How NISAR satellite will transform earth observation

How NISAR satellite will transform earth observation
by Clarence Oxford
Los Angeles CA (SPX) Jan 22, 2025

The NASA-ISRO Synthetic Aperture Radar (NISAR) satellite is poised to launch in the coming months, bringing an innovative capability to track Earth's surface changes with remarkable precision. Using synthetic aperture radar (SAR), the satellite will deliver high-resolution data, monitoring everything from tectonic shifts to ecosystem changes.

NISAR will survey nearly all of Earth's solid land masses every 12 days, capturing surface movement down to fractions of an inch. Its data will help scientists study the crust's flexing during natural disasters such as earthquakes, monitor glaciers and ice sheets, and track forest growth and deforestation.

This capability hinges on SAR technology, a technique that uses microwave radar signals to create detailed images. Unlike traditional radar systems, SAR integrates multiple measurements collected during an antenna's orbit to enhance resolution. Charles Elachi, a former director of NASA's Jet Propulsion Laboratory (JPL), explained, "Synthetic aperture radar allows us to refine things very accurately. The NISAR mission will open a whole new realm to learn about our planet as a dynamic system."

NISAR's radar antenna reflector is 39 feet (12 meters) wide, comparable to the length of a city bus. Without SAR, achieving the same resolution would require an antenna 12 miles (19 kilometers) across-far too large to feasibly launch or operate in space.

The Mechanics of SAR

SAR technology has roots in JPL's early radar experiments in the 1970s, including efforts to study Venus' surface. Radar's appeal lies in its ability to collect data both day and night and penetrate clouds. NASA leveraged this capability for missions like Magellan, which mapped Venus in 1989, and several radar-focused Space Shuttle missions.

The operation of SAR involves emitting microwave pulses from an antenna toward Earth. The reflected signals-which scatter off various surfaces-are analyzed to determine distance, speed, and physical characteristics. Unlike standard radar, SAR uses the Doppler shift, the frequency change caused by the radar's relative motion to the surface, to process return signals into highly detailed images. According to Paul Rosen, NISAR's project scientist at JPL, "It's a technique to create high-resolution images from a low-resolution system."

Applications of SAR

NISAR's SAR technology will provide valuable insights through techniques like interferometry and polarimetry. Interferograms-visual representations combining images from different times-reveal ground displacement caused by events such as earthquakes. The closer the colored bands in an interferogram, the greater the movement.

Polarimetry, another SAR-based analysis, examines the orientation of radar waves as they return. This helps differentiate surfaces: for example, waves bouncing off tree canopies behave differently than those reflecting off buildings. Such data are critical for tracking deforestation, flooding, and changes in land cover.

Deepak Putrevu, co-lead of ISRO's science team at the Space Applications Centre in India, highlighted NISAR's significance, stating, "This mission packs in a wide range of science toward a common goal of studying our changing planet and the impacts of natural hazards."