A mission to Tristan da Cunha: collecting data from the most remote inhabitated location on earth

The Provisional Technical Secretariat has just completed a mission to install three International Monitoring System stations on the remote island of Tristan da Cunha. Tristan da Cunha, a volcanic island situated in the South Atlantic, is a United Kingdom overseas territory, and the most remote inhabited place on earth. To reach the island, it is necessary to undertake a six day journey by ship from Cape Town, South Africa. Scheduled ship services are infrequent.

Preparations for the installation of the IMS stations began in 2001 with the first visit by PTS staff to the island to carry out site surveys. Three monitoring technologies are present on the island: infrasound, hydroacoustic and radionuclide. A follow up mission took place in 2003, with interim work being carried out by a contractor. The 2004 mission saw the installation of the stations and the establishment of a data connection to the International Data Centre in Vienna via satellite.

The island topography consists of a central volcanic peak, an elevated ring plateau, and a 700 metre wide strip of arable land some 30 metres above sea level to the north- and southwest of the island. The inhabitants of the island live in a settlement called Edinburgh on the northwest side. Arable land some five kilometres to the southwest is used to grow potatoes. A small hillock separates the settlement from the potato patches.

The 2001 site survey identified two locations for the IMS stations. The radionuclide station RN68 was built at a site just outside Edinburgh. A T phase hydroacoustic component, part of the hydroacoustic station HA09, is also located here, as is the Central Processing Facility (CPF) for all the IMS elements on the island. The CPF is built in a couple of prefabricated containers which were shipped in as part of the mission. The five elements, comprising the infrasound station IS49, and the second HA09 T phase hydroacoustic component, are located in the potato patches. As the hillock between the settlement and the potato patches blocks the transmission of radio signals, a repeater was installed on its western flank. This allows data to be relayed to the CPF, and onwards to the IDC.

Due to the remoteness of the location, the equipment was tested extensively in Vienna prior to the installation of the stations. For example, a full scale working infrasound array was set up in Vienna to test the efficiency of the station built on Tristan da Cunha. Other station adaptations included the erection of a fence to keep the island's grazing cattle from stepping on the array. Because of the scarcity of arable land on the island, it was important that the fence be erected as close to the array as possible to avoid any land wastage. The stations are now transmitting data in a steady stream to the IDC. Some islanders are assisting in operating and maintaining the stations on the island.