North Korea resigned from the Non-Proliferation Treaty in 2003. Subsequently, nuclear weapons were developed, with five subterranean nuclear tests culminating in a suspected thermonuclear explosion (a hydrogen bomb) on November 3, 2017. Now, a team of scientists led by Drs. KM Sreejith of the Space Applications Center of the Indian Space Research Organization (ISRO) uses satellite data to improve ground test measurements. The researchers found that the latest test shifted the ground a few feet, 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.
The conventional detection of nuclear tests relies on seismic measurements using the networks used to monitor earthquakes. However, there are no publicly available seismic data from stations near this particular test site, which means that there are great uncertainties as to where and how large the nuclear explosions are.
Dr. Sreejith and his team were looking for a solution. Using data from the ALOS-2 satellite and a technique called Synthetic Aperture Radar Interferometry (InSAR), the scientists measured surface changes above the test chamber resulting from the September 2017 blast on Mount Mantap in northeastern North Korea. InSAR uses multiple radar images to create strain maps over time, allowing for direct in-surface processes to be studied from outer space.
The new data suggest that the explosion was strong enough to move the surface of the mountain beyond the detonation point by several meters, and the summit's flank moved by up to half a meter. A detailed analysis of the InSAR values revealed that the explosion occurred about 540 meters below the summit, about 2.5 kilometers north of the tunnel entrance to the test chamber.
Due to the deformation of the ground, the ISRO team believed that an explosion predicted that the blast created a 66-meter radius. It had a yield between 245 and 271 kilotons, compared to the 15 kilo tonnes of the bomb Little Little, which was used in 1945 in the attack on Hiroshima.
The lead author of the study, dr. Sreejith commented, "Satellite-based radars are powerful tools to measure changes in the earth's surface and to estimate the position and yield of subsurface nuclear tests. In contrast, estimates in conventional seismology are indirect and depend on the availability of seismic monitoring stations. "
This study demonstrates the value of space-based InSAR data for the measurement of subterranean core properties with greater accuracy than conventional seismic methods. Currently, nuclear explosions are rarely observed from space due to lack of data. The team argues that satellites such as Sentinel-1 and ALOS-2, along with the NASA ISRO NISAR (Synthetic Aperture Radar) mission to be launched in 2022, could be used for this purpose.
Location, Depth and Yield of North Korean Nuclear Test from September 3, 2017 from InSAR Measurements and Models "by KM Sreejith, Ritesh Agrawal and AS Rajawat, October 9, 2019, Geophysical Journal International .
DOI: 10.1093 / gji / ggz451