Synthetic Aperture Radar (SAR), Working and Advantages

Context: Recently, NASA said the NASA-ISRO SAR mission had arrived at ISRO’s spaceport in Sriharikota.

What is Synthetic Aperture Radar (SAR)?

• Synthetic Aperture Radar (SAR) is a type of active remote sensing technology.
• It sends out microwave pulses and records the energy that bounces back after hitting Earth’s surface.
• Unlike optical sensors, SAR can capture high-resolution images day or night, and through clouds, smoke, or light rain.

How Synthetic Aperture Radar Works?

• A microwave signal is emitted toward the ground.
• The reflected signals (echoes) from surfaces like mountains, oceans, ice, or urban structures are recorded.
• A moving antenna (on a satellite or aircraft) captures these echoes from different positions.
• Using advanced signal processing, these signals are combined to simulate a much larger antenna (synthetic aperture).
• This technique allows sharp imaging with high resolution, without needing a physically huge antenna.

Advantages of SAR

• All-weather, day-night capability — unlike optical imaging, SAR works in darkness and cloudy conditions.
• Can image wide areas (hundreds of kilometers) in a single satellite pass.
• Works well for monitoring terrain, agriculture, deforestation, flooding, and military surveillance.

What SAR Can Detect

• Soil moisture, vegetation density, surface roughness.
• Differentiates materials like water, soil, vegetation, metal, and concrete based on their microwave reflectivity.
• Can detect minute surface changes that are invisible in optical imagery (e.g., after earthquakes or landslides).

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