North Korea withdrew from the 2003 Nuclear Non-Proliferation Treaty. It subsequently developed nuclear weapons, with five underground nuclear tests culminating in a suspected thermonuclear explosion (hydrogen bomb) on September 3, 2017. Now a team of scientists, led by Dr. KM Straight from the Center for Space Applications, Indian Space Research Organization (ISRO), have used satellite data to increase field test measurements. Researchers find that the latest test has moved the ground by a few meters and estimated it to be 17 times the size of the 1945 bomb dropped on Hiroshima. The new work appears in a paper in the Geophysical Journal International, a publication of the Royal Astronomical Society.
Conventional nuclear test detection relies on seismic measurements using networks deployed for earthquake tracking. But there is no open seismic data available from stations near this designated testing site, which means there are major uncertainties in pointing out the location and magnitude of the nuclear explosions that are occurring there.
Dr. Straight and his team turned to space for a solution. Using data from the ALOS-2 satellite and a technique called Synthetic Radar Interferometry (INSAR), scientists measured surface changes above the test chamber as a result of a September 2017 blast located on Mount Montap, northeast of North Korea. . InSAR uses multiple radar images to create deformation maps over time and allows direct study of the underlying surface processes from space.
New data suggests that the blast was strong enough to move the surface of the mountain above the detonation site within a few meters, with the wing flanking up to half a meter. Analyzing Insar's readings in detail, he reveals that the blast occurred about 540 meters below the summit, about 2.5 kilometers north of the tunnel entrance used for access to the test chamber.
Based on the deformation of the terrain, the ISRO team predicts that the blast created a gap of 66 meters. It had a yield of 245 to 271 kilotons, compared to the 15 kilotons of the "Little Boy" bomb used in the 1945 Hiroshima attack.
The study's lead author, Dr. Straight, commented: "Satellite radars are very powerful tools for measuring changes on the surface of the earth and allow us to estimate the location and yield of underground nuclear tests. Unlike conventional seismology, estimates are indirect and depend on the availability of seismic monitoring stations. "
This study demonstrates the value of InSAR data carried in the space to measure the characteristics of underground nuclear tests, more accurately than conventional seismic methods. At the moment, though, nuclear explosions are rarely monitored from space due to lack of data. The team claims that satellites such as Sentinel-1 and ALOS-2 currently operating in conjunction with the NASA-ISRO Synthetic Radar Aperture (NISAR) mission, due to launch in 2022, can be used for this purpose.
Reference: "North Korea Nuclear Test Location, Depth and Yield Limits on September 3, 2017 by InSAR Measurement and Modeling" by K M Sreejith, Ritesh Agrawal and A S Rajajat, October 9, 2019, Geophysical Journal International.
DOI: 10.1093 / bay / ggz451