Indigenously Developed S-Band Doppler Weather Radar
Science & Technology › Space Technology and ISRO · Topic 12.28
A Doppler weather radar sends out pulses of microwaves and listens for the echoes from raindrops, hail and ice in clouds. The strength of the echo, called reflectivity, shows how heavy the rain is, and the change in the frequency of the echo, called the Doppler shift, shows whether the rain is moving towards or away from the radar, which gives the wind inside storms. An S-band radar works at a frequency of 2 to 4 gigahertz with a wavelength of about 10 centimetres, so its signal passes through heavy rain with little loss and it can watch storms at ranges of 250 to 500 kilometres, which makes it the best band for tracking cyclones. India developed S-band radars indigenously through ISRO and Bharat Electronics Limited for the India Meteorological Department.
5 min read · UPSC Prelims · Science & Technology · Space Technology and ISRO
At a Glance
- S-band 2 to 4 GHz, about 10 cm
- Range 250 to 500 km
- Measures Rain intensity and wind
- Used by India Meteorological Department
- Programme Mission Mausam
- Exam link UPSC Prelims, Science & Technology: Space Technology and ISRO
Where Does It Fit?
This topic follows the account of lunar water. It returns to applications of technology on Earth and shows how radar, along with satellites, helps in weather forecasting and disaster warning. Previous topic: Global Map of Water on the Moon. Next topic: ISRO-Developed Satellite-Based Chip System.
How Does a Doppler Weather Radar Work?
| Concept | Details |
|---|---|
| Pulse and echo | The radar transmits short microwave pulses and receives the part reflected by raindrops and other particles |
| Reflectivity | The strength of the echo, shown in colour maps, tells the rainfall intensity and hail |
| Doppler effect | Motion of the targets towards or away from the radar changes the frequency of the echo |
| Radial velocity | The Doppler shift gives wind speed along the beam, which reveals rotation in storms and cyclones |
| Dual polarisation | Sending both horizontal and vertical waves helps to tell rain from hail and snow and improves rain estimates |
| Range | Distance is found from the time between pulse and echo |
| Coverage | One radar covers a circle around it; a network gives national coverage |
Why S-Band and What Is India’s Radar Programme?
- S-band: 2 to 4 GHz, wavelength about 10 cm. Little attenuation in heavy rain, so used for long range and cyclones. Needs a large antenna
- C-band: 4 to 8 GHz, wavelength about 5 cm. Medium range, more loss in heavy rain, smaller antenna
- X-band: 8 to 12 GHz, wavelength about 3 cm. Short range, high detail, used for local storms and airports
- IMD network: the India Meteorological Department operates a network of about 37 Doppler weather radars and has been adding more
- Mission Mausam: a mission announced in 2024 with an outlay of about Rs 2,000 crore to improve weather observation and forecasting, including new radars, satellites and supercomputers
- Indigenous production: Bharat Electronics Limited and ISRO’s Space Applications Centre developed the S-band radar technology, so that India need not rely on imports
- Uses: cyclone track and intensity, thunderstorms, cloudbursts, heavy rainfall alerts and aviation safety
- Nowcasting: forecasts for the next few hours using radar data to warn of severe local weather
What Else Should You Remember?
- Doppler effect: named after Christian Doppler, it is the change in frequency of a wave when the source and observer move relative to each other
- First Indian Doppler radar: IMD began installing Doppler radars around 2002 with a radar for Chennai in cyclone prone regions
- Cyclone warning: radar data helped to track cyclones such as Fani in 2019 and gave accurate landfall forecasts
- Gaps: the Himalayas, the Northeast and some interior regions have fewer radars
- Satellite plus radar: radar gives detailed storm structure near the coast, while satellites give wide coverage over the oceans, as in Earth Observation Systems and INSAT/GSAT/IRS Applications in Detail
- Radar on mountains: special radars are used in hills and for clouds in Himalayan valleys
- Wind profilers and lightning detectors: other instruments in IMD’s network
- Data and apps: IMD shares radar images through its website and mobile apps such as Mausam
- Weather models: radar data feed numerical models that give forecasts
- Other uses: monitoring of bird movement and airport wind shear
- Limits: radar beams are blocked by hills and curve above the ground at long range
- Climate: more intense rain events under warming increase the need for good radar coverage
- Rainfall estimation: radar rainfall maps are adjusted with rain gauge data to give area rainfall estimates for flood forecasts
Why Does It Matter for the Exam?
- Bands: S, C and X-band ranges
- Concepts: reflectivity and Doppler shift
- Indian effort: indigenous radars and Mission Mausam
- Current affairs link: new radars and cyclone warnings
- Common errors: saying that X-band is the best for long range or that the radar measures temperature directly
As an analytical point, radar fills the gap between satellite pictures and ground stations by showing storms in detail. A denser network, with indigenous technology, will improve warnings for heavy rain and cyclones.
Why Is This Topic Important?
- Principle Doppler
- Bands S, C, X
- Policy Mission Mausam
What Came Next?
The next topic covers the satellite-based chip system developed by ISRO. Next topic: ISRO-Developed Satellite-Based Chip System.
Key People and Terms
- Reflectivity Echo strength
- Doppler shift Frequency change of echo
- S-band 10 cm radar band
- Attenuation Signal loss
- Nowcasting Very short term forecast
- Polarisation Wave orientation
Exam Corner
Points to Remember
- S-band: about 10 cm wavelength, long range.
- X-band: about 3 cm, short range.
- IMD has about 37 Doppler radars.
- Mission Mausam outlay: about Rs 2,000 crore.
- Doppler shift gives wind speed.
Do Not Confuse With
- S-band and X-band radar Long range through rain versus short range with detail
- Reflectivity and velocity Rain strength versus motion
- Radar and satellite Local detail versus wide coverage
Memory Hook
S for the storm at distance, C in the middle, X for the detail near; Doppler gives the wind.
Mains Angle
Questions ask about bands and the Indian programme. These points help.
- Principle Echo and Doppler
- Use Cyclone warning
- Self-reliance Indigenous radars
A Question You May Face
An original practice question, not a past paper question.
“Explain the working of a Doppler weather radar and discuss the importance of indigenous S-band radars for weather forecasting in India.”
How to Answer
- Working Echo and shift.
- Bands S, C, X.
- Use Cyclones.
- Way More radars.
GS Relevance
Frequently Asked Questions
What is a Doppler weather radar?
A Doppler weather radar is a radar that sends microwave pulses and records the echoes from raindrops and ice. The strength of the echo shows the intensity of rain, and the frequency shift caused by the Doppler effect shows the speed of the wind towards or away from the radar, which shows the structure and rotation of storms.
Why is S-band radar preferred for cyclones?
S-band radar has a wavelength of about 10 centimetres, which is long enough for the signal to pass through very heavy rain with little loss. It can therefore see the whole structure of a cyclone at ranges of 250 to 500 kilometres, while shorter wavelength radars such as C-band and X-band lose strength in heavy rain.
What is the Doppler effect?
The Doppler effect is the change in the frequency of a wave when the source and the observer move toward or away from each other. In weather radar, raindrops moving towards the radar make the echo's frequency higher and those moving away make it lower, so the radar can measure wind speed along its beam.
What is Mission Mausam?
Mission Mausam is an Indian Government mission approved in 2024 with an outlay of about Rs 2,000 crore, to make India weather ready and climate smart. It aims to improve observations with more radars, satellites and sensors, develop better forecast models with supercomputers, and increase the accuracy of warnings for extreme events.
Who builds weather radars in India?
Weather radars for the India Meteorological Department have been developed with Indian technology by Bharat Electronics Limited and ISRO's Space Applications Centre, in addition to imports from earlier years. The aim is to build S-band and other radars indigenously so that the national radar network can expand without dependence on foreign suppliers.
PYQ Practice — Statement Analysis
1 S-band radars are suitable for tracking cyclones at long range.
Less loss in heavy rain.
2 The Doppler effect in radar allows measurement of wind speed.
By frequency shift.
3 X-band radars have a longer range than S-band radars.
Their range is shorter.
4 Mission Mausam was launched to improve India's weather forecasting.
Approved in 2024.
Past Mains Questions on This Topic
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