How the US–Indian NISAR satellite will offer unique window on Earth

The upcoming U.S.–India NISAR (NASA-ISRO Synthetic Aperture Radar) mission – expected to launch in March 2025 from the Satish Dhawan Space Centre in Sriharikota, India - will observe Earth like no mission before, offering insights about our planet's ever-changing surface.

The NISAR mission is a first-of-a-kind dual-band radar satellite that will measure land deformation from earthquakes, landslides, and volcanoes, producing data for science and disaster response. It will track how far glaciers and ice sheets are advancing or retreating, and it will monitor growth and loss of forests and wetlands to provide insights on the global carbon cycle.

As diverse as NISAR's impact will be, the mission's winding path to launch—in a few months' time—has also been remarkable. Paul Rosen, NISAR's project scientist at NASA's Jet Propulsion Laboratory in Southern California, has been there at every step. He recently discussed the mission and what sets it apart.

How will NISAR improve our understanding of Earth?

The planet's surfaces never stop changing—in some ways small and subtle, and in other ways monumental and sudden. With NISAR, we'll measure that change roughly every week, with each pixel capturing an area about half the size of a tennis court. Taking imagery of nearly all Earth's land and ice surfaces this frequently and at such a small scale—down to the centimeter—will help us put the pieces together into one coherent picture to create a story about the planet as a living system.

What sets NISAR apart from other Earth missions?

NISAR will be the first Earth-observing satellite with two kinds of radar—an L-band system with a 10-inch (25-centimeter) wavelength and an S-band system with a 4-inch (10-centimeter) wavelength.

Whether microwaves reflect or penetrate an object depends on their wavelength. Shorter wavelengths are more sensitive to smaller objects such as leaves and rough surfaces, whereas longer wavelengths are more reactive with larger structures like boulders and tree trunks.

So NISAR's two radar signals will react differently to some features on Earth's surface. By taking advantage of what each signal is or isn't sensitive to, researchers can study a broader range of features than they could with either radar on its own, observing the same features with different wavelengths.

Is this new technology?

The concept of a spaceborne synthetic aperture radar, or SAR, studying Earth's processes dates to the 1970s, when NASA launched Seasat. Though the mission lasted only a few months, it produced first-of-a-kind images that changed the remote-sensing landscape for decades to come.

It also drew me to JPL in 1981 as a college student: I spent two summers analyzing data from the mission. Seasat led to NASA's Shuttle Imaging Radar program and later to the Shuttle Radar Topography Mission.

What will happen to the data from the mission?

Our data products will fit the needs of users across the mission's science focus areas—ecosystems, cryosphere, and solid Earth—plus have many uses beyond basic research, like soil-moisture and water resources monitoring.

We'll make the data easily accessible. Given the volume of the data, NASA decided that it would be processed and stored in the cloud, where it'll be free to access.

How did the ISRO partnership come about?

We proposed DESDynI (Deformation, Ecosystem Structure, and Dynamics of Ice), an L-band satellite, following the 2007 Decadal Survey by the National Academy of Sciences. At the time, ISRO was exploring launching an S-band satellite. The two science teams proposed a dual-band mission, and in 2014 NASA and ISRO agreed to partner on NISAR.

Since then, the agencies have been collaborating across more than 9,000 miles (14,500 kilometers) and 13 time zones. Hardware was built on different continents before being assembled in India to complete the satellite. It's been a long journey—literally.

Story source: NASA