NISAR

Geography glossary

Also called: NASA-ISRO Synthetic Aperture Radar · Topic: Remote Sensing, GIS and GNSS · NCERT: Beyond NCERT

Meaning

NISAR (NASA-ISRO Synthetic Aperture Radar) is a joint Earth observation satellite built by NASA (USA) and ISRO (India). It is the first satellite to carry both L-band and S-band radar. It was launched on 30 July 2025 on GSLV-F16 from Sriharikota, Andhra Pradesh [1].

  • It images almost all of the earth's land and ice every 12 days, by day and by night, in all weather [1].
  • This lets India and the world track earthquakes, landslides, melting glaciers, crops and forests, even under thick monsoon cloud.

Explanation

How a radar satellite like NISAR works

  • Radar is an active sensor:
  • It sends out its own microwave pulses and records the echo that comes back from the ground.
  • It does not need sunlight, so it works at night.

  • Microwaves pass through cloud, so it works in the monsoon.

  • SAR (Synthetic Aperture Radar):

  • SAR is a radar that looks to one side from a moving satellite.
  • It joins the echoes from many points along its orbit, so together they work like one very long antenna.

  • Result: a small antenna gives a sharp image.

  • SweepSAR:

  • NISAR uses a technology called SweepSAR.
  • It gives sharp images over a very wide 242 km swath (the strip of ground seen in one pass) [1].
  • A wide swath is what lets it cover almost all land and ice every 12 days.

Two radar bands: why "dual-band" matters

  • L-band (about 24 cm wavelength):
  • It is the longer wave, so it goes deeper into the surface.
  • It passes through tree canopy and dry soil.

  • Good for forests, ground movement and soil moisture.

  • S-band (about 10 cm wavelength):

  • It is a shorter wave than L-band.

  • Rule to remember: the longer the wavelength, the deeper the wave goes into the surface.

  • Carrying both bands on one satellite is what makes NISAR the first of its kind.

Who built what

NASA (USA) ISRO (India)
L-band radar S-band radar
12 m unfolding (deployable) antenna Spacecraft bus (the satellite's main body)
GPS receiver, high-rate data link, solid-state recorder GSLV-F16 rocket and launch services

[1]

Orbit and what it tracks

  • Orbit: it is in a sun-synchronous polar orbit.
  • This is a near-polar orbit. The satellite crosses each place at the same local time on every pass, so the light conditions stay the same from image to image.

  • NISAR was the first GSLV mission to a sun-synchronous polar orbit [1].

  • Earthquakes and landslides:

  • It compares two radar images of the same place taken at different times.
  • This method is called interferometry.

  • It can find ground movement of just a few centimetres.

  • Glaciers and ice sheets: it tracks how fast they flow and how fast they melt.

  • Crops and forests: L-band passes through the tree canopy, so it can measure biomass (the amount of woody plant matter).
  • Main aims: to study how land and ice move or change shape, land ecosystems, and ocean areas [1].

Where it occurs

  • Launch site: Sriharikota, Andhra Pradesh, on GSLV-F16, 30 July 2025 [1].
  • Run by: NASA (USA) and ISRO (India) as equal partners [1].
  • Coverage: almost all of the earth's land and ice, every 12 days.
  • Glaciers and ice: the Himalaya, Greenland and Antarctica.
  • Uses in India:
  • Flood mapping in Assam and Bihar during the south-west monsoon (June–September), when cloud blocks optical satellites.
  • Land sinking (subsidence) and landslides in the Himalaya, such as the sinking of land at Joshimath.
  • Kharif paddy area estimates and forest biomass.

Don't confuse with

  • RISAT / EOS-04 (RISAT-1A): these are India's own C-band SAR satellites (about 5.6 cm wavelength). NISAR carries L-band + S-band and is a joint NASA-ISRO mission.
  • Sentinel-1 (EU Copernicus): also a radar satellite, but it uses C-band SAR. Only NISAR carries both L-band and S-band.
  • Optical satellites (Landsat, Resourcesat, Cartosat, Sentinel-2): these are passive. They record sunlight, so they need daylight and clear skies. NISAR is active radar and sees through cloud at night.
  • INSAT-3DS: a geostationary weather satellite (GSLV-F14, 2024) that watches the same area all the time [3]. NISAR is in a sun-synchronous polar orbit and revisits each place every 12 days.

Prelims Hooks

  • NISAR was launched on GSLV-F16 on 30 July 2025 from Sriharikota. It was the first GSLV launch to a sun-synchronous polar orbit [1].
  • NASA supplied the L-band radar and the 12 m antenna. ISRO supplied the S-band radar, the bus and the rocket [1]. A common trap swaps L and S.
  • It is the first satellite with both L-band and S-band radar. Wavelengths: L ≈ 24 cm > S ≈ 10 cm > C ≈ 5.6 cm.
  • SweepSAR technology gives a 242 km swath [1]. It images almost all land and ice every 12 days.
  • Interferometry (comparing two radar images of the same place taken at different times) → detects ground movement of a few centimetres (earthquakes, landslides).
  • Trap: RISAT, EOS-04 and Sentinel-1 are C-band. NISAR is L + S band.

Mains Points

  • Radar fills the monsoon gap (GS-III, disasters and agriculture):
  • Cloud covers India during the south-west monsoon, so optical images fail just when floods and kharif sowing happen.
  • NISAR's L- and S-band radar [1], along with C-band RISAT/EOS-04, gives flood maps for Assam and Bihar, paddy area estimates and early warning of land sinking at places like Joshimath.

  • The loss of EOS-09 on PSLV-C61 (18 May 2025) [2] shows why India needs more than one radar satellite to keep coverage going.

  • Tracking climate change and hazards (GS-I and GS-III):

  • Glacier flow and melt in the Himalaya, Greenland and Antarctica can be measured every 12 days.
  • Forest biomass data from L-band supports forest cover reports and carbon accounting.

  • Centimetre-level ground movement data helps with earthquake and landslide risk mapping in the Himalaya.

  • India as an equal space partner (GS-III, science and technology):

  • India moved from Bhaskara satellites launched on Soviet rockets to building half of a world-class mission and launching it on its own GSLV.
  • NISAR shows India is now an equal partner in the world's top Earth observation missions [1].

Related concepts

Read more

Sources

  1. 1ISRO — GSLV-F16/NISAR mission page and launch brochureisro.gov.in · tier 1
  2. 2PIB / ISRO — PSLV-C61/EOS-09 Missionpib.gov.in · tier 1
  3. 3ISRO — GSLV-F14/INSAT-3DS Mission; PIB — MoES-funded GSLV-F14/INSAT-3DS successfully launchedisro.gov.in · tier 1