NISAR: NASA-ISRO Satellite Sends First Images
A joint investment of $1.5 billion, a 12-meter-diameter mesh reflector — the largest ever launched by NASA — and the first time in history that an orbital radar satellite operates simultaneously at two frequencies. NISAR, which stands for NASA-ISRO Synthetic Aperture Radar, has sent its first images of the Earth's surface, and what they reveal about Seattle, Portland, Mount Rainier, and Mount St. Helens is just the beginning of what promises to be a revolution in planetary monitoring.
Launched on July 30, 2025, from the Sriharikota space center in India, NISAR represents the most ambitious collaboration ever undertaken between NASA and ISRO — and its data will change the way humanity observes earthquakes, volcanoes, glaciers, forests, and cities.
What Happened
The NISAR satellite was placed into orbit by ISRO's GSLV F-16 rocket on July 30, 2025, from the Satish Dhawan launch base in Sriharikota, in the state of Andhra Pradesh, on India's east coast. The launch was broadcast live and monitored by NASA teams at the Jet Propulsion Laboratory (JPL) in Pasadena, California, and by ISRO in Bengaluru.
After months of orbital calibration, systems testing, and fine-tuning of the radar instruments, NISAR sent its first operational images. The images show the northwestern United States with unprecedented detail for a radar satellite. Seattle and Portland appear with their urban grids clearly delineated, while Mount Rainier — an active stratovolcano standing 4,392 meters tall — and Mount St. Helens — famous for its catastrophic 1980 eruption — are captured with resolution that allows identification of individual geological structures on their slopes.
What makes these images extraordinary is not just their resolution, but the technology behind them. NISAR is the first imaging radar satellite to operate simultaneously at two frequencies: L-band, with a wavelength of 24 centimeters, and S-band, with a wavelength of 10 centimeters. The L-band, provided by NASA, penetrates dense vegetation and surface soil layers, revealing underground structures and terrain deformations. The S-band, provided by ISRO, offers greater sensitivity to changes in vegetation cover and soil moisture.
This dual-frequency combination allows NISAR to do something no previous satellite could: simultaneously generate two complementary data sets about the same area, creating a multidimensional view of the Earth's surface that goes far beyond what optical cameras or single-frequency radars can offer.
Background and Context
The NISAR project was born from a bilateral agreement between NASA and ISRO signed in 2014. The division of responsibilities reflects each agency's competencies: NASA, through JPL, developed the L-band radar, the 12-meter deployable mesh reflector, and the 9-meter boom that supports the antenna. ISRO developed the S-band radar, the spacecraft bus (the satellite structure housing the power, propulsion, and communication systems), and provided the GSLV F-16 launch vehicle.
The 12-meter mesh reflector deserves special attention. It is the largest radar antenna ever launched by NASA into space. To fit inside the rocket's fairing during launch, the reflector was folded like a giant umbrella and deployed — opened — once in orbit. This deployment engineering is one of the project's most impressive technical achievements, as any failure in opening the reflector would have compromised the entire $1.5 billion mission.
The 9-meter boom connecting the reflector to the satellite body is equally critical. It maintains the antenna at the precise distance and orientation necessary for the radar to function correctly. The combination of the 12-meter reflector and 9-meter boom gives NISAR a total wingspan rivaling that of a school bus.
Synthetic aperture radar (SAR) is a technology that creates high-resolution images using a relatively small antenna in motion. As the satellite orbits Earth, the radar emits microwave pulses and records the signals reflected by the surface. Computational processing of these signals simulates an antenna much larger than the one physically present on the satellite — hence the term "synthetic aperture." The result is images with meter-level resolution, obtained from an orbital altitude of hundreds of kilometers.
The fundamental advantage of radar over optical cameras is that it works regardless of sunlight and atmospheric conditions. NISAR can generate images of any point on Earth day or night, with clear skies or dense cloud cover. For disaster monitoring — earthquakes, volcanic eruptions, floods, landslides — this capability is invaluable, as natural disasters frequently occur under adverse weather conditions that prevent optical observation.
The NASA-ISRO partnership on NISAR also carries geopolitical significance. India, which in 2023 became the fourth country to land a probe on the Moon with the Chandrayaan-3 mission, consolidates with NISAR its position as a first-tier space power. For NASA, the collaboration with ISRO represents access to reliable and economical launch capabilities, while strengthening diplomatic ties with the world's largest democracy.
Impact on the Public
NISAR's data will have practical applications that directly affect the lives of billions of people. The table below details the main areas of impact.
| Application area | How NISAR contributes | Benefit to the public | Scale of impact |
|---|---|---|---|
| Volcanic monitoring | Detects millimeter-scale ground deformations preceding eruptions | Early warnings for evacuation of risk areas | 800 million people live near active volcanoes |
| Earthquakes and tectonics | Maps geological faults and measures stress accumulation in the ground | Improves seismic risk models for urban planning | Seismic zones house more than 1 billion people |
| Glaciers and sea level | Measures melting speed and ice flow with precision | More reliable sea level rise projections | Hundreds of millions in coastal zones |
| Agriculture and food security | Assesses soil moisture and vegetation health at two frequencies | Crop planning, early drought detection | Billions depend on rain-fed agriculture |
| Forests and deforestation | L-band penetrates forest canopy, measures biomass | Near-real-time monitoring of illegal deforestation | Tropical forests cover 6% of Earth's surface |
| Urban infrastructure | Detects ground subsidence beneath cities | Prevention of building and infrastructure collapse | Megacities on unstable soils (Jakarta, Mexico City) |
| Disaster response | Radar images work day/night, through clouds | Rapid mapping of affected areas for rescue | All regions subject to natural disasters |
Volcanic monitoring is perhaps the most immediately impactful application. Mount Rainier, one of the first areas imaged by NISAR, is classified by the United States Geological Survey (USGS) as one of the most dangerous volcanoes in the country. More than 80,000 people live in lahar risk zones — volcanic mudflows — that would descend Rainier's slopes in the event of an eruption. NISAR can detect the millimeter-scale swelling of the volcanic edifice caused by magma accumulation, potentially providing weeks or months of advance warning.
For countries with vast tropical forests, NISAR has direct relevance in monitoring deforestation. The L-band radar penetrates the tropical forest canopy, allowing measurement of forest biomass and detection of deforestation even under cloud cover — a condition that prevails in tropical regions during much of the year and limits the effectiveness of optical satellites like those in the Landsat series.
In agriculture, the ability to measure soil moisture at two frequencies simultaneously offers farmers and government agencies unprecedented data for water resource management and crop planning. In regions like the African Sahel, the Brazilian semi-arid, and the Indian subcontinent, where rain-fed agriculture feeds hundreds of millions of people, this data can mean the difference between a successful harvest and a food crisis.
What Stakeholders Are Saying
NASA described NISAR's first images as "a milestone in radar Earth observation." JPL scientists emphasized that the combination of two frequencies in a single satellite opens analytical possibilities that previously required data from multiple separate missions, with all the complications of cross-calibration and temporal differences that implies.
ISRO celebrated the successful launch and nominal operation of the S-band radar as a demonstration of Indian technological capability in cutting-edge space instrumentation. The ISRO chairman highlighted that NISAR is the most complex international cooperation project ever undertaken by the Indian agency and that the satellite's data will be made freely available to the global scientific community.
Scientists in the geosciences community expressed enthusiasm about the possibilities opened by NISAR. Researchers in volcanology, seismology, glaciology, and forest ecology are already planning research projects based on the satellite's data. The open data policy adopted by NASA and ISRO for NISAR means that any researcher, in any country, can access and use the satellite's images and measurements at no cost.
Disaster response organizations, including the United Nations Environment Programme (UNEP) and national civil defense agencies, highlighted NISAR's potential to significantly improve the speed and accuracy of mapping areas affected by natural disasters. The ability to operate regardless of weather conditions and lighting is particularly valuable in the first hours after an earthquake or flood, when accurate information about the extent of damage is critical for directing rescue teams.
What Comes Next
NISAR is programmed to operate for at least three years, mapping the entire Earth's surface every 12 days. This 12-day revisit cycle is fundamental for detecting gradual changes — such as the slow movement of glaciers or the subsidence of urban areas — and for providing baseline data that allows rapid assessment of the effects of sudden events like earthquakes.
In the coming months, NASA and ISRO teams will continue the calibration and validation process, comparing NISAR measurements with field data collected by ground stations and other satellites. This process is essential to ensure the accuracy and reliability of the data before its release to the broader scientific community.
NASA plans to integrate NISAR data with information from other Earth observation satellites, including those in the European Space Agency's Sentinel constellation and Japan's ALOS satellites, creating a global monitoring system with unprecedented coverage and temporal resolution.
For ISRO, NISAR's success paves the way for future radar missions, including possible next-generation radar satellites with even more advanced capabilities. The experience gained in developing the S-band radar and integrating systems with NASA positions India as a reference partner for future international space collaborations.
The scientific community eagerly awaits the first complete data sets from NISAR, which should be released throughout 2026. Researchers have already submitted hundreds of project proposals based on the satellite's data, covering areas ranging from archaeology — radar can reveal structures buried under vegetation or sand — to civil engineering, through climatology, hydrology, and natural resource management.
Dual-Frequency SAR Technology: A Revolution in Earth Observation
To grasp the magnitude of the advance NISAR represents, one must understand how dual-frequency synthetic aperture radar differs from everything that came before.
Previous radar satellites, such as the European Space Agency's Sentinel-1 and Japan's ALOS-2, operate at a single frequency. Sentinel-1 uses C-band (5.6-centimeter wavelength), while ALOS-2 uses L-band (24-centimeter wavelength). Each frequency has specific advantages and limitations. C-band is sensitive to surface changes and low vegetation but does not penetrate dense forests. L-band penetrates vegetation and surface soil layers but is less sensitive to subtle changes in vegetation cover.
NISAR combines L-band (24 centimeters, provided by NASA) and S-band (10 centimeters, provided by ISRO) in a single satellite, operating simultaneously. This means each satellite pass over an area generates two complementary data sets, captured at the same instant and with the same observation geometry. The elimination of temporal and geometric differences between the two data sets is crucial for precise scientific analyses.
NISAR's L-band penetrates the canopy of tropical forests, allowing measurement of forest biomass — the amount of organic matter stored in trees — with unprecedented precision. This capability is fundamental for forest carbon monitoring, an essential component of international climate agreements. Countries like Brazil, Indonesia, and the Democratic Republic of Congo, which harbor the world's largest tropical forests, will for the first time have access to consistent forest biomass data updated every 12 days.
The S-band complements the L-band by providing detailed information about the upper vegetation layer and soil moisture. The combination of the two frequencies allows distinguishing between different types of land cover — primary forest, secondary forest, agriculture, pasture, urban area — with significantly greater accuracy than any individual sensor.
For interferometry — the technique that allows measuring ground deformations with millimeter precision by comparing radar images obtained on different passes — NISAR's dual frequency offers redundancy and complementarity. If one frequency is affected by atmospheric conditions or terrain characteristics that degrade measurement quality, the other frequency can compensate, ensuring continuous and reliable coverage.
Closing Thoughts
NISAR is more than a satellite. It is the materialization of a partnership between two nations that, together, built the most powerful orbital radar system in history. Its first images of Seattle, Portland, Mount Rainier, and Mount St. Helens are merely the first pages of an atlas that, over the coming years, will document changes on our planet's surface with millimeter precision.
In a world where earthquakes, volcanic eruptions, glacier melting, and deforestation threaten billions of lives, having radar eyes that see through clouds, darkness, and dense forests is not a technological luxury. It is a civilizational necessity. And NISAR, with its 12-meter antenna and $1.5 billion investment, is the most sophisticated answer humanity has ever built for that necessity.
