North Korea withdrew from the Nuclear Non-Proliferation Treaty in 2003. It later developed nuclear weapons, with five underground nuclear tests culminating in a suspected thermonuclear explosion (a hydrogen bomb) on September 3, 2017. Now , a team of scientists, led by Dr. KM Sreejith of the Space Applications Center of the Indian Space Research Organization (ISRO), used satellite data to increase ground test measurements. The researchers found that the latest test changed the ground by a few meters and estimated it to be 17 times the size of the bomb dropped on Hiroshima in 1945. The new work appears in an article in the Geophysical Journal International, a publication of the Royal Astronomical Society. .
Conventional detection of nuclear tests relies on seismic measurements using deployed networks to monitor earthquakes. But seismic data is not openly available from stations near this test site, which means there is great uncertainty in identifying the location and size of nuclear explosions that occur there.
Dr. Sreejith and his team sought the space for a solution. Using data from the ALOS-2 satellite and a technique called Synthetic Aperture Radar Interferometry (InSAR), the scientists measured changes in the surface above the test chamber resulting from the September 2017 explosion at Mount Mantap in northeastern Korea. From north. InSAR uses multiple radar images to create deformation maps over time and allows direct study of space surface processes.
The new data suggest that the blast was powerful enough to displace the mountain surface above the blast point by a few meters, and the peak's flank moved up to half a meter. Detailed analysis of the InSAR readings reveals 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 soil deformation, the ISRO team predicts that the explosion created a cavity with a radius of 66 meters. It had a yield of between 245 and 271 kilotonnes, compared to the 15 kilotonnes of the & # 39; Little Boy & # 39; used in the attack on Hiroshima in 1945.
The lead author of the study, Dr. Sreejith, commented: “Satellite-based radars are very powerful tools for measuring changes on the earth's surface and allow you to estimate the location and yield of underground nuclear tests. In conventional seismology, on the other hand, estimates are indirect and depend on the availability of seismic monitoring stations. "
The present study demonstrates the value of InSAR data in space for measuring the characteristics of underground nuclear tests, with greater accuracy than conventional seismic methods. At the moment, nuclear explosions are rarely monitored from space due to lack of data. The team argues that satellites currently in operation such as Sentinel-1 and ALOS-2, along with the NASA-ISRO Synthetic Aperture Radar (NISAR) mission, launched in 2022, could be used for this purpose.
Reference: ”Restrictions on Location, Depth, and Yield of the North Korean Nuclear Test of InSAR September 3, 2017 of InSAR Measurements and Modeling” by K M Sreejith, Ritesh Agrawal and AS Rajawat, October 9, 2019, Geophysical Journal International.
DOI: 10,1093 / gji / ggz451