IS26, Freyung, Germany

Bavaria is Germany’s largest state and the country's southeastern province, bordering the Czech Republic and Austria. As one of the few places in Europe where nature is still left largely to its own devices, the Bavarian Forest offers spectacular views of alpine peaks and crystal clear forest streams. It reveals the last vestiges of pristine mixed woodlands and mountain forests with ancient fir trees, pines and beech trees reaching heights of over 50 m.
The Bavarian Forest is also home to lynx, fox, deer, wild boar, otters and badgers. Over 50 species of woodland birds can be observed in the wildlife enclosure. Through a successful reintroduction programme, the eagle owl, Ural owl and raven once again dwell in the Bavarian Forest.

It is here in the Bavarian forest near the small village of Bischofsreut in southeastern Germany that infrasound station IS26, Freyung, is co-located with primary seismic station PS19. IS26 monitors for infrasonic signals from within the Bavarian Forest National Park, which in 1970 became Germany’s first national park. Both stations can be accessed all year round for repairs and maintenance. Station Profile IS26 was installed in 1999 as one of 60 infrasound stations of the CTBTO's International Monitoring System (IMS) to monitor the atmosphere for ultra-low sound waves emitted by nuclear explosions. The site survey for IS26 was carried out as a collaborative project between the CTBTO Provisional Technical Secretariat (PTS) and the German Federal Institute for Geosciences and Natural Resources. The final Site Survey Report was completed in July 1998 and most of the work on the construction of the station finished by early October 1999.

The Freyung infrasound station is a five-element infrasonic array. It was constructed to take advantage of the geography of the Bavarian Forest, which provides ample shelter from ambient winds that can interfere with the atmospheric pressure sensors, or micro-barometers. An efficient wind-noise-reducing pipe array is installed at the input to each micro-barometer.This device provides an effective means to reduce the influence of micro-pressure fluctuations produced by turbulent eddies in the wind. Learn more about how the infrasound technology works.

Data transmission to the German National Data Centre in Hannover commenced in October 1999, while the International Data Centre (IDC) in Vienna started receiving transmissions in May 2000. After the initial testing period, a certification visit was carried out in August 2000.
In addition to infrasonic data, IS26 also monitors meteorological data, such as air temperature, wind speed and barometric pressure. These data from each array element are reformatted at the Central Processing Facility (CPF) into 20-second data frames, authenticated and then transmitted via the Global Communications Infrastructure (GCI) to the IDC in Vienna.

IS26 was the first infrasound station in the 60-station global network to undergo testing and evaluation to assess the operation and performance of the station and its ability to meet the minimum requirements for an IMS infrasound station. This phase began in October 1999 and the GCI was installed in early May 2000. Authenticated data has been received accurately and reliably at the IDC in Vienna from all array elements since October 2000. Accordingly, IS26 became the first fully certified infrasound station in the IMS network on 10 April 2001.
Apart from the  infrasound and primary seismic stations mentioned above, Germany hosts one other infrasound station in Antarctica and a radionuclide station in southern Germany.