Page 67 - Encyclopedia Of World History Vol IV

1368 berkshire encyclopedia of world history

could be found without the restriction of the traditional built up of digits and made visible on a computer screen)
noon observation of the sun. Douwes’s method was that can be linked to other relevant navigational data,
improved and remained in use until the nineteenth cen- including GPS data, the actual water depth found with
tury, when position line navigation gradually also came an electronic echo-sounding device, the ship’s speed
into use.This is the name for various methods by which, found with an electronic log, the gyrocompass, and
through an astronomical observation and subsequent radar-reflected images. In the decades to come, the elec-
calculation and construction in a chart, a ship’s position tronic chart is expected to replace the traditional paper
could be found at almost any time of the day.The first to sea chart.
develop a method by which a single observation of the In the early years of aviation, airplanes were navigated
sun or a star resulted in a position line was the American by visual reference to the ground. As altitudes increased,
captain Thomas Sumner, in 1843. The intersection of “blind flying” (in clouds) became unavoidable, and vari-
several “Sumner lines,” taken from stars in different direc- ous means of radio navigation were introduced. Most
tions, provided a fix. In the 1860s the Sumner method were non-directional radio beacons, and airplanes would
was improved by French astronomers and naval officers, fly from beacon to beacon. In the 1920s, the air plot
and by then celestial navigation had reached the level at technique, to find a dead-reckoned position, was derived
which it remained until long after World War II. from nautical practice.The first air almanac appeared in
1933, and five years later the first astronomical tables for
Electronic Means air navigation were published.
of Navigation In the 1940s sextants fitted with artificial (bubble)
The development of wireless radio, at the beginning of horizons were introduced, and a fix was found with
the twentieth century, opened new possibilities, first celestial altitudes and the use of an air almanac and
through radio direction finding and later through radar astronomical tables. Short-cut methods for calculation
and hyperbolic radio systems, such as Decca and loran were developed especially for aviation, as were navigat-
(long range navigation). With these systems, within cer- ing machines and navigational slide rules, such as
tain limitations, a position line or a fix could be obtained Bygrave’s cylindrical slide rule, which bypassed or
independently of weather conditions. The first practical skipped part of the calculation. During World War II
gyrocompass was invented in 1906, which made north- radio navigation was further improved. For civil aviation,
finding possible without using the earth’s magnetic field. non-directional beacons remained in use over land, and
The next major development was the introduction of for crossing oceans and deserts traditional celestial nav-
satellite navigation in the late 1970s. With the Global igation was applied.After the War loran was used in civil
Positioning System (GPS), which became fully opera- aviation for crossing oceans, as were radio signals from
tional in the 1990s, a position can be obtained instantly, dedicated ocean station vessels. During the 1960s, non-
and it is far more accurate than through celestial navi- directional beacons were gradually replaced by VOR
gation. As GPS became cheaper and easier to obtain, (Very high frequency Omnidirectional Range) stations;
satellites have now replaced sextants and nautical al- special techniques for polar navigation were already
manacs completely.The Global Positioning System is op- applied since 1957.
erated by the United States government, and to insure Due to the increase of aircraft in the 1960s and the
independence from this system, the European Union introduction of jet aircraft, the requirements for position
supports and owns the European satellite navigation sys- reporting became more stringent. Over land the use of
tem, named Galileo, which should be operational around ground radar by air traffic control increased but long-
2008. In the 1980s the electronic chart was developed. range (en route) navigation remained basically un-
This is a digitized chart (a chart of which the image is changed, although sextants were improved.