Navigation and Seamanship

6.2.1. RADAR (Radio Detecting And Ranging)

 

RADAR is an important navigational aid, working with radio waves. The word RADAR was coined in 1941 and stand for an acronym of RAdio Detection And Ranging. The radar is useful in guiding the navigator especially when sailing in coastal waters and always when visibility is poor. Radar is used to identify any objects including ships and buoys and to measure the range, altitude, direction, or speed of both moving and fixed objects. Radar can also be used in clear visibility for navigation or collision avoidance purposes by detecting the objects or targets above the water level. The range of visibility is optional a medium range radar could be useful up to 100 nautical miles. Sonar is known for its usage to identify the underwater objects with sound waves, but radar is using radio waves to find out things above the water level. It is also called as radio location. The frequency of electromagnetic energy used for radar is unaffected by darkness and also penetrates fog and clouds. This permits radar systems to determine the position of airplanes, ships, or other obstacles that are invisible to the naked eye because of distance, darkness, or weather. Modern radar can extract widely more information from a target's echo signal than its range. But the calculating of the range by measuring the delay time is one of its most important functions.

The waves applied in Radar are high frequency radio waves. The frequency ranges between 100MKz with a wave length of 3meters to 60,000MHz, with a wave length of 5mm. Most radar waves are within a band of radio waves known as microwaves. Microwaves tend to pierce the ionosphere, the electrified zone of the upper atmosphere that reflects radio broadcasting waves. Hence conventional radar can detect only those objects that are in a direct line of sight from the transmitting antenna.

The first practical radar was invented by the British physicist Robert Watson Wolt in 1935, but then many features were added to make the radar perfect for the use in the second world war, it has been in use since 1941.During 1940s differenttypes of radar sets were developed in the USA, Russia, Germany, France and Japan.