CTBTO completes Hydroacoustic Part of the International Monitoring System


Vienna, 20 June 2017

French version here.

The eleventh and final hydroacoustic station in the International Monitoring System (IMS) was certified on 19 June 2017, completing the hydroacoustic part of the network which monitors the globe 24/7 for signs of nuclear explosions under the Comprehensive Nuclear-Test-Ban Treaty (CTBT). One of the CTBTO’s longest running and most complicated engineering endeavours, hydroacoustic station HA04 was installed in Crozet Islands (France) in December 2016 after nearly 20 years of overcoming a number of challenges and hurdles.
CTBTO Executive Secretary Lassina Zerbo said: “This is a momentous occasion not only for the CTBTO, but for the international community. The completion of the hydroacoustic portion of the IMS brings us one step closer to achieving full and increasingly sensitive coverage of the globe, and thus closer to making the planet safer and more secure from nuclear testing.”

Once completed, the IMS will comprise of 337 monitoring facilities worldwide. Currently, the system is around 90% complete. HA04 is one of eleven hydroacoustic stations monitoring the oceans for signs of nuclear explosions. Low frequency underwater sound, which can be produced by a nuclear test, propagates very efficiently through water. Consequently these underwater sounds can be detected at great distances, sometimes thousands of kilometres, from their source. This means that the IMS requires only a few hydroacoustic stations to provide effective monitoring of all the world’s oceans for signs of nuclear explosions.

To monitor underwater sounds deep in the ocean HA04 uses six hydrophones (underwater microphones) configured in two sets of “triplets”, one to the North and one to the South of Possession Island. The station’s hydrophones transmit their data via underwater cables, which are around 50 kilometres in length, to a receiving facility — the Central Recording Facility (CRF) – on the island. From there, the data is forwarded via satellite link to the CTBTO in Vienna where it is received by the International Data Centre (IDC), analysed and shared with Member States.

Various aspects of the installation and certification of HA04 will be presented at the upcoming Science and Technology 2017 Conference (SnT2017), in Vienna, Austria (26–30 June 2017). For more, please see /news-and-events/science-and-technology-conference

A film detailing the installation of HA04 is being finalized. A preview is available here

B-roll footage and high resolution stills are also available.


The CTBT bans all nuclear explosions, thus hampering both the initial development of nuclear weapons as well as significant enhancements. The Treaty also helps prevent harmful radioactive releases from nuclear testing.

The CTBT has so far been signed by 183 States and ratified by 166 (map). However its demanding entry-into-force provision requires 44 particular “nuclear technology holder” States to ratify the Treaty for it to enter into force. Eight of them have yet to ratify: China, the Democratic People's Republic of Korea (DPRK), Egypt, India, Iran, Israel, Pakistan, and the United States (China, Egypt, Iran, Israel, and the United States have already signed the Treaty).

A verification regime to monitor the globe for nuclear explosions is nearing completion with around 90 percent of the 337 planned International Monitoring System (IMS) facilities already in operation. The system has proved its capabilities to detect even small nuclear tests during the announced DPRK nuclear tests in 2006, 2009, 2013 and 2016.

The data from the IMS facilities are also used by the wider scientific community to study a range of unrelated issues, from climate change to marine mammal migration, and contribute to disaster risk reduction, such as tsunami early warning systems and monitoring volcanic activity.

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Elisabeth Wächter,
Chief of Public Information
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