CTBTO International Monitoring System

A treaty and its eyes

The Comprehensive Nuclear-Test-Ban Treaty was opened for signature on 24 September 1996, and the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization was established in Vienna on 19 November 1996. The treaty has not entered into force, because some states whose ratification is required have not ratified it, but the Commission has built the International Monitoring System (IMS) to verify it.

The planned system comprises 337 facilities: seismic stations to detect ground waves, hydroacoustic stations to listen in the oceans, infrasound stations for low-frequency sound in the air, and radionuclide stations and laboratories to detect radioactive particles and gases. More than nine tenths are built and certified.

Four technologies, one picture

Each technology covers the others. Seismic and hydroacoustic stations detect explosions on land and sea, infrasound detects explosions in the atmosphere and radionuclide sampling shows whether an event was nuclear. Data flow in real time to the International Data Centre in Vienna, which processes them and sends results to the member states.

The system detected the first nuclear test of the Democratic People's Republic of Korea in 2006, and radioactivity from its 2013 test. More than 100 stations contributed to the analysis of the 3 September 2017 test.

Beyond verification

The same data serve other uses. IMS stations recorded the radioactive plume from Fukushima in 2011 and the shock wave of the Hunga Tonga eruption in January 2022 around the globe, and the data help tsunami warning and research on the atmosphere and the Earth. Lassina Zerbo was Executive Secretary from 2013 and Robert Floyd succeeded him in 2021.

A network of trust

The system exists because states needed to trust data produced by instruments on each other's territory. That trust is built by certification of the stations, by authentication of the data from sensor to centre, and by giving every state access to the same data at the same time. The network is expensive to run, and its reliability requirement is high: stations must send data at least 98 per cent of the time. The experience shows how an observation system can be designed for adversaries as well as for scientists, with signing, redundancy and independent verification as basic requirements.

Instruments and technologies

• Primary and auxiliary seismic stations Arrays and three-component stations whose records are sent in real time.
• Infrasound arrays Clusters of microbarometers with wind-noise reducers, measuring sound below 20 hertz.
• Radionuclide stations Air samplers collect particles on filters that are measured by gamma spectrometers, and noble-gas systems detect xenon isotopes.

The people

• Lassina Zerbo Executive Secretary from 2013 to 2021.
• Robert Floyd Executive Secretary since 2021.

Timeline

• 1996 Treaty opens for signature on 24 September; Preparatory Commission established on 19 November.
• 2006 Detects the first DPRK nuclear test.
• 2013 Detects radioactivity attributable to the DPRK test, the only organisation to do so.
• 2017 More than 100 stations contribute to analysis of the 3 September DPRK test.
• 2021 Robert Floyd succeeds Lassina Zerbo as Executive Secretary.

Key lessons for observation today

• Several technologies cross-check each other A seismic event with no radionuclide signature tells a different story from one with. Diverse sensing is a verification method.
• Certify the stations, then trust the data Stations pass tests before joining. Certification is what lets a state trust data from another's soil.
• A network built for one purpose serves others The system tracks volcanoes, tsunamis and radioactive releases as well. Open interfaces allow civil use of verification data.

Sources

• CTBTO, International Monitoring System
• CTBTO, CTBT verification brochure (2024)
• CTBTO, Robert Floyd takes office as CTBTO Executive Secretary
• Wikipedia, Preparatory Commission for the CTBTO (secondary)