Global Ocean Acoustic Monitoring and the CTBT
Martin W. Lawrence (Comprehensive Nuclear-Test-Ban Treaty Organization, Vienna International Centre, A- 1400 Vienna, Austria)
e-mail: martin.lawrence@ctbto.org
ABSTRACT
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) to ban all nuclear explosion tests was opened for signature in 1996. Verification of compliance with the CTBT requires establishment of a global network of sensors to detect, locate and identify the signal generated by a nuclear explosion in any environment. Monitoring of the world's oceans is primarily provided by a hydroacoustic network to be established for this purpose. Implementation of the monitoring networks began with establishment of the CTBTO Provisional Technical Secretariat (PTS) in Vienna in March 1997, although a critical mass of staff were not in place until late 1997.
The hydroacoustic network is based upon 11 stations that will provide hydroacoustic monitoring of the world's oceans for 24 hours a day, every day of the year, into the indefinite future. This unique resource will utilise two types of hydroacoustic stations: hydrophone and T-phase. A hydrophone station is based on an ocean-deployed hydrophone sensor working at the frequency range from 1 Hz to 100 Hz. The hydrophone sensor elements are at a fixed depth near the axis of the SOFAR channel, floated from an ocean-bottom anchor and cabled back to shore. A T-phase station is based on an island-deployed seismometer sensor. Each T-phase station is sited near the shore of a small island with steep bathymetry. It relies on the detection of a signal that has propagated predominantly through the ocean, but has been converted to seismic energy at the margin of the island.
Most hydroacoustic stations identified in the Treaty require a new station to be built. However, some statlons existed prior to the Treaty, but need upgrading. Work has began on site surveys and installations at some stations.
INTRODUCTION
The CTBT prohibits any nuclear weapon test explosion or any other nuclear explosion anywhere in the world. Drafted at the Conference on Disarmament in Geneva, the Treaty was adopted by the General Assembly on 10 September 1996. It was opened for signature on 24 September 1996 at United Nations Headquarters, and as of early 1999 there have been 152 signatures. To ensure compliance with the CTBT's ban on nuclear explosions, a global network of seismic, hydroacoustic, infrasonic and radionuclide sensors is being deployed. This global network is known as the International Monitoring System (IMS). It has been designed to be capable of detecting, locating and identifying signals from nuclear explosions of at least 1 kiloton.
Monitoring CTBT compliance is more challenging than prior nuclear test treaties because it requires high confidence identification of any nuclear explosion in all possible environments; the atmosphere, underwater, underground or in space. Therefore, a reliable IMS network has been designed, agreed and annexed to the Treaty text for signature.
