NISAR

1. Context

The Indian Space Research Organisation (ISRO) is planning to launch the NISAR satellite from Sriharikota on July 30 onboard a GSLV Mk-II rocket. ‘NISAR’ stands for NASA-ISRO Synthetic Aperture Radar and is a joint mission of the two space agencies. It is a sophisticated earth-observation satellite designed to study changes on the earth’s surface in fine detail, covering earthquakes, volcanoes, ecosystems, ice sheets, farmland, floods, and landslides

2. Necessity of NISAR

NISAR marks a significant milestone as the first large-scale Earth observation mission to use dual-frequency radar technology.
This capability enables it to detect ground changes with unmatched precision, regardless of whether it's day or night, and in all weather conditions—including through clouds, smoke, or dense vegetation.
Weighing about three tonnes and costing over $1.5 billion, NISAR ranks among the most expensive Earth-monitoring satellites ever launched.
The Earth’s landscape is constantly undergoing transformation due to natural phenomena, human interventions, and climate variations. Observing these changes from space provides essential insights for scientists, policymakers, and emergency response teams.
In response to this need, NASA and ISRO have joined forces on a mission that not only serves global monitoring goals but also ensures ISRO has reliable access to high-resolution data customized for Indian requirements.
The mission targets six key scientific and practical domains: geophysical processes of the solid Earth, ecosystem dynamics, glacial and ice-sheet monitoring, coastal and marine systems, disaster management, and a variety of other applications such as monitoring groundwater levels, oil deposits, and infrastructure like dams and levees.
Although the mission is officially planned to last three years, it has been engineered for a minimum lifespan of five years. Importantly, its open-data policy ensures that most of the data captured by NISAR will be made publicly available within hours of collection

3. How does NISAR work?

Once launched, NISAR will be positioned in a sun-synchronous polar orbit, circling the Earth at an altitude of 747 kilometers with an orbital inclination of 98.4º. Unlike conventional satellites that capture images, NISAR will utilize synthetic aperture radar (SAR) technology, which sends radar pulses toward the Earth's surface and then measures the return time and phase shift of the reflected signals.
The resolution of radar imaging improves with larger antenna sizes—known as aperture—but deploying physically large antennas in space is unfeasible. SAR overcomes this limitation by simulating a large antenna.
As the satellite advances in its orbit, it emits repeated radar pulses and collects their echoes, which are later processed to reconstruct an image as if a giant antenna had captured them all at once—thus earning the term "synthetic aperture."
NISAR will feature two radar systems: an L-band SAR operating at 1.257 GHz that penetrates vegetation and soil layers to detect subsurface changes and land deformations, and an S-band SAR at 3.2 GHz designed for observing finer surface details such as vegetation types and water bodies.
Globally, the satellite will mainly operate using the L-band radar, which aligns with NASA’s scientific objectives. However, over India, ISRO will routinely utilize the S-band radar for targeted observations.
These S-band acquisitions are tailored to India's specific needs, such as biomass estimation, soil moisture monitoring, and filtering out ionospheric interference, which are crucial for sectors like agriculture, forestry, and disaster response.
Both space agencies aim to coordinate radar operations efficiently so that simultaneous use of both radars is possible over the Indian subcontinent, reducing data conflicts.
In radar systems, polarisation refers to the orientation of the electric field in the radar wave. SAR can both send and receive horizontally or vertically polarised signals. Using various combinations of these allows NISAR to distinguish between different surface compositions such as snow, soil, crops, or forests.
NISAR’s radar system will cover a wide area with a swath width of 240 km, thanks to a SweepSAR design. This approach uses a beam transmission system that, upon signal return, employs multiple smaller apertures that steer electronically to create scanning beams sweeping across the satellite’s ground path.
This scan-on-receive method enables large-area coverage without sacrificing image clarity.
The mission will deliver spatial resolutions ranging from 3 to 10 meters and vertical accuracy down to a few centimeters. This high level of detail is suitable for tracking urban land subsidence or other subtle ground movements. Each point on the Earth’s surface will be revisited every 12 days.
NISAR is equipped with a massive 12-meter-wide mesh reflector antenna, enabling it to generate annual biomass maps at a resolution of 1 hectare and quarterly maps distinguishing between cultivated and fallow farmland.
It will also provide detailed floodplain maps and, in emergencies, can generate ‘damage proxy maps’ within five hours of data capture.
However, there are some limitations. Due to the satellite’s orbital geometry, certain data acquisition modes may not achieve full global coverage. At latitudes above 60º, NISAR will skip every other observation due to overlapping orbits.
Furthermore, around 10% of Earth’s surface may not be covered from both ascending and descending passes within a given 12-day cycle

Another important component of the satellite is its large 39-foot stationary antenna reflector.

Made of a gold-plated wire mesh, the reflector will be used to focus " the radar signals emitted and received by the upward-facing feed on the instrument structure".

4. How was NISAR built?

When NASA and ISRO agreed to collaborate on the NISAR project, both agencies committed to contributing equally in terms of funding, technology, and expertise.
ISRO was responsible for providing the I-3K satellite bus — the core spacecraft framework that handles system commands, propulsion, orientation, and includes solar panels capable of generating 4 kW of power.
In addition, ISRO delivered the complete S-band radar electronics system, a high-speed Ka-band communication unit, and a steerable high-gain antenna. The development of the S-band radar components was carried out at the Space Applications Centre in Ahmedabad.
On the other hand, NASA’s primary input was the L-band synthetic aperture radar system. This was developed at the Jet Propulsion Laboratory (JPL), which supplied all related radio-frequency components, a 12-meter radar antenna, a 9-meter carbon fiber boom, and the structural assembly that supports both radar units.
NASA also provided the L-band feed array and avionics systems, including a solid-state recorder with large data capacity, a GPS system, autonomous data management tools, and a Ka-band communication unit.
After integration of the radar payloads at JPL, the spacecraft was sent to ISRO’s Satellite Centre in Bengaluru for final assembly. Once fully tested, NISAR will be launched aboard ISRO’s GSLV Mk-II rocket from the spaceport in Sriharikota, with ISRO overseeing the entire launch sequence.
While the overall mission will be coordinated through NASA's Mission Operations Center at JPL, routine flight control and monitoring will be managed by ISRO’s Telemetry, Tracking and Command Network (ISTRAC) in Bengaluru.
After deployment into orbit, the bulk of the mission’s data—approximately 3 terabytes daily—will be transmitted through NASA’s Near Earth Network ground stations located in Alaska, Norway’s Svalbard, and Punta Arenas in Chile.
These facilities will work in conjunction with ISRO’s data reception stations in Shadnagar and Antarctica. Once the raw data are received, India’s National Remote Sensing Centre (NRSC) will process and distribute mission outputs tailored for Indian applications, in a workflow that parallels NASA’s global data distribution system

5. The Mission

Once launched into space, NISAR will observe subtle changes in Earth's surfaces, helping researchers better understand the causes and consequences of such phenomena.
It will spot warning signs of natural disasters, such as volcanic eruptions, earthquakes and landslides.
The satellite will also measure groundwater levels, track flow rates of glaciers and ice sheets and monitor the planet's forest and agricultural regions, which can improve our understanding of carbon exchange.

By using synthetic aperture radar (SAR), NISAR will produce high-resolution images.
SAR is capable of penetrating clouds and can collect data day and night regardless of the weather conditions. The instrument's imaging Swath the width of the strip of data collected along the length of the orbit track is greater than 150 miles (240 kilometres), which allows it to image the entire Earth in 12 days.

NISAR is expected to be launched in January 2024 from Satish Dhawan Space Centre into a near-polar orbit.
The satellite will operate for a minimum of three years.
NASA requires the L-band radar for its global science operations for at least three years.
Meanwhile, ISRO will utilise the S-band radar for a minimum of five years.

For Prelims & Mains

For Prelims: NISAR (NASA-ISRO Synthetic Aperture Radar), Satish Dhawan Space Centre, Earth-observation satellite, Jet Propulsion Laboratory, L-band and S-band synthetic aperture radar, GPS, GSLV launch system and spacecraft,

For Mains:

1. What is NISAR and Explain its benefits (250 Words)

Source: The Hindu

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