December 6, 2012
Radio Telescopes Can Detect Underground Nuclear Explosions
April Flowers for redOrbit.com - Your Universe Online
Scientists searching for rogue nukes have discovered an unlikely tool, astronomical radio telescopes.
When they demonstrated that South Korean GPS stations detected telltale atmospheric disturbances from North Korea's 2009 nuclear test, a research team from Ohio State University discovered another unlikely tool.
The discovery that underground nuclear explosions leave their mark on the outer reaches of Earth's atmosphere led to the development of both techniques.
The team has been working with astronomers at the U.S. Naval Research Laboratory (NRL) to analyze historical data from the Very Large Array (VLA), which is a constellation of 27 radio telescopes near Socorro, New Mexico. They discovered that the VLA recorded a very similar pattern of disturbances during the last two American underground nuclear tests. These tests took place in Nevada in 1992.
The new findings, presented at the December 4 meeting of the American Geophysical Union, will help to support the notion that GPS and global navigation satellite systems (GNSS) are viable tools for detecting clandestine nuclear tests around the world. Dorota Grejner-Brzezinska, professor of geodetic and geoinformation engineering at Ohio State, adds that it is a good time to begin developing the concept.
"With a global availability of permanently tracking GPS networks now extending to GNSS, tremendous amounts of information are becoming available, and the infrastructure is growing," she said. "We have a great opportunity to develop these ideas, and make a tool that will aid the global community."
Radio telescopes don't cover the entire globe the way GPS systems do. The two technologies complement each other, however, with telescopes offering higher-resolution measurements over a smaller area.
"The observations we make as radio astronomers are not so different from GPS," he said. "We may be looking up at a distant galaxy instead of down to the Earth, but either way, we're all looking at radio waves traveling through the ionosphere," said Joseph Helmboldt, a radio astronomer at NRL.
Beginning approximately 50 miles above the Earth's surface, the ionosphere is the outermost layer of the atmosphere, which contains charged particles that can interfere with radio waves and cause measurement errors in GPS and radio telescopes.
Because of this interference, both radio astronomers and geodetic scientists routinely monitor the ionosphere in order to detect these errors and compensate for them.
"We're talking about taking the error patterns–basically, the stuff we usually try to get rid of–and making something useful out of it," Grejner-Brzezinska said.
Jihye Park, a postdoctoral researcher in geodetic and geoinformation engineering at Ohio State, developed this analysis method to earn her doctoral degree. She cites key similarities and differences between the 2009 North Korean nuclear test GPS data and the 1992 American nuclear test VLA data - one on Sept. 18 named Hunters Trophy, and the other on Sept. 23, named Divider.
According to Park, the North Korean bomb is thought to have had a yield of about five kilotons. GPS data showed that the wave front of atmospheric disturbance spread outward from the test site in the village of P'unggye at approximately 540 miles per hour. In that first hour, the wave reached 11 GPS stations in South Korea, China, Japan, and Russia. The American tests, in contrast, each had a yield of 20 kilotons. The wave front from each blast covered the 700 miles from the Nevada Test Site to the VLA, reaching a top speed of approximately 1,500 miles per hour.
"Clearly, the U.S. explosions were much bigger than the North Korean explosion," Park said. "The wave fronts traveled faster, and the amplitudes were higher. There are still details missing from the North Korean test, but we can learn a lot by comparing the two events."
Park intends to continue the research at the University of Nottingham. So far, she has found that GPS stations in the North Pacific recorded ionospheric disturbances during the 2011 Japanese earthquake. Her new research will focus on how to differentiate between earthquake signals and nuclear test signals.