Infrasound monitoring in the Vestfold Hills

Figure 1. Location of the IS03 site (array of green circles around the square) and the cable runs (blue lines) back to Davis.
Figure 1. Location of the IS03 site (array of green circles around the square) and the cable runs (blue lines) back to Davis. (Photo: Geoscience Australia & Australian Antarctic Division)
Schematic of a typical array site showing the vault (square box) and rosettes which detect the infrasound.  An array vault box installed on site.Expeditioners hauling one of the power cables up a steep section of the Vestfold Hills.   The Central Power Distribution Facility (CPDF) with the high voltage transformer to the left.

The first stage of a facility to monitor nuclear explosions in the atmosphere was constructed in the Vestfold Hills, some five kilometres from Davis, this Antarctic summer.

The ‘infrasound monitoring facility’ (IS03) is being installed by the Australian Antarctic Division in conjunction with Geoscience Australia, to meet Australia’s obligations under the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The facility will form part of an International Monitoring System (IMS) of 337 facilities around the world, to verify compliance to the Treaty. Twenty one facilities will be in Australia, including the Australian Antarctic Territory.

International Monitoring System

The IMS network has been designed for detection threshold capability of approximately 1kt TNT-equivalent. To fulfil the global detection capability objective of the Treaty, infrasound facility IS03 has been specifically located near Davis to contribute to coverage of the eastern Antarctic, Southern Ocean and southern Indian Ocean regions.

As part of the IMS, Australia also has radionuclide detection facilities at Mawson (Australian Antarctic Magazine 31: 23, 2016) and Macquarie Island, and a CTBT seismic facility at Mawson, all supported by the Antarctic Division’s Engineering Branch.

Infrasound monitoring is an important technology for detecting and locating nuclear explosions in the atmosphere. The attenuation of sound waves in the atmosphere is frequency dependent and infrasound signals (0.001–20 Hz) can propagate over large distances, reaching altitudes in the atmosphere of more than 100 km.

The usefulness of infrasound data is also much broader than the study of explosive sources for CTBT verification. Infrasound data is also used in detecting and characterising a range of natural phenomena, including:

  • atmospheric disturbances such as auroras, thunderstorms, tornadoes, bolides (very bright meteors), upper-atmospheric lightning and volcanic eruptions;
  • earth-atmosphere coupled disturbances including earthquakes, volcanic activity, avalanches; and
  • ocean-atmosphere coupled signals from phenomena including tsunamis, ocean swells, and iceberg calving.

Data from Australian IMS facilities is available to the broader research community.

Infrasound facility

The infrasound facility at Davis (Figure 1 above) will be a seven element monitoring array (typical array shown in Figure 2) designed to detect atmospheric disturbances at infrasound frequencies. The seven sensing nodes of the array will be situated in the Vestfold Hills and cover an area approximately 0.5 km². Three nodes will form an outer triangle with sides approximately one kilometre long, and four nodes will form a central quadrilateral with sides approximately 300 m long.

The sensing array will also require construction of supporting infrastructure by the Antarctic Division:

  • a Central Power Distribution Facility (CPDF) – a small, pre-fabricated building located near the centre of the sensing-node array, containing the centralised uninterruptible power supply for the sensing nodes;
  • a Central Recording Facility (a rack of electronic equipment housed in the Operations building at Davis);
  • power infrastructure (3.3 kV to 415 V AC) connecting the CPDF to the Davis station power supply; and
  • communication (optic fibre) infrastructure connecting the CPDF to the Davis communications system.

Progress so far

Main facility

The Central Power Distribution (CPDF) building was initially constructed at Kingston during the 2015 winter and then flat-packed for shipment to Davis later that summer. Works began in earnest this summer with six pad-footings for the building installed.

A 925 kg mini excavator was slung to site by helicopter, as the site is well away from any access roads or tracks. Placement of the six footings and the steel frame was also undertaken by heli-sling loading. The building was up and clad by the end of December. However, before the cladding could be completed the four control and uninterruptible power supply cabinets needed to be installed – each weighing more than 250 kg.

Over January and February the building internal electrical systems and heating and cooling systems were installed. The building is now being monitored for power demand and internal temperature.

Cable haul

To deliver power to the CPDF building, electrical transformers were installed at the site and station, and high voltage power cables run back to the Davis power supply. To minimise any future maintenance issues the power cables were hauled out in a continuous 6000 m run. With no road access some 2800 m had to be hauled by hand.

The three high voltage power cables and an armoured fibre optic communications cable were installed by early February and power and communications to the infrasound site became operational.

Array element

Another goal was to install at least one of the array sensing node vaults so that the internal temperature and battery health within the insulated stainless steel vaults could be monitored during the 2017 winter. Four of the seven vaults have been installed, partially buried at their specific sites. Only array site two (pictured) has been connected to monitor the system performance, but none of the array sites have their ‘rosettes’ (sound detection tubes) installed as yet.

Next steps

The stability of the internal environment at the CPDF building and the array site two vault will be monitored over the 2017 winter. During the 2017–18 summer the remaining vaults will be installed, along with the rosettes, and all array sites connected back to the CPDF building. Once this work is complete a certification process will be undertaken and a six month long commissioning phase can commence. By late 2018 the facility should be live for detection.

Mark Pekin
Engineer, Australian Antarctic Division