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 businesses. It is a classy 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 can permit it to look at modifications extra exactly than another satellite. It will be capable to see by clouds, smoke, and even thick vegetation, each at day and evening, in all climate situations. The three-tonne machine has been a decade in the making and prices greater than $1.5 billion, additionally making it one among the costliest earth-observing satellites thus far.
The earth’s floor is consistently altering. Natural disasters, human-driven modifications, and local weather shifts all have an effect on environments and human societies. Satellites present important data by taking snapshots of those modifications from house, serving to scientists, governments, and reduction businesses put together for, reply to or research them. To this finish, NASA and ISRO have created a robust international mission that additionally permits ISRO assured entry to a stream of excessive‑decision knowledge tailor-made to India’s wants.
NISAR’s science and software objectives 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 at the very least 5 years. Notably, the mission’s knowledge coverage entails that the knowledge NISAR produces shall be freely out there to all customers (sometimes) 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 a substitute 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 part 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 tons of of metres lengthy is impractical. SAR will get round this by mimicking a large antenna. As the spacecraft strikes ahead, it transmits a prepare of radar pulses and information the echoes. Later, a pc coherently combines all these echoes as if that they had 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 underneath 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, comparable to 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 software for NASA’s mission objectives, the instrument is predicted to function in as much as 70% of each orbit. This stated, working each radars collectively is an official implementation objective so that mode conflicts over the Indian subcontinent are minimised.
Polarisation is the path by which the electrical area of some electromagnetic radiation, like radiowaves, oscillates. SAR can transmit and obtain radar alerts with horizontal or vertical polarisation. Using completely different mixtures will permit the devices to determine the construction and varieties of completely 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 methodology permits the 240‑km swath with out compromising decision.
The ensuing scans may 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 shall 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 energetic and inactive cropland. High-resolution maps of flooded versus dry areas shall be out there as properly. During a catastrophe, NISAR may also be directed to gather knowledge for ‘damage proxy maps’ to be delivered in underneath 5 hours.
This stated, for sure acquisition modes, NISAR gained’t be capable to obtain full international protection at the highest decision. Above roughly 60º latitude, each various remark shall be skipped as a result of converging floor tracks. Similarly, some 10% of the floor is probably not mapped from both path (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‑important.
The organisation equipped the I‑3K spacecraft bus, the platform that homes the controls to deal with command and knowledge, propulsion, and perspective, plus 4 kW of solar energy. The identical package deal additionally included the whole S‑band radar electronics, a excessive‑charge Ka‑band telecom subsystem, and a gimballed excessive‑achieve antenna. The S‑band electronics had been designed and constructed at the Space Applications Centre in Ahmedabad.
NASA’s greatest 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 increase, 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 knowledge 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 had been mated at JPL. The closing observatory‑stage checks will due to this fact have taken place on Indian soil. After that the mission will raise 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 shall be led from the ISRO Telemetry, Tracking and Command Network in Bengaluru. Once NISAR is in orbit, most of its knowledge shall be despatched by NASA’s Near Earth Network services in Alaska, Svalbard (Norway), and Punta Arenas (Chile), which may collectively obtain round 3 TB of radar knowledge per day. They shall be complemented by ISRO’s floor stations in Shadnagar and Antarctica.
After the uncooked knowledge arrive, India’s National Remote Sensing Centre will course of and distribute all merchandise required for Indian customers, mirroring NASA’s pipeline.
