Nuclear surveillance from space

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 left), which produce a distinct polarization signature in the two radar bands used in the analysis. Algorithms designed to distinguish rural areas from suburban areas have previously struggled to separate the two regions in optical images. Machine-learning techniques appear more capable of differentiating between the two, however, when the data used are invisible to the human eye. (Image courtesy of Jeffrey Lewis. Radar data from Copernicus Sentinel-1; near-IR data provided by Planet Labs PBC.)