The VLBI correlator in Bonn

Historical Development

Participation in astronomically motivated VLBI activities at the Max Planck Institut for Radioastronomy (MPIfR) dates back to the early seventies. The first VLBI processor (a copy of NRAO's 3-baseline MKII correlator) was installed at the institute in 1978. Aready in 1979 the first geodetic observation was correlated under the direction of the Geodetic Institute of the University of Bonn (now Institute for Geodesy and Geoinformation of Bonn University [IGG]). Routine correlation for the European VLBI Network (EVN) began in 1980. The MKII correlator was taken out of operation in 1992.

In 1982 a MKIII correlator was aquired from MIT Haystack Obervatory; geodetic correlation switched to the MKIII system in Bonn in 1983. The first correlation of the IRIS series was performed in Bonn in 1984. In 1989 a copy of Haystack's MKIIIA correlator became operational with a capacity of up to 12 baselines. It had been implemented at MPIfR with the 'multi-wire' technique and was taken out of operation in mid-2000. The MKIII correlator remained operational until summer 1999.

The first of the geodetic EUROPE observation series was correlated in 1990, the first O'Higgins (Antartika) observation in 1995. In the middle of the 90th the Institute for Applied Geodesy (IFAG - today named Federal Agency for Cartography and Geodesy [BKG]) agreed with the MPIfR to jointly acquire and operate the MKIV correlator. It was installed by Haystack at MPIfR in December 1999.

In 1993 MPIfR and BKG signed an MoU to build and operate a MKIV correlator on a 50/50 basis. This fruitful cooperation meanwhile resulted in the new Distributed FX (DiFX) correlator (Deller et al.,2007) which was installed in 2007/2008. It is the first software correlator used at MPIfR. In 2015 it is planned to upgrade the current DiFX cluster to a brand-new system.


Today the correlator in Bonn is operated jointly by the Federal Agency for Cartography and Geodesy [BKG] in cooperation with the Institute for Geodesy and Geoinformation of Bonn University [IGG] and the Max Planck Institute for Radio Astronomy [MPIfR].

The correlator is a supercomputer able to compare the signals from a quasar (quasi stellar radio source) arriving at two telescopes and to measure the difference in arrival time of the signals at the telescopes. The difference in arrival time depends on the position of the quasar and the positions of the telescopes. This technique localizes telescopes separated by up to 10000 km with millimetric precision. These positions are used to study the Earth tectonic, the polar motion, Earth rotation, and other geophysical phenomena.
The data recorded at the stations are saved on computer disks and then shipped to the correlator or transferred via high-speed network connections. About 25 % of the yearly scheduled geodetic experiments are correlated in Bonn:

  • IVS-R1 experiments to measure the Earth Orientation Parameters (EOP).
  • EUROPE-VLBI sessions to determine the intra-European plate stability and tectonically induced strain accumulation.
  • Southern Hemisphere VLBI Project (IVS-OHIG sessions) to evaluate the southern hemisphere station displacements.
  • One hour-long intensive sessions yield one UT1 measurement daily. The Monday observations (IVS-INT3) are scheduled and correlated in Bonn.
  • IVS-T2 sessions to monitor the Terrestrial Reference Frame (TRF).

More information about the VLBI correlator.

Our main fields of work are

  • Project management VLBI-Correlator
  • Correlation of geodetic VLBI observations
  • Primary analysis and quality control of correlated data
  • Safeguarding the integrity of the correlated data
  • Post processing the experiment
  • Scheduling VLBI experiments
  • Analysis of the performance of the observing stations
  • Disk logistics and e-transfer
  • Maintenance of e-transfer webpage
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