Research Highlights

N Korea’s underground nuke explosion 17 times bigger than Hiroshima

Eye in space detects blasts better than ear to the ground, scientists say.

doi:10.1038/nindia.2019.154 Published online 18 November 2019

Scientists at the Indian Space Research Organization (ISRO) estimate that an underground nuclear test carried out by North Korea in 2017 may have been 17 times bigger in its explosive strength than the bomb dropped on Hiroshima during the Second World War in 19451.

Reporting the precise range of North Korea’s largest affirmed nuclear test, they say its explosive yield was 245–271 kiloton (kt) of TNT as compared to the Hiroshima bomb’s 15 kt.

Previous yield estimations of this explosion were in the range of 70 to 400 kt. The ISRO scientists bettered the tracking through a space-based method using satellite radar data. They contend that having an eye in the space is better than relying on the conventional ‘hearing’ through a network of earthquake-measuring seismometers deployed on the ground to detect such explosions.

Underground blasts may escape notice if no seismic monitoring stations are available near the test site or if the seismic data is not openly available. Earth observation satellites such as the Sentinel-1, of the European Space Agency, and the Japanese ALOS-2, carry advanced synthetic aperture radars (SARs) that can provide data to map changing land cover and ground deformation, their report says.

Using data from the ALOS-2 satellite and a technique called Synthetic Aperture Radar Interferometry (InSAR), the ISRO team led by Sreejith Kattumadam at the Ahmedabad-based Space Applications Centre in Gujarat, India tracked changes over ground after the underground explosion on 3 September 2017. The test chamber was located on Mount Mantap in the northeast of North Korea.

After careful analysis of data, they now suggest that the explosion was 17 times the size of the bomb dropped on Hiroshima in 1945 and powerful enough to shift the surface above the detonation point by a few metres. The scientists also determined the depth of the nuclear source at 542 ± 30 m below Mt. Mantap. Their study demonstrates the value of space-borne InSAR data for measurement of the characteristics of underground nuclear tests with greater precision.

Though nuclear explosions are rarely monitored from space at present, the authors argue that satellites Sentinel-1 and ALOS-2, along with the NASA-ISRO Synthetic Aperture Radar (NISAR) mission to be launched in 2022, could be used for this purpose.


References

1. K. M. Sreejith, et al. Constraints on the location, depth and yield of the 2017 September 3 North Korean nuclear test from InSAR measurements and modelling. Geophys. J. Int. 220,  345–351 (2020) DOI: 10.1093/gji/ggz451