To track the spread of nuclear weapons, nonproliferation experts need to identify new activity at reactors and various other nuclear-related sites. Some of the latest space-based observations of Earth’s surface may offer just what the experts need. Steven De La Fuente, a graduate research assistant at the Middlebury Institute of International Studies at Monterey in California, produced the composite image shown here. It was made using high-quality, rapidly updated near-IR data from the satellite-data company Planet Labs and two sets of radar data collected by the Sentinel-1 satellites as part of the European Space Agency’s Earth observation program. The image shows North Korea’s Yongbyon nuclear-science center as it looked in late February 2021.

The vegetation in the surrounding rural countryside (green) strongly reflects the near-IR band of light and is thus easily separated visually from the bare mountainsides (pink, on the right) and the nuclear site’s buildings (pink, on the...

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