Context:
India’s ISRO and the U.S. space agency NASA are set to jointly launch NISAR (NASA-ISRO Synthetic Aperture Radar) from Sriharikota on July 30, 2025, using the GSLV Mk-II. It will be the world’s most advanced radar-based earth observation satellite, designed for high-resolution tracking of changes on Earth’s surface.
What is NISAR?
- A joint mission between NASA and ISRO.
- The first dual-frequency SAR (Synthetic Aperture Radar) satellite, combining:
- L-band SAR (1.257 GHz) by NASA – better for ground deformation, forests, and subsurface imaging.
- S-band SAR (3.2 GHz) by ISRO – sensitive to vegetation, moisture, crops, and surface texture.
Objectives of the Mission
- Monitor changes in:
- Solid Earth processes (earthquakes, landslides, ground subsidence)
- Ecosystems and biomass
- Ice sheets and glaciers
- Agricultural croplands
- Flooded vs. dry land areas
- Infrastructure stability (dams, levees)
- Help in climate change research, disaster management, and resource monitoring.
Technical Highlights
- Orbit: Sun-synchronous polar orbit at 747 km altitude, 98.4° inclination.
- Antenna: 12-metre wide mesh reflector.
- Swath width: 240 km (ultra-wide), thanks to SweepSAR technology.
- Spatial resolution: 3–10 meters; vertical accuracy in centimetres.
- Revisit time: Every 12 days per location.
- Data accessibility: Freely available to the public typically within a few hours.
- Annual biomass maps (1 ha resolution) and quarterly cropland maps.
Region-Specific Use
- ISRO has reserved routine S-band operations over India, ensuring:
- Better mapping of soil moisture, crop health, and biomass.
- Reduced atmospheric distortion in Indian observations.
How NISAR Works
- Uses radar pulses to scan Earth’s surface — it measures return time and phase of the signal.
- Synthetic Aperture Radar (SAR) mimics a large antenna by combining sequential echoes as the satellite moves.
- It can penetrate clouds, smoke, vegetation, and work day or night, making it reliable for all-weather monitoring.
- Different polarisation modes (horizontal/vertical) help classify materials (soil, water, crops, snow).
