HA08, British Indian Ocean Territory (BIOT) Chagos Archipelago, United Kingdom

HA08, British Indian Ocean Territory (BIOT)
Chagos Archipelago, United Kingdom

Thumbnail profile: BIOT/Chagos Archipelago

The British Indian Ocean Territory (BIOT) is an overseas territory belonging to the United Kingdom. Situated in the Indian Ocean about equidistant from Africa to the west and Indonesia to the East, the BIOT consists of six main island groups that are part of the Chagos Archipelago. The largest, Diego Garcia, is the site of a military facility operated jointly by the United Kingdom and the United States.


The Islands of Chagos Archipelago were discovered by Vasco da Gama in the early 16th century, then claimed by France in the 18th century as a possession of Mauritius. However, in 1810, Mauritius was captured by the United Kingdom, and France ceded the territory in the Treaty of Paris. In the late 19th century agricultural workers migrated to these islands, settling on the main island of Diego Garcia where they established copra plantations.

In 1965, the United Kingdom restructured its possessions to form the British Indian Ocean Territory (BIOT) to facilitate the construction of joint military facilities for the United Kingdom and the United States. In 1971, the UK and the US signed a treaty, leasing the island of Diego Garcia to the American military to build a large air and naval base.

Work on the military base commenced in 1971, including the construction of a large airbase with several long range runways and a harbour suitable for large naval vessels. The United States Air Force used the base during the 1991 Gulf War and the 2001 war in Afghanistan, as well as the during the Iraq War, which began in 2003.

Geography, Climate and Terrain

Diego Garcia is the most southerly island in the archipelago and the only one that is inhabited. The total area of the territory is 60 km². The terrain is flat and low, with a typical elevation of four metres. The climate is tropical marine: hot, humid and moderated by trade winds.

With the exception of one four-lane motorway, the only one of its kind in the South Indian Ocean, most of the islands in the territory have no roads of any sort and most transport is by bicycle. Diego Garcia's military base is home to the territory's only airport—one paved runway over 3,000 metres long—and only major port.



Station Location

The decision to construct the station on the island of Diego Garcia was made for several reasons: in part because of its strategic importance in the centre of the Indian Ocean; and in part due to the cooperation with the United States, which had leased the island from the United Kingdom and was operating a major military facility there.  The station is located within the US Naval support Support Facility.

HA08 is one of three International Monitoring System (IMS) hydroacoustic stations covering the Indian Ocean. Radionuclide station RN66 and infrasound station IS52 are also situated at the BIOT/Chagos Archipelago. This particular trilogy of IMS stations is also found also on another remote British overseas territory, Tristan da Cunha.

Station Profile

This pioneering hydroacoustic station, HA08, was the first of its type to be certified. The underwater segment of HA08 employs two sets of hydrophone triplets, one to the north of the island and the other to the south. Hydroacoustic data collected by the hydrophones is transmitted to an electronics bottle where it is converted to an optical signal, amplified and transmitted via a deep water trunk cable to the Shore Terminus.

The deep water trunk cable terminates onshore at a splice pit located about 30 metres from the shoreline. From there, it travels via cable to the onshore facility, where it is processed and transmitted to the US National Data Center and the International Data Centre (IDC) of the CTBTO.


Learn more about how the hydroacoustic technology works.

Build-up, Certification, Testing and Evaluation

The certification process started in November 1999 and took 13 months to complete. Build-up began in March/April 2000 with the completion of the station installation and Acceptance Testing. The station was officially placed in service by the Station Operator on 4 April 2000. In June 2000, the IMS began receiving data from the north hydrophone triplet. By September the VSAT installation was complete and the GCI link to Vienna had been established.

After extensive testing, it was agreed that the station equipment and infrastructure met the technical specifications required for an IMS hydroacoustic station. HA08 was therefore recommended for certification, which was formalized on 18 December 2000.

In total, the United Kingdom hosts one auxiliary seismic station, two hydroacoustic stations, four infrasound stations, four radionuclide stations and one radionuclide laboratory.


Learn more about the United Kingdom and the CTBT.