Artist Rendering of NISAR satellite. Image courtesy of NASA/JPL-Caltech.
NISAR is a joint mission between the United States’ National Aeronautics and Space Administration (NASA) and the Indian Space Research Organisation (ISRO). It began over a decade ago when, in September 2014, the two space agencies signed a partnership agreement, and with a reported total cost of over US$1.5 billion it is expected to be one of the most expensive Earth Observation satellites ever launched. The satellite is expected to be placed into an orbit at 747 km altitude, enabling it to scan almost the entire planet’s land and ice surfaces twice every 12 days.
This will be the first mission to have both L-band and S-band synthetic aperture radar (SAR) instruments onboard, which operate at different frequencies. They will both beam down a signal towards the ground, and measure the reflection, known as backscatter, using NISAR’s 12-metre mesh antenna. The strength and time delay of this backscatter allows the image to be built.
By having different frequencies, the instruments will be able to measure tiny changes to the Earth’s surface, even as small as 10 millimetres. The L-band SAR has a spatial resolution between 3 – 48 metres with a swath width of 242 km, while the S-Band instrument will have a spatial resolution of between 3 – 24 metres with the same swath size. The specific resolution of each observation mode varies with the chosen bandwidth and polarisation.
Using the two SAR instruments means that they can penetrate both clouds and forest canopies, and the L-band can go even further by obtaining imagery through the thicker vegetation on the planet’s surface. The focus of the L-band will be landscape topography and heavily forested area, while the S-band is focused on monitoring soil moisture, particularly in polar regions.
Over the course of its three-year mission, the satellite will measure changes in the planet’s ecosystems, such as the flow rates of glaciers and ice masses, alongside the dynamics of earthquakes and volcanoes. It will also provide valuable information about biomass, natural hazards, sea level rise, groundwater, amongst other things. It’s anticipated the data will be used for applications such as infrastructure monitoring, disaster response, biomass assessment, and agricultural management.
Conclusion
It is exciting to see NISAR ready for launch, as this satellite has the potential to offer innovative insights into what is happening around the world alongside existing SAR instruments, such as Sentinel-1, and we will be watching the data and images from NISAR with great interest.
