- During the 20th century,highly sophisticated ways of location objects were developed.Most of these developments were for military use,but civilian applications quickly followed.
- Sonar and radar were developed to detect unseen enemy equipment from reflected sound or radio waves-sonar for submarines,radar for surface ships or aircraft in flight
- Both radar and radio navigation make use of the fact that a loop aerial transmits radio waves in a narrow beam, rather than through 360 degrees
- Sonar uses high - frequency sound waves because these travel very quickly and efficiently in water - radio waves do not travel through water at all
The development of radar occurred independently in Britain,France,Germany,the USA and Japan in the 1930s
Radar is now also used in ICBM early warning system and missile guidance, air traffic control,shipping,astronomy,meteorology,archaeology, satellite tracking and speed detection by traffiic police.
What is sonar?
- The Asdic system was developed by Allied scientists in 1917-18,it was rename sonar by the Us navy during the Second World War.
- Active sonar detects echoes from sound or ultrasound (extremely high frequency sound) generated by the system itself
- Passive sonar detects sounds made by the target, for instance a ship or submarine
- Modern system are hull-mounted ,or operate from an air -launched sonobuoy or unit suspended from a helicopter,passive sonar arrays are also installed on a seabed
- The echo sounder found in many private boats uses sonar echoes from the seabed to determine water depth
Radio navigation was developed during the Second World War as a means of directing bomber aircraft to their targets at night
The German Knickebein (bent leg) system,developed by Hans Plendl from 1934 was typical.It use a radio beam transmitted from Kleve,western Germany,to guide an aircraft to the target (Morse signals in the radio beam warned to the pilot if he strayed off course).An interceptor beam from Breadstadt,northern Germany,signalled when the aircraft was over its targets .Britain's Gee system and the US Loran Were similar.
Modern radio navigation system include the VOR system of radio beacons in commercial air corridoors
EYE ON THE SKY The VOR system in combination with radar, enables air traffic to be controlled from a rellatively small number of centres on the ground.
Global positioning
The US Department of Defense's Navstar global positioning system (GPS) is the world's most widely used navigational system. Time signals regulated by atomic clock are transmitted by 24 satellites in precise orbit at least four satellites are always simutaneously within range of any point on the Earth's surface.Gps recivers in boats,car and even mobile phones compare signals from several satellites to plot a location accurate to a few metres.
PINPOINTED A GPS receiver calculates its distance from four or more satellites, as if it is on the surface of imaginary spheres centred on each of the satellites. The receiver's location is at the point where the spheres intercept.
** Note**
EYE ON THE SKY The VOR system in combination with radar, enables air traffic to be controlled from a rellatively small number of centres on the ground.
Global positioning
The US Department of Defense's Navstar global positioning system (GPS) is the world's most widely used navigational system. Time signals regulated by atomic clock are transmitted by 24 satellites in precise orbit at least four satellites are always simutaneously within range of any point on the Earth's surface.Gps recivers in boats,car and even mobile phones compare signals from several satellites to plot a location accurate to a few metres.
** Note**
- ASDIC: Anti submarine Detection Investigation Committee (an apocryphal Allied scientific committee of the First World War)
- Gee: Grid navigation system
- GPS: Global Positioning System
- Loran: Long-range Radio Navigation System
- Radar: Radio Detection and Ranging
- Sonar: Sound Navigation and Ranging
- VOR : VHF (Very High Frequency) Omnidirectional Radio
TIMESCALE
- 1904: German Cristian Hulsmeyer builds a primitive radar system
- 1908: Herman Anschutz Kaempfe (Germany) invents the gyrocompass
- 1911: Practical gyrocompasses built by Elmer Ambrose Sperry go on sale in the USA
- 1917-1918: Allied naval vessels are fitted with Asdic anti-submarine detection systems
- 1922: Guglielmo Marconi proposes using radio wave echoes to detect ships.
- 1935: Tests in Britain prove radio wave echoes can detect distant aircraft
- 1936: An early radar is fitted to the liner Normandie to detect icebergs
- 1938: A chain of radar detectors to warn of aircraft attack is completed around Britain's south and east coasts
- 1940-1941:Germany's Knickebein, X-Gerat and Y-Gerat radio navigation systems guild bombers to their targets in Britain, all are soon jammed
- 1964:The first satellite navigation system is created , using US navy satellites
- 1978-1995: The Navstar GPS system is set up,initially for the US military