NISAR Satellite: NASA‑ISRO Radar Mission, How It Works and What It Watches

NISAR Satellite: The First NASA‑ISRO Earth Observation Mission

NISAR Mission Launch of 30 July 2025 and Its Orbit

NISAR lifted off at 5.40 p.m. IST on 30 July 2025 from the Satish Dhawan Space Centre at Sriharikota. It marked the first time NASA and ISRO had cooperated on hardware for an Earth-observing mission, and its orbit was chosen so that it returns to the same places on a fixed schedule.

• Orbit: A circular sun-synchronous orbit 747 km high, inclined at 98.4°, circling the Earth about 14 times a day.
• Repeat cycle: It covers nearly all the planet's land and ice surfaces twice every 12 days, on ascending and descending passes, giving an average revisit of about six days.
• Crossing time: 6 a.m. on the ascending pass and 6 p.m. on the descending pass, so it passes over each place at the same local times.
• Mission life: NASA's prime mission is three years; ISRO gives a mission life of five years.

A sun-synchronous orbit, one of the main types of satellite orbit, is a near-polar orbit that keeps the same orientation to the Sun, so the satellite visits a spot at the same local time on every pass. That regularity lets scientists compare how a place changes over time.

Who Built What: NASA's L-Band and ISRO's S-Band Radar

The two agencies divided the satellite between them. Each built one radar, and both radars share a large unfurlable reflector antenna 12 m across, mounted on a 9 m boom.

The satellite weighed about 2,400 kg at lift-off. ISRO commands and operates it, while NASA provides the orbit manoeuvre plan and the radar operations plan; ground stations of both agencies download the images.

Synthetic Aperture Radar: How NISAR Sees Through Cloud and Darkness

What Is Synthetic Aperture Radar in Remote Sensing

Remote sensing is of two kinds. Passive remote sensing records energy the target reflects or emits, most often reflected sunlight, as an ordinary camera does. Active remote sensing sends out its own energy and measures what comes back; radar is the standard example.

Synthetic aperture radar (SAR) is an active imaging radar flown on an aircraft or a satellite. It sends pulses of microwaves to the ground and records each echo. The finer the image, the larger the antenna it needs, so SAR uses the motion of a small antenna along its path to build a very long synthetic one.

Because it makes its own signal, SAR works by day or night. Its microwaves pass through cloud and most weather, so it can image a flood or a cyclone-hit coast while the sky is still overcast, when an optical camera sees only cloud.

L-Band and S-Band Radar, SweepSAR and InSAR Ground Measurement

NISAR's two radars use different wavelengths. The L‑band radar works at 24 cm and the S‑band radar at 9.4 cm. Choosing two low-frequency bands lets the satellite characterise targets beneath a tree canopy and below the surface, because the two waves penetrate to different depths.

Four features of the radar decide how much ground it covers and what it can tell apart:

• SweepSAR: A new technique that gives both high resolution and a large swath, about 240 km wide.
• Polarimetric mode: The radar records how a target changes the polarisation of the wave; water, natural landscape, urban areas and farmland respond differently and can be told apart.
• Interferometric mode: Precise repeat orbits let two images of the same place be compared, the basis of InSAR.
• Coverage: L‑band images the whole globe; S‑band images India and selected calibration sites.

Interferometric SAR (InSAR) compares two or more radar images of the same place taken from the same orbit. It uses the difference in the phase of the returning waves to map how the surface has moved, and can detect changes of millimetres to centimetres.

NISAR can detect about 1 cm of vertical movement over a patch of land or ice about half the size of a tennis court. That precision is what turns radar images into a record of earthquakes, sinking land and moving ice.

NISAR Satellite Uses: Disasters, Crops, Forests, Ice and Coasts

Ground Deformation, Vegetation, Ice and Coastal Monitoring by NISAR

NISAR characterises land deformation linked to earthquakes, volcanoes and landslides, and the subsidence and uplift caused by changes in underground aquifers and hydrocarbon reservoirs. It also monitors infrastructure such as dams, bridges and roads.

Its early data already show such movement. Measurements from October 2025 to January 2026 showed parts of Mexico City sinking by about 2 cm a month, around 24 cm a year, as heavy groundwater pumping shrinks the aquifer; researchers hope to measure such sinking building by building and to use the data in volcano warnings.

For India, ISRO lists earthquakes, tsunamis, volcanoes and landslides among the natural hazards the mission will help study, along with groundwater and sea-level rise. Beyond hazards, NISAR's data serve five other fields:

• Crops and soil: It tracks changes in the extent of active crops and produces global soil moisture data at a resolution of 200 m.
• Forests and carbon: It measures woody biomass and its changes, and the low-frequency bands help characterise vegetation, which is vital for estimating the global carbon stock.
• Wetlands: It maps changes in the extent of wetlands.
• Ice: It maps the Greenland and Antarctic ice sheets and tracks how sea ice and mountain glaciers move, including the sea ice around India's Antarctic stations.
• Coasts and oceans: It monitors bathymetry in deltas, shoreline erosion and accretion along India's coasts, and can detect marine oil spills.

India's Earth Observation and SAR Satellites: IRS, EOS‑04 and Mission Drishti

Indian Remote Sensing Satellites and EOS‑04 Radar Imaging

India's satellites fall into two groups by purpose. The Indian National Satellite System (INSAT), set up in 1983, serves telecommunication and meteorology. The Indian Remote Sensing (IRS) system, operational since IRS-1A was launched in March 1988, collects data in several spectral bands for the management of natural resources; the National Remote Sensing Centre at Hyderabad receives and processes its data. IRS data are put to four main uses:

• Agriculture: Pre-harvest estimates of crop area and production, and drought monitoring from the condition of vegetation.
• Groundwater and snow: Hydro-geomorphological maps that locate underground water for drilling wells, and snow-melt run-off estimates.
• Land and minerals: Land use and land cover mapping, forest and wetland surveys, and mineral prospecting.
• Hazards: Flood risk zone mapping and flood damage assessment.

India also flies its own radar imaging satellite. EOS‑04, formerly RISAT-1A, carries a C‑band synthetic aperture radar and was launched on PSLV-C52 on 14 February 2022 to give high-quality images in all weather. India's Earth-observation fleet also includes EOS‑05, launched in September 2026 as its first imaging satellite in geosynchronous orbit.

Mission Drishti: World's First OptoSAR Satellite

Private industry has entered radar imaging too. On 3 May 2026 a SpaceX Falcon 9 launched Mission Drishti from Vandenberg in California. Built by the Bengaluru start-up GalaxEye, it weighs 190 kg and is India's largest privately developed Earth-observation satellite.

• Imaging technique: It carries an electro-optical sensor, a camera that records reflected sunlight, and a synthetic aperture radar.
• Why it is a first: It is the first satellite in the world to integrate electro-optical and SAR sensors on a single operational platform, which its maker calls OptoSAR.
• What it gains: All-weather, day-and-night imaging, with the radar filling the gaps when cloud or darkness blinds the optical camera.

NISAR pairs two radar bands for science on a global scale; Mission Drishti pairs a camera with a radar for imagery that stays consistent across weather and light.

NISAR Data Access and the India-US Space Partnership

Open NISAR Data and the India-US Civil Space Partnership

NISAR's data policy is free and open. L‑band data are archived at the Alaska Satellite Facility in the United States. ISRO releases the S‑band data, and the L‑band data over India and selected sites, through its Bhoonidhi portal. The mission reached open data in three stages:

• Commissioning: The first 90 days after launch went to checking the systems and deploying the boom and reflector; the first image was released in this phase.
• Science phase: ISRO announced the start of the science phase on 28 November 2025; NASA dates routine science operations from early January 2026.
• Provisional data: The first provisional L‑band data products were released on 20 July 2026; they are fully calibrated but have so far been validated at only a limited number of sites.

NISAR is the most visible result of a long civil space partnership. The India-US Civil Space Joint Working Group (CSJWG), set up in 2005, brings ISRO and other Indian agencies together with NASA and US agencies.

At its ninth meeting, held in Bengaluru in August 2026, both sides discussed expanding cooperation after NISAR's successful launch, and NASA invited ISRO to join its Moon Base programme, building on India's place in the Artemis Accords. NISAR, a mission costing more than a billion dollars, is now a reference point for that cooperation.