Radar detects objects by transmitting
a pulse of radio waves and looking for signals reflected back from
the object. By measuring the time taken for the pulse to reach the
object and travel back to the radar, the distance can be calculated.
By rotating the antenna and sending out a stream of pulses, the radar
can build up a picture of objects.
Rain, snow and hail reflect radar waves. Using radar we can get
a picture of the extent and intensity - the greater the intensity
of rainfall, the stronger the signal returned - of the rainfall.
At longer ranges, typically over 100km, the accuracy falls off due
to the curvature of the Earth. Sometimes the radar will not 'see'
rain at long ranges or report rain at high altitudes that does not
reach the ground.
Radars also ‘see’ the ground and while measures are
taken to reduce echoes returned from the ground, some appear on the
images. Frequently echoes can be seen from the Mourne and Galtee
mountains even when no rainfall is present.
The images here are a composite of data from two radars - one at
Dublin Airport and the other at Shannon Airport. The shaded area
shows the coverage of the radars that are present. Data is updated
every 15 minutes.
Note: On some images a linear feature may be seen extending from
Limerick towards Waterford. This is due to interference from a WiFi system. Occasionally
other similar features may be seen extending from Dublin towards the South-east.