Seeing a volcano in the clouds

NISAR, an Earth observation satellite jointly developed by the National Aeronautics and Space Administration (NASA) and the Indian Space Research Organization (ISRO), released images taken of St. Helens Volcano in Washington state, USA, on November 10, 2025. The video is attracting attention because it contains clear ground surface information despite the thick clouds.

The L-band synthetic aperture radar (SAR) mounted on NISAR is a technology that can observe the ground surface through clouds, enabling stable data collection regardless of weather conditions. In the released image, magenta dots indicate strong reflection of radar signals from flat surfaces such as roads and buildings, while yellow and yellow-green dots indicate vegetation and wetlands. The dark blue area at the top of the volcano was analyzed as a relatively smooth surface without vegetation.

The largest radar antenna in space history

The NISAR satellite was launched from the Satish Dhawan Space Center on the southeastern coast of India in July 2025. The satellite's most notable feature is its drum-shaped reflector, which measures 12 meters (39 feet) in diameter, making it the largest radar antenna NASA has ever sent into space.

It is also significant that it is the first satellite to be equipped with SAR equipment in two wavelength bands simultaneously. NASA's Jet Propulsion Laboratory (JPL) provided the L-band SAR and antenna reflector, and ISRO was responsible for the satellite body and S-band SAR. With this combination, NISAR will observe the entire Earth's land and ice surfaces twice every 12 days.

Traces of human activity revealed through video analysis

The released video of St. Helens Volcano captured not only the natural environment but also traces of human activity. The purple rectangular patterns discovered at the bottom of the mountain are precisely right-angled and are presumed to be forest thinning work or vegetation regenerating after past thinning. In this way, NISAR's high-resolution radar images show that land surface changes and land use status can be precisely tracked.

The NISAR project is managed by the California Institute of Technology (Caltech) and is expected to be used for various earth science research, including monitoring seismic activity, glacial changes, and forest ecosystems.