Network
To establish an acoustic thermometry network in the Indian Ocean requires consideration of potential source and receiver sites. A number of options have been examined, and a site for an acoustic source that offers excellent, nearly complete coverage of the basin is Cocos Island. It has the usual advantages of an island of volcanic origin. It is small in aerial extent, and therefore casts a small acoustic shadow. It is steep sided, so cable run to power an underwater acoustic source is short.
The Pacific Ocean has a number of SOSUS arrays that have been made available for research purposes under the US Government's dual use initiative. The Indian Ocean has no such network, so in order to establish an acoustic thermometry network, alternate receivers are needed. Development of inexpensive receivers is proceeding at several research institutes in the US and Europe, but they are still at the prototype stage.
The fact that the PTS of the Comprehensive Nuclear Test Ban Treaty Organisation is establishing three new hydroacoustic monitoring stations in the Indian Ocean is fortuitous. Crozet Is. in the southwestern Indian Ocean, British Indian Ocean Territory/Diego Garcia in the northern region and Cape Leeuwin/Western Australia in southeastern region comprise the three CTBT monitoring sites. If dual use of these facilities proves possible, the installation of a single source will form the skeleton of an acoustic thermometry network that can be enhanced by simple receivers as the reach maturity.
Acoustic Coverage
Shadow plots of acoustic coverage of the Indian Ocean show partial blockage by bathymetric features in the northwestern and to a lesser extent, to the west and southwest. Coverage is good however, for the northern and eastern regions that exhibit the capacity to profoundly influence the climate of substantial parts of Asia and Australia.
Evidence of commitment to establishing an Indian Ocean acoustic thermometry network comes from the US, who are prepared to provide a low frequency source ATOC. Telstra (Australia) has offered to supply sufficient underwater cable to connect the source to shore power, and CSIRO (Australia) is funding a site survey at Cocos Island in October '99 using the research vessel Franklin.
References:
The ATOC Consortium, 1998, Ocean Climate Change: Comparison of Acoustic Tomography, Satellite Altimetry, and Modeling, Science, 281, pp. 1327-1332
