Hydroacoustic monitoring system for the Comprehensive Nuclear-Test-Ban Treaty

The first ever fully global hydroacoustic monitoring system is being planned and implemented for use in verification of a new international treaty, the Comprehensive Nuclear Test Ban Treaty (CTBT). The system is based upon a network of eleven 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 station: hydrophone and T-phase. A hydrophone station is based on an ocean-deployed hydrophone sensor at the SOFAR axis and cabled back to shore. A T-phase station is based on an island-deployed seismometer sensor. 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. Of the eleven hydroacoustic stations, two hydrophone stations and one T-phase station existed prior to the treaty. All the other stations will be installed over the next few years and upgrading action will be taken at the existing sites.