North Korea withdrew from the Treaty on the Non-Proliferation of Nuclear Weapons in 2003. Subsequently, it developed nuclear weapons, completing five underground nuclear tests with an alleged thermonuclear explosion (hydrogen bomb) on September 3, 2017. a team of scientists led by Dr. KM Sridjit of the Center for Space Applications, Indian Space Research Organization (ISRO), use satellite data to increase the measurement of ground tests. The researchers found that the latest test displaced the earth by several meters and estimated it to be equivalent to 17 times the bomb dropped on Hiroshima in 1945. The new work appears in a publication in the Geophysical Journal International, a publication of the Royal Astronomical Society.
The conventional detection of nuclear tests is based on seismic measurements using networks located for earthquake monitoring. But there is no open seismic data from stations near this particular test site, which means that there is great uncertainty in determining the location and magnitude of nuclear explosions taking place there.
Dr. Sreejith and his team turned to the decision space. Using data from the ALOS-2 satellite and a technique called Synthetic Aperture Radar Interferometry (InSAR), scientists measured surface changes above the test chamber as a result of the September 2017 explosion on Mount Mantap in northeastern North Korea. InSAR uses multiple radar images to create deformation maps over time and allows direct exploration of the processes of the attic from space.
New data suggest that the explosion was powerful enough to displace the surface of the mountain above the point of detonation. a few meters, and the flank at the top moves up to half a meter. Analyzing in detail the INSAR readings revealed that the explosion occurred about 540 meters below the summit, about 2.5 kilometers north of the tunnel entrance used to access the test chamber.
Based on ground deformation, the ISRO team estimates that the explosion created a cavity with a radius of 66 meters. The yield is between 245 and 271 kilotons, compared to the 15 kilotons of the Little Boy bomb used in the 1945 Hiroshima attack.
Leading author of the study, Dr. Srijit commented: radars are very powerful tools for measuring changes in the earth's surface and allowing us to estimate the location and yield of underground nuclear tests. In conventional seismology, in contrast, estimates are indirect and dependent on the availability of seismic monitoring stations. ”
This study demonstrates the value of InSAR space data for measuring the characteristics of underground nuclear tests with greater accuracy than conventional seismic methods. Currently, although nuclear explosions are rarely observed from space due to lack of data. The team claims that currently operating satellites such as Sentinel-1 and ALOS-2, together with the NASA-ISRO Synthetic Aperture Mission (NISAR), which is scheduled to launch in 2022, can be used for this purpose.
Reference: "North Korean Nuclear Test Location, Depth, and Yield Restrictions on InSAR Measurement and Modeling 2017" by KM Sreejith, Ritesh Agrawal, and AS Rajawat, 9 October 2019, Geophysical Journal International .
doi: 10.1093 / gji / ggz451