Context: NASA and ISRO are set to launch the NISAR (NASA-ISRO SAR) satellite, a $1.5 billion Earth-observing mission in July 2025. NISAR has arrived at ISRO’s spaceport in Sriharikota, Andhra Pradesh.
Relevance of the Topic: Prelims: Key facts about Synthetic Aperture Radar; Advantages & Applications of SAR
Synthetic Aperture Radar:
- Synthetic aperture radar (SAR) is a form of active remote sensing that uses microwave radar signals to create high-resolution images of Earth.
How does SAR work?
- SAR systems send out microwave pulses towards Earth. These signals bounce off from surfaces like ground, ocean, ice, vegetation, buildings etc.
- These echoes (reflected signal) are collected by the antenna carried on a moving platform like a satellite. Since the satellite is moving, each echo is recorded at a slightly different position.
- Via complex signal processing those echoes are stitched together into detailed images. Usually, the longer a physical antenna, the better is the resolution. However, a large antenna is hard to build and maintain. Hence, SAR mimics the effect of having a single giant antenna (hundreds of metres long).
Advantages of SAR:
- Since microwaves penetrate clouds, smoke, dense vegetation, and even light rainfall, SAR can collect data 24/7.
- If a SAR unit is mounted on an orbiting satellite, it can map swaths of land hundreds of kilometres wide in a single overpass.
- Different materials like soil, vegetation, water, and metals reflect microwaves differently, allowing SAR to detect changes invisible to optical sensors.
Applications of SAR:
SAR can observe natural processes and changes in earth’s complex ecosystems.
- Study Earth’s dynamic land and ice surfaces in greater detail and observe subtle changes in Earth’s surfaces. E.g., Track flow rates of glaciers and ice sheets, landslide-prone areas and changes in the coastline etc.
- Spot warning signs of natural disasters, such as earthquakes, tsunamis, volcanoes and landslides.
- Measure groundwater levels, agricultural mapping, vegetation biomass, natural resource mapping and monitor Earth’s forest and agricultural regions to improve understanding of carbon exchange.
NISAR will scan nearly all of Earth’s land and ice surfaces twice every 12 days, providing an unprecedented amount of information about our planet’s environment.
Also Read: NASA-ISRO Synthetic Aperture Radar