Radio Detection and Ranging (RADAR)

RADAR is an acronym for Radio Detection And Ranging and is useful in many ways.

  1. Observation of atmospheric objects and phenomena like clouds, cyclones, rain drops and prediction of weather
  2. Air Traffic Control
  3. Ship navigation
  4. In military use (early warning and fighter control radar)

RADAR is radio wave equivalent of SONAR. In RADAR, a radio wave does the same job as sound wave in SONAR. The basic elements of RADAR system are:

  1. A pulse source and a transmitter with an aerial which would emit radio waves
  2. An object which would reflect the radio wave
  3. A receiver with an antenna and a display system like Cathode Ray Tube (somewhat like a television or a computer monitor)


The transmitter in a RADAR system generates and sends a radio wave. The radio waves go in all directions. If there is any object, the wave is reflected by it. There has to be a receiver to detect the reflected wave.

The radio waves are electromagnetic radiation and travels at the velocity of light. The time gap between the outgoing radio wave and arrival of the reflected wave is very small. So, as soon as a radio wave is emitted, the transmitter is switched off and the receiver is switched on. Thus, the reflected wave is not masked by the emitted wave and even a weak reflected wave is not missed by the receiver.

If, after certain gap, there is no reflection received, we can presume that there is no object within certain distance and we can switch off the receiver and switch on the transmitter. This process goes on as was the case with SONAR. This is called a pulsed transmitter. However, for detecting moving objects, one can use continuous wave transmitter.

If an object is moving away, the frequency of the reflected wave will be lower than the transmitted wave. If the object is moving closer, the frequency will be higher for the reflected wave. This is called Doppler Effect for sound. One can always adjust the receiver such that it doesn't receive the radio waves of the frequency emitted, but receives the radio waves of lower or higher frequencies. Called Doppler RADAR, such RADAR can only detect a moving object because it can't receive the frequency at which a radio wave was transmitted and only a moving object will change the frequency of the reflected wave.


RADAR is useful in air traffic control as it can see in the dark. RADAR can monitor movement of clouds, detect rain drops. It can also detect presence of distant ships and big animals like whale in the sea. It can also be used to estimate the speed of the object approaching or moving away from us. It is used by weather scientists to track storms, tornadoes and hurricanes.

Space and earth scientists make its use in tracking satellites and also in mapping earth surface. In fact it is useful even in making auto-open doors in shops or airports. This is because a wave will be reflected and sensed only if there is an obstacle in the way of emitted radio wave.