Communicating with the South Pole
Antarctica is one of the most challenging natural environments on earth. The southernmost continent on the globe is also the coldest one. Even in summer average temperatures in most parts of the continent do not climb above freezing point. Due to its extreme latitudes, the continent sinks into almost complete darkness for many months only to be followed by long periods of constant daylight. Yet, despite its forbidding conditions, the place seems to be very inviting to science. It is teeming with scientific outposts. Over 30 countries have established scientific stations on the continent, its surrounding ice shelf or on nearby islands.
The CTBTO Preparatory Commission maintains thirteen stations of its International Monitoring System (IMS) in Antarctica. These stations represent three of the four technologies that are used to monitor the globe for nuclear explosions. Once the Comprehensive Nuclear-Test-Ban Treaty (CTBT) has entered into force, the five seismic, four radionuclide and four infrasound stations will send data to the International Data Centre (IDC) in Vienna where these data will be analysed and then made available to States Signatories in the form of data products. Currently, eight of these stations already send data to Vienna in test operation.
IMS monitoring stations transmit data in near real-time to the IDC in Vienna through the Global Communications Infrastructure (GCI). The GCI normally relies on satellite links using very small aperture technology, also known as VSAT. Six communication satellites are stationed at a height of 36.000 kilometres above the equator at various longitudes. These satellites are geostationary, rotating along with the earth. Under normal circumstances, data from several VSAT sites are sent through these satellites to a central communication hub on the ground and then forwarded to Vienna.
Auxiliary Seismic Station (AS114) at the South Pole is one of the very few exceptions where the usual communication set-up cannot be applied. Due to the station's extreme geographic location at exactly 90° south, the satellites stationed above the equator are not visible over the horizon and the station cannot establish a connection to them. As the Treaty demands constant availability of data, a solution had to be found for this unique situation.
Currently, two older Intelsat satellites are used to provide some coverage for the transmission of data from the station at the South Pole to the IDC in Vienna. These satellites which are operated by the US National Science Foundation are rounding the earth in an inclined orbit above the equator region. For some time during their orbiting, these satellites drift more than 8 degrees south of the equator and can then be seen just over the horizon at the South Pole. In combination, the two Intelsat satellites provide coverage for twelve hours a day. Still, communication needs to be ensured for the remaining twelve hours. This gap will now be filled by satellites of the Iridium network. Iridium is a constellation of 66 communication satellites that round the earth on pole-to-pole orbits at a height of 780 kilometres. This particular constellation design provides for excellent communication coverage at the poles from where other satellites are not visible. For the development of this service, the CTBTO Preparatory Commission again closely cooperated with the US National Science Foundation. In February 2007, communication officer Allan Gray of the CTBTO Preparatory Commission went to the South Pole to inspect the communication set-up at auxiliary station AS114 and to ensure its correct operation. The IMS station is located approximately eight kilometres away from the US-run Amundsen-Scott South Pole Station at an observatory facility of the United States Geological Survey. Staff from the Amundsen-Scott South Pole Station provide for the site AS114 and the associated communication links.
Mr. Gray spent five days at Amundsen-Scott South Pole Station and coordinated the testing and integration of the Iridium constellation into the GCI. He assisted the deployment of equipment and supervised the trial operation. The monitoring station sent test data into the CTBTO communication network through a communications hub in Denver, Colorado, USA. In Vienna, data traffic from the station at the South Pole was closely monitored. A team of CTBTO personnel comprising IMS and IDC staff were on stand-by in Vienna to observe data reception and provide feed-back on data transmission. Since February 2007 the new communication installation is in place. Full coverage of the station AS114 is now possible and data from the station are available in Vienna on a 24-hour basis. The installation of a monitoring station with functioning communication links is always a challenging task. Some stations are built in such difficult locations that they put the ingenuity and creativity of the technical experts to the test. Auxiliary seismic station AS114 is one of these stations. Despite its climatic extremes and its remoteness, the station is now integrated in the global net of CTBTO international monitoring stations through a dedicated communication set-up. It now fulfills the requirement under the CTBT to send data continuously in near real-time to the International Data Centre in Vienna.