Weather Tutorials: Synoptic Charts | COLA Charts | Radar Images

Where do weather radar images come from?

All radar images are obtained from the Bureau of Meteorology but is post processed by the Weather Company.

How does radar work?

Radar works on the principle of the scattering of radio waves off targets from a highly directional antenna system. In the case of weather radar, these targets are water droplets of a raindroplet size, ice, hail and snow. However, any object of a similar size to the wavelength of the radar transmission will produce an echo and therefore show up on the radar display.

The different coloured pixels on the display are related to the intensity of the echo which for the Weather Watch radar is dependent on the size of the water droplets, ice crystals, snow or hailstones and their respective densities. The direction from which an echo is received and hence the location of the precipitation at any one time is calculated by the Weather Watch Radar's Computer and is dependent on the zenith angle (angle between the horizon and the antenna element) and azimuth (horizontal direction) of the antenna beam. However, in the case of the Weather Watch radar images, only a horizontal or plan position image is obtained. That is an indication of where the precipitation is while the zenith angle of the radar beam is unchanged.

Problems with observing snow on the Alps

As seen by the picture below the radar is a line of sight instrument and so if the clouds are down near the peaks then the snow falling from them is essentially hidden from the radar. That combined with the fact that the mountains reflect lots of energy as well and this must be removed from the signal. The overall result is that precipitation tends to approach the Alps and then "disappear" from the radars. This is just a limitation of the instruments and not a real phenomenon.

Diagram of the limitations of weather radar when observing cloud over peaks.

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