BL Explainer. All you wanted to know about Doppler Weather Radars

RADAR is the expansion for Radio, Detection and Ranging. Its basic components are a transmitter, receiver, antenna, power supply system, signal processing and high computing devices. It works on the principle of electromagnetic waves sent out by the transmitter. The same wave that strikes an object/dense medium is reflected back to the receiver. The distance up to the object is determined based on the speed of the electromagnetic wave, and the time to travel to the object and back. 

There are at least ten types of radars. The Ground Penetrating Radar studies the Earth’s crust up to 9-metre in depth and is being used by the Defence Geoinformatics Research Establishment (DGRE) at Joshimath. The InSAR (Inferometric Synthetic Aperture Radar) that makes high-density measurements over large areas by using radar signals from Earth-orbiting satellites and measures changes in land-surface is also being used in Joshimath and other parts of Uttarakhand. 

Also read: BL Explainer: What led to the sinking of Joshimath

What is a Doppler Radar?

A Doppler Radar is a specialised radar that uses the Doppler effect to produce velocity data about objects at a distance. When the source and the signal are in relative motion to each other, there is a change in the frequency observed by the observer. This is called the Doppler effect. If they are moving closer, the frequency increases and vice versa.  

A Doppler Weather Radar (DWR) works on the Doppler principle. It is designed to improve precision in long-range weather forecasting and surveillance using a parabolic dish antenna and a foam sandwich spherical radome. DWR has the equipment to measure rainfall intensity, wind shear and velocity and locate a storm centre and the direction of a tornado or gust front. 

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How are DWRs superior to other radars? What is the cost of operation, maintenance and running? 

Unlike others, a DWR has the ability to detect air motion, wind, speed of wind, rains, temperature, thunderstorms, hail, squalls, lightning, cyclones and cloud movements and volumetric analysis of cloud and reflectivity index, among others. It costs approximately ₹10-20 crore per unit, says Sanjay Srivastava, Chairman, Climate Resilient Observing Systems Promotion Council, and a veteran of air defence with core specialisation in radar, satellite and remote sensing. Operation and maintenance cost depending on type is generally ₹20-40 lakh per annum. 

Read more: A Vedic meteorologist taps into ancient wisdom to make weather forecasts

Does India have enough of them? Are more needed? 

As on January 15, 2023, the country has 37 DWRs. These are mainly spread across the plains. But mountainous and coastal terrain requires more radars, which are being procured. By 2024-25, India is expected to have 25 more DWRs taking the total number to 62 radars. That would improve forecast precision. 

How have DWRs improved the weather forecast? 

The major advantages of DWRs are, they:

• cover the entire country
• give the most precise detection of weather parameters including dynamic weather events turbulence, cyclones, thunderstorms or lightning
• alone do volumetric analysis of clouds that help in the quantification of rain forecasts and cyclonic intensity and precipitation; and
• precisely detect in real-time normal or routine events

Their best and famously documented use is in cyclone forecasting. As a cyclone comes within a 200 km range of the coast, the DWRs begin tracking it. This enables almost error-free forecasts with pinpoint precision. DWRs are also of great help in long-time lightning forecast of up to three to five days, down to 24 hours or even nowcast. 

Are doppler weather radars popular globally? 

DWRs are one of the most popular radars. The National Ocean and Atmospheric Administration (NOAA) of the US uses 148 of them, which speaks volumes about their efficacy. The Indian Army and Air Force have deployed the Indian Doppler Radar (INDRA) for the detection of aircraft and other objects in the air.

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