What makes a Doppler radar special?

It can provide information on both the position of targets as well as their movement.

• It does this by tracking the ‘phase’ of transmitted radio wave pulses; phase meaning the shape, position, and form of those pulses.
• As computers measure the shift in phase between the original pulse and the received echo, the movement of raindrops can be calculated, and it is possible to tell whether the precipitation is moving toward or away from the radar.

Doppler radars in India:

In India, Doppler radars of varying frequencies — S-band, C-band and X-band.

• These are commonly used by the IMD to track the movement of weather systems and cloud bands, and gauge rainfall over its coverage area of about 500 km.
• The radars guide meteorologists, particularly in times of extreme weather events like cyclones and associated heavy rainfall.
• An X-band radar is used to detect thunderstorms and lightning whereas C-band guides in cyclone tracking.

Why are they called ‘Doppler’ radars?

The phase shift in these radars works on the same lines as the “Doppler effect” observed in sound waves– in which the sound pitch of an object approaching the observer is higher due to compression of sound waves.

• As this object moves away from the observer, the sound waves stretch, resulting in lower frequency.
• This effect explains why an approaching train’s whistle sounds louder than the whistle when the train moves away.
• The discovery of the phenomenon is attributed to Christian Doppler, a 19th-century Austrian physicist.

Significance:

With the radar observations, updated every 10 minutes, forecasters can follow the development of weather systems as well as their varying intensities, and accordingly predict weather events and their impact.

Source: IE / IMD