IS24 infrasound station
(Tahiti-French Polynesia) of the CTBTO (Comprehensive Test-Ban Treaty Organization)

The IS24 infrasound station is part of the infrasound network of the CTBTO (Comprehensive Nuclear Test-Ban Organization) international monitoring system that includes 60 infrasound stations and 170 seismic stations. One of these stations is located in Tahiti (French Polynesia), next to the LDG/Pamatai laboratory (PS18-PPT station).

The IS24 station is located on the island of Tahiti, 20 km south east of Papeete, in the Taravao district.

With its central location, this station monitors the entire Pacific Ocean.
It also detects numerous natural phenomena that produce sound waves. These include the huge swells in the South Pacific, storms around Tahiti and meteors that enter the atmosphere above the Pacific Ocean.

click to enlarge the image
Map of IS24 station location.

The IS24 station includes five sub-elements (i.e. five sensors), three located in a triangle with a basis of 2 km, the fourth at the center of the triangle, and the fifth further to the east. This configuration enables calculation of the speed and direction of infrasonic waves. In addition, the infrasound stations are equipped with meteorological sensors that measure wind speed and direction, atmospheric pressure and temperature. These various local parameters are taken into account during data processing.

click to enlarge the image
Overview of facility no. 3.

The site hosting the station was chosen on completion of a survey conducted in March 1998. The station was set up in March 2000 and certified by the CTBTO in August 2002.
Facility infrastructure includes:
click here to enlarge the image
Inside the measuring vault of an IS24 station sub-element.

A cave containing an MB-2000 microbarometer a digitization unit and a transmission unit.

An antenna secured to a tower.

A solar power supply.

A set of 32 inlet ports, pipes of 8 m length, entirely covered with gravel.

Filtering system (20m/20m) of an IS24 station facility.

Infrasound station equipment.

Layout of an infrasound station facility.
Data signals from the microbarometers are recorded at a sampling rate of 20 samples per second. Meteorological data (wind speed and direction, temperature) are also recorded at one facility.

click to enlarge the image

click to enlarge the image
A room at the IS24 station's central facility.
Signals are transmitted continuously by radio-modem to the central facility where they are recorded. A modem transmits signals via a dedicated telephone line to LDG/Pamatai (Geophysics Laboratory). They are then sent by modem to the French National Data Center of the DASE, and to the CTBTO (Comprehensive Test-Ban Treaty Organization) International Data Center in Vienna.