NISAR — the NASA-ISRO Synthetic Aperture Radar satellite — maps Mexico City subsiding at over 2 cm/month in its first major science result, validating dual-band radar from orbit.
Why in News
On 29 April 2026, NASA released the first major science result from the joint NASA-ISRO Synthetic Aperture Radar (NISAR) mission: a high-resolution map of land subsidence in Mexico City based on data captured between 25 October 2025 and 17 January 2026. The map confirms parts of the metropolitan area are sinking by more than 2 cm per month, primarily due to long-term groundwater extraction from the ancient lakebed and aquifer system on which ~20 million people live. The result validates that NISAR — the first satellite to carry two SAR instruments at different wavelengths — is performing as expected. The mission was launched on 30 July 2025 from the Satish Dhawan Space Centre, Sriharikota, marking a high point in India-US space cooperation.
At a Glance
- Mission
- NISAR (NASA-ISRO Synthetic Aperture Radar) — joint US-India Earth observation satellite
- Launch
- 30 July 2025 from Satish Dhawan Space Centre, Sriharikota (GSLV launcher)
- Cost
- approximately USD 1.5 billion (one of the most expensive Earth-observation missions to date)
- First-of-its-kind
- first satellite carrying two SAR instruments at different wavelengths
- L-band SAR (NASA)
- 24 cm wavelength — penetrates dense vegetation, ideal for forests/glaciers
- S-band SAR (ISRO Space Applications Centre)
- 10 cm wavelength — sensitive to small vegetation, agriculture
- Antenna
- ~12-m deployable mesh reflector — among the largest deployed in space
- Orbit
- ~747 km altitude, sun-synchronous; revisit cycle 12 days
- Coverage
- observes Earth's land and ice surfaces twice every 12 days
- Mexico City finding
- parts subsiding >2 cm/month (Oct 25, 2025 – Jan 17, 2026)
- Cause
- groundwater pumping from ancient lakebed/aquifer; ~20 million population
- Historical comparison
- late-20th-century rates reached ~35 cm/year in worst-affected zones
What NISAR is and why it's exceptional
NISAR is a joint Earth-observation mission of NASA's Jet Propulsion Laboratory (JPL, Caltech-managed) and the Indian Space Research Organisation. It was launched on 30 July 2025 from the Satish Dhawan Space Centre at Sriharikota and operates in a sun-synchronous orbit at about 747 km altitude. NISAR is the first space mission to carry two Synthetic Aperture Radar (SAR) instruments at different wavelengths — NASA's L-band radar (24 cm wavelength, deeper penetration through canopies) paired with ISRO's Space Applications Centre (Ahmedabad)-built S-band radar (10 cm wavelength, more sensitive to small vegetation and agriculture). The two SARs share a single ~12-m deployable mesh reflector — among the largest antennas ever flown. SAR uses microwave pulses, which can image Earth's surface day or night and through cloud cover, making it complementary to optical satellites.
What the Mexico City result demonstrates
Mexico City sits on an aquifer system layered above the dried bed of ancient Lake Texcoco. Heavy groundwater extraction over the past century has compacted underlying soil layers, producing one of the world's most severe documented urban subsidence problems — with rates that reached ~35 cm/year in the late 20th century. NISAR data captured between 25 October 2025 and 17 January 2026 shows parts of the metropolitan area still sinking by more than 2 cm per month — equivalent to over 24 cm/year sustained at this pace. The Angel of Independence monument (built 1910) has had 14 steps added at its base as the surrounding land has dropped. This first major NISAR result confirms the satellite's interferometric SAR (InSAR) accuracy and its ability to support real-time urban-planning, infrastructure-risk and aquifer-management decisions globally.
How interferometric SAR maps subsidence
Interferometric SAR (InSAR) compares two or more SAR images of the same area taken at different times. Each image is a complex measurement of phase and amplitude; differences in phase between successive passes can be converted into millimetre-precision elevation changes once orbital positions and atmospheric effects are corrected. Because L-band (longer wavelength) penetrates vegetation, it preserves coherence over forested and agricultural areas — ideal for slow-moving ground-deformation problems like aquifer compaction, landslides, glacier creep, and post-seismic relaxation. The dark blue regions in NISAR's Mexico City map indicate >2 cm/month subsidence; yellow/red areas are labelled as 'residual noise signals' expected to decrease as more passes are stacked.
Strategic significance for India and the US
NISAR is a flagship of India-US space cooperation under the iCET (initiative on Critical and Emerging Technology) framework. ISRO contributed the spacecraft bus, S-band radar, GSLV launch, and downlink infrastructure; NASA contributed the L-band SAR, antenna reflector, and the bulk of mission operations. Use cases include: monitoring the cryosphere (Antarctic ice-sheet velocity, Himalayan glaciers), tracking deforestation and biomass (L-band penetrates dense canopy), supporting disaster response (rapid pre/post imaging of earthquakes, floods, cyclones), and aquifer/groundwater mapping (Mexico City being an early case study). Indian scientific applications — Indo-Gangetic groundwater stress, Sundarbans subsidence, urban land-use change — are expected to be major beneficiaries.
Static GK
- •: ISRO was established on 15 August 1969, succeeding INCOSPAR (Indian National Committee for Space Research, set up 1962 under Vikram Sarabhai).
- •: NASA was established by the National Aeronautics and Space Act on 29 July 1958.
- •: Satish Dhawan Space Centre (SDSC SHAR) at Sriharikota is ISRO's primary launch facility, in Andhra Pradesh.
- •: ISRO's Space Applications Centre (SAC) is in Ahmedabad — handles satellite payload development and applications.
- •: GSLV (Geosynchronous Satellite Launch Vehicle) Mk-II/Mk-III is ISRO's heavy-lift launcher — used for NISAR.
- •Other NASA Earth-observation missions: Landsat-9 (2021), Sentinel-6 (joint with ESA, 2020), GRACE-FO (2018).
- •Major InSAR-capable missions (pre-NISAR): Sentinel-1 (ESA), TerraSAR-X (Germany), ALOS-2 (JAXA).
- •: Mexico City was founded as Tenochtitlán on Lake Texcoco by the Aztecs in 1325; the lake was drained by the Spanish post-conquest.
- •: The most groundwater-stressed region of the world is the Indo-Gangetic Plain — making NISAR's aquifer-monitoring capability particularly relevant for India.
- •: iCET (US-India initiative on Critical and Emerging Technology) was announced in 2023 by NSAs Jake Sullivan and Ajit Doval.
Timeline
- 1958NASA established by the National Aeronautics and Space Act
- 1969ISRO formally established
- 2014NASA-ISRO sign the partnership agreement for what becomes NISAR
- 2018-2024NISAR development — radars, antenna, spacecraft bus assembled
- 2023US-India iCET launched; NISAR becomes a flagship deliverable
- 30 July 2025NISAR launched from Satish Dhawan Space Centre, Sriharikota
- Aug-Oct 2025NISAR commissioning, antenna deployment, science calibration
- 25 Oct 2025 – 17 Jan 2026Mexico City subsidence observation window
- 29 April 2026NASA releases first major NISAR science result on Mexico City subsidence
- →NISAR = NASA + ISRO Synthetic Aperture Radar.
- →Launch: 30 July 2025 from Sriharikota (SDSC SHAR).
- →Cost: ~$1.5 billion.
- →First satellite with TWO SAR bands: L (NASA) + S (ISRO).
- →L-band: 24 cm — penetrates canopies (forests).
- →S-band: 10 cm — surface vegetation, agriculture.
- →Antenna: ~12 m deployable mesh — one of the largest.
- →Orbit: ~747 km, sun-synchronous, 12-day revisit.
- →Mexico City: >2 cm/month sinking (Oct 2025 - Jan 2026).
- →Cause: groundwater pumping from ancient Lake Texcoco aquifer.
- →Historical Mexico City rate: ~35 cm/year (late 20th C).
- →ISRO HQ: Bengaluru. SAC (S-band built): Ahmedabad.
- →JPL leads NASA side; managed by Caltech.
- →Part of US-India iCET (2023).
Exam Angles
The NASA-ISRO NISAR satellite has mapped Mexico City subsidence at over 2 cm/month — the first high-profile science result from the dual-band radar mission launched in July 2025.
Q1. NISAR — launched on 30 July 2025 from Satish Dhawan Space Centre — is a joint Earth-observation mission between NASA and which other space agency?
- A.ISRO (Indian Space Research Organisation)
- B.JAXA (Japan Aerospace Exploration Agency)
- C.ESA (European Space Agency)
- D.Roscosmos (Russian Federal Space Agency)
tap to reveal answer
Answer: A. ISRO (Indian Space Research Organisation)
NISAR stands for NASA-ISRO Synthetic Aperture Radar — a joint mission with the Indian Space Research Organisation. NASA provided the L-band radar; ISRO's Space Applications Centre in Ahmedabad provided the S-band radar; the launch was on India's GSLV from Sriharikota. The other agencies — JAXA, ESA, Roscosmos — have separate Earth-observation programmes but were not partners in NISAR.
NISAR represents the most expensive and ambitious civilian space mission ever undertaken jointly by India and the US. Conceived in 2014 and accelerated under the iCET framework (2023), it operationalises the long-standing Indo-US strategic partnership in the space domain. The mission also showcases ISRO's transition from launching navigation and communication satellites to co-leading frontier Earth-observation science.
- Filling the global SAR coverage gapNISAR's 12-day global revisit and dual-band capability fill a long-standing gap in civilian SAR — between Sentinel-1 (C-band, ESA), TerraSAR-X (X-band, Germany), and ALOS-2 (L-band, JAXA). The L-band's penetration through dense vegetation makes NISAR uniquely suited to measuring biomass change, glacier velocity in Himalayan and Antarctic regions, and ground deformation in agricultural and forested terrain — areas where shorter-wavelength radars lose coherence.
- Indian applications — Indo-Gangetic groundwater and beyondNISAR's Mexico City result is methodologically important for India: the Indo-Gangetic Plain is one of the world's most groundwater-stressed regions and aquifer compaction is documented across Punjab, Haryana, and western UP. NISAR's InSAR capability could support PMKSY (irrigation) targeting, Atal Bhujal Yojana (groundwater management) monitoring, and disaster response (post-flood ground deformation, landslide tracking in the Himalayan states).
- iCET and the strategic technology pillarNISAR cements space as one of the iCET 'strategic technology pillars' — alongside semiconductors, AI, biotech, telecom, defence and clean energy. It is one of the few civilian flagship deliverables that can be measured in concrete capability terms (data products, joint operations, IP arrangements) rather than declarations. The success of NISAR strengthens the case for follow-on missions (e.g., a NISAR-2 or higher-frequency successor) and broader iCET cooperation.