SEOUL • Global concerns over North Korea's latest nuclear test and long-range rocket launch have shone a spotlight on the perennial, high-tech game of hide-and-seek played around Pyongyang's advanced weapons programmes.

On the seeking side are analysts using high-resolution images from a circling constellation of commercial satellites to pick up whatever data they can on the North's fast-developing nuclear and ballistic missile capabilities. It is a challenging task as the number of clues to work with is being diminished by an increasingly effective North Korean concealment programme.

Satellite imaging has been around for decades, but was almost exclusively for government and military use. It was only at the start of the 21st century that high-resolution commercial images became publicly available.

For civilian North Korea watchers, the aerial snapshots provided by organisations such as DigitalGlobe and Airbus DS opened an entirely new window onto one of the most closed regions in the world. Two of the main monitoring targets are the Punggye-ri nuclear test site in the north-east and the Sohae satellite launch complex in the north-west.

Effective analysis requires high- level expertise in areas like nuclear fuel cycles and advanced weapons systems. But the key raw materials are images and the North has become far more adept at hiding its activities from satellite lenses.

One tactic is to work at night or on cloudy, rainy days, limiting what is visible to commercial imaging satellites. North Korean scientists have also covered, screened or moved underground structures at sensitive sites. At the Sohae site, a rocket can be brought in, assembled and erected on the launch pad without being directly caught on camera.

AGENCE FRANCE-PRESSE