Scientists Would Tell of a NKorea Nuclear Test

Earthquake monitors, sound wave detectors and sensors on planes that pick up airborne traces of atomic material are all ways that global scientists will know within minutes if North Korea conducts a nuclear test.

The ability of global scientists to detect such events has improved since the hermit state's last two nuclear tests in 2006 and 2009. Scientists today, for example, have a larger network of worldwide seismology stations and more sensitive instruments, experts say.

Here are some of the top methods scientists will use:

EARTHQUAKE DETECTION: Seismic monitoring is the most effective and quickest way to detect a nuclear test. Seismic waves travel about five miles per second.

The closest monitoring stations are in Japan and South Korea.

The number of certified international monitoring stations grew from three in October 2000 to 264 in February of 2011, bring the global network to near 90 percent completion, according to the U.S. National Research Council (NRC).

Regional monitors can sense an explosion as small as 20 tons or 0.020 kilotons explosive yield.

The 2006 North Korea explosion was detected at a magnitude 4.1 and was believed to be less than one kiloton explosive yield; while the 2009 test registered 4.5 and was believed to be a few kilotons.

RADIONUCLIDE SIGNALS

This extremely sensitive technique allows scientists to use instruments that "sniff" fission products of the explosive material that have seeped out of the ground or been released in the air.

Then, scientists can use atmospheric transport modeling (ATM) to calculate the likely origin of the radionuclides and predict where the nuclear plume may be headed.

The process is typically used as a secondary confirmation day after the event to show the test was indeed nuclear and not a large chemical explosion.

As of mid-2010, there were 80 international monitoring stations where radionuclides could be measured.

INFRASOUND DETECTORS and HYDROACOUSTIC TECHNOLOGY:

Undetectable to the human ear, infrasound waves have frequencies between 0.01 and 10 Hz. They are typically produced by explosions in the atmosphere but can also come from underground explosions.

There were 43 such stations globally in 2011, up from one in 2000, allowing for detection across 80 percent of the Earth's surface, according to the NRC.

A very small infrasound signal was detected following the 2009 North Korea test, but none in 2006.

Hydroacoustic technology can be used to detect nuclear explosions in or near bodies of water by tracking sound waves that travel in the water column.

Global monitors can detect an in-water explosion as small as one ton (0.001 kiloton) across most of the world's oceans. There were 11 hydroacoustic stations worldwide in 2010.

U.S. PLANES, SATELLITES

The U.S. Air Force was first tasked in 1947 with monitoring atomic explosions worldwide, and today employs nearly 1,000 Department of Defense personnel at its Air Force Technical Applications Center (AFTAC) for that job.

AFTAC operates a WC-135 aircraft for detecting radioactive debris that could come from nuclear explosions. The plane flies to the location of the debris plume and collects particulates for lab analysis.

The U.S. also uses satellites to detect potential nuclear explosions in space or in the atmosphere -- a capacity that is not part the Comprehensive Test Ban Treaty Organization (CTBTO) international monitoring system.

Satellites can collect data on electromagnetic pulses, optical flashes and nuclear radiation.

U.S. monitoring capacity is bolstered by the Department of Energy, Department of Defense, and U.S. Geological Survey.

TOP CONFIRMING AUTHORITIES

The Comprehensive Test Ban Treaty Organization is the leading authority for providing data on detected events, but is not responsible for identifying whether a seismic event is a nuclear explosion, earthquake or chemical blast.

That inherently political responsibility tends to lie with individual countries, particularly those with leading nuclear test detection skills such as Russia, Japan, South Korea and the United States.

The International Atomic Energy Agency in Vienna, Austria, is the top authority when it comes to verifying North Korea's nuclear program, but Pyongyang has not granted access to its U.N. inspectors.