The Heard Island global program: Today Heard Island, tomorrow the world.

Abstract

The objective of the Heard Island global program is to develop and implement a global acoustic network for the detection of climatic variability in the ocean, using the principle that sound travels faster in warmer water. The first phase was the Heard Island feasibility test, which showed in January 1991 that m-sequence coded acoustic signals transmitted 18 000 km could easily be heard and that their travel times could be measured to a few tens of milliseconds; this is sufficient to detect potential ocean warming against background oceanic fluctuations after about ten years of monitoring. The second phase of the global program (FY92–94) will prepare for the implementation of acoustic sources and receivers at sites around the world. The preparations consist of the development and testing of improved sources and receivers, of a network design that takes into account global models of greenhouse warming and ocean response, and of working with the marine mammal research and protection communities so that the acoustic programs can also provide much-needed information on the response of marine mammals to low-frequency sounds. The third and fourth phases of the global program are the actual implementation of the acoustic network (FY94–97) and the operation of the network for at least a decade (FY95–05). The implementation will first take place in a sparse network configuration for broad ocean monitoring that is global, starting in the Atlantic, the Indian, then the Pacific Ocean, followed by implementation of higher-resolution regional (mapping) networks.