Navigation

Summary

Navigation is the process of plotting an object from one point to another. This is accomplished by determining one's exact position on Earth by visual or electronic means and determining the course to the exact position of the intended destination. Specific points are often defined as measurements of latitude and longitude.

Definition and Basic Principles

Location of one's position is based on trigonometry and the process of triangulation. Triangulation involves determining the location of a point by measuring angles to it from two or more known points. The intersection of the lines from the known points represents one's position.

Prior to the development of electronic instruments such as radio, radar, and Global Positioning System (GPS), the determination of one's position was accomplished using a sextant. The sextant was able to pinpoint one's location accurately by measuring the angular distance between the horizon and a celestial object. Repeated sightings were plotted on a nautical chart. This method was suitable for ships and propeller aircraft.

After the development of the radio, a position could be determined by triangulating radio stations with known positions. With the development of radar, images of known landmasses or buoys could be used for triangulation.

GPS also involves triangulation. The device electronically determines one's position by triangulation of orbiting satellites and marks the position on a map overlay.

Navigation also involves correction for ocean currents and obstacles such as landmasses and other vessels. Experienced seamen past and present, aided by experience, can predict current with reasonable accuracy. Wind affects currents, which can be estimated by the sailor or measured with an anemometer (wind gauge). Airplanes are affected by currents known as jet streams. Spacecraft are affected by gravitational forces, which increase in power as the craft approaches. That force can be used to change the direction of the craft substantially.

Background and History

Human migration and discovering new lands by navigation of the oceans was accomplished by many ancient cultures, including the Phoenicians, ancient Greeks, the Norse, the Persians, and the Polynesians. Primitive navigation depended on knowledge of ocean currents and the position of celestial objects.

The magnetic compass was first used in China around 200 BCE. The ancient compasses used a naturally magnetic lodestone, which pointed to the magnetic North Pole. In eighth-century China, the lodestone was replaced by a magnetized needle.

Navigation charts first appeared in Italy at the close of the thirteenth century. Called portolan charts, they were rough maps based on accounts of sailors plying the coastlines of the Mediterranean and Black seas. The octant, precursor to the sextant and developed around 1730, made it possible to determine latitude accurately but not longitude. The sextant and acccurate chronometers added the ability to determine longitude. At the close of the nineteenth century, radios that transmitted and received Morse code began to appear on oceangoing vessels.

The prototype of the modern radar was installed on the USS Leary in 1937. In 1942, the first long-range navigation system (loran) was installed at various points along the Atlantic Coast of the United States. Loran is based on using the intersection of two radio waves to determine one's position. The subsequent proliferation of satellites, after the Soviet Union launched Sputnik I, the first Earth-orbiting satellite, in 1957, led to the development of satellite technology and the highly accurate GPS.

How It Works

Compasses. The magnetic compass needle points to magnetic north and floats over a 360-degree compass face, which displays the cardinal points: north (0 degree), east (90 degrees), south (180 degrees), and west (270 degrees). The deviation (declination) of magnetic north is not a constant and is updated annually. Nautical charts display the amount of needed correction from the baseline, which is the declination value of the year the chart was published. The magnetic compass is a simple, reliable instrument; however, its readings can be affected by any magnetic field in the vicinity. Marine electronics located near the compass generate magnetic fields; ferrous (iron) material often has a magnetic field. To improve accuracy, the compass can be calibrated by small magnets or other devices to correct for extraneous magnetic fields. The compass must be recalibrated with the addition of any new electronics. A gyrocompass points to true north and is unaffected by stray magnetic fields. The gyrocompass, first invented in practical form in 1906, employs a rapidly spinning gyroscope, which is motor driven. A disadvantage of the gyrocompass is that electrical or mechanical failure can render it useless.

Loran. Loran is an acronym for long-range navigation. The system relies on land-based low-frequency radio transmitters. The device calculates a ship's position by the time difference between the receipt of signals from two radio transmitters. The device can display a line of position, which can be plotted on a nautical chart. Most lorans convert the data into longitude and latitude. Since GPS became available, the use of loran has markedly declined.

Radar. Radar consists of a transmitter and receiver. The transmitter emits radio waves, which are deflected from a fixed or moving object. The receiver, which can be a dish or an antenna, receives the wave. Radar circuitry then displays an image of the object in real time. The screen displays the distance of the object from the radar. If the object is moving, consecutive readings can calculate the speed and direction of the object. If the object is airborne, and the radio is so equipped, the altitude is displayed. Radar is invaluable in foggy weather when visibility can be severely reduced.

Sonar.Sonar, which is an acronym for sound navigation ranging, transmits and receives sound waves for underwater navigation by submarines. Passive sonar is a related technology in which the equipment merely listens for underwater sound made by vessels. Active sonar emits a pulse of sound (a “ping”) then listens for a reflection or echo of the pulse. The distance of the object is determined by the time difference from transmission to reception of the ping (the speed of sound in water is a constant). To measure the bearing, two or more separated transmitter/receivers are used for triangulation of the object. Sonar can also be used by both submarines and surface vessels to determine the depth and contour of the ocean (or other body of water). By consulting a nautical chart, which is marked with depth gradients, the distance from the shoreline can be calculated.

Global Positioning System (GPS). GPS is a space-based global navigation satellite system that provides accurate location and time information for any point on Earth where there is an unobstructed line of sight to four or more GPS satellites. GPS can function under any weather condition anywhere on the planet, except underwater—a submarine must surface to use a GPS system. The technology depends on triangulation, just as a land-based system such as loran employs. GPS is composed of three segments: the space segment, the control segment, and the user segment. The US Space Force operates and maintains both the space and control segments. The space segment is made up of satellites, which are in medium-space orbit. The satellites broadcast signals from space, and a GPS receiver (user segment) uses these signals to calculate a three-dimensional location (latitude, longitude, and altitude). The signal transmits the time, accurate within nanoseconds.

Navigational Aids. According to the US Coast Guard, a navigational aid is a device external to a vessel or aircraft specifically intended to assist navigators in determining their position or safe course, or to warn them of dangers or obstructions to navigation. Navigational aids include buoys, lighthouses, fog signals, and day beacons. Buoys are used worldwide to mark nautical channels. They are color coded: Red buoys mark the right (starboard) side of the channel for a vessel returning to a port; green buoys mark the port (left) side of the channel; and red-and-green-striped buoys mark the junction of two channels. Buoys often contain gongs, which are activated by wave motion and solar-powered lights. Some buoys do not mark safe channels and are referred to as “nonlateral markers.” They contain shapes identifying their purpose. Squares depict information, such as food, fuel, and repairs. Diamonds warn of dangers such as rocks. Circles mark areas of reduced speed. Crossed diamonds indicate off-limits areas such as dams and places where people may be swimming.

Applications and Products

Navigational aids have many applications, which are tailored to underwater, water surface, terrestrial, atmospheric, and space use.

Water-Surface Navigation. Any vessel, which is capable of venturing offshore, must contain some basic navigation equipment. A magnetic compass is mandatory, as is a marine radio, which can be used to call for help. A knot meter, which consists of an underwater paddle wheel connected to a dial, can give the relative speed over water. The vessel should contain nautical charts of the area, which are prepared by the National Oceanic and Atmospheric Administration (NOAA). Another essential is an accurate timepiece (chronometer). By combining the readings of speed registered on the knot meter, the compass heading, and chronometer, one can plot the vessel's approximate position on the nautical chart. All inboard marine engines are equipped (or can be equipped) with a tachometer, which registers engine speed in revolutions per minute (rpm). A prudent skipper can run his boat over a known distance (between measured mile markers) and construct a chart of the vessel's speed at various rpm. If the vessel does not have a knot meter, or it fails, the approximate boat speed can be determined via the tachometer. Another relatively inexpensive piece of equipment is a simple depth sounder, which displays depth (more expensive models display a graphic representation of the seabed). The depth sounder can aid in determining the vessel's position, and more importantly, alert the skipper to shallow water, which could damage the hull. Binoculars, which can help identify shoreline features, are another inexpensive necessity. The sextant, which can pinpoint one's position, is another inexpensive navigation aid; however, most recreational boaters are unfamiliar with its use.

Many recreational vessels of modest size (thirty-two to forty-two feet long) have an automatic pilot, radar, and GPS in addition to the aforementioned items. Some utilize a loran receiver, which may be less expensive than a GPS, and it can accurately display the ship's position. An automatic pilot adjusts the rudder(s) to maintain a desired heading. Radar can be adjusted for the distance it displays; ranges of less than one mile and more than thirty miles are commonplace. In many situations, the shortest range is the most valuable because it can clearly depict an approaching vessel or a small landmass (an islet or an offshore oil rig). Even in clear weather, radar can provide invaluable navigation information. Ship-mounted GPS devices can be purchased and installed relatively inexpensively and are becoming commonplace on recreational vessels.

Large commercial and naval vessels (and many luxury yachts) contain sophisticated navigation equipment. Large vessels also boast onboard computers, which interpret data from radar, GPS, and the tachometers to display detailed navigation information. These computers also replace the automatic pilot found on smaller vessels. The computer can adjust the rudders and throttles to maintain the ship's heading and time of arrival. Depth sounders with graphic displays and sonar are components of most large vessels as well as fishing boats, which use them for locating schools of fish.

Underwater Navigation. Unlike surface vessels, submarines must navigate in three dimensions. Active sonar is employed by distance to a target and depth. Transmission of sound from two separate sources can give the submarine's heading. Submarines are equipped with GPS, which can be used to determine position only when the vessel is on the surface. When below the surface, an inertial navigation system (INS) is employed. The INS is composed of precise accelerometers and gyroscopes to record every change in the submarine's speed and direction. The data from these instruments is fed to a computer, which determines the vessel's position. Over time, small errors accrue; these errors are corrected when the submarine surfaces and the GPS is activated.

Terrestrial Navigation. When traveling on a road, a motorist can navigate using street and highway signs as well as a map of the area. Many motor vehicles are equipped with a GPS. The GPS gives a visual display of the vehicle's position on a map overlay. Useful information such as distance to the next turn and the destination are given. The GPS in most automobiles has an audio system, which informs the motorist of upcoming turns. The GPS of many vehicles also give additional information such as gasoline stations, rest areas, local restaurants, and hospitals. Smartphones are generally equipped with internal GPS and users can employ mapping apps that plot courses and give turn-by-turn instructions. Celestial navigation with a sextant can also be utilized. Being able to locate Polaris (the North Star), which is the brightest star in the constellation Ursa Minor (the Little Dipper or Little Bear), is a necessary skill for all off-road travelers. The rising and setting sun or other visual aids such as the glow from a city at night can also aid in navigation.

Atmospheric Navigation. Aircraft navigate in three-dimensional space, so latitude, longitude, and elevation must be known. All aircraft contain basic instrumentation, which includes: a magnetic compass; an altimeter, which displays the altitude; an airspeed indicator; a heading indicator, which is similar to a gyrocompass; a turn indicator, which displays direction and rate of turn; a vertical-speed indicator, which displays the rate of climb or descent; and an attitude indicator. The attitude indicator, which is also known as an artificial horizon, is an invaluable navigation instrument. It contains a gyroscope that reflects both the horizontal and vertical alignment of the aircraft. When visibility is reduced, the pilot is unable to visualize the horizon. Many small aircraft and virtually all large aircraft contain a GPS. Other navigation equipment commonly found on larger aircraft include a course deviation indicator (CDI) and a radio magnetic indicator (RMI). However, a GPS is much superior to either a CDI or RMI. The CDI displays an aircraft's lateral position in relation to a track, which is provided by a very high frequency (VHF) omnidirectional range (VOR) or an instrument landing system. A VOR is a ground-based station that transmits a magnetic bearing of the ship from the station. An instrument landing system is a ground-based system that can provide precision guidance of the aircraft to a runway. It includes radio signals, and often, high-intensity lighting arrays. An RMI is usually coupled to an automatic direction finder (ADF); the RMI displays a bearing to a nondirectional beacon (NDB), which is a ground-based radio transmitter.

Unmanned aerial vehicles (drones) and guided missiles must also be navigated. In the case of an unmanned drone, a pilot sits at a console on the ground and directs the flight via radio. Guided missiles are internally or externally guided, and sometimes both. Some missiles contain inertial navigation systems similar to those found on submarines. The system is programmed to strike a specified target. External control can be via radio waves or laser. In some cases of laser guidance, the missile contains a laser homing device in which the projectile “rides” the laser beam to the target. More commonly, a technique referred to as semi-active laser homing (SALH) is employed. With SALH, the laser beam is kept pointed at the target after the projectile is launched. Laser energy is scattered from the target, and as the missile approaches the target, heat sensors home in on this energy.

Space Navigation. Space navigation is a complex and highly technical science. In addition to involving three dimensions it also requires plotting a course between two moving objects (the Earth and a space station or an orbiting space shuttle and the Earth). Space navigation also entails calculating the gravitational force of celestial objects such as the Moon and planets. Space navigation requires the collaboration between computers (both ground and ship based) and complex instrumentation. It also requires collaborative effort between highly skilled personnel and either astronauts or navigation equipment within unmanned spacecraft.

Careers and Course Work

Any navigation course requires knowledge of trigonometry. Whether navigation is based on visual or electronic information, triangulation to fix a position is required. The military offers many careers and course work involving navigation. Following military service, this training can be applied to many civilian job opportunities, up to and including piloting an aircraft or navigating a ship. The US Coast Guard Auxiliary and the US Power Squadrons offer free boating-safety courses, which include navigational skills. Courses are available throughout the United States as well as online. For individuals interested in more advanced courses, such as ones for preparation for the US Coast Guard captain's license, reasonably priced courses are available throughout the US and online. For those not interested in a military career, navigation training is available at civilian institutions. These include California Maritime Academy in Vallejo; Great Lakes Maritime Academy in Traverse City, Michigan; Maine Maritime Academy in Castine; Massachusetts Maritime Academy in Buzzards Bay; State University of New York Maritime College in the Bronx; Texas Maritime Academy, which is part of Texas A&M University at Galveston; and the US Merchant Marine Academy in Kings Point, New York.

Although the basic principles of navigation can be learned and applied by any high school graduate, more advanced topics require a college degree and often a postgraduate degree such as a master of arts (MA) or doctorate (PhD). An MA requires one year of study after four years of college; however, an academically aggressive student can earn an MA concurrently with a bachelor's degree. A PhD requires two to three additional years of study followed by submission of a thesis or dissertation. Course work should include mathematics, engineering, computer science, and robotics. Positions are available for individuals with a degree in laser engineering in both the government and private sector. The ability to be a team player is often of value for these positions because ongoing research is often a collaborative effort.

Social Context and Future Prospects

Although the basic concepts of navigation have remained unchanged for centuries, modern navigation technology is highly advanced and continues to evolve. The frontier of navigation research lies in military and extraterrestrial applications. The military is focused on guidance systems for missiles and drones. Extraterrestrial applications range from the navigation of Earth-orbiting shuttles to interplanetary (and beyond) navigation. New emphasis is placed on navigation as more autonomous vehicles, such as private automobiles and taxis, emerge on public streets around the world. Navigation is an essential component of daily life—both civilian and military.

Bibliography

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