Navigation

Navigation

Overview

Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigator
Navigator
A navigator is the person on board a ship or aircraft responsible for its navigation. The navigator's primary responsibility is to be aware of ship or aircraft position at all times. Responsibilities include planning the journey, advising the Captain or aircraft Commander of estimated timing to...

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

In the European medieval period, navigation was considered part of the set of seven mechanical arts
Mechanic arts
Mechanic arts is an obsolete and archaic term. In the medieval period, the Seven Mechanical Arts were intended as a complement to the Seven Liberal Arts, and consisted of weaving, blacksmithing, war, navigation, agriculture, hunting, medicine, and the ars theatrica. In the 19th century it referred...

.

1530s, from L.
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Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigator
Navigator
A navigator is the person on board a ship or aircraft responsible for its navigation. The navigator's primary responsibility is to be aware of ship or aircraft position at all times. Responsibilities include planning the journey, advising the Captain or aircraft Commander of estimated timing to...

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

History


In the European medieval period, navigation was considered part of the set of seven mechanical arts
Mechanic arts
Mechanic arts is an obsolete and archaic term. In the medieval period, the Seven Mechanical Arts were intended as a complement to the Seven Liberal Arts, and consisted of weaving, blacksmithing, war, navigation, agriculture, hunting, medicine, and the ars theatrica. In the 19th century it referred...

.

Etymology


1530s, from L. navigationem (nom. 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" .

Latitude



The latitude of a place on the Earth's surface is the angular distance north or south of the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

. Latitude is usually expressed in degrees
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...

 (marked with °) ranging from 0° at the Equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

 to 90° at the North and South poles. The latitude of the North Pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...

 is 90° N, and the latitude of the South Pole
South Pole
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 the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

 is 90° S. Historically, mariners calculated latitude in the Northern Hemisphere by sighting the North Star Polaris
Polaris
Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....

 with a sextant
Sextant
A sextant is an instrument used to measure the angle between any two visible objects. Its primary use is to determine the angle between a celestial object and the horizon which is known as the altitude. Making this measurement is known as sighting the object, shooting the object, or taking a sight...

 and sight reduction tables to take out error for height of eye and atmospheric refraction. Generally, the height of Polaris
Polaris
Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....

 in degrees of arc above the horizon is the latitude of the observer.

Longitude



Similar to latitude, the longitude of a place on the Earth's surface is the angular distance east or west of the prime meridian
Prime Meridian
The Prime Meridian is the meridian at which the longitude is defined to be 0°.The Prime Meridian and its opposite the 180th meridian , which the International Date Line generally follows, form a great circle that divides the Earth into the Eastern and Western Hemispheres.An international...

 or Greenwich meridian. Longitude is usually expressed in degrees
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...

 (marked with °) ranging from
Prime Meridian
The Prime Meridian is the meridian at which the longitude is defined to be 0°.The Prime Meridian and its opposite the 180th meridian , which the International Date Line generally follows, form a great circle that divides the Earth into the Eastern and Western Hemispheres.An international...

 at the Greenwich meridian to 180°
180th meridian
The 180th meridian or antimeridian is the meridian which is 180° east or west of the Prime Meridian passing through the Royal Observatory, Greenwich. It is common to both east longitude and west longitude. It is used as the basis for the International Date Line because it for the most part passes...

 east and west. Sydney, Australia, for example, has a longitude of about 151° east
151st meridian east
The meridian 151° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Pacific Ocean, Australasia, the Southern Ocean, and Antarctica to the South Pole....

. New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

 has a longitude of about 74° west
74th meridian west
The meridian 74° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Atlantic Ocean, the Caribbean Sea, South America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole....

. For most of history, mariners struggled to determine precise longitude. The problem was solved with the invention of the marine chronometer
Marine chronometer
A marine chronometer is a clock that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation...

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

Modern technique


Most modern navigation relies primarily on positions determined electronically by receivers collecting information from satellites. Most other modern techniques rely on crossing lines of position or LOP. A line of position can refer to two different things: a line on a chart and a line between the observer and an object in real life. A bearing is a measure of the direction to an object. If the navigator measures the direction in real life, the angle can then be drawn on a nautical chart
Nautical chart
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...

 and the navigator will be on that line on the chart.

In addition to bearings, navigators also often measure distances to objects. On the chart, a distance produces a circle or arc of position. Circles, arcs, and hyperbolae of positions are often referred to as lines of position.

If the navigator draws two lines of position, and they intersect he must be at that position. A fix
Fix (position)
In position fixing navigation, a position fix or simply a fix is a position derived from measuring external reference points.The term is generally used with manual or visual techniques such as the use of intersecting visual or radio position lines rather than the use of more automated and accurate...

 is the intersection of two or more LOPs.

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

Lines (or circles) of position can be derived from a variety of sources:
  • celestial observation (a short segment of the circle of equal altitude, but generally represented as a line),
  • terrestrial range (natural or man made) when two charted points are observed to be in line with each other,
  • compass bearing to a charted object,
  • radar range to a charted object,
  • on certain coastlines, a depth sounding from echo sounder or hand lead line
    Sounding line
    A sounding line or lead line is a length of thin rope with a plummet, generally of lead, at its end. Regardless of the actual composition of the plummet, it is still called a "lead."...

    .


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

Methods of navigation have changed through history. Each new method has enhanced the mariner’s ability to complete his voyage. One of the most important judgments the navigator must make is the best method to use. Some types of navigation are depicted in the table.
Modern navigation methods
Illustration Description Application
Dead reckoning
Dead reckoning
In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course...

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
Leeway
Leeway is the motion of an object that is floating in the water to leeward due to the component of the wind vector perpendicular to the object’s. The National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual defines leeway as "the movement of a...

, current effects, and steering error result in an estimated position or EP. An inertial navigator develops an extremely accurate EP.
Used at all times.
Pilotage
Pilotage
Pilotage 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...

involves navigating in restricted waters with frequent determination of position relative to geographic and hydrographic features.
When within sight of land.
Celestial navigation
Celestial navigation
Celestial navigation, also known as astronavigation, is a position fixing technique that has evolved over several thousand years to help sailors cross oceans without having to rely on estimated calculations, or dead reckoning, to know their position...

involves reducing celestial measurements to lines of position using tables, spherical trigonometry
Spherical trigonometry
Spherical trigonometry is a branch of spherical geometry which deals with polygons on the sphere and the relationships between the sides and the angles...

, and almanacs
Nautical almanac
A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea...

.
Used primarily as a backup to satellite and other electronic systems
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...

 in the open ocean.
Electronic navigation
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...

covers any method of position fixing using electronic means, including:
Radio navigation
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...

uses radio waves to determine position by either radio direction finding systems
Radio direction finder
A radio direction finder is a device for finding the direction to a radio source. Due to low frequency propagation characteristic 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...

 or hyperbolic systems, such as Decca
Decca Navigator System
The Decca Navigator System was a low frequency hyperbolic navigation system that was first deployed during World War II when the Allied forces needed a system which could be used to achieve accurate landings...

, Omega
OMEGA Navigation System
OMEGA was the first truly global radio navigation system for aircraft, operated by the United States in cooperation with six partner nations.-History:OMEGA was originally developed by the United States Navy for military aviation users...

 and LORAN-C.
Losing ground to GPS.
Radar navigation
Radar navigation
Marine and aviation radar systems can provide very useful navigation information in a variety of situations. 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...

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.
Primarily when within radar range of land.
Satellite navigation uses artificial earth satellite systems, such as GPS, to determine position. Used in all situations.


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

Dead reckoning



Dead reckoning is the process of estimating present position by projecting course and speed from a known past position. It is also used to predict a future position by projecting course and speed from a known present position. The DR position is only an approximate position because it does not allow for the effect of leeway, current, helmsman error, compass error, or any other external influences.

The navigator uses dead reckoning in many ways, such as:
  • to determine sunrise and sunset,
  • to predict landfall, sighting lights and arrival times,
  • to evaluate the accuracy of electronic positioning information,
  • to predict which celestial bodies will be available for future observation.


The most important use of dead reckoning is to project the position of the ship into the immediate future and avoid hazards to navigation.

The navigator carefully tends the DR plot, updating it when required, and uses it to evaluate external forces acting on the ship. The navigator also consults the DR plot to avoid navigation hazards. A fix taken at each DR position will reveal the effects of current, wind, and steering error, and allow the navigator to stay on track by correcting for them.

The use of DR when an Electronic Charts Display and Information System (ECDIS) is the primary plotting method will vary with the type of system. An ECDIS allows the display of the ship’s heading projected out to some future position as a function of time, the display of waypoint information, and progress toward each waypoint in turn.

Until ECDIS is proven to provide the level of safety and accuracy required, the use of a traditional DR plot on paper charts is a prudent backup, especially in restricted waters.

Before the development of the lunar distance method or the marine chronometer
Marine chronometer
A marine chronometer is a clock that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation...

, dead reckoning was the primary method of determining longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

 available to mariners such as Christopher Columbus
Christopher Columbus
Christopher Columbus was an explorer, colonizer, and navigator, born in the Republic of Genoa, in northwestern Italy. Under the auspices of the Catholic Monarchs of Spain, he completed four voyages across the Atlantic Ocean that led to general European awareness of the American continents in the...

 and John Cabot
John Cabot
John Cabot was an Italian navigator and explorer whose 1497 discovery of parts of North America is commonly held to have been the first European encounter with the continent of North America since the Norse Vikings in the eleventh century...

 on their trans-Atlantic voyages.

Piloting



Piloting (also called pilotage) involves navigating a vessel in restricted waters and fixing its position as precisely as possible at frequent intervals. More so than in other phases of navigation, proper preparation and attention to detail are important. Procedures vary from vessel to vessel, and between military, commercial, and private vessels.

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

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

Celestial navigation



Celestial navigation systems are based on observation of the positions of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

, Planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

s and navigational stars
Navigational stars
Fifty-eight selected navigational stars are given a special status in the field of celestial navigation. Of the approximately 6,000 stars visible to the naked eye under optimal conditions, the selected stars are among the brightest and span thirty-eight constellations of the celestial sphere from...

. Such systems are in use as well for terrestrial navigating as for interstellar navigating. 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. A Nautical almanac
Nautical almanac
A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea...

 and a chronometer
Chronometer
Chronometer may refer to:* Chronometer watch, a watch tested and certified to meet certain precision standards* Hydrochronometer, a water clock* Marine chronometer, a timekeeper used for celestial navigation...

 are used to compute the subpoint on earth a celestial body is over, and a sextant
Sextant
A sextant is an instrument used to measure the angle between any two visible objects. Its primary use is to determine the angle between a celestial object and the horizon which is known as the altitude. Making this measurement is known as sighting the object, shooting the object, or taking a sight...

 is used to measure the body's angular height above the horizon. That height can then be used to compute distance from the subpoint to create a circular line of position. A navigator shoots a number of stars in succession to give a series of overlapping lines of position. Where they intersect is the celestial fix. The moon and sun may also be used. 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.

Marine chronometer




In order to accurately measure longitude, the precise time of a sextant sighting (down to the second, if possible) must be recorded. Each second of error is equivalent to 15 seconds of longitude error, which at the equator is a position error of .29 mile, about the accuracy limit of manual celestial navigation.

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

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. The difference between GMT and chronometer time is carefully determined and applied as a correction to all chronometer readings. Spring-driven chronometers must be wound at about the same time each day.

Quartz crystal marine chronometers have replaced spring-driven chronometers aboard many ships because of their greater accuracy. They are maintained on GMT directly from radio time signals. This eliminates chronometer error and watch error corrections. Should the second hand be in error by a readable amount, it can be reset electrically.

The basic element for time generation is a quartz crystal oscillator. The quartz crystal is temperature compensated and is hermetically sealed in an evacuated envelope. A calibrated adjustment capability is provided to adjust for the aging of the crystal.

The chronometer is designed to operate for a minimum of 1 year on a single set of batteries. 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. In practice, a wrist watch coordinated to the nearest second with the chronometer will be adequate.

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

All chronometers and watches should be checked regularly with a radio time signal. Times and frequencies of radio time signals are listed in publications such as Radio Navigational Aids
Radio Navigational Aids
The Radio Navigational Aids publication contains a detailed list of selected worldwide radio stations that provide services to the mariner. The publication is divided into chapters according to the nature of the service provided by the radio stations...

.

The marine sextant




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. The sextant, an optical instrument, is used to perform this function. The sextant consists of two primary assemblies. 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. The second component is the index arm, which is attached to the pivot at the top of the frame. At the bottom is an endless vernier which clamps into teeth on the bottom of the "arc". The optical system consists of two mirrors and, generally, a low power telescope. One mirror, referred to as the "index mirror" is fixed to the top of the index arm, over the pivot. As the index arm is moved, this mirror rotates, and the graduated scale on the arc indicates the measured angle ("altitude").

The second mirror, referred to as the "horizon glass", is fixed to the front of the frame. One half of the horizon glass is silvered and the other half is clear. 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. 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.

Adjustment of the sextant consists of checking and aligning all the optical elements to eliminate "index correction". Index correction should be checked, using the horizon or more preferably a star, each time the sextant is used. 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

Inertial navigation


Inertial navigation is a dead reckoning
Dead reckoning
In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course...

 type of navigation system that computes its position based on motion sensors. Once the initial latitude and longitude is established, the system receives impulses from motion detectors that measure the acceleration along three or more axes enabling it to continually and accurately calculate the current latitude and longitude. Its advantages over other navigation systems are that, once the starting position is set, it does not require outside information, it is not affected by adverse weather conditions and it cannot be detected or jammed. Its disadvantage is that since the current position is calculated solely from previous positions, its errors are cumulative, increasing at a rate roughly proportional to the time since the initial position was input. Inertial navigation systems must therefore be frequently corrected with a location 'fix' from some other type of navigation system. The US Navy developed a Ships Inertial Navigation System (SINS) during the Polaris missile program to ensure a safe, reliable and accurate navigation system for its missile submarines. Inertial navigation systems were in wide use until satellite navigation systems (GPS) became available.

Radio navigation



A radio direction finder
Radio direction finder
A radio direction finder is a device for finding the direction to a radio source. Due to low frequency propagation characteristic 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...

 or RDF is a device for finding the direction to a radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 source. 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.

RDFs works by rotating a directional antenna and listening for the direction in which the signal from a known station comes through most strongly. This sort of system was widely used in the 1930s and 1940s. RDF antennas are easy to spot on German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 aircraft, as loops under the rear section of the fuselage, whereas most US
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 aircraft enclosed the antenna in a small teardrop-shaped fairing.

In navigational applications, RDF signals are provided in the form of radio beacons, the radio version of a lighthouse
Lighthouse
A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....

. The signal is typically a simple AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...

 broadcast of a morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

 series of letters, which the RDF can tune in to see if the beacon is "on the air". 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.

Decca
Decca Navigator System
The Decca Navigator System was a low frequency hyperbolic navigation system that was first deployed during World War II when the Allied forces needed a system which could be used to achieve accurate landings...

, OMEGA
OMEGA Navigation System
OMEGA was the first truly global radio navigation system for aircraft, operated by the United States in cooperation with six partner nations.-History:OMEGA was originally developed by the United States Navy for military aviation users...

, and LORAN-C are three similar hyperbolic navigation systems. Decca was a hyperbolic
Hyperbola
In mathematics a hyperbola is a curve, specifically a smooth curve that lies in a plane, which can be defined either by its geometric properties or by the kinds of equations for which it is the solution set. A hyperbola has two pieces, called connected components or branches, which are mirror...

 low frequency
Low frequency
Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

 radio navigation
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...

 system (also known as multilateration
Multilateration
Multilateration is a navigation technique based on the measurement of the difference in distance to two or more stations at known locations that broadcast signals at known times. Unlike measurements of absolute distance or angle, measuring the difference in distance results in an infinite number of...

) that was first deployed during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 when the Allied forces needed a system which could be used to achieve accurate landings. As was the case with Loran C, its primary use was for ship navigation in coastal waters. Fishing vessels were major post-war users, but it was also used on aircraft, including a very early (1949) application of moving-map displays. The system was deployed in the North Sea and was used by helicopters operating to oil platform
Oil platform
An oil platform, also referred to as an offshore platform or, somewhat incorrectly, oil rig, is a lаrge structure with facilities to drill wells, to extract and process oil and natural gas, and to temporarily store product until it can be brought to shore for refining and marketing...

s.

The OMEGA Navigation System was the first truly global radio navigation
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...

 system for aircraft, operated by the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in cooperation with six partner nations. OMEGA was developed by the United States Navy for military aviation users. 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. Initially, the system was to be used for navigating nuclear bombers across the North Pole to Russia. Later, it was found useful for submarines.http://www.jproc.ca/hyperbolic/omega.html Due to the success of the Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 the use of Omega declined during the 1990s, to a point where the cost of operating Omega could no longer be justified. Omega was terminated on September 30, 1997 and all stations ceased operation.

LORAN is a terrestrial navigation system using low frequency
Low frequency
Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

 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. The current version of LORAN in common use is LORAN-C, which operates in the low frequency
Low frequency
Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

 portion of the EM spectrum from 90 to 110 kHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

. Many nations are users of the system, including the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, and several European countries. Russia uses a nearly exact system in the same frequency range, called CHAYKA
CHAYKA
Chayka is a Russian terrestrial radio navigation system, similar to LORAN-C. It is also run on 100 kHz and is described like LORAN-C by its GRI.-Chayka-Chains:There are 5 Chayka-chains in use:...

. LORAN use is in steep decline, with GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 being the primary replacement. However, there are attempts to enhance and re-popularize LORAN. LORAN signals are less susceptible to interference and can penetrate better into foliage and buildings than GPS signals.

Radar navigation



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

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

Parallel indexing is a technique defined by William Burger in the 1957 book The Radar Observer's Handbook.National Imagery and Mapping Agency, 2001:169. 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. This parallel line allows the navigator to maintain a given distance away from hazards.

Some techniques have been developed for special situations. 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.National Imagery and Mapping Agency, 2001:164.

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.National Imagery and Mapping Agency, 2001:182. During the transit, the navigator can check that the ship is on track by checking that the pip lies on the drawn line.

Satellite navigation



Global Navigation Satellite System or GNSS is the term for satellite navigation systems that provide positioning with global coverage. A GNSS allow small electronic
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 receivers to determine their location (longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

, latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

, and altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

) to within a few metres using time signal
Time signal
A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:...

s transmitted along a line of sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...

 by radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 from satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

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

, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 NAVSTAR Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 (GPS) is the only fully operational GNSS. The Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n GLONASS
GLONASS
GLONASS , acronym for Globalnaya navigatsionnaya sputnikovaya sistema or Global Navigation Satellite System, is a radio-based satellite navigation system operated for the Russian government by the Russian Space Forces...

 is a GNSS in the process of being restored to full operation. The European Union's
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 Galileo positioning system
Galileo positioning system
Galileo is a global navigation satellite system currently being built by the European Union and European Space Agency . The €20 billion project is named after the famous Italian astronomer Galileo Galilei...

 is a next generation GNSS in the initial deployment phase, scheduled to be operational by 2013. China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 has indicated it may expand its regional Beidou navigation system
Beidou navigation system
The BeiDou Navigation System or BeiDou Navigation Satellite System is a project by China to develop an independent satellite navigation system...

 into a global system.

More than two dozen GPS satellites are in medium Earth orbit
Medium Earth Orbit
Medium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....

, transmitting signals allowing GPS receivers to determine the receiver's location, speed and direction.

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
Cartography
Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.The fundamental problems of traditional cartography are to:*Set the map's...

 and land surveying
Surveying
See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...

. GPS also provides a precise time reference
Time transfer
Time transfer is a scheme where multiple sites share a precise reference time. Time transfer solves problems such as astronomical observatories correlating observed flashes or other phenomenon with each other, as well as cell phone towers coordinating handoffs as a phone moves from one cell to...

 used in many applications including scientific study of earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

s, and synchronization
Synchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....

 of telecommunications networks.

Developed by the United States Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...

, GPS is officially named NAVSTAR GPS (NAVigation Satellite Timing And Ranging Global Positioning System). The satellite constellation
Satellite constellation
A group of artificial satellites working in concert is known as a satellite constellation. Such a constellation can be considered to be a number of satellites with coordinated ground coverage, operating together under shared control, synchronised so that they overlap well in coverage and...

 is managed by the United States Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

 50th Space Wing
50th Space Wing
The 50th Space Wing is a wing of the United States Air Force under the major command of Air Force Space Command . It was activated on 30 January 1992, replacing the 2d Space Wing, which was deactivated on the same date.-Overview:...

. The cost of maintaining the system is approximately US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....

750 million per year, including the replacement of aging satellites, and research and development. Despite this fact, GPS is free for civilian use as a public good
Public good
In economics, a public good is a good that is non-rival and non-excludable. Non-rivalry means that consumption of the good by one individual does not reduce availability of the good for consumption by others; and non-excludability means that no one can be effectively excluded from using the good...

.

Day's work in navigation


The Day's work in navigation is a minimal set of tasks consistent with prudent navigation. The definition will vary on military and civilian vessels, and from ship to ship, but takes a form resembling:
  1. Maintain continuous dead reckoning plot.
  2. Take two or more star observations at morning twilight for a celestial fix. (prudent to observe 6 stars)
  3. Morning sun observation. Can be taken on or near prime vertical
    Prime vertical
    In astronomy and astrology, the prime vertical is the vertical circle passing east and west through the zenith, and intersecting the horizon in its east and west points....

     for longitude, or at any time for a line of position.
  4. Determine compass error by azimuth observation of the sun.
  5. Computation of the interval to noon, watch time of local apparent noon, and constants for meridian or ex-meridian sights.
  6. Noontime meridian or ex-meridian observation of the sun for noon latitude line. Running fix or cross with Venus line for noon fix.
  7. Noontime determination the day's run and day's set and drift.
  8. At least one afternoon sun line, in case the stars are not visible at twilight.
  9. Determine compass error by azimuth observation of the sun.
  10. Take two or more star observations at evening twilight for a celestial fix. (prudent to observe 6 stars)

Passage planning



Passage planning or voyage planning is a procedure to develop a complete description of vessel's voyage from start to finish. The plan includes leaving the dock and harbor area, the enroute portion of a voyage, approaching the destination, and mooring. According to international law, a vessel's captain
Captain (nautical)
A sea captain is a licensed mariner in ultimate command of the vessel. The captain is responsible for its safe and efficient operation, including cargo operations, navigation, crew management and ensuring that the vessel complies with local and international laws, as well as company and flag...

 is legally responsible for passage planning, however on larger vessels, the task will be delegated to the ship's navigator
Navigator
A navigator is the person on board a ship or aircraft responsible for its navigation. The navigator's primary responsibility is to be aware of ship or aircraft position at all times. Responsibilities include planning the journey, advising the Captain or aircraft Commander of estimated timing to...

.

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. The practice of voyage planning has evolved from penciling lines on nautical chart
Nautical chart
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...

s to a process of risk management
Risk management
Risk management is the identification, assessment, and prioritization of risks followed by coordinated and economical application of resources to minimize, monitor, and control the probability and/or impact of unfortunate events or to maximize the realization of opportunities...

.

Passage planning consists of three stages: appraisal, planning, execution, and monitoring, which are specified in International Maritime Organization
International Maritime Organization
The International Maritime Organization , formerly known as the Inter-Governmental Maritime Consultative Organization , was established in Geneva in 1948, and came into force ten years later, meeting for the first time in 1959...

 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
Code of Federal Regulations
The Code of Federal Regulations is the codification of the general and permanent rules and regulations published in the Federal Register by the executive departments and agencies of the Federal Government of the United States.The CFR is published by the Office of the Federal Register, an agency...

), and a number of professional books or publications. There are some fifty elements of a comprehensive passage plan depending on the size and type of vessel.

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

Integrated bridge systems


Electronic integrated bridge concepts are driving future navigation system planning. 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. The navigator becomes a system manager, choosing system presets, interpreting system output, and monitoring vessel response.

External links