Sensor Network Detects Nuclear Blasts Worldwide

WASHINGTON, July 12, 2011 — At any time of the day or night, on any day of the year, if a nuclear device explodes any­where on Earth, a Defense Depart­ment net­work estab­lished in 1947 will know about it.

Air Force's WC-135 Constant Phoenix aircraft
The Air Force’s WC-135 Con­stant Phoenix air­craft col­lects air sam­ples from areas around the world where nuclear explo­sions have occurred.
U.S. Air Force pho­to
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That was the year Army Gen. Dwight D. Eisen­how­er direct­ed the Army Air Corps to devel­op such a capa­bil­i­ty, and the U.S. Atom­ic Ener­gy Detec­tion Sys­tem has evolved over 64 years into a one-of-a-kind glob­al web of sen­sors that see, feel, hear and sniff out nuclear explo­sions that occur under land or sea, in the atmos­phere or in space.

The Air Force detec­tion sys­tem and the job of mon­i­tor­ing three nuclear treaties — the 1963 Lim­it­ed Test Ban Treaty, the 1974 Thresh­old Test Ban Treaty and the 1976 Peace­ful Nuclear Explo­sions Treaty — in 1980 became a respon­si­bil­i­ty of the U.S. Air Force Tech­ni­cal Appli­ca­tions Cen­ter, called AFTAC, at Patrick Air Force Base, Fla.

When the sys­tem detects a nuclear event, AFTAC sci­en­tists ana­lyze it and report find­ings to nation­al com­mand author­i­ties through U.S. Air Force head­quar­ters.

David O’Brien is AFTAC’s chief sci­en­tist.

“Our respon­si­bil­i­ty is to ensure that for­eign nations are adher­ing to the pro­vi­sions of those treaties,” O’Brien told Amer­i­can Forces Press Ser­vice.

To mon­i­tor the atmos­phere and space, he said, the U.S. Atom­ic Ener­gy Detec­tion Sys­tem, called USAEDS, has sen­sors aboard more than 20 satel­lites that make up the Glob­al Posi­tion­ing Sys­tem and the infrared-sens­ing satel­lites that make up the Defense Sup­port Pro­gram.

“The lat­ter,” O’Brien said, “are what the Unit­ed States uses to detect launch­es of inter­con­ti­nen­tal bal­lis­tic mis­siles.”

Mul­ti­ple sen­sors on all those satel­lites “look for phe­nom­e­nol­o­gy from a nuclear explo­sion that occurs in space or in the atmos­phere,” he added, “whether it’s nuclear radi­a­tion or the flash from the fire­ball.”

The network’s five hydroa­coustic sta­tions detect under­sea nuclear explo­sions.

“Those are just under­wa­ter micro­phones, and they lis­ten for the explo­sion that goes off under­wa­ter,” the sci­en­tist said. “By detect­ing the explo­sions on more than one under­wa­ter micro­phone, we can tri­an­gu­late where it occurred.”

But the work­horse since the treaties came into effect to ban atmos­pher­ic nuclear test­ing, O’Brien said, has been the under­ground nuclear mon­i­tor­ing capa­bil­i­ty.

“Those sen­sors are seis­mic, and the rea­son they’re seis­mic is that when a large explo­sion occurs under­ground, it cre­ates a sig­na­ture that looks just like an earth­quake,” he said.

Infra­sound sen­sors mea­sure changes in the atmos­phere gen­er­at­ed by very-low-fre­quen­cy acoustic waves that can come from above-ground nuclear explo­sions.

USAEDS still sup­ple­ments some of its 40 seis­mic sta­tions with infra­sound, the sci­en­tist said, and in the 1960s used infra­sound as the main way to detect nuclear explo­sions in the atmos­phere.

“But once we were able to get sen­sors on satel­lites,” he said, “that gave us a much bet­ter capa­bil­i­ty.”

When the pro­gram first began, its only sen­sor, an air sam­pler, flew on a B-29 air­craft over the Pacif­ic Ocean. In 1949, fly­ing between Alas­ka and Japan, the sam­pler detect­ed debris from the first Russ­ian atom­ic test.

Today the sys­tem uses anoth­er air­craft, a WC-135 in a pro­gram called Con­stant Phoenix to col­lect air sam­ples from areas where nuclear explo­sions have occurred.

If there is a nuclear explo­sion, O’Brien said, “we will [use mete­o­rol­o­gy] to project where radioac­tive debris would go. Then when it gets into inter­na­tion­al air­space, the air­craft can go to that spot.”

The plane col­lects par­ti­cles so ana­lysts on the ground can test them to see if they con­tain radionu­clides, or radioac­tive ele­ments.

The plane also col­lects radioac­tive gas­es, espe­cial­ly radioac­tive xenon, which is a good indi­ca­tor that a nuclear explo­sion has occurred.

With all these sen­sors, the U.S. Atom­ic Ener­gy Nuclear Detec­tion Sys­tem is the only net­work that oper­ates 24 hours a day, sev­en days a week, but it isn’t the only glob­al detec­tion sys­tem.

In 1996, the Unit­ed Nations Gen­er­al Assem­bly adopt­ed the pro­vi­sions of the Com­pre­hen­sive Nuclear Test Ban Treaty. One major pro­vi­sion pro­hib­it­ed nuclear explo­sions any­where, by any­one.

Anoth­er pro­vi­sion described a 337-facil­i­ty Inter­na­tion­al Mon­i­tor­ing Sys­tem that would scan the earth for nuclear treaty vio­la­tions. The IMS facil­i­ties include seis­mic, hydroa­coustic, infra­sound and radionu­clide sta­tions, but no satel­lite sen­sors.

Most of the world’s coun­tries have signed and rat­i­fied the treaty. Three coun­tries that have not signed the treaty have since test­ed nuclear devices — India and Pak­istan in 1998 and North Korea in 2006.

The treaty has not yet entered into force — sev­er­al more coun­tries must rat­i­fy the treaty before that hap­pens. Until it does enter into force, some of the IMS mon­i­tor­ing sta­tions oper­ate 24 hours a day, but many do not.

The Unit­ed States has signed, but not yet rat­i­fied, the treaty, and it has helped devel­op the Inter­na­tion­al Mon­i­tor­ing Sys­tem, O’Brien said.

The IMS archi­tects “were start­ing from scratch in the mid-1990s, and we had many years of expe­ri­ence in these kinds of sys­tems,” he said.

“So they came to us ask­ing for any advice that would help them avoid the pit­falls of putting a new sys­tem in,” the sci­en­tist added.

The experts at USAEDS advised the mon­i­tor­ing sys­tem builders on world­wide logis­tics involved in estab­lish­ing such a sys­tem and onsite instal­la­tions.

USAEDS con­tributes the data from many of its seis­mic and hydroa­coustic sta­tions to the Inter­na­tion­al Mon­i­tor­ing Sys­tem.

“Out­side of the USAEDS,” O’Brien said, “the Unit­ed States through the Office of the Sec­re­tary of Defense con­tributes seis­mic, infra­sound and radionu­clide sta­tions to the IMS.”

As a sig­na­to­ry to the Com­pre­hen­sive Nuclear Test Ban Treaty, the Unit­ed States is enti­tled to and receives all the data that the Inter­na­tion­al Mon­i­tor­ing Sys­tem pro­duces.

“We par­tic­i­pate in all their inter­na­tion­al meet­ings, and we have since [the system’s] incep­tion. They occa­sion­al­ly come here and vis­it,” O’Brien said. “I think both the IMS and our­selves are right at the state of the art of any tech­nol­o­gy that is prac­ti­cal for use in detect­ing nuclear explo­sions.”

U.S. Depart­ment of Defense
Office of the Assis­tant Sec­re­tary of Defense (Pub­lic Affairs)

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