NISAR: The NASA-ISRO Earth Observation Mission Explained

NISAR, short for NASA-ISRO Synthetic Aperture Radar, is a joint Earth-observation satellite of the National Aeronautics and Space Administration (NASA) and the Indian Space Research Organisation (ISRO), launched in 2025 from Sriharikota, that uses two radar frequencies to map changes on the land and ice of the whole planet roughly every 12 days. It is the first radar imaging satellite to carry two different radar frequencies, an L-band system from NASA and an S-band system from ISRO, and it can see through cloud, rain and darkness.

The mission is designed to measure very small changes in the Earth’s surface, including the ground movement caused by earthquakes, volcanoes, landslides and groundwater extraction, the flow of glaciers and ice sheets, and the growth and loss of forests and crops. NISAR is also regarded as one of the most expensive civilian Earth-imaging satellites ever built. This explainer sets out how it works, what each partner contributes and why its data matter.

Key Takeaways

• NISAR is a joint Earth-observation mission of NASA and ISRO that was launched in 2025 on a Geosynchronous Satellite Launch Vehicle (GSLV) from Sriharikota in Andhra Pradesh.
• NISAR is the first radar imaging satellite to operate at two frequencies, using NASA’s L-band synthetic aperture radar and ISRO’s S-band synthetic aperture radar together.
• NISAR carries a deployable mesh reflector antenna of about 12 metres in diameter, one of the largest antennas flown on an Earth-observation satellite.
• NISAR images almost the entire land and ice surface of the Earth repeatedly, about every 12 days, through cloud and in darkness.
• NISAR is designed to track tiny ground movements, glaciers and ice sheets, forest biomass, crop growth, wetlands and floods, which supports earthquake, landslide and disaster studies.
• NISAR is among the most expensive Earth-imaging missions ever built, with a cost widely reported at over a billion US dollars, and its data are intended to be freely available.

What is NISAR?

NISAR is an Earth-observation satellite carrying synthetic aperture radar instruments that measure the shape and motion of the Earth’s surface with great precision. It was developed jointly by NASA and ISRO and is the first satellite of its kind to combine two radar frequencies in a single mission.

The mission began as a collaboration agreed in 2014, when NASA and ISRO signed an agreement to build a radar satellite for global observation. The partners divided responsibilities according to their strengths. NASA’s Jet Propulsion Laboratory (JPL) led the development of the L-band radar, while ISRO’s Space Applications Centre (SAC) in Ahmedabad developed the S-band radar. The satellite is intended to serve scientists and governments dealing with climate, natural hazards, agriculture and infrastructure.

The name reflects the instrument type. Synthetic aperture radar (SAR) is an active imaging method that sends microwave pulses towards the ground and records the returning echoes. By combining the echoes recorded as the satellite moves, it builds an image with much finer detail than the physical size of its antenna would otherwise allow.

How does synthetic aperture radar work?

Synthetic aperture radar works by transmitting microwave pulses from a moving platform and processing the returned signals to simulate a much larger antenna, which allows detailed images to be formed. Because the radar provides its own illumination, it can image the ground day or night, and microwaves pass through cloud, smoke and most rain.

This makes radar especially valuable in regions that are frequently covered by cloud, such as the tropics and monsoon belts. Optical satellites depend on sunlight and clear skies, so they often miss events during storms, floods or the monsoon. A radar satellite can image the same place regardless of weather.

What is interferometry?

Interferometric SAR, known as InSAR, compares radar images of the same place taken at different times to detect tiny changes in distance between the satellite and the ground. Changes of a few millimetres to centimetres can be measured, which makes InSAR a standard technique for observing earthquakes, volcanic swelling, landslides and land subsidence. NISAR is built to generate such measurements systematically over the whole world.

Why does NISAR use two radar frequencies?

NISAR uses two radar frequencies, L-band and S-band, because the wavelength of the radar determines what it is sensitive to, and the two together give a fuller picture of the surface. The combination is the main feature that distinguishes it from earlier missions.

• L-band (NASA): has a longer wavelength, of roughly 24 centimetres, that penetrates vegetation canopies and is sensitive to tree trunks, branches and soil moisture. It is well suited to measuring forest structure, biomass and ground motion in vegetated areas.
• S-band (ISRO): has a shorter wavelength, of roughly 12 centimetres, that responds more to smaller structures such as leaves, crops and surface roughness. It is valuable for agriculture, soil moisture and monitoring of fine surface features.

Operating both bands from the same platform allows researchers to compare how the same area appears at two wavelengths and to distinguish different surface features. Regions can be imaged by either or both radars depending on the observation plan, so the mission can focus on priorities such as global science targets and areas of special interest to India.

What does the 12-metre reflector do?

The 12-metre reflector is a large, lightweight, gold-plated mesh antenna that focuses the radar signals and collects the returning echoes for both radars. The reflector unfolds in orbit on a long boom, extending far beyond the main body of the spacecraft.

The large size of the reflector is necessary to illuminate a wide strip of ground in each pass. NISAR uses a technique called SweepSAR, in which the radar illuminates a wide swath of around 240 kilometres and uses multiple receiving beams to preserve detail. This is what allows the satellite to cover nearly the whole globe in a repeat cycle of about 12 days while maintaining high spatial detail. The reflector was built by NASA, and its deployment in orbit is a major engineering milestone for the mission.

How was NISAR launched and what orbit does it use?

NISAR was launched in 2025 by ISRO’s Geosynchronous Satellite Launch Vehicle (GSLV) from the Satish Dhawan Space Centre at Sriharikota, and it was placed in a near-polar, sun-synchronous orbit. The launch was designated GSLV-F16, and the mission is the first time that a GSLV has put a satellite into a sun-synchronous polar orbit.

The satellite has a mass of well over two tonnes, and its orbit at about 740 kilometres altitude is chosen so that it passes over the same location at the same local solar time on each pass. This is a dawn-dusk arrangement that provides consistent lighting conditions for comparison, ensures good power from the sun and reduces the effect of the ionosphere on the L-band signal. After launch came a period of commissioning, in which the antenna was deployed, the instruments were checked and calibrated, and early images were collected before regular science operations.

What does each partner contribute to NISAR?

NASA and ISRO share the work of building and operating NISAR, with each agency supplying specific hardware and services. The division reflects the technical strengths of each organisation.

The two agencies assembled the satellite by integrating NASA’s L-band payload with ISRO’s spacecraft and S-band payload at ISRO’s facility in Bengaluru, after which the combined satellite was tested and shipped to the launch site. This level of hardware integration, with major payloads built on two continents, made the project complex and slowed its schedule, but also strengthened the working relationship between the two agencies.

What will NISAR observe?

NISAR will observe changes across the solid Earth, ecosystems, the cryosphere and the water cycle, and it is built to collect a consistent, global time series of these changes. The mission’s science goals fall into several broad groups.

Solid Earth and natural hazards

NISAR will measure surface deformation before, during and after earthquakes, volcanic eruptions and landslides. It can detect slow ground sinking from groundwater withdrawal, mining or building loads, and it can track fault movement along plate boundaries. For a country like India, which has both seismically active mountain belts and rapidly growing cities, such data are relevant to hazard assessment.

Ecosystems and forests

The L-band radar is sensitive to the woody material in trees and can be used to estimate forest biomass and detect disturbance, such as deforestation or degradation. These measurements contribute to understanding the global carbon cycle. The mission will also monitor wetlands, mangroves and changes in agricultural land.

Glaciers, ice sheets and sea ice

NISAR will measure how fast glaciers and ice sheets move and how the ice surface changes. This applies to polar regions as well as to the Himalaya, where glacier retreat and glacial lake hazards are of concern. The data help to understand contributions to sea-level rise.

Water, floods and agriculture

Radar images identify standing water and are useful for mapping floods, even when the sky is overcast. S-band and L-band measurements also help track crop growth stages, soil moisture and changes in land cover, which can support agricultural monitoring and food security planning.

How often does NISAR image the Earth?

NISAR images nearly the entire land and ice surface of the Earth about every 12 days, and in many places it will provide observations on both ascending and descending passes. This regular schedule makes it possible to build time series rather than isolated pictures.

The repeat cycle is the key to InSAR measurement, since consistent revisits allow images to be compared. The wide swath, the long antenna and the large data volume are all aimed at systematic, wall-to-wall coverage rather than the targeted imaging of small areas. The mission therefore generates a very large quantity of data, among the largest of any Earth-observing mission, which has to be transmitted, stored and processed on the ground.

Why is NISAR so expensive?

NISAR is expensive because it combines two advanced radars, a very large deployable antenna and a long development programme, and it is widely reported as one of the costliest civilian Earth-observation satellites ever built. Public reporting has put the combined cost at over a billion US dollars, though exact figures depend on how contributions are counted.

• Technology: building a large mesh reflector that deploys reliably in space is difficult and costly.
• Dual radars: two separate SAR systems, with processing and calibration, double the instrument effort.
• Data handling: the high data rate requires powerful recorders, communications and ground systems.
• International collaboration: hardware built in two countries requires shipping, integration, testing and coordination.
• Schedule: the programme took roughly a decade from agreement to launch, with delays for technical reasons and for the pandemic.

Supporters argue that the cost is justified because of the breadth of the data and its use across science and public safety. Because the mission is intended to provide open data, the same investment can serve scientists, agencies and companies worldwide.

Why does NISAR matter for India?

NISAR matters for India because it provides a regular, all-weather view of a country that is exposed to earthquakes, floods, landslides, cyclones, glacier hazards and coastal change, and because it strengthens ISRO’s role in international space science. The monsoon makes cloud-free optical imaging difficult for large parts of the year, so radar data are especially useful.

Indian agencies and researchers can use the data for agricultural monitoring, forest assessment, flood mapping, infrastructure monitoring and the study of the Himalayan glaciers. The mission also demonstrates cooperation between India and the United States in civil space, a field in which both countries have expanded joint work since the 2000s. For ISRO, it offers experience in building a spacecraft for a complex international payload and in handling large radar datasets.

How can NISAR data be used and who can access it?

NISAR data are intended to be made openly available to scientists, government agencies and the public, in line with NASA’s open data policy and ISRO’s data-sharing practices. Data products range from raw radar signals to processed images and derived measurements.

Because the data are large and specialised, users generally need tools for radar processing, but the mission also plans higher-level products that are easier to use. Possible users include geologists studying fault movement, foresters tracking biomass, hydrologists mapping floods, city planners monitoring subsidence and insurers assessing risk. Exact data release schedules and formats are announced by the mission teams and can change as the mission progresses.

Bottom Line

NISAR is a NASA-ISRO radar satellite that images the Earth’s land and ice surface in all weather using two radar bands, an approach no earlier mission has combined. Its value lies in the steady, consistent record it will build of how the planet’s surface moves and changes, which supports science and disaster preparedness in India and across the world.

Frequently Asked Questions

What does NISAR stand for?

NISAR stands for NASA-ISRO Synthetic Aperture Radar. It is a joint Earth-observation satellite of the US space agency NASA and the Indian Space Research Organisation (ISRO).

When and where was NISAR launched?

NISAR was launched in 2025 from the Satish Dhawan Space Centre at Sriharikota, India, on an ISRO Geosynchronous Satellite Launch Vehicle (GSLV). It was placed in a near-polar, sun-synchronous orbit at an altitude of roughly 740 kilometres.

Why is NISAR called the first dual-frequency radar satellite?

NISAR is called the first dual-frequency radar imaging satellite because it carries two synthetic aperture radars, NASA’s L-band and ISRO’s S-band, on a single spacecraft. Each band responds to different surface features, so together they give a more complete view of forests, crops, ice and ground motion.

What can NISAR detect?

NISAR can detect small ground movements from earthquakes, volcanoes, landslides and subsidence, the motion of glaciers and ice sheets, changes in forests and crops, and flooded areas. It can do so through cloud and in darkness because radar provides its own illumination.

How often does NISAR scan the Earth?

NISAR images nearly all of the Earth’s land and ice surfaces about every 12 days. This regular revisit schedule allows scientists to compare images over time and measure millimetre- to centimetre-scale changes.

Is NISAR data free to use?

NISAR data are intended to be openly available to scientists, government agencies and the public, following NASA’s open data policy and ISRO’s data-sharing practices. The precise release schedule and product types are announced by the mission teams.

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