Navigation

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Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another. Navigation_sentence_0

The field of navigation includes four general categories: land navigation, marine navigation, aeronautic navigation, and space navigation. Navigation_sentence_1

It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks. Navigation_sentence_2

All navigational techniques involve locating the navigator's position compared to known locations or patterns. Navigation_sentence_3

Navigation, in a broader sense, can refer to any skill or study that involves the determination of position and direction. Navigation_sentence_4

In this sense, navigation includes orienteering and pedestrian navigation. Navigation_sentence_5

History Navigation_section_0

Further information: History of navigation Navigation_sentence_6

See also: History of geodesy Navigation_sentence_7

In the European medieval period, navigation was considered part of the set of seven mechanical arts, none of which were used for long voyages across open ocean. Navigation_sentence_8

Polynesian navigation is probably the earliest form of open-ocean navigation, it was based on memory and observation recorded on scientific instruments like the Marshall Islands Stick Charts of Ocean Swells. Navigation_sentence_9

Early Pacific Polynesians used the motion of stars, weather, the position of certain wildlife species, or the size of waves to find the path from one island to another. Navigation_sentence_10

Maritime navigation using scientific instruments such as the mariner's astrolabe first occurred in the Mediterranean during the Middle Ages. Navigation_sentence_11

Although land astrolabes were invented in the Hellenistic period and existed in classical antiquity and the Islamic Golden Age, the oldest record of a sea astrolabe is that of Majorcan astronomer Ramon Llull dating from 1295. Navigation_sentence_12

The perfecting of this navigation instrument is attributed to Portuguese navigators during early Portuguese discoveries in the Age of Discovery. Navigation_sentence_13

The earliest known description of how to make and use a sea astrolabe comes from Spanish cosmographer Martín Cortés de Albacar's Arte de Navegar (The Art of Navigation) published in 1551, based on the principle of the archipendulum used in constructing the Egyptian pyramids. Navigation_sentence_14

Open-seas navigation using the astrolabe and the compass started during the Age of Discovery in the 15th century. Navigation_sentence_15

The Portuguese began systematically exploring the Atlantic coast of Africa from 1418, under the sponsorship of Prince Henry. Navigation_sentence_16

In 1488 Bartolomeu Dias reached the Indian Ocean by this route. Navigation_sentence_17

In 1492 the Spanish monarchs funded Christopher Columbus's expedition to sail west to reach the Indies by crossing the Atlantic, which resulted in the Discovery of the Americas. Navigation_sentence_18

In 1498, a Portuguese expedition commanded by Vasco da Gama reached India by sailing around Africa, opening up direct trade with Asia. Navigation_sentence_19

Soon, the Portuguese sailed further eastward, to the Spice Islands in 1512, landing in China one year later. Navigation_sentence_20

The first circumnavigation of the earth was completed in 1522 with the Magellan-Elcano expedition, a Spanish voyage of discovery led by Portuguese explorer Ferdinand Magellan and completed by Spanish navigator Juan Sebastián Elcano after the former's death in the Philippines in 1521. Navigation_sentence_21

The fleet of seven ships sailed from Sanlúcar de Barrameda in Southern Spain in 1519, crossed the Atlantic Ocean and after several stopovers rounded the southern tip of South America. Navigation_sentence_22

Some ships were lost, but the remaining fleet continued across the Pacific making a number of discoveries including Guam and the Philippines. Navigation_sentence_23

By then, only two galleons were left from the original seven. Navigation_sentence_24

The Victoria led by Elcano sailed across the Indian Ocean and north along the coast of Africa, to finally arrive in Spain in 1522, three years after its departure. Navigation_sentence_25

The Trinidad sailed east from the Philippines, trying to find a maritime path back to the Americas, but was unsuccessful. Navigation_sentence_26

The eastward route across the Pacific, also known as the tornaviaje (return trip) was only discovered forty years later, when Spanish cosmographer Andrés de Urdaneta sailed from the Philippines, north to parallel 39°, and hit the eastward Kuroshio Current which took its galleon across the Pacific. Navigation_sentence_27

He arrived in Acapulco on October 8, 1565. Navigation_sentence_28

Etymology Navigation_section_1

The term stems from the 1530s, from Latin navigationem (nom. Navigation_sentence_29

navigatio), from navigatus, pp. of navigare "to sail, sail over, go by sea, steer a ship," from navis "ship" and the root of agere "to drive". Navigation_sentence_30

Basic concepts Navigation_section_2

Latitude Navigation_section_3

Further information: Latitude Navigation_sentence_31

Roughly, the latitude of a place on Earth is its angular distance north or south of the equator. Navigation_sentence_32

Latitude is usually expressed in degrees (marked with °) ranging from 0° at the Equator to 90° at the North and South poles. Navigation_sentence_33

The latitude of the North Pole is 90° N, and the latitude of the South Pole is 90° S. Mariners calculated latitude in the Northern Hemisphere by sighting the North Star Polaris with a sextant and using sight reduction tables to correct for height of eye and atmospheric refraction. Navigation_sentence_34

The height of Polaris in degrees above the horizon is the latitude of the observer, within a degree or so. Navigation_sentence_35

Longitude Navigation_section_4

Further information: Longitude Navigation_sentence_36

Similar to latitude, the longitude of a place on Earth is the angular distance east or west of the prime meridian or Greenwich meridian. Navigation_sentence_37

Longitude is usually expressed in degrees (marked with °) ranging from at the Greenwich meridian to 180° east and west. Navigation_sentence_38

Sydney, for example, has a longitude of about 151° east. Navigation_sentence_39

New York City has a longitude of 74° west. Navigation_sentence_40

For most of history, mariners struggled to determine longitude. Navigation_sentence_41

Longitude can be calculated if the precise time of a sighting is known. Navigation_sentence_42

Lacking that, one can use a sextant to take a lunar distance (also called the lunar observation, or "lunar" for short) that, with a nautical almanac, can be used to calculate the time at zero longitude (see Greenwich Mean Time). Navigation_sentence_43

Reliable marine chronometers were unavailable until the late 18th century and not affordable until the 19th century. Navigation_sentence_44

For about a hundred years, from about 1767 until about 1850, mariners lacking a chronometer used the method of lunar distances to determine Greenwich time to find their longitude. Navigation_sentence_45

A mariner with a chronometer could check its reading using a lunar determination of Greenwich time. Navigation_sentence_46

Loxodrome Navigation_section_5

Further information: Rhumb line Navigation_sentence_47

In navigation, a rhumb line (or loxodrome) is a line crossing all meridians of longitude at the same angle, i.e. a path derived from a defined initial bearing. Navigation_sentence_48

That is, upon taking an initial bearing, one proceeds along the same bearing, without changing the direction as measured relative to true or magnetic north. Navigation_sentence_49

Methods of navigation Navigation_section_6

Most modern navigation relies primarily on positions determined electronically by receivers collecting information from satellites. Navigation_sentence_50

Most other modern techniques rely on crossing lines of position or LOP. Navigation_sentence_51

A line of position can refer to two different things, either a line on a chart or a line between the observer and an object in real life. Navigation_sentence_52

A bearing is a measure of the direction to an object. Navigation_sentence_53

If the navigator measures the direction in real life, the angle can then be drawn on a nautical chart and the navigator will be on that line on the chart. Navigation_sentence_54

In addition to bearings, navigators also often measure distances to objects. Navigation_sentence_55

On the chart, a distance produces a circle or arc of position. Navigation_sentence_56

Circles, arcs, and hyperbolae of positions are often referred to as lines of position. Navigation_sentence_57

If the navigator draws two lines of position, and they intersect he must be at that position. Navigation_sentence_58

A fix is the intersection of two or more LOPs. Navigation_sentence_59

If only one line of position is available, this may be evaluated against the dead reckoning position to establish an estimated position. Navigation_sentence_60

Lines (or circles) of position can be derived from a variety of sources: Navigation_sentence_61

Navigation_unordered_list_0

  • celestial observation (a short segment of the circle of equal altitude, but generally represented as a line),Navigation_item_0_0
  • terrestrial range (natural or man made) when two charted points are observed to be in line with each other,Navigation_item_0_1
  • compass bearing to a charted object,Navigation_item_0_2
  • radar range to a charted object,Navigation_item_0_3
  • on certain coastlines, a depth sounding from echo sounder or hand lead line.Navigation_item_0_4

There are some methods seldom used today such as "dipping a light" to calculate the geographic range from observer to lighthouse. Navigation_sentence_62

Methods of navigation have changed through history. Navigation_sentence_63

Each new method has enhanced the mariner's ability to complete his voyage. Navigation_sentence_64

One of the most important judgments the navigator must make is the best method to use. Navigation_sentence_65

Some types of navigation are depicted in the table. Navigation_sentence_66

Navigation_table_general_0

IllustrationNavigation_header_cell_0_0_0 DescriptionNavigation_header_cell_0_0_1 ApplicationNavigation_header_cell_0_0_2
Traditional navigation methods include:Navigation_header_cell_0_1_0
Navigation_cell_0_2_0 In marine navigation, 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 accepted that 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.Navigation_cell_0_2_1 Used at all times.Navigation_cell_0_2_2
Navigation_cell_0_3_0 In marine navigation, Pilotage involves navigating in restricted/coastal waters with frequent determination of position relative to geographic and hydrographic features.Navigation_cell_0_3_1 When within sight of land.Navigation_cell_0_3_2
Navigation_cell_0_4_0 Land navigation is the discipline of following a route through terrain on foot or by vehicle, using maps with reference to terrain, a compass, and other basic navigational tools and/or using landmarks and signs. Wayfinding is the more basic form.Navigation_cell_0_4_1 Used at all times.Navigation_cell_0_4_2
Navigation_cell_0_5_0 Celestial navigation involves reducing celestial measurements to lines of position using tables, spherical trigonometry, and almanacs. It is primarily used at sea but can also be used on land.Navigation_cell_0_5_1 Used primarily as a backup to satellite and other electronic systems in the open ocean.Navigation_cell_0_5_2
Electronic navigation covers any method of position fixing using electronic means, including:Navigation_header_cell_0_6_0
Navigation_cell_0_7_0 Radio navigation uses radio waves to determine position by either radio direction finding systems or hyperbolic systems, such as Decca, Omega and LORAN-C.Navigation_cell_0_7_1 Availability has declined due to the development of accurate GNSS.Navigation_cell_0_7_2
Navigation_cell_0_8_0 Radar navigation uses radar to determine the distance from or bearing of objects whose position is known. This process is separate from radar's use as a collision avoidance system.Navigation_cell_0_8_1 Primarily when within radar range of land.Navigation_cell_0_8_2
Navigation_cell_0_9_0 Satellite navigation uses the Global Navigation Satellite System (GNSS) to determine position.Navigation_cell_0_9_1 Used in all situations.Navigation_cell_0_9_2

The practice of navigation usually involves a combination of these different methods. Navigation_sentence_67

Mental navigation checks Navigation_section_7

By mental navigation checks, a pilot or a navigator estimates tracks, distances, and altitudes which will then help the pilot avoid gross navigation errors. Navigation_sentence_68

Piloting Navigation_section_8

Further information: Pilotage Navigation_sentence_69

Piloting (also called pilotage) involves navigating an aircraft by visual reference to landmarks, or a water vessel in restricted waters and fixing its position as precisely as possible at frequent intervals. Navigation_sentence_70

More so than in other phases of navigation, proper preparation and attention to detail are important. Navigation_sentence_71

Procedures vary from vessel to vessel, and between military, commercial, and private vessels. Navigation_sentence_72

A military navigation team will nearly always consist of several people. Navigation_sentence_73

A military navigator might have bearing takers stationed at the gyro repeaters on the bridge wings for taking simultaneous bearings, while the civilian navigator must often take and plot them himself. Navigation_sentence_74

While the military navigator will have a bearing book and someone to record entries for each fix, the civilian navigator will simply pilot the bearings on the chart as they are taken and not record them at all. Navigation_sentence_75

If the ship is equipped with an ECDIS, it is reasonable for the navigator to simply monitor the progress of the ship along the chosen track, visually ensuring that the ship is proceeding as desired, checking the compass, sounder and other indicators only occasionally. Navigation_sentence_76

If a pilot is aboard, as is often the case in the most restricted of waters, his judgement can generally be relied upon, further easing the workload. Navigation_sentence_77

But should the ECDIS fail, the navigator will have to rely on his skill in the manual and time-tested procedures. Navigation_sentence_78

Celestial navigation Navigation_section_9

Main article: Celestial navigation Navigation_sentence_79

Celestial navigation systems are based on observation of the positions of the Sun, Moon, Planets and navigational stars. Navigation_sentence_80

Such systems are in use as well for terrestrial navigating as for interstellar navigating. Navigation_sentence_81

By knowing which point on the rotating earth a celestial object is above and measuring its height above the observer's horizon, the navigator can determine his distance from that subpoint. Navigation_sentence_82

A nautical almanac and a marine chronometer are used to compute the subpoint on earth a celestial body is over, and a sextant is used to measure the body's angular height above the horizon. Navigation_sentence_83

That height can then be used to compute distance from the subpoint to create a circular line of position. Navigation_sentence_84

A navigator shoots a number of stars in succession to give a series of overlapping lines of position. Navigation_sentence_85

Where they intersect is the celestial fix. Navigation_sentence_86

The moon and sun may also be used. Navigation_sentence_87

The sun can also be used by itself to shoot a succession of lines of position (best done around local noon) to determine a position. Navigation_sentence_88

Marine chronometer Navigation_section_10

Main article: Marine chronometer Navigation_sentence_89

In order to accurately measure longitude, the precise time of a sextant sighting (down to the second, if possible) must be recorded. Navigation_sentence_90

Each second of error is equivalent to 15 seconds of longitude error, which at the equator is a position error of .25 of a nautical mile, about the accuracy limit of manual celestial navigation. Navigation_sentence_91

The spring-driven marine chronometer is a precision timepiece used aboard ship to provide accurate time for celestial observations. Navigation_sentence_92

A chronometer differs from a spring-driven watch principally in that it contains a variable lever device to maintain even pressure on the mainspring, and a special balance designed to compensate for temperature variations. Navigation_sentence_93

A spring-driven chronometer is set approximately to Greenwich mean time (GMT) and is not reset until the instrument is overhauled and cleaned, usually at three-year intervals. Navigation_sentence_94

The difference between GMT and chronometer time is carefully determined and applied as a correction to all chronometer readings. Navigation_sentence_95

Spring-driven chronometers must be wound at about the same time each day. Navigation_sentence_96

Quartz crystal marine chronometers have replaced spring-driven chronometers aboard many ships because of their greater accuracy. Navigation_sentence_97

They are maintained on GMT directly from radio time signals. Navigation_sentence_98

This eliminates chronometer error and watch error corrections. Navigation_sentence_99

Should the second hand be in error by a readable amount, it can be reset electrically. Navigation_sentence_100

The basic element for time generation is a quartz crystal oscillator. Navigation_sentence_101

The quartz crystal is temperature compensated and is hermetically sealed in an evacuated envelope. Navigation_sentence_102

A calibrated adjustment capability is provided to adjust for the aging of the crystal. Navigation_sentence_103

The chronometer is designed to operate for a minimum of 1 year on a single set of batteries. Navigation_sentence_104

Observations may be timed and ship's clocks set with a comparing watch, which is set to chronometer time and taken to the bridge wing for recording sight times. Navigation_sentence_105

In practice, a wrist watch coordinated to the nearest second with the chronometer will be adequate. Navigation_sentence_106

A stop watch, either spring wound or digital, may also be used for celestial observations. Navigation_sentence_107

In this case, the watch is started at a known GMT by chronometer, and the elapsed time of each sight added to this to obtain GMT of the sight. Navigation_sentence_108

All chronometers and watches should be checked regularly with a radio time signal. Navigation_sentence_109

Times and frequencies of radio time signals are listed in publications such as Radio Navigational Aids. Navigation_sentence_110

The marine sextant Navigation_section_11

Further information: Sextant Navigation_sentence_111

The second critical component of celestial navigation is to measure the angle formed at the observer's eye between the celestial body and the sensible horizon. Navigation_sentence_112

The sextant, an optical instrument, is used to perform this function. Navigation_sentence_113

The sextant consists of two primary assemblies. Navigation_sentence_114

The frame is a rigid triangular structure with a pivot at the top and a graduated segment of a circle, referred to as the "arc", at the bottom. Navigation_sentence_115

The second component is the index arm, which is attached to the pivot at the top of the frame. Navigation_sentence_116

At the bottom is an endless vernier which clamps into teeth on the bottom of the "arc". Navigation_sentence_117

The optical system consists of two mirrors and, generally, a low power telescope. Navigation_sentence_118

One mirror, referred to as the "index mirror" is fixed to the top of the index arm, over the pivot. Navigation_sentence_119

As the index arm is moved, this mirror rotates, and the graduated scale on the arc indicates the measured angle ("altitude"). Navigation_sentence_120

The second mirror, referred to as the "horizon glass", is fixed to the front of the frame. Navigation_sentence_121

One half of the horizon glass is silvered and the other half is clear. Navigation_sentence_122

Light from the celestial body strikes the index mirror and is reflected to the silvered portion of the horizon glass, then back to the observer's eye through the telescope. Navigation_sentence_123

The observer manipulates the index arm so the reflected image of the body in the horizon glass is just resting on the visual horizon, seen through the clear side of the horizon glass. Navigation_sentence_124

Adjustment of the sextant consists of checking and aligning all the optical elements to eliminate "index correction". Navigation_sentence_125

Index correction should be checked, using the horizon or more preferably a star, each time the sextant is used. Navigation_sentence_126

The practice of taking celestial observations from the deck of a rolling ship, often through cloud cover and with a hazy horizon, is by far the most challenging part of celestial navigation. Navigation_sentence_127

Inertial navigation Navigation_section_12

Further information: Inertial navigation system Navigation_sentence_128

Inertial navigation system (INS) is a dead reckoning type of navigation system that computes its position based on motion sensors. Navigation_sentence_129

Before actually navigating, the initial latitude and longitude and the INS's physical orientation relative to the earth (e.g., north and level) are established. Navigation_sentence_130

After alignment, an INS receives impulses from motion detectors that measure (a) the acceleration along three axes (accelerometers), and (b) rate of rotation about three orthogonal axes (gyroscopes). Navigation_sentence_131

These enable an INS to continually and accurately calculate its current latitude and longitude (and often velocity). Navigation_sentence_132

Advantages over other navigation systems are that, once aligned, an INS does not require outside information. Navigation_sentence_133

An INS is not affected by adverse weather conditions and it cannot be detected or jammed. Navigation_sentence_134

Its disadvantage is that since the current position is calculated solely from previous positions and motion sensors, its errors are cumulative, increasing at a rate roughly proportional to the time since the initial position was input. Navigation_sentence_135

Inertial navigation systems must therefore be frequently corrected with a location 'fix' from some other type of navigation system. Navigation_sentence_136

The first inertial system is considered to be the V-2 guidance system deployed by the Germans in 1942. Navigation_sentence_137

However, inertial sensors are traced to the early 19th century. Navigation_sentence_138

The advantages INSs led their use in aircraft, missiles, surface ships and submarines. Navigation_sentence_139

For example, the U.S. Navy developed the Ships Inertial Navigation System (SINS) during the Polaris missile program to ensure a reliable and accurate navigation system to initial its missile guidance systems. Navigation_sentence_140

Inertial navigation systems were in wide use until satellite navigation systems (GPS) became available. Navigation_sentence_141

INSs are still in common use on submarines (since GPS reception or other fix sources are not possible while submerged) and long-range missiles. Navigation_sentence_142

Electronic navigation Navigation_section_13

Radio navigation Navigation_section_14

Main articles: Radio navigation and Radio direction finder Navigation_sentence_143

A radio direction finder or RDF is a device for finding the direction to a radio source. Navigation_sentence_144

Due to radio's ability to travel very long distances "over the horizon", it makes a particularly good navigation system for ships and aircraft that might be flying at a distance from land. Navigation_sentence_145

RDFs works by rotating a directional antenna and listening for the direction in which the signal from a known station comes through most strongly. Navigation_sentence_146

This sort of system was widely used in the 1930s and 1940s. Navigation_sentence_147

RDF antennas are easy to spot on German World War II aircraft, as loops under the rear section of the fuselage, whereas most US aircraft enclosed the antenna in a small teardrop-shaped fairing. Navigation_sentence_148

In navigational applications, RDF signals are provided in the form of radio beacons, the radio version of a lighthouse. Navigation_sentence_149

The signal is typically a simple AM broadcast of a morse code series of letters, which the RDF can tune in to see if the beacon is "on the air". Navigation_sentence_150

Most modern detectors can also tune in any commercial radio stations, which is particularly useful due to their high power and location near major cities. Navigation_sentence_151

Decca, OMEGA, and LORAN-C are three similar hyperbolic navigation systems. Navigation_sentence_152

Decca 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. Navigation_sentence_153

As was the case with Loran C, its primary use was for ship navigation in coastal waters. Navigation_sentence_154

Fishing vessels were major post-war users, but it was also used on aircraft, including a very early (1949) application of moving-map displays. Navigation_sentence_155

The system was deployed in the North Sea and was used by helicopters operating to oil platforms. Navigation_sentence_156

The OMEGA Navigation System was the first truly global radio navigation system for aircraft, operated by the United States in cooperation with six partner nations. Navigation_sentence_157

OMEGA was developed by the United States Navy for military aviation users. Navigation_sentence_158

It was approved for development in 1968 and promised a true worldwide oceanic coverage capability with only eight transmitters and the ability to achieve a four-mile (6 km) accuracy when fixing a position. Navigation_sentence_159

Initially, the system was to be used for navigating nuclear bombers across the North Pole to Russia. Navigation_sentence_160

Later, it was found useful for submarines. Navigation_sentence_161

Due to the success of the Global Positioning System the use of Omega declined during the 1990s, to a point where the cost of operating Omega could no longer be justified. Navigation_sentence_162

Omega was terminated on September 30, 1997 and all stations ceased operation. Navigation_sentence_163

LORAN is a terrestrial navigation system using low frequency radio transmitters that use the time interval between radio signals received from three or more stations to determine the position of a ship or aircraft. Navigation_sentence_164

The current version of LORAN in common use is LORAN-C, which operates in the low frequency portion of the EM spectrum from 90 to 110 kHz. Navigation_sentence_165

Many nations are users of the system, including the United States, Japan, and several European countries. Navigation_sentence_166

Russia uses a nearly exact system in the same frequency range, called CHAYKA. Navigation_sentence_167

LORAN use is in steep decline, with GPS being the primary replacement. Navigation_sentence_168

However, there are attempts to enhance and re-popularize LORAN. Navigation_sentence_169

LORAN signals are less susceptible to interference and can penetrate better into foliage and buildings than GPS signals. Navigation_sentence_170

Radar navigation Navigation_section_15

Further information: Radar navigation and Doppler radar § navigation Navigation_sentence_171

When a vessel is within radar range of land or special radar aids to navigation, the navigator can take distances and angular bearings to charted objects and use these to establish arcs of position and lines of position on a chart. Navigation_sentence_172

A fix consisting of only radar information is called a radar fix. Navigation_sentence_173

Types of radar fixes include "range and bearing to a single object," "two or more bearings," "tangent bearings," and "two or more ranges." Navigation_sentence_174

Parallel indexing is a technique defined by William Burger in the 1957 book The Radar Observer's Handbook. Navigation_sentence_175

This technique involves creating a line on the screen that is parallel to the ship's course, but offset to the left or right by some distance. Navigation_sentence_176

This parallel line allows the navigator to maintain a given distance away from hazards. Navigation_sentence_177

Some techniques have been developed for special situations. Navigation_sentence_178

One, known as the "contour method," involves marking a transparent plastic template on the radar screen and moving it to the chart to fix a position. Navigation_sentence_179

Another special technique, known as the Franklin Continuous Radar Plot Technique, involves drawing the path a radar object should follow on the radar display if the ship stays on its planned course. Navigation_sentence_180

During the transit, the navigator can check that the ship is on track by checking that the pip lies on the drawn line. Navigation_sentence_181

Satellite navigation Navigation_section_16

Further information: Satellite navigation Navigation_sentence_182

Global Navigation Satellite System or GNSS is the term for satellite navigation systems that provide positioning with global coverage. Navigation_sentence_183

A GNSS allow 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. Navigation_sentence_184

Receivers on the ground with a fixed position can also be used to calculate the precise time as a reference for scientific experiments. Navigation_sentence_185

As of October 2011, only the United States NAVSTAR Global Positioning System (GPS) and the Russian GLONASS are fully globally operational GNSSs. Navigation_sentence_186

The European Union's Galileo positioning system is a next generation GNSS in the final deployment phase, and became operational in 2016. Navigation_sentence_187

China has indicated it may expand its regional Beidou navigation system into a global system. Navigation_sentence_188

More than two dozen GPS satellites are in medium Earth orbit, transmitting signals allowing GPS receivers to determine the receiver's location, speed and direction. Navigation_sentence_189

Since the first experimental satellite was launched in 1978, GPS has become an indispensable aid to navigation around the world, and an important tool for map-making and land surveying. Navigation_sentence_190

GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks. Navigation_sentence_191

Developed by the United States Department of Defense, GPS is officially named NAVSTAR GPS (NAVigation Satellite Timing And Ranging Global Positioning System). Navigation_sentence_192

The satellite constellation is managed by the United States Air Force 50th Space Wing. Navigation_sentence_193

The cost of maintaining the system is approximately US$750 million per year, including the replacement of aging satellites, and research and development. Navigation_sentence_194

Despite this fact, GPS is free for civilian use as a public good. Navigation_sentence_195

Modern smartphones act as personal GPS navigators for civilians who own them. Navigation_sentence_196

Overuse of these devices, whether in the vehicle or on foot, can lead to a relative inability to learn about navigated environments, resulting in sub-optimal navigation abilities when and if these devices become unavailable . Navigation_sentence_197

Typically a compass is also provided to determine direction when not moving. Navigation_sentence_198

Acoustic navigation Navigation_section_17

Main articles: Sonar and Acoustic location Navigation_sentence_199

Navigation processes Navigation_section_18

Ships and similar vessels Navigation_section_19

One day's work in navigation Navigation_section_20

The day's work in navigation is a minimal set of tasks consistent with prudent navigation. Navigation_sentence_200

The definition will vary on military and civilian vessels, and from ship to ship, but the traditional method takes a form resembling: Navigation_sentence_201

Navigation_ordered_list_1

  1. Maintain a continuous dead reckoning plot.Navigation_item_1_5
  2. Take two or more star observations at morning twilight for a celestial fix (prudent to observe 6 stars).Navigation_item_1_6
  3. Morning sun observation. Can be taken on or near prime vertical for longitude, or at any time for a line of position.Navigation_item_1_7
  4. Determine compass error by azimuth observation of the sun.Navigation_item_1_8
  5. Computation of the interval to noon, watch time of local apparent noon, and constants for meridian or ex-meridian sights.Navigation_item_1_9
  6. Noontime meridian or ex-meridian observation of the sun for noon latitude line. Running fix or cross with Venus line for noon fix.Navigation_item_1_10
  7. Noontime determination the day's run and day's set and drift.Navigation_item_1_11
  8. At least one afternoon sun line, in case the stars are not visible at twilight.Navigation_item_1_12
  9. Determine compass error by azimuth observation of the sun.Navigation_item_1_13
  10. Take two or more star observations at evening twilight for a celestial fix (prudent to observe 6 stars).Navigation_item_1_14

Navigation on ships is usually always conducted on the bridge. Navigation_sentence_202

It may also take place in adjacent space, where chart tables and publications are available. Navigation_sentence_203

Passage planning Navigation_section_21

Main article: Passage planning Navigation_sentence_204

Passage planning or voyage planning is a procedure to develop a complete description of vessel's voyage from start to finish. Navigation_sentence_205

The plan includes leaving the dock and harbor area, the en route portion of a voyage, approaching the destination, and mooring. Navigation_sentence_206

According to international law, a vessel's captain is legally responsible for passage planning, however on larger vessels, the task will be delegated to the ship's navigator. Navigation_sentence_207

Studies show that human error is a factor in 80 percent of navigational accidents and that in many cases the human making the error had access to information that could have prevented the accident. Navigation_sentence_208

The practice of voyage planning has evolved from penciling lines on nautical charts to a process of risk management. Navigation_sentence_209

Passage planning consists of four stages: appraisal, planning, execution, and monitoring, which are specified in International Maritime Organization Resolution A.893(21), Guidelines For Voyage Planning, and these guidelines are reflected in the local laws of IMO signatory countries (for example, Title 33 of the U.S. Code of Federal Regulations), and a number of professional books or publications. Navigation_sentence_210

There are some fifty elements of a comprehensive passage plan depending on the size and type of vessel. Navigation_sentence_211

The appraisal stage deals with the collection of information relevant to the proposed voyage as well as ascertaining risks and assessing the key features of the voyage. Navigation_sentence_212

This will involve considering the type of navigation required e.g. Ice navigation, the region the ship will be passing through and the hydrographic information on the route. Navigation_sentence_213

In the next stage, the written plan is created. Navigation_sentence_214

The third stage is the execution of the finalised voyage plan, taking into account any special circumstances which may arise such as changes in the weather, which may require the plan to be reviewed or altered. Navigation_sentence_215

The final stage of passage planning consists of monitoring the vessel's progress in relation to the plan and responding to deviations and unforeseen circumstances. Navigation_sentence_216

Integrated bridge systems Navigation_section_22

Electronic integrated bridge concepts are driving future navigation system planning. Navigation_sentence_217

Integrated systems take inputs from various ship sensors, electronically display positioning information, and provide control signals required to maintain a vessel on a preset course. Navigation_sentence_218

The navigator becomes a system manager, choosing system presets, interpreting system output, and monitoring vessel response. Navigation_sentence_219

Land navigation Navigation_section_23

Main article: Land navigation Navigation_sentence_220

Navigation for cars and other land-based travel typically uses maps, landmarks, and in recent times computer navigation ("satnav", short for satellite navigation), as well as any means available on water. Navigation_sentence_221

Computerized navigation commonly relies on GPS for current location information, a navigational map database of roads and navigable routes, and uses algorithms related to the shortest path problem to identify optimal routes. Navigation_sentence_222

Underwater navigation Navigation_section_24

Main articles: Diver navigation and Submarine navigation Navigation_sentence_223

Standards, Training and Organisations Navigation_section_25

Professional standards for navigation depend on the type of navigation and vary by country. Navigation_sentence_224

For marine navigation, Merchant Navy deck officers are trained and internationally certified according to the STCW Convention. Navigation_sentence_225

Leisure and amateur mariners may undertake lessons in navigation at local/regional training schools. Navigation_sentence_226

Naval officers receive navigation training as part of their naval training. Navigation_sentence_227

In land navigation, courses and training is often provided to young persons as part of general or extra-curricular education. Navigation_sentence_228

Land navigation is also an essential part of army training. Navigation_sentence_229

Additionally, organisations such as the Scouts and DoE programme teach navigation to their students. Navigation_sentence_230

Orienteering organisations are a type of sports that require navigational skills using a map and compass to navigate from point to point in diverse and usually unfamiliar terrain whilst moving at speed. Navigation_sentence_231

In aviation, pilots undertake air navigation training as part of learning to fly. Navigation_sentence_232

Professional organisations also assist to encourage improvements in navigation or bring together navigators in learned environments. Navigation_sentence_233

The Royal Institute of Navigation (RIN) is a learned society with charitable status, aimed at furthering the development of navigation on land and sea, in the air and in space. Navigation_sentence_234

It was founded in 1947 as a forum for mariners, pilots, engineers and academics to compare their experiences and exchange information. Navigation_sentence_235

In the US, the Institute of Navigation (ION) is a non-profit professional organisation advancing the art and science of positioning, navigation and timing. Navigation_sentence_236

Publications Navigation_section_26

Numerous nautical publications are available on navigation, which are published by professional sources all over the world. Navigation_sentence_237

In the UK, the United Kingdom Hydrographic Office, the Witherby Publishing Group and the Nautical Institute provide numerous navigational publications, including the comprehensive Admiralty Manual of Navigation. Navigation_sentence_238

In the US, Bowditch's American Practical Navigator is a free available encyclopedia of navigation issued by the US Government. Navigation_sentence_239

See also Navigation_section_27

Navigation_unordered_list_2


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Navigation.