Electronic Navigation Systems: From Astrolabe to GPS

Introduction to Electronic Navigation

Electronic navigation systems are continually developing in order to provide pilots and captains the ability to precisely navigate both ships and aircraft under even the most treacherous conditions. Modern technological advances have changed the way navigators estimate time, location, and distance to destination. Among the electronic navigational instruments used in contemporary society are radar devices including the DECCA and LORAN. GPS is also a commonly used electronic navigational system that has afforded pilots the ability to estimate distance and location with high precision. Electronic navigation has enabled pilots of aircraft to make estimates that are within a 90% or greater accuracy range. The primitive systems utilized by early navigators would never approach the precision of modern systems. Both electronic navigation and the instruments used historically for navigational purposes are explored in greater detail below.

Historical Navigation Methods

The history of navigation is varied. In earlier times, non-electronic systems were used to gauge location and distance. Celestial navigation was commonly used in the earliest periods to help ship captains navigate. Up until the 20th century, in fact, the term "navigation" was limited primarily to defining how ships were guided across seas (Johansen, 1999). In contemporary society, however, electronic navigation now determines where a ship is located using radar and radio waves, via electronic instruments that interpret the directional properties of those waves (Johansen, 1999). Even more relevant, electronic navigation is being used by aircraft and air control towers to ensure accurate and precise landing in inclement weather and under tight airport conditions.

Prior to the use of electronic navigation instruments, charts were used to aid sailors traveling across land and sea. Charts were usually crafted from observations of the sun and stars; they took into consideration the distance of a foreign land based on the time it took to cover the area (Johansen, 1999). The magnetic compass was later invented, further supporting navigational efforts. In addition to use of the compass, early navigators utilized the cross-staff and astrolabe — two devices that the ancient Greeks had used to measure the altitudes of celestial bodies. The astrolabe was a disk made of bronze or brass, generally 10 to 50 centimeters in diameter, with a pointer in the center; a person holding the disk would point the device at the sun and read the angle of the sun's shadow to obtain information about approximate location and time (Johansen, 1999). Many early explorers utilized these devices with some success, although the results were certainly less precise than what can be achieved today. Most navigating captains were nonetheless able to estimate with fair accuracy their location and proximity to their destination at any point in time.

Developments in navigation occurred during the 17th century when mapmaking and related advances were encouraged. During this period, John Hadley and Thomas Godfrey are credited with inventing the quadrant, which made accurate observation of celestial bodies possible. The quadrant is very similar to the sextant still used by navigators today (Johansen, 1999). Trigonometric calculations followed in the 19th century. Electronic navigation came about during the 20th century and entails the use of hyperbolic and satellite systems as principal navigational tools (Walls, 1999).

Hyperbolic Systems: DECCA and LORAN

Hyperbolic systems include DECCA and LORAN, which are used to coordinate transmissions between two or more stations; the signals form a hyperbola (Walls, 1999). Radio frequency is most commonly used for a variety of functions and provides fast, efficient means of communicating location and time.

LORAN — an acronym for Long-Range Aviation Navigation — generally uses a 90–110 kHz frequency range and has a range of up to 600 miles. Alternatively, DECCA uses a 70–130 kHz frequency and a range of up to 400 miles (Walls, 1999). LORAN is essentially a radio system capable of calculating the position of an aircraft while also providing navigation assistance (Nolan, 2004).

GPS and Modern Navigation Instruments

In the 1980s, a system called the Navstar Global Positioning System was implemented. It enables spacecraft and vessel crews to map out and store their projected path on an onboard computer system, which then allows members to verify the location of their ship to within a few feet (Johansen, 2001). The system also enables accurate assessment of a ship's speed to within a few feet per second (Johansen, 2001). Most vessels additionally utilize an automatic pilot function. The U.S. Air Force also uses GPS — a satellite system that aids navigators in determining latitude and longitude with a 10-meter accuracy (Johansen, 2001).

GPS systems are currently considered the most accurate available. The FAA and the ICAO (International Civil Aviation Organization) have agreed that GPS systems should serve as the international standard for navigation (Nolan, 2004). These navigation instruments are widely used in contemporary aviation; however, they are used primarily as a means of guiding aircraft that are within one mile of an airport. More sensitive instruments are used in cases of bad weather or for precision landing. For example, Instrument Landing Systems (ILS) are used on runways to help aircraft land. These instruments utilize transmitters to guide aircraft to within 0.5 miles of the runway (Nolan, 2004).

GPS systems are often used in combination with color animated maps. These maps are electronically based and include features of airports such as restricted areas, control zones, surrounding airspace, and major land features (GA, 2004). Used in combination with GPS, navigation has become much easier and more precise. A majority of new aircraft and ships currently use these systems to pinpoint time, location, and distance. Similar smaller-scale systems are even being developed for use in everyday equipment — one can observe comparable navigational tools in luxury automobiles. GPS systems are often utilized in combination with other electronic navigation tools to deliver the greatest amount of information; however, GPS systems of the future are more likely to be standalone systems that offer convenience and reliability.