In a few weeks, Earth scientists will launch a satellite that will provide unprecedented, high-resolution coverage of some of the most remote and rapidly changing parts of the world. The NASA-ISRO Synthetic Aperture Radar (NISAR) satellite, a joint mission between NASA and the Indian Space Research Organisation (ISRO), will scan nearly the entire globe twice every 12 days to measure changes in Earth’s ecosystems, cryosphere, and land surface.
“In my eyes, it’s orbiting magic,” said Alex Gardner, a glaciologist at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., and a member of NISAR’s cryosphere science team. NISAR will provide high-resolution radar imagery that will enable scientists to track glaciers and ice, biodiversity, soil moisture and water placement, and land displacements from events like earthquakes and landslides.
“When there’s an earthquake, and you can see displacements from 500 kilometers up that you wouldn’t even be able to notice if you were standing on the ground…that’s orbiting magic,” Gardner said.
Double Radar
NISAR is currently scheduled to launch on 20 May from the Satish Dhawan Space Centre in India. It will be the largest, but not the first, satellite collaboration between NASA and ISRO, explained Paul Rosen, NISAR project scientist at JPL. “We had some other collaborations in both planetary and Earth science, but not at this level of magnitude,” he said.
The satellite will host two synthetic aperture radar (SAR) systems that operate at different microwave wavelengths, one longer (L band, at a wavelength of 24 centimeters) and one shorter (S band, at a wavelength of 10 centimeters). SAR is a technique used to create high-resolution images from lower-resolution instruments. The instruments emit continuous pulses of microwave radiation and use the light that bounces back, as well as the time delay, to create backscatter images.
“We made sure that the two radars could work together,” Rosen said. “They’re highly in sync, and we can turn them on together or operate them separately.”
“It’s got a lot to deliver on, but I don’t feel that nervous about it.”
Unlike visible-light imaging, SAR is not limited by the time of day or the weather, explained Deepak Putrevu, an engineer and colead of NISAR’s ISRO science team at the Space Applications Centre in Ahmedabad, India. “It uses microwaves for imaging, so that that makes it able to penetrate the clouds and to image even during the nighttime.…The SAR technology enables us to have day and night coverage and all-weather imaging capability.”
NISAR’s orbit will cause it to pass over the same locations every 12 days. Because SAR can map an area both as it approaches (ascending orbit) and departs (descending orbit), NISAR will be able to scan each area twice every 12 days. Each space agency provided one of the radar systems, as well as other components of the satellite, the launch system, and the data management infrastructure.
“We jointly operate the mission and jointly do the science,” Rosen added.
“It’s got a lot to deliver on, but I don’t feel that nervous about it,” Gardner said. “Aspects of these technologies have flown before,” he added. For example, the European Space Agency’s Sentinel satellites carry SAR instruments that have helped scientists understand the cryosphere, Earth surface processes, and ecosystems. But NISAR’s dual radar frequency bands are a first for Earth-observing satellites. The systems will be able to detect changes at different physical scales—L band for large structures and S band for smaller ones—as well as provide higher-resolution images together than can be achieved individually.
Global Surface Changes
One of NISAR’s primary science objectives is to observe changes to the cryosphere and glaciers around the world. That’s Gardner’s wheelhouse.
“Glaciers are just these really fantastic living creatures,” he said. NISAR will monitor seasonal growth and retreat patterns of glaciers around the world, with a special focus on those of the West Antarctic Ice Sheet like Pine Island and Thwaites.
“They just have such large societal consequence that there’ll be a lot of attention there,” Gardner explained. More broadly, he said, those seasonal patterns can be a good predictor of long-term changes in the cryosphere.
NISAR will also be able to observe the vertical displacements of ice sheets, which Gardner said will allow cryosphere scientists to map where floating ice sheets meet grounded ice, a boundary called the grounding line.
“It’s really hard to measure, and it’s been done locally but not really at large scale,” he said. “We can watch that position of that grounding line change with time, which is an indicator of vulnerability” to warming temperatures.
NISAR will also measure global biodiversity and soil moisture. The two radar frequency bands will be especially helpful with this, Putrevu explained. “With forest biomass, the L-band system will be able to see the dense forest with more sensitivity. But when we use the S-band system, you can use it for sparse vegetation, as well.”
The SAR systems will be able to see through crop cover and measure soil moisture, Putrevu added, which will provide key information for farmers and agribusiness. He also highlighted the importance of closely monitoring changes in land deformation, which might suggest imminent earthquakes or landslides.
“All the applications have a societal benefit attached,” Putrevu said. “It gives a great deal of satisfaction that this will actually be useful for society.”
A Data Deluge
After launch, it will take 90 days for the satellite to conduct its commissioning tests and reach its science orbit. “But as we progress, we’re going to get little peeks behind the curtains that we are going to be so enthusiastic about as we see the imagery start to really mature, and the data processing mature, the data acquisition mature,” Gardner explained. “There’ll be a progression from a first light image to science ready data.”
Every pass of the satellite will provide an order of magnitude more data than past satellites have delivered. Much of the final preparation before launch has involved developing the infrastructure needed to efficiently receive, process, and make available such large quantities of data.
“The sheer volume of new data that we’re going to be dealing with requires the development of novel tools.”
“Once NISAR comes online, the sheer volume of new data that we’re going to be dealing with requires the development of novel tools,” Gardner said. “NISAR is really leaning into cloud architecture” for data storage, availability, and computing, so that users don’t have to download massive quantities of data to individual servers. “Moving data around is one of the largest bottlenecks with missions like this.”
“We have been preparing for the last couple years to get all of our algorithms working really efficiently in the cloud,” Gardner said, “so that when the fire hose of data comes online, we can get in there, plug into that data stream, and benefit from it really early on.”
Putrevu said that scientists and students across India have been participating in workshops since 2014 to learn how to access, process, and produce science from NISAR’s data. “That shows how the community is getting geared up to use the data,” he said. “Everyone is eagerly looking forward to [launch] day.”
Because the volume of information requires such novel processing tools, Gardner cautioned that it might be a year or two before NISAR data yield new scientific outcomes. The mission’s nominal lifetime is 3 years, and once the analysis gets up to speed, discoveries derived from those data will likely continue for decades.
“Without a doubt, it will be a legacy dataset,” Gardner said. “It’s going to be transformational.”
—Kimberly M. S. Cartier (@astrokimcartier.bsky.social), Staff Writer
