Science Concepts: Radar

Radar is based on a really simple concept that’s very familiar- the echo.

When we make a sound, energy travels in sound waves away from us. When the wave hits a surface, part of the sound energy is absorbed and the rest bounces back, being heard as an ‘echo’ when it reaches our ears. Because sound takes time to travel, there’s a delay between making the sound and hearing the echo- this delay can be used to work out how far the sound has travelled and so also the distance to the point of reflection.

There are animals that rely on the reflection of sounds they make for navigating their way around the world – bats, dolphins, whales and some birds – it’s a skill called ‘echolocation’, used for avoiding obstacles in the dark and hunting prey.

RADAR is based on the same principle – wave reflection – but makes use of the reflection of radio waves instead of sound. The word is shortened from ‘RAdio Detection And Ranging’.

Radar has all sorts of applications. As well as simply detecting the presence of an object and where it is, radar can be used to work out its shape and what it is (although that’s far more complicated to do).

Radar can also be used to work out if something is moving and how  – how fast and in what direction. This makes use of something called ‘Doppler shift’ – some of you may remember this from high school science lessons and it’s something that most of us will have experienced without even realising.

When a wave bounces off a moving object the reflected wave is ‘squashed’ or ‘stretched’ depending on whether the (reflecting) object is moving towards or away from us. This happens with any kind of wave – we’re used to experiencing it with sound waves, the movement causing a change of pitch as a car drives past us blaring its horn for example – but it happens with radio waves too. This allows a radar system to work out whether the reflecting object is moving towards or away from us and how fast.

In the early days at Jodrell Bank, radar was used to study meteors (‘shooting stars’ – particles of dust or rock falling through Earth’s atmosphere from space) as well as to study the Moon and Venus. Radar continues to be a really useful technology today – as well as its obvious military purposes it is used by weather-watchers to track storms, air traffic control to track and guide planes and scientists to map the surface of planets in our solar system, including our own.

Global view of the surface of Venus created from radar imaging by NASA’s Magellan spacecraft Source: NASA/Jet Propulsion Laboratory-Caltech Published: May 7, 2008

For more information, explore these great BBC Bitesize clips here:

Sound reverberation
Electromagnetic waves and radar