Marine navigation is the art and science of steering a ship from a starting point (sailing) to a destination, efficiently and responsibly. It is an art because of the skill that the navigator must have to avoid the dangers of navigation, and it is a science because it is based on physical, mathematical, oceanographic, cartographic, astronomical, and other knowledge.
Marine navigation can be surface or submarine.
Etymology
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Navigation (from the Latin word navigatio) is the act of sailing or voyaging. Nautical (from Latin nautĭca, and this from Greek ναυτική [τέχνη] nautik&#; [téjne] "[art of] sailing" and from ναύτης nautes "sailor") is that pertaining to navigation and the science and art of sailing. Naval (from the Latin adjective navalis) is that relating to ships and navigation, or particularly to the navy.[1]
In Ancient Rome, the navicularii conducted long-distance trade by sea.
History
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Coastal navigation was practiced since the most ancient times.[2] The biblical account of the great flood, where the Noah's Ark appears, is based both on myths and on the navigational practice of the Mesopotamian civilizations, who from the Sumerians onwards navigated their two rivers (Tigris and Euphrates) and the Persian Gulf. The ancient Egyptians did not limit themselves to inland navigation of the Nile either, and used the Mediterranean sea routes existing since the Neolithic &#; through which cultural phenomena such as megalithism or the metallurgy would have spread for millennia. The Cretans even established a true thalassocracy (government of the seas, attributed to King Minos) until the Mycenaean period (2nd millennium BC), when the events mythologized in the Homeric poems[Note 1] ought to be placed.
flotilla or "procession of boats".Fresco from the Western House of Akrotiri , calledor "procession of boats".
The Hittites, led by King Šuppiluliuma II faced the Cyprus in the first historically recorded naval battle (ca. BC); at the same time, all the civilizations of the Eastern Mediterranean suffered from the incursions of the denominated "Sea Peoples".
The Phoenicians &#; whom the Greeks considered their masters in navigation and who are also cited in the Bible &#;[Note 2][3] would have been the first Mediterranean civilization to sail the high seas by sculling and sailing, guided by the sun during the day and by the North Star at night. It is recorded that, crossing the Strait of Gibraltar &#; the "Rock of Gibraltar", the so-called "Pillars of Hercules" in the Greek myths &#; they sailed across the Atlantic Ocean reaching the south to some point on the west coast of Africa and the north to the British Isles (or even beyond, to the place that the texts call Thule), but it is unclear if they circumnavigated Africa or crossed the Atlantic reaching America, something most likely achieved by the Norsemen in the 10th century.
Boat depicted on Egyptian pottery from the Predynastic period (Naqada II, mid-4th millennium BC). Boat building depicted in reliefs from the Mastaba of Ti at Saqqara, dynasty V, mid-3rd millennium BC. Model of an Egyptian ship and crew. Type of Phoenician ships called hippos (name given by the Greeks, because of its mascaron shaped like a horse's head) carrying wood, depicted in an Assyrian relief from Sargon's palace at Khorsabad. King Luli of Sidon flees from his city, attacked by Sargon II, in a type of Phoenician warship called dieris (bireme, with two rows of rowers). Assyrian relief from the palace of Sennacherib, ca. 700-692 BC. One of the Phoenician vessels of Mazarrón, 7th century BC. Dionysus Cup, by Exekias, 6th Century Scene from the Odyssey (Ulysses' companions manage to free their ship from the Sirens' trap, while their leader listens to their song tied to the mast). 5th century. Roman ship represented in a fresco of the 2nd or 3rd century in the port city of Ostia. The inscriptions reflect the name of the ship (Isis Giminiana), the name of the captain or magister (Farnaces, at the helm) and the name of the owner (Arascanius, in charge of the cargo).[4] Roman sarcophagus from the 3rd century. It is the oldest representation of a spritsail. Byzantine ships in Classe (the port of Ravenna), depicted in a mosaic of Basilica of Sant'Apollinare Nuovo, 6th century. Norman ship represented in the Bayeux tapestry, 11th century. Viking ships depicted in a 12th-century manuscript. Nautical combat with Greek fire depicted in a 12th-century Byzantine manuscript (Madrid Skylitzes). Replica of a Spanish-Muslim ship from the 10th to 14th century. Galley or dromon in a Byzantine fresco from the 13th century. The design of the flags is similar to the Senyera of the Crown of Aragon, and the design of the ship can be compared to the traditional mitjana ship. The earliest known representation of a compass, used aboard ship, depicted in an illustration dated .Remains of a 1st-century Gallo-Roman ship archaeologically named
Roman ship depicted on a coin.
Relief of a 2nd-century sarcophagus representing a "gauloi", a trading ship.
Model depicting a naval confrontation between a Roman ship and Omani ships in the Indian Ocean, 2nd century.
In the Indian and Pacific oceans, the oceanic navigations made it possible to populate all the archipelagoes (Polynesian navigation). However, the possibility of reaching South America is still a matter of debate &#; the settlement of the Americas through the Bering Strait would not have required navigation, or in any case, coastal navigation would have sufficed &#; as well as other possible pre-Columbian transoceanic contacts. In the first quarter of the 15th century, the Chinese expeditions led by Zheng He reached the African coasts of the Indian Ocean. It has been proposed that they might have reached the South Atlantic and even America and Europe, but this proposal has not been accepted beyond mere speculation.
Mediterranean navigation, which the Romans had come to control (undisputed Mare Nostrum since their victories over the Carthaginians in the Punic Wars [264-146 BC], the Egyptians during the Battle of Actium [31 BC], and pirates), was once again a contested environment in the Middle Ages, from the moment the Vandals managed to attack the Italian coasts from the sea. In the 6th century, the Byzantines managed to regain control, and in the 7th century it was the Arabs who ended up dividing the Mediterranean area,[5] which even the Vikings and Normans were able to access. Since the time of the Crusades, Venetian,[6] Genoese[7] and Crown of Aragon[8] navigators also had a strong presence. Knowledge of the compass, transmitted to the Europeans by the Arabs (who in turn had obtained it from the Chinese), together with other improvements in astronomical techniques (astrolabe, Jacob's staff, sextant, cartographic techniques (portulan and shipbuilding (caravel, nau, galleon), made the Age of Discovery &#; initially led by the Portuguese and Castilians &#; possible, especially after Henry the Navigator impulsed the school of Sagres. In , the first voyage of Christopher Columbus took place. In , Bartolomeu Dias rounded the Cape of Good Hope, which opened the route to the Indian Ocean &#; Vasco de Gama reached Calicut (India) in . Between and , the Magellan-Elcano expedition circumnavigated the world &#; measuring the geographical longitude with the method of its scientific organizer, Rui Faleiro. Until the 6th century, the Spanish-Portuguese hegemony in navigation was patent in fields such as geography and cosmography. Both English and French pilots learned to navigate from the texts of Pedro de Medina, Martín Fernández de Enciso and Martín Cortés, among others.[9][10] The conjunction of "cannons and sails" has been argued to have given European states the advantage to prevail over the rest,[11] launching the modern "world system".[12]
Permanent navigation routes of the Spanish (in white) and Portuguese (in blue) fleets since the 16th century. The Spanish treasure fleet crossed the Atlantic, the Manila Galleon the Pacific; the India armada circumnavigated Africa.
Navigation of Henry Hudson in search of the Northeast Passage , &#;.
, flagship of the Swedish navy, sunk on her maiden voyage, .
Dutch ships of the VOC ) in Batavia (today Jakarta ), .
Since the 18th century, England exercised maritime hegemony, a fact that was confirmed in the early 19th century with the Battle of Trafalgar (). Among the main English expeditions of the time were Captain Cook's (-), also the second expedition of the Beagle (-) &#; which was of great importance for the later development of Charles Darwin's theory of evolution. Already fully in the age of steam navigation, techniques and vessels continued to be perfected in transoceanic sailing (clipper), that did not become obsolete for commercial navigation until the 20th century &#; especially after the opening of the Panama Canal. Even then, the unbridled optimism that characterized the naval design of the time suffered a severe blow with the sinking of the Titanic ().
Contemporary shipping has massively ceased to perform one of its traditional functions and has been replaced by aviation, such as passenger transport, although with two important exceptions: leisure travel (tourism by cruise ships) and irregular traffic of people (irregular immigration). Since the Second Industrial Revolution, the main volume of freight transport has been hydrocarbons (oil tankers and gas tankers). Other raw materials are also transported in bulk on cargo ships, but from onward, a large part of goods of all kinds were adapted to standardized containers that speed up loading and unloading, allowing a combination with land transport (hub). Highly technological navigation has reduced crews and increased the size of ships. For example, in deep-sea fishing, which locates its prey with sophisticated means and lasts indefinitely in time &#; freezer ships or factory ships &#; which in some circumstances has made them vulnerable to new forms of piracy.
Hellespont Alhambra, a TI-class supertanker that is considered among the largest ships in the world in dimensions, displacement and cargo capacity., a TI-class supertanker that is considered among the largest ships in the world in dimensions, displacement and cargo capacity.
Methods and techniques
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These are the methods used in maritime navigation to solve the three problems of the navigator:
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Navigation and location of the ship by positioning techniques based on the observation of bearings and distances to notable points on the coast (lighthouses, capes, buoys, etc.) by visual means (pelorus), observation of horizontal angles (sextant) or electronic methods (bearings from radar to racons, transponders, etc.)
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Navigation and location of the ship by analytical means, after considering the following elements: initial location, bearing(s) &#; whether absolute bearings, surface bearings, or relative bearings. Also velocity as well as the external factors that have influenced the course either partially or entirely, such as the wind (leeway) and/or the current (bearing of the current and hourly current intensity). The point obtained from the calculations is called the "Dead reckoning location", with its corresponding latitude and longitude. This point is also known as Fantasy point.
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Rhumb line navigation path: β = constantNavigation that follows a rhumb line &#; that is, all meridians are cut at the same angle. On a nautical chart following the Mercator projection, a loxodromic is represented by a straight line.
This type of navigation is useful for not too long distances, as it allows the course to remain steady,[16] but it does not offer the shortest distance.
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Navigation that follows the shortest distance between two points, i.e., that which follows a great circle. Such routes yield the shortest distance between two points on the globe.[16] To calculate the bearing and distance between two points it is necessary to solve a spherical triangle whose vertices are the origin, the destination, and the pole.[17]
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Navigation and location of the ship by geopositioning techniques based on the observation of the stars and other celestial bodies. The variables measured to find the location are: the observed angular height of the stars above the horizon, measured with the sextant (formerly with the astrolabe or other instrument), and the time, measured with the chronometer.
Conceptually, the process is not complex to understand:
In practice, the mathematical process, called "reduction" of the observation, can be complex for the uninitiated. To the height observed with the sextant, it is necessary to apply a series of corrections to compensate for atmospheric refraction, parallax and other errors. Once this is done, it is necessary to solve a spherical triangle by mathematical and trigonometric methods.
There are many methods to do this. The manual methods use tables (trigonometric, logarithms, etc.) to facilitate the calculations. The introduction of calculators and electronic computers at the end of the 20th century greatly facilitated the calculation, but the creation of GPS made celestial navigation no longer important, relegating it to the background as an alternative method in case of failure of the on-board electronics or as a hobby of scientific interest.
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Navigation and location of the ship by positioning techniques based on the aids provided by global positioning systems, such as GPS, GLONASS, or GALILEO. It is the system most widely spread and easiest to use, in spite of the errors that may arise.
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Navigation and location of the ship by means of the analysis of the data provided by accelerometers and/or gyroscopes located on board, which integrate the accelerations experienced in complex electronic systems, that converted into velocities (in the 3 possible axes of displacement) and according to the observed courses, make it possible to obtain the location of the ship.
Iconography
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The harbinger of a successful navigation was the dolphin, which is why its representation became the symbol carried by all ships.
More recently, navigation was represented as a woman crowned with ship's sterns whose clothes are agitated by the winds. She rests one hand on a rudder and the other holds the instrument for measuring height. At her feet, the ampoule, the compass, the trident of Neptune and the riches of commerce, while the sea can be seen on the horizon, completed by a lighthouse and traversed by ships at full sail.[10]
See also
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Notes
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References
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(in Spanish)
(in Spanish)
(in Portuguese)
Navigation[1] 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.[2] The field of navigation includes four general categories: land navigation,[3] marine navigation, aeronautic navigation, and space navigation.[1]
It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks. All navigational techniques involve locating the navigator's position compared to known locations or patterns.
Navigation, in a broader sense, can refer to any skill or study that involves the determination of position and direction.[1] In this sense, navigation includes orienteering and pedestrian navigation.[1]
History
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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. 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. 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.[citation needed] Maritime navigation using scientific instruments such as the mariner's astrolabe first occurred in the Mediterranean during the Middle Ages. 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 Spanish astronomer Ramon Llull dating from .[4] The perfecting of this navigation instrument is attributed to Portuguese navigators during early Portuguese discoveries in the Age of Discovery.[5][6] 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 ,[7] based on the principle of the archipendulum used in constructing the Egyptian pyramids.
Open-seas navigation using the astrolabe and the compass started during the Age of Discovery in the 15th century. The Portuguese began systematically exploring the Atlantic coast of Africa from , under the sponsorship of Prince Henry. In Bartolomeu Dias reached the Indian Ocean by this route. In 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. In , a Portuguese expedition commanded by Vasco da Gama reached India by sailing around Africa, opening up direct trade with Asia. Soon, the Portuguese sailed further eastward, to the Spice Islands in , landing in China one year later.
The first circumnavigation of the earth was completed in 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 . The fleet of seven ships sailed from Sanlúcar de Barrameda in Southern Spain in , crossed the Atlantic Ocean and after several stopovers rounded the southern tip of South America. Some ships were lost, but the remaining fleet continued across the Pacific making a number of discoveries including Guam and the Philippines. By then, only two galleons were left from the original seven. The Victoria led by Elcano sailed across the Indian Ocean and north along the coast of Africa, to finally arrive in Spain in , three years after its departure. The Trinidad sailed east from the Philippines, trying to find a maritime path back to the Americas, but was unsuccessful. 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. He arrived in Acapulco on October 8, .
Etymology
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The term stems from the s, from Latin 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".[8]
Basic concepts
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Latitude
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Roughly, the latitude of a place on Earth is its angular distance north or south of the equator.[9] Latitude is usually expressed in degrees (marked with °) ranging from 0° at the Equator to 90° at the North and South poles.[9] The latitude of the North Pole is 90° N, and the latitude of the South Pole is 90° S.[9] Mariners calculated latitude in the Northern Hemisphere by sighting the pole star (Polaris) with a sextant and using sight reduction tables to correct for height of eye and atmospheric refraction. The height of Polaris in degrees above the horizon is the latitude of the observer, within a degree or so.
Longitude
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Similar to latitude, the longitude of a place on Earth is the angular distance east or west of the prime meridian or Greenwich meridian.[9] Longitude is usually expressed in degrees (marked with °) ranging from 0° at the Greenwich meridian to 180° east and west. Sydney, for example, has a longitude of about 151° east. New York City has a longitude of 74° west. For most of history, mariners struggled to determine longitude. Longitude can be calculated if the precise time of a sighting is known. 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).[10] Reliable marine chronometers were unavailable until the late 18th century and not affordable until the 19th century.[11][12][13] For about a hundred years, from about until about ,[14] mariners lacking a chronometer used the method of lunar distances to determine Greenwich time to find their longitude. A mariner with a chronometer could check its reading using a lunar determination of Greenwich time.[11][15]
Loxodrome
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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. 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.
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Most modern navigation relies primarily on positions determined electronically by receivers collecting information from satellites. Most other modern techniques rely on finding intersecting lines of position or LOP.[16]
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.[17] A bearing is a measure of the direction to an object.[17] If the navigator measures the direction in real life, the angle can then be drawn on a nautical chart and the navigator will be somewhere on that bearing line on the chart.[17]
In addition to bearings, navigators also often measure distances to objects.[16] On the chart, a distance produces a circle or arc of position.[16] 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.[16] A fix is the intersection of two or more LOPs.[16]
If only one line of position is available, this may be evaluated against the dead reckoning position to establish an estimated position.[18]
Lines (or circles) of position can be derived from a variety of sources:
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.[20] Each new method has enhanced the mariner's ability to complete his voyage.[20] One of the most important judgments the navigator must make is the best method to use.[20] Some types of navigation are depicted in the table.
The practice of navigation usually involves a combination of these different methods.[20]
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By mental navigation checks, a pilot or a navigator estimates tracks, distances, and altitudes which will then help the pilot avoid gross navigation errors.[21]
Piloting
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Manual navigation through Dutch airspacePiloting (also called pilotage) involves navigating an aircraft by visual reference to landmarks,[22] or a water vessel in restricted waters and fixing its position as precisely as possible at frequent intervals.[23] More so than in other phases of navigation, proper preparation and attention to detail are important.[23] Procedures vary from vessel to vessel, and between military, commercial, and private vessels.[23] As pilotage takes place in shallow waters, it typically involves following courses to ensure sufficient under keel clearance, ensuring a sufficient depth of water below the hull as well as a consideration for squat.[24] It may also involve navigating a ship within a river, canal or channel in close proximity to land.[24]
A military navigation team will nearly always consist of several people.[23] A military navigator might have bearing takers stationed at the gyro repeaters on the bridge wings for taking simultaneous bearings, while the civilian navigator on a merchant ship or leisure craft must often take and plot their position themselves, typically with the aid of electronic position fixing.[23] 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.[23] 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.[23] 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.[23] But should the ECDIS fail, the navigator will have to rely on his skill in the manual and time-tested procedures.[23]
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A celestial fix will be at the intersection of two or more circles.Celestial navigation systems are based on observation of the positions of the Sun, Moon, planets and navigational stars. 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 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. 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.[25]
Marine chronometer
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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 .25 of a nautical 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.[25] 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.[25]
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.[25] The difference between GMT and chronometer time is carefully determined and applied as a correction to all chronometer readings.[25] Spring-driven chronometers must be wound at about the same time each day.[25]
Quartz crystal marine chronometers have replaced spring-driven chronometers aboard many ships because of their greater accuracy.[25] They are maintained on GMT directly from radio time signals.[25] This eliminates chronometer error and watch error corrections.[25] Should the second hand be in error by a readable amount, it can be reset electrically.[25]
The basic element for time generation is a quartz crystal oscillator.[25] The quartz crystal is temperature compensated and is hermetically sealed in an evacuated envelope.[25] A calibrated adjustment capability is provided to adjust for the aging of the crystal.[25]
The chronometer is designed to operate for a minimum of one year on a single set of batteries.[25] 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.[25] In practice, a wrist watch coordinated to the nearest second with the chronometer will be adequate.[25]
A stop watch, either spring wound or digital, may also be used for celestial observations.[25] 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.[25]
All chronometers and watches should be checked regularly with a radio time signal.[25] Times and frequencies of radio time signals are listed in publications such as Radio Navigational Aids.[25]
The marine sextant
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The marine sextant is used to measure the elevation of celestial bodies above the horizon.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.[26]
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Inertial navigation system (INS) is a dead reckoning type of navigation system that computes its position based on motion sensors. 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. 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). These enable an INS to continually and accurately calculate its current latitude and longitude (and often velocity).
Advantages over other navigation systems are that, once aligned, an INS does not require outside information. An INS 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 and motion sensors, 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 first inertial system is considered to be the V-2 guidance system deployed by the Germans in . However, inertial sensors are traced to the early 19th century.[27] The advantages INSs led their use in aircraft, missiles, surface ships and submarines. 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. Inertial navigation systems were in wide use until satellite navigation systems (GPS) became available. INSs are still in common use on submarines (since GPS reception or other fix sources are not possible while submerged) and long-range missiles.
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Not to be confused with satellite navigation, which depends upon satellites to function, space navigation refers to the navigation of spacecraft themselves. This has historically been achieved (during the Apollo program) via a navigational computer, an Inertial navigation system, and via celestial inputs entered by astronauts which were recorded by sextant and telescope. Space rated navigational computers, like those found on Apollo and later missions, are designed to be hardened against possible data corruption from radiation.
Another possibility that has been explored for deep space navigation is Pulsar navigation, which compares the X-ray bursts from a collection of known pulsars in order to determine the position of a spacecraft. This method has been tested by multiple space agencies, such as NASA and ESA.[28][29]
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A radio direction finder or RDF is a device for finding the direction to a radio 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 s and s. 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.
In navigational applications, RDF signals are provided in the form of radio beacons, the radio version of a lighthouse. 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". 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, OMEGA, and LORAN-C are three similar hyperbolic navigation systems. 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. 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 () application of moving-map displays. The system was deployed in the North Sea and was used by helicopters operating to oil platforms.
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. OMEGA was developed by the United States Navy for military aviation users. It was approved for development in 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.Omega Due to the success of the Global Positioning System the use of Omega declined during the s, to a point where the cost of operating Omega could no longer be justified. Omega was terminated on September 30, , and all stations ceased operation.
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. 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. Many nations are users of the system, including the United States, Japan, and several European countries. Russia uses a nearly exact system in the same frequency range, called CHAYKA. LORAN use is in steep decline, with GPS 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.
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Radar ranges and bearings can be used to determine a position.Radar is an effective aid to navigation because it provides ranges and bearings to objects within range of the radar scanner.[30] When a vessel (ship or boat) is within radar range of land or fixed objects (such as special radar aids to navigation and navigation marks) 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.[31] A fix consisting of only radar information is called a radar fix.[32] Types of radar fixes include "range and bearing to a single object,"[33] "two or more bearings,"[33] "tangent bearings,"[33] and "two or more ranges."[33] Radar can also be used with ECDIS as a means of position fixing with the radar image or distance/bearing overlaid onto an Electronic nautical chart.[30]
Parallel indexing is a technique defined by William Burger in the book The Radar Observer's Handbook.[34] 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.[34] This parallel line allows the navigator to maintain a given distance away from hazards.[34] The line on the radar screen is set to a specific distance and angle, then the ship's position relative to the parallel line is observed. This can provide an immediate reference to the navigator as to whether the ship is on or off its intended course for navigation.[35]
Other techniques that are less used in general navigation 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.[36] 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.[37] During the transit, the navigator can check that the ship is on track by checking that the pip lies on the drawn line.[37]
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Global Navigation Satellite System or GNSS is the term for satellite navigation systems that provide positioning with global coverage. A GNSS allow small electronic receivers to determine their location (longitude, latitude, and altitude) within a few meters using time signals transmitted along a line of sight by radio from satellites. Receivers on the ground with a fixed position can also be used to calculate the precise time as a reference for scientific experiments.
As of October , only the United States NAVSTAR Global Positioning System (GPS) and the Russian GLONASS are fully globally operational GNSSs. The European Union's Galileo positioning system is a next generation GNSS in the final deployment phase, and became operational in . China has indicated it may expand its regional Beidou navigation system into a global system.
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.
Since the first experimental satellite was launched in , GPS has become an indispensable aid to navigation around the world, and an important tool for map-making and land surveying. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.
Developed by the United States Department of Defense, GPS is officially named NAVSTAR GPS (NAVigation Satellite Timing And Ranging Global Positioning System). The satellite constellation is managed by the United States Air Force 50th Space Wing. The cost of maintaining the system is approximately US$750 million per year,[38] including the replacement of aging satellites, and research and development. Despite this fact, GPS is free for civilian use as a public good.
Modern smartphones act as personal GPS navigators for civilians who own them. 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.[39][40][41] Typically a compass is also provided to determine direction when not moving.
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Ships and similar vessels
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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 the traditional method takes a form resembling:[42]
Navigation on ships is usually always conducted on the bridge. It may also take place in adjacent space, where chart tables and publications are available.
Passage planning
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Poor passage planning and deviation from the plan can lead to groundings, ship damage and cargo loss.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 en route portion of a voyage, approaching the destination, and mooring. According to international law, a vessel's captain is legally responsible for passage planning,[43] however on larger vessels, the task will be delegated to the ship's navigator.[44]
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.[44] The practice of voyage planning has evolved from penciling lines on nautical charts to a process of risk management.[44]
Passage planning consists of four stages: appraisal, planning, execution, and monitoring,[44] which are specified in International Maritime Organization Resolution A.893(21), Guidelines For Voyage Planning,[45] 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. 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. 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. 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
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Integrated Bridge System, integrated on an Offshore Service ShipElectronic integrated bridge concepts are driving future navigation system planning.[20] 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.[20] The navigator becomes a system manager, choosing system presets, interpreting system output, and monitoring vessel response.[20]
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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.
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.
Pedestrian navigation is involved in orienteering, land navigation (military), and wayfinding.
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Standards, training and organisations
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Professional standards for navigation depend on the type of navigation and vary by country. For marine navigation, Merchant Navy deck officers are trained and internationally certified according to the STCW Convention.[46] Leisure and amateur mariners may undertake lessons in navigation at local/regional training schools. Naval officers receive navigation training as part of their naval training.
In land navigation, courses and training is often provided to young persons as part of general or extra-curricular education. Land navigation is also an essential part of army training. Additionally, organisations such as the Scouts and DoE programme teach navigation to their students. 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.[47]
In aviation, pilots undertake air navigation training as part of learning to fly.
Professional organisations also assist to encourage improvements in navigation or bring together navigators in learned environments. 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. It was founded in as a forum for mariners, pilots, engineers and academics to compare their experiences and exchange information.[48] In the US, the Institute of Navigation (ION) is a non-profit professional organisation advancing the art and science of positioning, navigation and timing.[49]
Publications
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An illustration showing a compass used for navigation from Bowditch's American Practical NavigatorNumerous nautical publications are available on navigation, which are published by professional sources all over the world. 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.[50][51]
In the US, Bowditch's American Practical Navigator is a free available encyclopedia of navigation issued by the US Government.[52]
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Navigation is an essential everyday activity that involves a series of abilities that help humans and animals to locate, track, and follow paths in order to arrive at different destinations.[53][54] Navigation, in spatial cognition, allows for acquiring information about the environment by using the body and landmarks of the environment as frames of references to create mental representations of our environment, also known as a cognitive map. Humans navigate by transitioning between different spaces and coordinating both egocentric and allocentric frames of reference.
Navigation can be distinguished into two sptial components: locomotion and wayfinding.[55] Locomotion is the process of movement from one place to another, both in humans and in animals. Locomotion helps you understand an environment by moving through a space in order to create a mental representation of it.[56] Wayfinding is defined as an active process of following or deciding upon a path between one place to another through mental representations.[57] It involves processes such as representation, planning and decision which help to avoid obstacles, to stay on course or to regulate pace when approaching particular objects.[55][58]
Navigation and wayfinding can be approached in the environmental space. According to Dan Montello&#;s space classification, there are four levels of space with the third being the environmental space. The environmental space represents a very large space, like a city, and can only be fully explored through movement since all objects and space are not directly visible.[59] Also Barbara Tversky systematized the space, but this time taking into consideration the three dimensions that correspond to the axes of the human body and its extensions: above/below, front/back and left/right. Tversky ultimately proposed a fourfold classification of navigable space: space of the body, space around the body, space of navigation and space of graphics.[60]
Wayfinding
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There are two types of wayfinding in navigation: aided and unaided.[59] Aided wayfinding requires a person to use various types of media, such as maps, GPS, directional signage, etc., in their navigation process which generally involves low spatial reasoning and is less cognitively demanding. Unaided wayfinding involves no such devices for the person who is navigating.[59] Unaided wayfinding can be subdivided into a taxonomy of tasks depending on whether it is undirected or directed, which basically makes the distinction of whether there is a precise destination or not: undirected wayfinding means that a person is simply exploring an environment for pleasure without any set destination.[61]
Directed wayfinding, instead, can be further subdivided into search vs. target approximation.[61] Search means that a person does not know where the destination is located and must find it either in an unfamiliar environment, which is labeled as an uninformed search, or in a familiar environment, labeled as an informed search. In target approximation, on the other hand, the location of the destination is known to the navigator but a further distinction is made based on whether the navigator knows how to arrive or not to the destination. Path following means that the environment, the path, and the destination are all known which means that the navigator simply follows the path they already know and arrive at the destination without much thought. For example, when you are in your city and walking on the same path as you normally take from your house to your job or university.[61] However, path finding means that the navigator knows where the destination is but does not know the route they have to take to arrive at the destination: you know where a specific store is but you do not know how to arrive there or what path to take. If the navigator does not know the environment, it is called path search which means that only the destination is known while neither the path nor the environment is: you are in a new city and need to arrive at the train station but do not know how to get there.[61] Path planning, on the other hand, means that the navigator knows both where the destination is and is familiar with the environment so they only need to plan the route or path that they should take to arrive at their target. For example, if you are in your city and need to get to a specific store that you know the destination of but do not know the specific path you need to take to get there.[61]
See also
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Notes
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References
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