Overview of the hydroacoustic monitoring system for the Comprehensive Nuclear‐Test‐Ban Treaty

A global hydroacoustic monitoring system is being implemented for use in verification of the Comprehensive Nuclear‐Test‐Ban Treaty (CTBT). This system will provide hydroacoustic monitoring of all the world’s oceans for 24 h a day, every day of the year, into the indefinite future. This unique resource will utilize two types of station. One type will be based on a hydrophone at the SOFAR axis depth, cabled back to shore. The other will be based on a seismometer on a small island using detection of the T‐phase signal. This latter station relies on a signal which has propagated predominantly through the ocean, but has been converted to seismic energy at the margin of the island. This new application of hydroacoustics highlights a number of scientific questions which have not been adequately addressed. Progress in implementation of this network will be described.