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. The field of navigation includes four general categories: land navigation, marine navigation, aeronautic navigation, and space navigation.
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. In this sense, navigation includes orienteering and pedestrian navigation. For information about different navigation strategies that people use, visit human navigation .
* 1 History * 2 Etymology
* 3 Basic concepts
* 4 Modern technique
* 4.1 Mental navigation checks * 4.2 Piloting
* 4.4 Inertial navigation
* 4.5 Electronic navigation
* 5.1 Day\'s work in navigation
* 6 Integrated bridge systems * 7 See also * 8 Notes * 9 References * 10 External links
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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
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 Majorcan astronomer
Open-seas navigation using the astrolabe and the compass started
Age of Discovery in the 15th century. The Portuguese began
systematically exploring the
The first circumnavigation of the earth was completed in 1522 with
the Magellan-Elcano expedition , a Spanish voyage of discovery led by
The term stems from the 1530s, from
Lines of longitude appear vertical with varying curvature in this projection, but are actually halves of great ellipses, with identical radii at a given latitude.
Lines of latitude appear horizontal with varying curvature in this projection; but are actually circular with different radii. All locations with a given latitude are collectively referred to as a circle of latitude .
* v * t * e
Roughly, the latitude of a place on
Similar to latitude, the longitude of a place on
Further information: Rhumb Line
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.
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, either a line on a chart or 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 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 is the intersection of two or more LOPs.
If only one line of position is available, this may be evaluated
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 .
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
ELECTRONIC NAVIGATION COVERS ANY METHOD OF POSITION FIXING USING ELECTRONIC MEANS, INCLUDING:
Radar navigation uses radar to determine the distance from or bearing of objects whose position is known. This process is separate from radar's use as a collision avoidance system. Primarily when within radar range of land.
The practice of navigation usually involves a combination of these different methods.
MENTAL NAVIGATION CHECKS
By mental navigation checks, a pilot or a navigator estimates tracks, distances, and altitudes which then will help him or her avoid gross navigation errors.
Piloting (also called pilotage) involves navigating an aircraft by visual reference to landmarks, or a water vessel in restricted waters and fixing its position as precisely as possible at frequent intervals. 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.
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. 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 .
The Marine Sextant
The marine sextant is used to measure the elevation of celestial bodies above the horizon. For more details on this topic, see 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 system
Inertial navigation system
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 1930s and 1940s.
RDF antennas are easy to spot on German
World War II
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 (1949) application of moving-map displays. The system was deployed in the North Sea and was used by helicopters operating to oil platforms .
OMEGA Navigation System
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
Further information: Radar navigation and Doppler radar § navigation Radar ranges and bearings can be very useful 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. 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.
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. During the transit, the navigator can check that the ship is on track by checking that the pip lies on the drawn line.
The TVMDC App, running on an iPhone, available from the App Store: provides for a simple-to-use visual calculator, leading to a better understanding of: TVMDC Bearing Corrections, Set "> Poor passage planning and deviation from the plan can lead to groundings, ship damage and cargo loss.
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 charts to a process of risk management .
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
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. Integrated Bridge System, integrated on an Offshore Service Ship
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