North Korea withdrew from the Treaty on the Non-Proliferation of Nuclear Weapons in 2003.
It subsequently developed nuclear weapons, with five underground nuclear tests culminating in a suspected thermonuclear explosion (a hydrogen bomb) on 3 September 2017.
Now a team of scientists, led by Dr K. M. Sreejith of the Space Applications Centre, Indian Space Research Organisation (ISRO), have used satellite data to augment measurements of tests on the ground.
The researchers find that the most recent test shifted the ground by a few metres, and estimate it to be equivalent to 17 times the size of the bomb dropped on Hiroshima in 1945.
Dr Sreejith and his team turned to space for a solution.
Using data from the ALOS-2 satellite and a technique called Synthetic Aperture Radar Interferometry (InSAR), the scientists measured the changes on the surface above the test chamber resulting from the September 2017 explosion, sited at Mount Mantap in the northeast of North Korea.