The story so far: 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 house companies. It is a complicated earth-observation satellite designed to check modifications on the earth’s floor in high quality element, overlaying earthquakes, volcanoes, ecosystems, ice sheets, farmland, floods, and landslides.
What’s the want for NISAR?
NISAR is the first main earth-observing mission with a dual-band radar, which is able to permit it to watch modifications extra exactly than every other satellite. It will be capable of see via clouds, smoke, and even thick vegetation, each at day and evening, in all climate circumstances. The three-tonne machine has been a decade in the making and prices greater than $1.5 billion, additionally making it one in every of the most costly earth-observing satellites so far.
The earth’s floor is continually altering. Natural disasters, human-driven modifications, and local weather shifts all have an effect on environments and human societies. Satellites present vital data by taking snapshots of those modifications from house, serving to scientists, governments, and aid companies put together for, reply to or examine them. To this finish, NASA and ISRO have created a robust world mission that additionally permits ISRO assured entry to a stream of excessive‑decision information tailor-made to India’s wants.
NISAR’s science and utility targets span six areas: stable earth processes, ecosystems, ice dynamics, coastal and ocean processes, catastrophe response, and extra purposes (together with monitoring groundwater, oil reservoirs, and infrastructure like levees, dams, and roads for subsidence or deformation and supporting meals safety analysis).
The deliberate mission lifetime is three years though its design lifetime is no less than 5 years. Notably, the mission’s information coverage entails that the information NISAR produces might be freely accessible to all customers (usually) inside just a few hours.
How does NISAR work?
Once it’s launched, NISAR will enter right into a sun-synchronous polar orbit at 747 km altitude and an inclination of 98.4º. From right here, as an alternative of snapping footage, NISAR’s artificial aperture radar (SAR) will bounce radar waves off the planet’s floor and measure how lengthy the sign takes to return again and the way its section modifications.
The potential of a radar antenna to resolve smaller particulars will increase with its size, referred to as its aperture. In orbit, deploying an antenna a whole bunch of metres lengthy is impractical. SAR will get round this by mimicking a large antenna. As the spacecraft strikes ahead, it transmits a practice of radar pulses and data the echoes. Later, a pc coherently combines all these echoes as if they’d been captured concurrently by one very lengthy antenna, therefore the “synthetic aperture”.
NISAR will mix an L-band SAR (1.257 GHz), which makes use of longer-wavelength radiowaves to trace modifications below thick forests and soil and deformations on the floor, and an S-band SAR (3.2 GHz), which makes use of shorter-wavelength radiowaves to seize floor particulars, resembling crops and water surfaces.
Although NISAR will function globally at L‑band, ISRO has reserved routine, deliberate acquisitions with the S‑band SAR over India. The latter acquisitions have prolonged sensitivity to biomass, higher soil‑moisture retrieval, and mitigate ionospheric noise — all capabilities tuned to India’s wants in agriculture, forestry, and catastrophe administration.
Because the L‑band radar is the principal device for NASA’s mission targets, the instrument is anticipated to function in as much as 70% of each orbit. This mentioned, working each radars collectively is an official implementation purpose so that mode conflicts over the Indian subcontinent are minimised.
Polarisation is the course wherein the electrical subject of some electromagnetic radiation, like radiowaves, oscillates. SAR can transmit and obtain radar alerts with horizontal or vertical polarisation. Using totally different mixtures will permit the devices to determine the construction and varieties of totally different floor supplies, like soil, snow, crop or wooden.
The swath width, i.e. the breadth of the bands on the floor the SARs will scan, is an ultra-wide 240 km. The radars’ SweepSAR design will transmit this beam and, upon its return, digitally steer a number of small sub‑apertures in sequence, synthesising beams that sweep throughout the floor observe. This scan‑on‑obtain technique permits the 240‑km swath with out compromising decision.
The ensuing scans can have a spatial decision of 3-10 m and centrimetre-scale vertical mapping — sufficient to identify impending land subsidence in cities, for instance — relying on the mode. Each spot on the floor might be scanned as soon as each 12 days.The satellite additionally options a big 12-m-wide mesh antenna.
NISAR will produce annual maps of aboveground woody biomass of 1 ha decision and quarterly maps of lively and inactive cropland. High-resolution maps of flooded versus dry areas might be accessible as nicely. During a catastrophe, NISAR may also be directed to gather information for ‘damage proxy maps’ to be delivered in below 5 hours.
This mentioned, for sure acquisition modes, NISAR received’t be capable of obtain full world protection at the highest decision. Above roughly 60º latitude, each various commentary might be skipped because of converging floor tracks. Similarly, some 10% of the floor might not be mapped from both course (of the satellite’s passage over the floor) in any given 12-day cycle.
How was NISAR constructed?
At the time the two house organisations agreed to construct NISAR, NASA and ISRO determined every physique would contribute equal‑scale {hardware}, experience, and funding. ISRO’s contributions specifically are mission‑vital.
The organisation equipped the I‑3K spacecraft bus, the platform that homes the controls to deal with command and information, propulsion, and angle, plus 4 kW of solar energy. The identical bundle additionally included the whole S‑band radar electronics, a excessive‑price Ka‑band telecom subsystem, and a gimballed excessive‑achieve antenna. The S‑band electronics have been designed and constructed at the Space Applications Centre in Ahmedabad.
NASA’s largest contribution was the full L‑band SAR system. NASA’s Jet Propulsion Laboratory equipped all radio‑frequency electronics, the 12‑m antenna, a 9-m carbon-composite growth, and the instrument construction that carries each radars. The company additionally fabricated the L‑band feed aperture and offered the supporting avionics, together with a excessive‑capability stable‑state recorder, a GPS receiver, an autonomous payload information system, and a Ka‑band payload communications subsystem.
The spacecraft was to be built-in at the ISRO Satellite Centre in Bengaluru after the two radars have been mated at JPL. The remaining observatory‑stage checks will subsequently have taken place on Indian soil. After that the mission will carry off from Sriharikota onboard a GSLV Mk-II launch automobile, with ISRO offering finish‑to‑finish launch providers and documentation.
While themission operations are to be centred at the JPL Mission Operations Center, day‑to‑day flight operations might be led from the ISRO Telemetry, Tracking and Command Network in Bengaluru. Once NISAR is in orbit, most of its information might be despatched via NASA’s Near Earth Network services in Alaska, Svalbard (Norway), and Punta Arenas (Chile), which may collectively obtain round 3 TB of radar information per day. They might be complemented by ISRO’s floor stations in Shadnagar and Antarctica.
After the uncooked information arrive, India’s National Remote Sensing Centre will course of and distribute all merchandise required for Indian customers, mirroring NASA’s pipeline.
