Rain Radar 101

A number of PWL viewers have asked us about how the weather radar works. To put it in simple terms, a radar is a device that sends and receives high frequency radio waves, also called microwaves. Imagine a lighthouse, but instead of a beam of light, a radar is a beam of energy. The signal is sent out and if it hits any particles in the atmosphere (rain, hail, ice, dust and even insect swarms) those particles ‘reflect’ the beam back towards the radar, which receives the signal. In many ways, it is like an echo. If you shout into a deep well, the sound waves will reflect of the walls and bounce back to your ears.

Different particles in the atmosphere reflect the signal in different ways, so the radar is able to determine how dense the particles are. Basically, denser particles reflect more signal back. This is then colour coded to illustrate what we might call ‘light’ or ‘heavy’ rain. In the example below, the Bureau of Meteorology uses a colour scale to indicate the estimated rain rate. radar01

It is also important to note that distance and even the curvature of the earth affect the accuracy of the radar’s results. As the following diagram shows, the further away from the radar source the beam travels, the higher up in the atmosphere it ‘sees’. This means that even though there might be heavy rain 200-300km away, it will only show up as light to moderate.

radcurve

For a more detailed article on how the rain radar works, check out the Bureau of Meteorology’s page here.

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