphoric or other indicators to provide
important information, such as the status of an
airport, by the colour and rotational pattern of
its airport beacon, or of pending weather as
indicated on a weather beacon mounted at thetop of a tall building or similar site. When used
in such fashion, beacons can be considered a
form of optical telegraphy.
A Scandinavian beacon being lit.
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Beacons -help guide navigators to their destinations. Types of navigationalbeacons include radar reflectors, radio beacons, sonic and visual signals. Visual
beacons range from small, single-pile structures to large lighthouses or light
stations and can be located on land or on water. Lighted beacons are called lights;unlighted beacons are called day beacons.
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MajorL
ights
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A radio direction finder(RDF) is a device for finding the direction to a radio source.
Due to radio's ability to travel very long distances and "over the horizon", it makes
a particularly good navigation system for ships, small boats, and aircraft that might
be some distance from their destination.
Civil Air Patrol members practice using a handheld radio direction finder to
locate an emergency locator transmitter.
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The first usable radio direction finder was created in 1907 by italian engineers Ettore
Bellini and Alessandro Tosi. In 1919 it was replaced by the more efficient Adcock
antenna.
US Navy model DAQ high frequency radio direction finder
Amelia Earhart's Lockheed Model 10 Electra with the circularRDFaerial visible
above the cockpit
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Usage in maritime and aircraft navigation
Radio transmitters for air and sea navigation are known as beacons and are the radio
equivalent to a lighthouse. The transmitter sends a Morse Code transmission on a Long
wave (150 - 400 Khz) or Medium wave (AM) (520 - 1720 Khz) frequency incorporating the
station's identifier that is used to confirm the station and its operational status. Since
these radio signals are broadcast in all directions (omnidirectional) during the day, the
signal itself does not include direction information, and these beacons are therefore
referred to as non-directional beacons, or NDBs
Today many NDBs have been decommissioned in favor of
faster and far more accurate GPS navigational systems.
However the low cost of ADF and RDF systems, and the
continued existence of AM broadcast stations (as well as
navigational beacons in countries outside North America)
has allowed these devices to continue to function, primarilyfor use in small boats, as an adjunct or backup to GPS.
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A non-directional (radio) beacon (NDB) is a radio transmitter
at a known location, used as an aviation or marine
navigational aid. As the name implies, the signal transmitted
does not include inherentdirectional information, in contrast
to other navigational aids such as low frequency radio range,
VHF omnidirectional range (VOR) and TACAN. NDB signals
follow the curvature of the earth, so they can be received at
much greater distances at lower altitudes, a major advantage
over VOR. However, NDB signals are also affected more by
atmospheric conditions, mountainous terrain, coastal
refraction and electrical storms, particularly at long range.
Even with the advent of VHF omnidirectional range (VOR)
systems and Global Positioning System (GPS) navigation,
NDBs continue to be the most widely-used radio navigational
aid worldwide.
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Use of non-directional beacons
Airways
A bearing is a line passing through the station that points in a specific direction, such as
270 degrees (due West). NDB bearings provide a charted, consistent method for definingpaths aircraft can fly. In this fashion, NDBs can, like VORs, define "airways" in the sky.
Aircraft follow these pre-defined routes to complete a flight plan.
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Common adverseeffects
Navigation using an ADF to track NDBs is subject to several common effects:
Night effect: radio waves reflected back by the ionosphere can cause signal strengthfluctuations 30 to 60 nautical miles (54 to 108 km) from the transmitter, especially just
before sunrise and just after sunset (more common on frequencies above 350 kHz)
Terrain effect: high terrain like mountains and cliffs can reflect radio waves, giving
erroneous readings; magnetic deposits can also cause erroneous readings
Electricaleffect: electrical storms, and sometimes also electrical interference (from a
ground-based source or from a source within the aircraft) can cause the ADF needle todeflect towards the electrical source
Shorelineeffect: low-frequency radio waves will refract or bend near a shoreline,
especially if they are close to parallel to it
Bank effect: when the aircraft is banked, the needle reading will be offset
While pilots study these effects during initial training, trying to compensate for them in
flight is very difficult; instead, pilots generally simply choose a heading that seems to
average out any fluctuations.
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Automatic direction finder (ADF)
An automatic direction finder(ADF) is a marine or aircraft radio-navigation
instrument which automatically and continuously displays the relative bearing fromthe ship or aircraft to a suitable radio station. ADF receivers are normally tuned to
aviation or marine NDBs operating in the LW band between 190 535 kHz. Like
RDF units, most ADF receivers can also receive medium wave (AM) broadcast
stations, though as mentioned, these are less reliable for navigational purposes.
A typical aircraft ADF indicator
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LIMITATIONSAND BENEFITS
Pilots using ADF should be aware of the following limitations:
Radio waves reflected by the ionosphere return to the earth 30 to 60 miles from thestation and may cause the ADF pointer to fluctuate.
Mountains orcliffs can reflect radio waves, producing a terrain effect. Furthermore, some
of these slopes may have magnetic deposits that cause indefinite indications. Pilots flying
near mountains should use only strong stations that give definite directional indications,
and should not use stations obstructed by mountains.
Shorelines can refract or bend low frequency radio waves as they pass from land to water.Pilots flying over water should not use an NDB signal that crosses over the shoreline to the
aircraft at an angle less than 30. The shoreline has little or no effect on radio waves
reaching the aircraft at angles greater than 30.
When an electrical storm is nearby, the ADF needle points to the source of lightning rather
than to the selected station because the lighting sends out radio waves. The pilot should
note the flashes and not use the indications caused by them.The ADF is subject to errors when the aircraft is banked. Bank erroris present in all turns
because the loop antenna which rotates to sense the direction of the incoming signal is
mounted so that its axis is parallel to the normal axis of the aircraft. Bank error is a
significant factor during NDB approaches.
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BEARING INDICATOR displays the bearing to the station relative to the nose of
the aircraft. If the pilot is flying directly to the station, the bearing indicator
points to 0. An ADF with a fixed card bearing indicator always represents the
nose of the aircraft as 0 and the tail as 180.
Relative bearing (see NDB Bearings figure, on the left) is the angle formed by the
intersection of a line drawn through the centerline of the aircraft and a line drawn
from the aircraft to the radio station. This angle is always measured clockwise fromthe nose of the aircraft and is indicated directly by the pointer on the bearing
indicator.
Magnetic bearing (see NDB Bearings figure, on the left) is the angle formed by the
intersection of a line drawn from the aircraft to the radio station and a line drawn
from the aircraft to magnetic north.
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HOMING: One of the most common ADF uses is "homing to a station". When using this
procedure, the pilot flies to a station by keeping the bearing indicator needle on 0
when using a fixed-card ADF. The pilot should follow these steps:
tune the desired frequency and identify the station. Set the function selector knob to ADF and note
the relative bearing; turn the aircraft toward the relative bearing until the bearing indicator pointer is
0; and
continue flight to the station by maintaining a relative bearing of 0.
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A radio beacon is a transmitter at a
known location, which transmits a
continuous or periodic radio signal with
limited information content (for exampleits identification or location), on a
specified radio frequency.
Radio beacons have many applications,
including air and sea navigation,
propagation research, robotic mapping,
radio frequency identification (radio-frequency identification, RFID) and
indoor guidance as with real time
locating systems
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RADAR
Radar is an object detection system that uses electromagnetic waves to identify the
range, altitude, direction, or speed of both moving and fixed objects such as aircraft,ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in
1940 by the U.S. Navy as an acronym for radio detection and ranging. The term has
since entered the English language as a standard word, radar, losing the capitalization.
Radar was originally called RDF (Range and Direction Finding) in the United Kingdom,
using the same acronym as Radio Direction Finding to preserve the secrecy of its
ranging capability.
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If you send out a loud
sound toward a car
moving toward you. Someof the sound waves will
bounce off the car (an
echo). Because the car is
moving toward you,
however, the sound waveswill be compressed.
Therefore, the sound of
the echo will have a higher
pitch than the original
sound you sent. If you
measure the pitch of the
echo, you can determine
how fast the car is going.
When people use radar they are usually trying to accomplish one of three things
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When people use radar, they are usually trying to accomplish one of three things:
Detect the presence of an object at a distance- Usually the "something" is moving, like
an airplane, but radar can also be used to detect stationary objects buried underground.
In some cases, radar can identify an object as well; for example, it can identify the typeof aircraft it has detected.
Detect the speed of an object - This is the reason why police use radar.
Map something - The space shuttle and orbiting satellites use something called Synthetic
Aperture Radar to create detailed topographic maps of the surface of planets andmoons.
All three of these activities can be accomplished using two things you may be familiar
with from everyday life: echo and Doppler shift. These two concepts are easy to
understand in the realm of sound because your ears hear echo and Doppler shift every
day. Radar makes use of the same techniques using radio waves.
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Applications of Radar
The information provided by radar includes the bearing and range (and therefore
position) of the object from the radar scanner. It is thus used in many different fields
where the need for such positioning is crucial. The first use of radar was for military
purposes; to locate air, ground and sea targets. This has evolved in the civilian field
into applications for aircraft, ships and roads.
In aviation, aircraft are equipped with radar devices that warn of obstacles in or
approaching their path and give accurate altitude readings. They can land in fog at
airports equipped with radar-assisted ground-controlled approach (GCA) systems, inwhich the plane's flight is observed on radar screens while operators radio landing
directions to the pilot.
Marineradars are used to measure the bearing and distance of ships to prevent
collision with other ships, to navigate and to fix their position at sea when within
range of shore or other fixed references such as islands, buoys, and lightships. In portor in harbour, Vessel traffic service radar systems are used to monitor and regulate
ship movements in busy waters.
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Also, all airliners are
equipped with radarequipment in the
aircraft's nose. Short
bursts of radio signals
are emitted from the
nose cone of theaircraft. These signals
reflect off clouds ahead
of the aircraft.
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Alexander Behm was a German physicist.
As head of a research laboratory in Vienna (Austria) heconducted experiments concerning the propagation of sound.
He tried to develop an iceberg detection system using reflected
sound waves after the Titanic disaster on 15 April 1912. In the
end reflected sound waves proved not to be suitable for the
detection of icebergs but for measuring the depth of the sea,because the bottom of the sea reflected them well. Thus, echo
sounding was born.
Behm was granted German patent No. 282009 for the inventionof echo sounding (device for measuring depths of the sea and
distances and headings of ships or obstacles by means of
reflected sound waves) on 22 July 1913.
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Hyperbolic Navigational Systems
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Hyperbolic Navigational Systems
hyperbolic navigation system is a navigation system that
produces hyperbolic lines of position by the measurement of thedifference in the time of reception, or the phase, of radio signals
from multiple synchronized transmitters at fixed locations
Hyperbolic Navigational Systems
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yp g y
GEE
The British GEE system was developed during World War II. GEEused a series of transmitters sending out precisely timed signals,
and the aircraft using GEE, RAF Bomber Command's heavy
bombers, examined the time of arrival on an oscilloscope at the
navigator's station. If the signal from two stations arrived at the
same time, the aircraft must be an equal distance from bothtransmitters, allowing the navigator to determine a line of
position on his chart of all the positions at that distance from
both stations. By making similar measurements with other
stations, additional lines of position can be produced, leading to
a fix. GEE was accurate to about 165 yards (150 m) at short
ranges, and up to a mile (1.6 km) at longer ranges over Germany.
Used after WWII as late as the 1960s in the RAF (approx freq was
by then 68 MHz).
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The Decca Navigator System was a hyperbolic low frequency
radio navigation system (also known as multilateration) that
was first deployed during World War II when the Allied forces
needed a system which could be used to achieve accurate
landings.
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OMEGA was originally developed by the United States Navy for
military aviation users. It was approved for development in 1968
with only eight transmitters and the ability to achieve a four mile(6 km) accuracy when fixing a position. Each Omega station
transmitted a very low frequency signal which consisted of a
pattern of four tones unique to the station that was repeated
every ten seconds. OMEGA employed hyperbolic radionavigation
techniques and the chain operated in the VLF portion of the
spectrum between 10 to 14 kHz. Near its end, it evolved into a
system used primarily by the civil community. By receiving signals
from three stations, an Omega receiver could locate a position to
within 4 nautical miles (7.4 km) using the principle of phasecomparison of signals.
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John Alvin Pierce, the "Father of Omega," first proposed
the use of continuous wave modulation of VLF signals for
navigation purposes in the 1940's. Working at the
Radiation Laboratory at the Massachusetts Institute ofTechnology, he proved the viability of measuring the
phase difference of radio signals to compute a location
solution. Pierce originally called this system RADUX. After
experimenting with various frequencies, he settled on a
phase stable, 10 kHz transmission in the 1950's. Thinking
this frequency was the far end of the radio spectrumPierce dubbed the transmission "Omega," for the last
letter of the Greek alphabet.
John (Jack) A. Pierce, who retired from a position as a senior research fellow atHarvard University, Cambridge, Mass. was awarded the Medal For Engineering
Excellence in 1990 for the "design , teaching and advocacy of radio propagation,
navigation and timing which led to the development ofLoran, Loran C and
Omega.
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OMEGA-Transmitter Paynesville was inaugaurated in 1976 and used as radio antenna anumbrella aerial mounted on a 417 metre high guyed mast of lattice steel, which was the
tallest structure ever built in Africa. The station was directed to the government of
Liberia after the termination of the Omega Navigation System on September 30, 1997.
As of February, 2006, the Omega Tower near Paynesville is still standing, although it is
unused. Access to the tower is not restricted, and it is possible to climb it.
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LORAN (LOng RAnge Navigation) is a terrestrial radio navigation system using low
frequency radio transmitters that uses multiple transmitters (multilateration) to
determine the location and speed of the receiver.
The current version ofLORAN in common use is LORAN-C, which operates in the low
frequency portion of the EM spectrum from 90 to 110 kHz. Many nations use the
system, including the United States, Japan, and several European countries.
A LORAN-C receiver for use on merchant ships
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Timing and Synchronization
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Timing and Synchronization
Each LORAN station is equipped with a suite of specialized equipment to generate
the precisely timed signals used to modulate / drive the transmitting equipment. Up
to three commercial cesium atomic clocks are used to generate 5 MHz and pulse persecond (or 1 Hz) signals that are used by timing equipment to generate the various
GRI-dependent drive signals for the transmitting equipment.
Each U.S.-operated LORAN station is synchronized to within 100 ns of UTC
Cesium atomic clocks
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Transmitters and Antennas
LORAN-C transmitters
operate at peak powers of100 kilowatts to four
megawatts, comparable to
longwave broadcasting
stations. Most LORAN-C
transmitters use mast
radiators insulated fromground with heights
between 190 and 220
metres.
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Map ofLORAN stations.
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Gl b l i i lli
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Global navigation satellite system
Global Navigation Satellite Systems (GNSS) is the standard generic term for satellite
navigation systems ("sat nav") that provide autonomous geo-spatial positioning with
global coverage. GNSS allows small electronic receivers to determine their location
(longitude, latitude, and altitude) to within a few metres using time signals
transmitted along a line-of-sight by radio from satellites. Receivers calculate the
precise time as well as position,
Early predecessors were the ground based DECCA, LORAN and Omega systems,
which used terrestrial longwave radio transmitters instead of satellites. Thesepositioning systems broadcast a radio pulse from a known "master" location,
followed by repeated pulses from a number of "slave" stations. The delay
between the reception and sending of the signal at the slaves was carefully
controlled, allowing the receivers to compare the delay between reception and
the delay between sending.
Common Applications
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Common Applications
Automobiles can be equipped with GNSS receivers at the factory or as aftermarket
equipment. Units often display moving maps and information about location, speed,
direction, and nearby streets and points of interest.
Aircraft navigation systems usually display a "moving map" and are often connected to the
autopilot for en-route navigation. Cockpit-mounted GNSS receivers and glass cockpits are
appearing in general aviation aircraft of all sizes.
Boats and ships can use GNSS to navigate all of the world's lakes, seas and oceans.
Heavy Equipment can use GNSS in construction, mining and precision agriculture. The blades
and buckets of construction equipment are controlled automatically in GNSS-based machine
guidance systems.
Bicycles often use GNSS in racing and touring. GNSS navigation allows cyclists to plot theircourse in advance and follow this course, which may include quieter, narrower streets,
without having to stop frequently to refer to separate maps.
Spacecraft are now beginning to use GNSS as a navigational tool. The addition of a GNSS
receiver to a spacecraft allows precise orbit determination without ground tracking.
Civil and military uses
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The original motivation for satellite navigation was for military applications. Satellite
navigation allows for hitherto impossible precision in the delivery of weapons to
targets, greatly increasing their lethality whilst reducing inadvertent casualties frommis-directed weapons. (See smart bomb). Satellite navigation also allows forces to be
directed and to locate themselves more easily, reducing the fog of war.
In these ways, satellite
navigation can be
regarded as a force
multiplier. In particular,
the ability to reduce
unintended casualties
has particular
advantages for wars
where public relations
is an important aspect
of warfare. For these
reasons, a satellite
navigation system is an
essential asset for any
aspiring military power.
Gl b l i ti t
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Global navigation systems
Operational
GPS Global Positioning System
The United States' Global Positioning
System (GPS) consists of up to 32 medium
Earth orbit satellites in six different orbital
planes, with the exact number of satellitesvarying as older satellites are retired and
replaced. Operational since 1978 and
globally available since 1994, GPS is
currently the world's most utilized satellite
navigation system.
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In development
Galileo
The European Union and European Space Agency agreed on March 2002 to introduce
their own alternative to GPS, called the Galileo positioning system. At a cost of about
GBP 2.4 billion,[3] the system is scheduled to be working from 2012. The first
experimental satellite was launched on 28 December 2005. Galileo is expected to be
compatible with the modernized GPS system. The receivers will be able to combine the
signals from both Galileo and GPS satellites to greatly increase the accuracy.
GLONASS
The formerly Soviet, and now Russian, GLObal'naya NAvigatsionnaya Sputnikovaya
Sistema(GLObal NAvigation Satellite System), or GLONASS, was a fully functional
navigation constellation but since the collapse of the Soviet Union has fallen intodisrepair, leading to gaps in coverage and only partial availability. The Russian Federation
has pledged to restore it to full global availability by 2010. As of April 2010 GLONASS is
practically restored (21 of 24 satellites are operational).
Compass
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Compass
China has indicated they intend to expand their regional navigation system, called Beidou
or Big Dipper, into a global navigation system by 2020[4] a program that has been calledCompass in China's official news agency Xinhua. The Compass system is proposed to utilize
30 medium Earth orbit satellites and five geostationary satellites.
Comparison of GNSS systems
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A satellite-based augmentation
system (SBAS) is a system that
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system (SBAS) is a system that
supports wide-area or regional
augmentation through the use of
additional satellite-broadcastmessages. Such systems are
commonly composed of multiple
ground stations, located at
accurately-surveyed points. The
ground stations take measurements
of one or more of the GNSS
satellites, the satellite signals, or
other environmental factors which
may impact the signal received by
the users. Using these
measurements, information
messages are created and sent to
one or more satellites for broadcast
to the end users.
Regional navigation systems
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Regional navigation systems
Operational:
China
Beidou 1
Chinese regional network to be expanded into the global
COMPASS Navigation System.
France
DORIS
Doppler Orbitography and Radio-positioning Integrated by
Satellite (DORIS) is a French precision navigation system.
Regional navigation systems
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In development
IRNSS -Indian Regional NavigationalSatelliteSystem
The Indian Regional Navigational Satellite System (IRNSS) is an autonomous regional
satellite navigation system being developed by Indian Space Research Organisation
which would be under the total control of Indian government. The government approved
the project in May 2006, with the intention of the system to be completed and
implemented by 2014. It will consist of a constellation of 7 navigational satellites. All the
7 satellites will be placed in the Geostationary orbit (GEO) to have a larger signalfootprint and lower number of satellites to map the region. It is intended to provide an
all-weather absolute position accuracy of better than 7.6 meters throughout India and
within a region extending approximately 1,500 km around it. A goal of complete Indian
control has been stated, with the space segment, ground segment and user receivers all
being built in India.
QZSS Quasi-ZenithSatelliteSystem
The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time
transfer system and enhancement for GPS covering Japan. The first demonstration
satellite is scheduled to be launched in 2009
The Wide Area Augmentation System (WAAS) is an air navigation aid developed by
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The Wide Area Augmentation System (WAAS) is an air navigation aid developed by
the Federal Aviation Administration to augment the Global Positioning System (GPS),
with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is
intended to enable aircraft to rely on GPS for all phases of flight, including precision
approaches to any airport within its coverage area.
WAAS System Overview
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The European Geostationary Navigation
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The European Geostationary Navigation
Overlay Service (EGNOS) is a satellite based
augmentation system (SBAS) under
development by the European Space Agency,
the European Commission and EUROCONTROL.
It is intended to supplement the GPS,
GLONASS and Galileo systems by reporting on
the reliability and accuracy of the signals. The
official start of operations was announced by
the European Commission on 1 October 2009
The system started its initial operations in July 2005, showing outstanding
performances in terms of accuracy (better than two metres) and availability
(above 99%); it is intended to be certified for use in safety of life applications in
2010. A commercial service is under test and will also be made available in 2010.
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Map of the EGNOS ground network
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GLONASS (Russian: , abbreviation of
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; tr.: GLObal'naya NAvigatsionnaya Sputnikovaya Sistema; "GLObal
NAvigation Satellite System" in English) is a radio-based satellite navigation system,
developed by the former Soviet Union and now operated for the Russian government
by the Russian Space Forces. It is an alternative and complementary to the UnitedStates' Global Positioning System (GPS), the Chinese Compass navigation system, and
the planned Galileo positioning system of the European Union (EU).
GLONASSGLONASS logo
D l t th GLONASS b i 1976 ith l f l b l b
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Development on the GLONASS began in 1976, with a goal of global coverage by
1991. Beginning on 12 October 1982, numerous rocket launches added satellites
to the system until the constellation was completed in 1995. Following
completion, the system rapidly fell into disrepair with the collapse of the Russianeconomy. Beginning in 2001, Russia committed to restoring the system and by
April 2010 it is practically restored (21 of 24 satellites are operational).
A combined GLONASS/GPS Personal Radio Beacon
A Russian military rugged, combined
GLONASS/GPS receiver
Aircraft Navigation
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A marker beacon is a particular type of low frequency radio beacon used in
aviation, usually in conjunction with an instrument landing system (ILS), to give
pilots a means to determine position along an established route to a destination
such as a runway. From the 1930s until the 1950s, markers were used extensively
along airways to provide an indication of an aircraft's specific position along the
route, but from the 1960s they have become increasingly limited to ILS approach
installations.
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OuterMarkerThe outer marker, which normally identifies the final approack
fix, is situated on the same line with the localizer and the
runway centerline, four to seven nautical miles before the
runway threshold. It is typically located about 1-nautical-mile
(2 km) inside the point where the glideslope intercepts the
intermediate altitude and transmits a low-powered (3 watt),
400 Hz tone signal on a 75 MHz carrier frequency. Its antenna is
highly directional, and is pointed straight up. The valid signal
area is a 2,400 ft (730 m) 4,200 ft (1,280 m) ellipse (as
measured 1,000 ft (300 m) above the antenna.) When the
aircraft passes over the outer marker antenna, its marker
beacon receiver detects the signal. The system gives the pilot a
visual (blinking blue outer marker light) and aural (continuous
series of audio tone morse code-like 'dashes') indication.
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MiddleMarkerA middle marker works on the same principle
as an outer marker. It is normally positioned
0.5 to 0.8 nautical miles (1 km) before the
runway threshold. When the aircraft is above
the middle marker, the receivers amber
middle marker light starts blinking, and a
repeating pattern of audible morse code-like
dot-dashes at a frequency of 1,300 Hz in the
headset. This alerts the pilot, that the CAT I
missed approach point (typically 200 feet
(60 m) above the ground level or AGL on the
glideslope) has been passed and should have
already initiated the missed approach if one of
several visual cues has not been spotted.
InnerMarker
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InnerMarkerSimilar to the outer and middle markers;
located at the beginning (threshold) of the
runway on some ILS approach systems (usuallyCategory II and III) having decision heights of
less than 200 feet (60 m) AGL. Triggers a
flashing white light on the same marker
beacon receiver used for the outer and middle
markers; also a series of audio tone 'dots' at a
frequency of 3,000 Hz in the headset.
The ILS Components
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When you fly the ILS, you're really following two signals: a localizer for lateral
guidance (VHF); and a glide slope for vertical guidance (UHF). When you tune
your Nav. receiver to a localizer frequency a second receiver, the glide-slope
receiver, is automatically tuned to its proper frequency. The pairing is
automatic.
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Tracking inbound on the Localizer to Runway 067, Green airport, Providence, R.I. From left to right, the aircraft is 1 Right of
course, two dots (turn left to return); On course; and 1 Left of course (turn right to return).
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