/ref> is the process of navigating on water or in the air using fixed points of reference on the sea or on land, usually with reference to a nautical chart
A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land ( topographic map), natural features of the seabed, details of the coa ...
or aeronautical chart
An aeronautical chart is a map designed to assist in the navigation of aircraft, much as nautical charts do for watercraft, or a roadmap does for drivers. Using these charts and other tools, pilots are able to determine their position, safe a ...
to obtain a fix of the position of the vessel or aircraft with respect to a desired course
Course may refer to:
Directions or navigation
* Course (navigation), the path of travel
* Course (orienteering), a series of control points visited by orienteers during a competition, marked with red/white flags in the terrain, and corresponding ...
or location. Horizontal fixes of position from known reference points may be obtained by sight or by radar
Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
. Vertical position may be obtained by depth sounder to determine depth of the water body below a vessel or by altimeter
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water. The m ...
to determine an aircraft's altitude, from which its distance above the ground can be deduced. Piloting a vessel is usually practiced close to shore or on inland waterways. Pilotage of an aircraft is practiced under visual meteorological conditions for flight.
Land navigation is a related discipline, using a topographic map
In modern mapping, a topographic map or topographic sheet is a type of map characterized by large-scale detail and quantitative representation of relief features, usually using contour lines (connecting points of equal elevation), but histori ...
, especially when applied over trackless terrain. Divers use related techniques for underwater navigation.
Piloting references
Charts
Depending on whether one is navigating on a water course, in the air or on land, a different chart applies for the navigator:
*''Nautical charts'' – show coast
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
al regions and depict depths of water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
and land features, natural features of the seabed, details of the coastline, navigational hazards, locations of natural and human-made aids to navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
, and human-made structures such as harbours
A harbor (American English), harbour (British English; see spelling differences), or haven is a sheltered body of water where ships, boats, and barges can be docked. The term ''harbor'' is often used interchangeably with ''port'', which is a ...
, buildings and bridge
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
s.
*''Aeronautical charts'' – for visual meteorological conditions depict terrain, geographic features, navigational aids and other aids to navigation. They vary in scale from 1:1,000,000 for world aeronautical chart
A World Aeronautical Chart (WAC) is a type of aeronautical chart used for navigation by pilots of moderate speed aircraft and aircraft at high altitudes. They are at a scale of 1:1,000,000 (about 1 inch = 13.7 nautical miles or 16 statute miles) ...
s to 1:250,000.
*''Topographic maps'' – show landforms and terrain, lakes and rivers, forest cover, administrative areas, populated areas, roads and railways, and other man-made features.
File:NOAA chart 25664 1976 detail.png, ''Nautical chart'' – includes water depth.
File:Minimum Safe Altitude.gif, ''Aeronautical chart'' – includes elevation.
File:Conness-topo.jpg, ''Topographic map'' – emphasizes contours – suitable for land navigation.
Maritime piloting
Coastal mariners often use reference manuals, called "pilots" for navigating coastal waters. In addition to providing descriptions of shipping channels and coastal profiles, they discuss weather, currents and other topics of interest to mariners. Notable guides include a worldwide series of "Sailing Directions" by the United Kingdom Hydrographic Office
The United Kingdom Hydrographic Office (UKHO) is the UK's agency for providing hydrographic and marine geospatial data to mariners and maritime organisations across the world. The UKHO is a trading fund of the Ministry of Defence (MoD) and is ...
(formerly by the British Admiralty) that includes, most notably, the English Channel
The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" ( Cotentinais) or (Jèrriais), ( Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Kan ...
, the Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...
, the Red Sea
The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...
and the Persian Gulf
The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a mediterranean sea in Western Asia. The bo ...
. Another series worldwide series of Sailing Directions is by the US National Geospatial-Intelligence Agency
The National Geospatial-Intelligence Agency (NGA) is a combat support agency within the United States Department of Defense whose primary mission is collecting, analyzing, and distributing geospatial intelligence (GEOINT) in support of natio ...
, which has planning guide and enroute portions. The "United States Coast Pilot", by the National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditi ...
(NOAA) Office of Coast Survey, covers the coastal and intracoastal waters and the Great Lakes of the United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
.
Points of reference
Common types of visual reference point used for piloting and pilotage include:
Day
* Natural features: Mountain
A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher t ...
s, hill
A hill is a landform that extends above the surrounding terrain. It often has a distinct summit.
Terminology
The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be not as ...
s, lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much lar ...
s, river
A river is a natural flowing watercourse, usually freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the ...
s and coastal features such as cliff
In geography and geology, a cliff is an area of rock which has a general angle defined by the vertical, or nearly vertical. Cliffs are formed by the processes of weathering and erosion, with the effect of gravity. Cliffs are common on ...
s, rocks
In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's ...
and beach
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shell ...
es
* Navigational aids: sea mark
A sea mark, also seamark and navigation mark, is a form of aid to navigation and pilotage that identifies the approximate position of a maritime channel, hazard, or administrative area to allow boats, ships, and seaplanes to navigate safely.
Th ...
s (including buoy
A buoy () is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents.
Types
Navigational buoys
* Race course marker buoys are used for buoy racing, the most prevalent form of ya ...
s and beacon
A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...
s) and landmarks
A landmark is a recognizable natural or artificial feature used for navigation, a feature that stands out from its near environment and is often visible from long distances.
In modern use, the term can also be applied to smaller structures or f ...
* Other structures: Airport
An airport is an aerodrome with extended facilities, mostly for commercial air transport. Airports usually consists of a landing area, which comprises an aerially accessible open space including at least one operationally active surfa ...
s, cities
A city is a human settlement of notable size.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routledge. It can be def ...
, dams, highway
A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks. In some areas of the United States, it is used as an equivalent term to controlled-access ...
s, and radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transm ...
antennas
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies a ...
Night
* Lighted navigational aids: Lighthouses, lightvessel
A lightvessel, or lightship, is a ship that acts as a lighthouse. They are used in waters that are too deep or otherwise unsuitable for lighthouse construction. Although some records exist of fire beacons being placed on ships in Roman times, ...
s and lighted sea marks
* Lighted structures: Airports, illuminated towers and buildings
Vertical
Depth, measured with a depth sounder or lead line, can be used to identify a bathymetric
Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water de ...
contour or crossing point. Similarly, elevation can be used to confirm a geographic
Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and ...
contour or crossing point. Measurement of depth and altitude allow vessels and aircraft navigators to confirm clear passage over obstructions.
Fix of position
Instruments used
On shipboard, navigators may use a pelorus to obtain bearings, relative to the vessel, from charted objects. A hand bearing compass provides magnetic bearings. On land a hand compass provides bearings to landmarks.[Frazer, Persifor, ''A Convenient Device to be Applied to the Hand Compass'', Proceedings of the American Philosophical Society, Vol. 22, No. 118 (Mar., 1885), p. 216]
Afloat
Mariners use position-fixing navigation, to obtain a "position fix" or "fix" by measuring the bearing of the navigator's current position from known points of reference. A visual fix of position can be made by using any sighting device with a bearing indicator to obtain position line
A position line or line of position (LOP) is a line (or, on the surface of the earth, a curve) that can be both identified on a chart (nautical chart or aeronautical chart) and translated to the surface of the earth. The intersection of a minimum ...
s from the navigator's current position to each point of reference. Two or more objects of known position are sighted as points of reference, and the bearings recorded. Bearing lines or transits are then plotted on a chart through the locations of the sighted items. The intersection of these lines is then the current position of the navigator.
Usually, a fix is where two or more position lines intersect at any given time. If three position lines can be obtained, the resulting "cocked hat", where the 3 lines do not intersect at the same point, but create a triangle where the vessel is inside, gives the navigator an indication of the accuracy in the three separate position lines.
If two geographic features are visually aligned (the edge of an island aligned with the edge of an island behind, a flag pole and a building, etc.), the extension of the line joining the features is called a "transit". A transit is not affected by compass accuracy, and is often used to check a compass for errors.
The most accurate fixes occur when the position lines are at right angles to each other.
Aloft
Flying at low altitudes and with sufficient visibility, aircraft pilots use nearby rivers, roads, railroad tracks and other visual references to establish their position.
Course versus ground track
The line connecting fixes is the track over the ground or sea bottom. The navigator compares the ground track with the navigational course for that leg of the intended route, in order to make a correction in "heading", the direction in which the craft is pointed to maintain its course in compensation for cross-currents of wind or water that may carry the craft off course.
In channels and rivers
Where a channel is narrow, as in some harbor entrances and on some rivers, a system of beacons
A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mod ...
allows mariners to align pairs of daymark
A daymark is a navigational aid for sailors and pilots, distinctively marked to maximize its visibility in daylight.
The word is also used in a more specific, technical sense to refer to a signboard or daytime identifier that is attached to ...
s, called "range markers", to form a "leading line" (British English) or "range axis" (American English
American English, sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. English is the most widely spoken language in the United States and in most circumstances ...
), along which to navigate safely. When lighted, these markers are called "leading lights
Leading lights (also known as range lights in the United States) are a pair of light beacons used in navigation to indicate a safe passage for vessels entering a shallow or dangerous channel; they may also be used for position fixing. At night ...
" (British English) or "range lights" (American English). The relative positions of the marks and the vessel affect the accuracy of perceiving the leading line.
See also
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References
{{Reflist, 30em
External links
American Practical Navigator – Chapter 8: Piloting
American Practical Navigator (complete 2019 edition, Parts I and II available in both high- and low-resolution versions, and select older versions)
American Practical Navigator – Chapter 8: Piloting at WikiSource
Navigation
Navigational aids
Maritime signalling
Underwater diving procedures