Named after Austrian physicist Christian Doppler (who described the phenomenon in 1842), the Doppler effect refers to the change in frequency of waves as their source moves relative to an observer. In weather radar, radio waves are emitted from an antenna; when they strike precipitation particles (raindrops, hailstones, snowflakes) moving toward the radar, the returned frequency is higher; when moving away, it is lower. This frequency shift directly reveals the velocity and direction of the precipitation.
Step 1 — Emission: A beam of microwave energy (radio waves) is transmitted from a rotating antenna.
Step 2 — Scattering: When the beam strikes precipitation particles in the atmosphere, energy scatters in all directions; some reflects back to the radar. Larger particles reflect more energy.
Step 3 — Distance measurement: The time delay between transmission and return indicates the distance of the precipitation from the radar station.
Step 4 — Velocity measurement: The frequency shift (Doppler shift) of the return signal reveals the speed and direction of particle movement.
Step 5 — Display: Processed data is displayed as colour-coded maps showing precipitation intensity, storm movement, and wind patterns within the storm.
| Parameter | What It Tells | Application |
|---|---|---|
| Reflectivity (dBZ) | Rainfall intensity / precipitation amount | Flood warnings, rainfall estimation |
| Radial Velocity | Speed of precipitation toward/away from radar | Cyclone tracking, wind shear detection |
| Spectrum Width | Turbulence within storm | Aviation hazard warnings |
| Dual-Polarization | Size/shape of particles (rain vs hail vs snow) | Precipitation type identification |
| Coverage Area | Area monitored per radar station | ~500 km for S-band, ~250 km for C-band, ~150 km for X-band |
IMD has been operating radars since 1949. The first radar was imported and installed to aid aircraft operations in the 1950s. Digital Doppler Weather Radars came to India in Phase III (post-2000).
The India Meteorological Department (IMD) was established in 1875 under British rule with H.F. Blanford as the first Meteorological Reporter, driven by the devastating Bengal cyclone of 1864 (60,000 deaths) and consecutive monsoon failures of 1866 and 1871.
| Year | Event | Significance |
|---|---|---|
| 1875 | IMD established | Meteorological Reporter: H.F. Blanford |
| 1949 | IMD begins radar operations | Earliest weather radar use in India |
| 1954 | First wind-finding radar (Dum Dum) | Support for aviation + storm tracking |
| 1958 | Indigenous radar, Safdarjung, Delhi | First locally developed radar from WWII remnants |
| 1970 | First S-band cyclone radar — Visakhapatnam | Bay of Bengal cyclone monitoring begins |
| 2002 | First DWR — Chennai | Digital Doppler era begins in India |
| 2016 | First indigenously made Polarimetric DWR — Cherrapunjee | ISRO/ISTRAC + BEL collaboration; world's wettest site |
| Sep 2024 | Mission Mausam Cabinet approval + ARKA/ARUNIKA inaugurated | ₹2,000 crore mission; 21.91 PF computing capacity |
| Apr 2026 | DWR network target: 73 → 126 by end-2026 | 92% geographic coverage achieved |
| Jun 2026 | 7th Regional Meteorological Centre, Jammu | Covers J&K, Ladakh, Himachal Pradesh |
UPSC has asked about IMD's founding year (1875) and the significance of its 150th anniversary (2025). Also note: the ACROSS scheme (predecessor) was replaced by Mission Mausam. Cherrapunjee DWR was the first indigenous polarimetric DWR — a high-frequency exam trap (the location matters — not Mumbai, not Chennai, not Delhi).
IMD uses DWRs of varying frequencies — S-band, C-band, and X-band — to detect and track the movement of weather systems, cloud bands, and gauge rainfall over a coverage area of about 500 km.
| Band | Frequency | Wavelength | Range | Key Application | India Use |
|---|---|---|---|---|---|
| S-band | 2–4 GHz | 8–15 cm | ~500 km (long range) | Cyclone detection & tracking; near + far range; not easily attenuated by rain | First cyclone radar: Visakhapatnam, 1970; IMD's primary weather band; Cherrapunjee DWR is S-band |
| C-band | 4–8 GHz | 4–8 cm | ~250 km (medium range) | Cyclone tracking; general weather monitoring; good weather penetration; most common IMD DWR type | IMD's DWR network is predominantly C-band; Mangaluru C-band radar installed 2024 |
| X-band | 8–12 GHz | 2.5–4 cm | ~150 km (short range) | Thunderstorm & lightning detection; high resolution; smaller particles; attenuates easily in heavy rain | Wayanad X-band (2024); 10 X-band DWRs for NE + Himachal; Mahabaleshwar X-band (IITM, Apr 2026) |
| K-band / Ka-band | 18–40 GHz | <2 cm | Very short range | Fine detail; fog, drizzle; atmospheric absorption limits range | Research use; police speed guns (Ka-band) |
| L-band | 1–2 GHz | 15–30 cm | Very long range | Clear air turbulence research; wind profiling | Limited; used in research |
Traditional radars send only horizontally polarized waves. Dual-polarization (Dual-Pol) DWRs emit and receive both horizontal and vertical polarized waves simultaneously. By comparing the two returns, meteorologists can:
The Mahabaleshwar X-band DWR (IITM, April 2026) is a dual-polarization radar installed at 1,400 m altitude in the Western Ghats, providing high-resolution nowcasting for up to 3–6 hours for Pune, Satara, Konkan and Mumbai.
Students confuse: "X-band is used for cyclones, C-band for thunderstorms" — this is WRONG. It's the reverse: X-band → thunderstorm/lightning detection; C-band (and S-band) → cyclone tracking. X-band attenuates too easily for long-range cyclone monitoring.
| Parameter | Details |
|---|---|
| Full Name | Mission Mausam (meaning: Weather Mission) |
| Launched by | Prime Minister Narendra Modi; Cabinet approval 11 September 2024 |
| Nodal Ministry | Ministry of Earth Sciences (MoES) |
| Budget | ₹2,000 crore — ₹258 crore (2024–25) + ₹1,742 crore (2025–26) |
| Duration | Phase I: 2024–2026 (until March 2026); Phase II: 2026–2031 |
| Primary Implementing Agencies | IMD + IITM (Pune) + NCMRWF (Noida) |
| Supporting Agencies | INCOIS (ocean info) + NIOT + collaborating national/international institutes, academia, industries |
| Goal | Make India "Weather Ready and Climate Smart" |
| Predecessor Scheme | ACROSS (Atmospheric and Climate Research-Modelling Observing Systems and Services) |
| NWP Model Resolution | Current 12 km → targeting 6 km with Bharat Forecast System |
| Forecasting interval target | Hourly nowcasting (replacing current 3-hour interval) |
| DWR Expansion | 37 (baseline) → 73 (by 2025–26) → 126 (by 2026) |
| New AWS target (Delhi) | 18 operational → 50 (expedited) → 100 (long-term goal) |
| Operative since | November 2024 |
| Instrument | Target Count | Purpose |
|---|---|---|
| Doppler Weather Radars (DWR) | ~70 new radars (total 126 by 2026) | Storm detection, cyclone tracking, rainfall estimation |
| Radio Sonde / Radio Wind (RS/RW) Stations | 60 stations | Upper atmosphere wind & temperature profiling |
| Disdrometers | 100 units | Raindrop size distribution measurement |
| Wind Profilers | 10 units | Continuous wind speed/direction at various altitudes (first ever for IMD) |
| Radiometers | 25 units (10 initially per Tribune report) | Temperature/humidity profiling using microwave radiation |
| Urban Testbed | 1 (Chennai, SRMIST — May 2026) | Hyper-local urban weather & aerosol monitoring |
| Process Testbed | 1 | Cloud physics research & weather process studies |
| Radar Data Centre | 1 | Centralised radar data storage and processing |
UPSC frequently asks which ministry and which institutes implement schemes. Mission Mausam = Ministry of Earth Sciences (NOT Environment Ministry, NOT Science & Technology alone). The three implementing institutes are IMD + IITM (Pune) + NCMRWF (Noida). Wind profilers under Phase I mark India's first-ever operational wind profiler deployment.
| Institution | Full Name | Location | Role under Mission Mausam |
|---|---|---|---|
| IMD | India Meteorological Department | New Delhi (HQ) | Principal agency; operates DWR network; issues forecasts and warnings; 7 Regional Meteorological Centres |
| IITM | Indian Institute of Tropical Meteorology | Pune | HPC (ARKA, 11.77 PF); climate modelling; Mithuna-FS development; Mahabaleshwar X-band DWR; Urban Testbed Chennai |
| NCMRWF | National Centre for Medium Range Weather Forecasting | Noida | HPC (ARUNIKA, 8.24 PF); Bharat Forecast System; numerical weather prediction; AI/ML model integration |
| INCOIS | Indian National Centre for Ocean Information Services | Hyderabad | Ocean weather services; integration of ocean data for coastal forecasting |
| NIOT | National Institute of Ocean Technology | Chennai | Supporting ocean observations |
| ISRO/SAC | Space Applications Centre, ISRO | Ahmedabad | MoU with IITM (Apr 2026); satellite-based met products; cloud, air pollution, atmospheric profiling |
| Feature | ARKA (at IITM, Pune) | ARUNIKA (at NCMRWF, Noida) |
|---|---|---|
| Computing Power | 11.77 Petaflops | 8.24 Petaflops |
| Storage | 33 Petabytes | 24 Petabytes |
| Predecessor | Mihir | Pratyush |
| AI/ML Dedicated System | 1.9 Petaflops (standalone, at NCMRWF) | |
| Total Capacity (MoES) | 21.91 Petaflops (up from 6.8 PF previously) | |
| Manufacturer | Eviden (BullSequana XH2000); AMD + NVIDIA + DDN tech; ₹850 crore investment | |
| Inaugurated by | PM Narendra Modi, September 26, 2024 | |
| Naming convention | All named after celestial/sun entities — previous: Aditya, Bhaskara, Pratyush, Mihir → now Arka (sun) + Arunika (dawn) | |
| System | Key Feature | Significance |
|---|---|---|
| Bharat Forecast System (BharatFS) | Operational at 6 km spatial resolution; 10-day forecasts; panchayat-level predictions | First high-resolution model covering short and medium range; developed by NCMRWF |
| Mithuna Forecast System | Global coupled model: atmosphere + ocean + land + sea ice; upgraded data assimilation | Next-generation prediction integrating all Earth system components |
| AI/ML Models on Arunika | Pangu-Weather, GraphCast, FourCastNet run at ~25 km resolution | Data-driven forecasting as supplement to physics-based models |
IMD achieved 100% accuracy in all-India Southwest Monsoon forecasting (2021–2024) within the permissible margin of error. Cyclone deaths reduced from ~10,000 in 1999 to near zero (2020–2024). Heavy rainfall forecast Probability of Detection (POD) in 2025: 0.85 (Rajya Sabha, Feb 2026).
As of June 2026, India has 7 Regional Meteorological Centres (RMCs): New Delhi, Mumbai, Kolkata, Nagpur, Guwahati, Chennai, and Jammu (inaugurated June 5, 2026). An 8th centre in Lucknow was also announced.
| City / Region | State | Strategic Reason |
|---|---|---|
| Bengaluru | Karnataka | Rapid urban expansion, tech hub, extreme rain events |
| Raipur | Chhattisgarh | Interior of peninsular India; currently underserved |
| Ahmedabad | Gujarat | Arabian Sea cyclone tracking; industrial hub |
| Ranchi | Jharkhand | Chota Nagpur plateau; gap in central coverage |
| Guwahati | Assam | NE India gateway; flash floods, cyclonic depressions |
| Port Blair | Andaman & Nicobar Islands | Bay of Bengal early warning; remote island monitoring |
In 2014, there were zero Doppler Weather Radars in J&K and Ladakh. By June 2026, the situation has transformed:
| Status | DWR Locations |
|---|---|
| Currently Operational (2026) | Jammu · Srinagar · Leh · Banihal Top |
| Proposed under Mission Mausam | Anantnag · Rajouri · Baramulla · Kishtwar · Doda |
| Associated Infrastructure (AWS) — 2014 vs 2026 | 13 AWSs in 2014 → 25 AWSs in 2026; 14 ARGs → 16 ARGs |
The 7th Regional Meteorological Centre inaugurated at Jammu on June 5, 2026 will serve J&K, Ladakh, and Himachal Pradesh with district-level forecasts, avalanche warnings, cloudburst alerts, and pilgrimage advisories for the Amarnath and Vaishno Devi yatras.
| Radar / Location | Type | Year | Key Feature |
|---|---|---|---|
| Cherrapunjee, Meghalaya | S-band Polarimetric DWR | 2016 | First indigenous Polarimetric DWR; designed ISRO/ISTRAC; made by BEL; world's wettest site; 500 km range |
| Wayanad, Kerala | X-band DWR | 2024 | Western Ghats landslide-prone; post-Wayanad disaster monitoring |
| Mahabaleshwar, Maharashtra | X-band Dual-Pol DWR | April 24, 2026 | IITM facility at 1,400 m altitude; HACPL; nowcasting Pune/Satara/Mumbai up to 3–6 hours |
| Banihal Top, J&K | DWR | Post-2014 | High-altitude radar covering mountain pass; critical for cloudburst warning |
As of February 2026 (Rajya Sabha data), India's DWR network covers nearly 92% of the country's geographic area. The remaining 8% includes remote Himalayan areas, deep interior zones, and some island territories.
| Sector | How DWR / Mission Mausam Helps |
|---|---|
| Agriculture | Sowing/harvesting advisories; agro-met services; localised rainfall forecasts at panchayat level; Kisan SMS alerts |
| Disaster Management | Cyclone track and landfall prediction; cloudburst/flash flood early warning; avalanche alerts; heatwave & cold wave warnings |
| Aviation | Thunderstorm detection; clear air turbulence; low visibility fog alerts; safer routing around severe weather |
| Fisheries / Fishing | Ocean state forecasts; cyclone warnings for fishermen; high wave alerts via INCOIS |
| Defence & Security Forces | Terrain-specific forecasts for Himalayan operations; avalanche warning systems |
| Urban Planning | Flood risk modelling; heat island monitoring; urban testbed data for city planners |
| Power & Water Resources | Hydro-power reservoir management; flood forecasting for dams; solar/wind energy planning |
| Tourism & Pilgrimage | Advisories for Amarnath Yatra, Vaishno Devi Yatra; mountain weather forecasts; tourist safety alerts |
| Health | Heatwave & extreme cold alerts for public health authorities; disease vector surveillance via monsoon data |
| Shipping & Transport | Port weather advisories; road/rail disruption warnings; offshore operations safety |
| Concept / Term | Link to DWR / Mission Mausam |
|---|---|
| NDMA (National Disaster Management Authority) | Uses IMD DWR data for disaster preparedness; DWR supports Disaster Risk Reduction |
| NWP — Numerical Weather Prediction | Mission Mausam improves NWP from 12 km → 6 km resolution (BharatFS) |
| Cloud Seeding / Weather Modification | Mission Mausam includes weather modification research; DWR data essential for targeting cloud seeding operations |
| INSAT-3D / INSAT-3DR / OceanSat | Satellite complement to DWR network; combined use for weather monitoring |
| Sendai Framework for Disaster Risk Reduction | Mission Mausam aligns with Sendai's emphasis on early warning systems |
| COP / Climate Change | Climate change increasing extreme weather frequency → stronger DWR network = greater climate resilience |
| Project Mausam | DIFFERENT: ASI-led cultural diplomacy initiative connecting Indian Ocean communities via UNESCO — NOT a weather project |
| Doppler Effect | Discovered by Christian Doppler (Austrian physicist), 1842 — physics basis of DWR |
| NISAR Satellite | NASA-ISRO joint SAR satellite (launched Jul 30, 2025) — uses S-band + L-band for Earth observation; complements weather monitoring |
| Country / Organisation | Network / System | Number of Radars | Key Feature |
|---|---|---|---|
| USA | NEXRAD (WSR-88D) | 159–160 radars | World's largest; S-band; dual-polarization since 2012; jointly operated by NWS, FAA, US Air Force; deployed since 1988 |
| India | IMD DWR Network | 37 (current) → 126 (2026 target) | Mission Mausam expansion; S/C/X-band mix; 92% geographic coverage (Feb 2026) |
| Europe | OPERA (EUMETNET) | ~200+ radars (network of 30 countries) | Pan-European composite radar network; operational since 1999 |
| Russia | Meteorad network | ~36 radars | Concentrated near major population centres; Moscow has 2 (Vnukovo + Sheremetyevo) |
| China | CINRAD (China Next-Generation Radar) | 200+ radars | CINRAD-SA (S-band) and CINRAD-CA (C-band); expanded through 2000s–2010s |
| World Total (WMO) | All global radars | ~1,500 radars | WMO estimate; compared to ~40,000 meteorological surface stations globally |
IMD has accurately predicted cyclones Fani, Amphan, Tauktae, Biparjoy, reducing cyclone fatalities from ~10,000 in 1999 to near zero (2020–2024). Forecast accuracy improved by 20–40% for various severe weather events over the last five years.
In a high-level IMD review chaired by Union Minister Dr Jitendra Singh, it was announced that the Doppler Weather Radar network will rise from 37 operational radars to 73 by 2025–26, and further to 126 by 2026. New installations are planned in Bengaluru, Raipur, Ahmedabad, Ranchi, Guwahati and Port Blair. Delhi's Automatic Weather Stations (AWS) to be scaled up from 18 to eventually 100.
Union Minister Dr Jitendra Singh informed the Rajya Sabha that India's DWR network now covers nearly 92% of the country's geographic area. The 2025 Southwest Monsoon forecast was highly accurate — IMD predicted 105% of LPA in April; actual rainfall was 108% of LPA. Heavy rainfall forecast Probability of Detection (POD) in 2025: 0.85.
Parliament was informed that Mission Mausam has been operational since November 2024. Phase I focus: expanding DWR network, radiosonde stations, disdrometers. Proposed Phase II (2026–31): further strengthening observation networks, enhanced High-Performance Computing, and deeper AI/ML integration. The Bharat Forecast System (BharatFS) already operational at 6 km resolution, with panchayat-level output.
IITM Pune commissioned an X-band dual-polarisation Doppler Weather Radar at its High Altitude Cloud Physics Laboratory (HACPL) in Mahabaleshwar, Maharashtra — installed at 1,400 m altitude in the Western Ghats. Provides nowcasting up to 3–6 hours for Pune, Satara, Konkan and Mumbai. Simultaneously, IITM signed an MoU with ISRO's Space Applications Centre (SAC) to develop satellite-based meteorological products covering cloud characteristics, air pollution, atmospheric profiling, deep convection, lightning and climate change impacts.
Union Minister Dr Jitendra Singh inaugurated India's 7th Regional Meteorological Centre (RMC) in Jammu, which will serve J&K, Ladakh, and Himachal Pradesh. Services include district-level forecasts, avalanche warnings, cloudburst alerts, and pilgrimage advisories for Amarnath and Vaishno Devi yatras. Under Mission Mausam, 5 additional DWRs proposed for Anantnag, Rajouri, Baramulla, Kishtwar, and Doda. An 8th RMC in Lucknow also announced.
IITM Pune established India's first integrated Urban Testbed and Aerosol Observatory in Chennai (at SRMIST, Ramapuram) under Mission Mausam, inaugurated May 6, 2026. Produces hyper-local, high-resolution atmospheric intelligence for the climate-vulnerable Chennai metropolitan region. An MoU was signed between IITM and SRMIST.
Five numbers UPSC may ask: 37 → 73 → 126 (DWR count milestones); ₹2,000 crore (Mission Mausam budget); 21.91 petaflops (total HPC capacity); 92% (DWR geographic coverage, Feb 2026); 6 km (BharatFS resolution). The 7th RMC is Jammu (June 5, 2026) — extremely exam-relevant as the most recent development at time of writing.
| Statement | Verdict | Reason |
|---|---|---|
| Mission Mausam was launched under the Ministry of Environment, Forests and Climate Change. | ❌ FALSE | It is under the Ministry of Earth Sciences (MoES), not MoEFCC. |
| Project Mausam and Mission Mausam are two names for the same government initiative. | ❌ FALSE | Project Mausam is an ASI/Ministry of Culture cultural diplomacy initiative on Indian Ocean heritage; Mission Mausam is a MoES weather infrastructure scheme. |
| X-band Doppler radar is used for long-range cyclone tracking due to its superior penetration. | ❌ FALSE | X-band is used for short-range (150 km) thunderstorm detection. S-band and C-band are used for cyclone tracking. |
| India's first indigenous Polarimetric Doppler Weather Radar was installed at Cherrapunjee, Meghalaya, in 2016. | ✅ TRUE | Designed by ISRO/ISTRAC, manufactured by BEL; dedicated by PM Modi on May 27, 2016. |
| ARKA is the HPC supercomputer located at NCMRWF, Noida, with a capacity of 11.77 petaflops. | ❌ FALSE | ARKA is at IITM, Pune (11.77 PF). ARUNIKA is at NCMRWF, Noida (8.24 PF). |
| The Doppler Effect was first described by Christian Doppler, an Austrian physicist, in 1842. | ✅ TRUE | Named after him; describes frequency change of waves relative to moving source/observer. |
| Mission Mausam's Phase I budget includes ₹258 crore for 2024–25 and ₹1,742 crore for 2025–26. | ✅ TRUE | Stated by MoES Minister Dr Jitendra Singh in Rajya Sabha, July 31, 2025. |
| IMD's Bharat Forecast System (BharatFS) provides forecasts at 12 km spatial resolution. | ❌ FALSE | BharatFS operates at 6 km resolution — an improvement from the earlier 12 km NWP model resolution. |
| The first S-band cyclone detection radar in India was installed in Visakhapatnam in 1970. | ✅ TRUE | Chosen for Bay of Bengal cyclone monitoring; S-band selected for long range and rain penetration. |
| Wind Profilers under Mission Mausam Phase I represent India's first-ever deployment of this instrument operationally. | ✅ TRUE | IMD had never set up a wind profiler before Mission Mausam (confirmed in The Tribune, Sep 2024). |
Project Mausam = Ministry of Culture / Archaeological Survey of India (ASI) initiative to reconnect Indian Ocean maritime heritage nations under UNESCO World Heritage inscription. It has ZERO connection to weather. Mission Mausam = Ministry of Earth Sciences weather infrastructure expansion. UPSC has asked about both — never confuse them.
Students consistently swap these: ARKA = IITM, Pune (sun, 11.77 PF); ARUNIKA = NCMRWF, Noida (dawn, 8.24 PF). Memory tip: "A for ARKA, A for Atmospheric/IITM; N for NCMRWF → ARUNIKA".
Students who know "X-band has the highest frequency/smallest wavelength = most sensitive" often wrongly conclude X-band is best for cyclone tracking. Wrong. X-band attenuates easily in heavy rain and has short range (150 km). Cyclones need S-band or C-band with 250–500 km range and rain penetration.
The first indigenous Polarimetric DWR was at Cherrapunjee (Meghalaya) — not Sriharikota, not Mumbai, not Delhi. Also: it was the first Polarimetric DWR — not the first DWR in India (first DWR was Chennai, 2002).
The evolving numbers are a UPSC trap: 37 (baseline/pre-2024), 73 (target 2025–26), 126 (target by 2026). Some older sources say "39 DWRs" (pre-2024 different count), and an older news item mentioned "50 to nearly 100" as the framing. Use the most recent: 37 → 73 → 126 as confirmed in April 2025 and Rajya Sabha March 2026.
ACROSS (Atmospheric and Climate Research-Modelling Observing Systems and Services) was the predecessor scheme to Mission Mausam. Mission Mausam replaces and expands ACROSS. Do not describe ACROSS as a current active scheme.
Questions on Mission Mausam most often test: (1) Which ministry? (2) Which three institutes? (3) DWR count milestones. (4) Band-type applications. (5) Project Mausam vs Mission Mausam. (6) ARKA vs ARUNIKA. (7) What is new/first under the mission.
| Year / Period | DWR Count | Milestone |
|---|---|---|
| 2002 | 1 (Chennai) | First DWR in India |
| 2006 | 4 | 4 along east coast |
| 2023 (IMD 150th anniversary year) | 39 | Pre-Mission Mausam snapshot |
| 2024 (Mission Mausam baseline) | 37 | Cabinet approval; expansion begins |
| 2025–26 (Phase I target) | 73 | Mid-mission milestone |
| 2026 (end-target) | 126 | Final Phase I target |