An international team of security experts — from the Max Planck Institute for Security and Privacy (MPI-SP) in Bochum, Ruhr University Bochum, the School of Public and International Affairs at Princeton University, the University of Connecticut, Harvard University, PHYSEC GmbH and Technische Universität Berlin — have created an approach using radio waves to remotely detect if changes are being made in a particular room.

Inspired by a scenario wherein State A wants to ensure that no changes have been made to State B's nuclear weapons stockpile, but without having to perform permanent on-site monitoring, the new system is designed to detect when and if a stored nuclear warhead is removed from its stockpile and prepared for deployment.

Source: RUB, MarquardSource: RUB, Marquard

The researchers explain that the system uses two antennas to record a radio fingerprint of the room, with one antenna emitting a radio signal that is reflected off the walls and objects within the room while the other antenna records the signal.

In the event that one of the objects in the room was moved even slightly, the radio fingerprint would be distinctly altered. As such, significant changes — such as the removal of a stored nuclear warhead — are thus detectable.

To further ensure its systems works, so that State B measures the radio fingerprint at the exact same time when state A requests it, and without State B sending a recording of the radio fingerprint and not its real-time signal, the team proposes installing 20 rotating mirrors in the room under surveillance. The researchers explain that if the position of the mirrors changes, the radio fingerprint will subsequently change. As such, State A could possibly record the radio fingerprints for assorted mirror positions during an on-site visit, storing them in a secret database.

If the radio fingerprint for a specific mirror position does not match a position stored in the secret database, State A, requesting the radio fingerprint for a specific mirror position from State B, could determine that changes have occurred in the room.

"Seventy percent of the world nuclear weapons are kept in storage for military reserve or awaiting dismantlement,” the researchers explained. "The presence and number of such weapons at any given site cannot be verified easily via satellite imagery or other means that are unable to see into the storage vaults. Because of the difficulties to monitor them, these 9,000 nuclear weapons are not accounted for under existing nuclear arms control agreements. This new verification technology addresses this long-standing challenge and contributes to future diplomatic efforts that would seek to limit all nuclear weapon types."

To determine the effectiveness of the approach, the researchers set up a container featuring movable barrels, which they monitored using radio wave technology. With this setup, the team determined that the radio fingerprints were reproducible and distinguishable for various mirror settings. Further, when the team moved one of the barrels in the container — even just a few millimeters — it was reflected in the radio fingerprint.

An article detailing the approach, Remote inspection of adversary-controlled environments, appears in the journal Nature Communications.

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