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final image before content GSFC VLBI Overview


On the most basic level, Very Long Baseline Interferometry, or VLBI, is a geodetic technique that determines the positions of observing stations (sites) on the Earth by measuring the time it takes a radio wavefront from a quasar (source) to reach pairs of sites. For each pair, as the wavefront travels from the source at a constant rate in all directions, the front will arrive at each site at a different time, yielding differences in position, or distance, between the sites. As these distances are measured over time for a network of sites, site positions and position changes over time can be measured. Other factors must be applied to model complications in observing -- for example, changes in the atmosphere that slow the wavefront down. A good expansion of this explanation is available in the 1990's VLBI brochure .

Where VLBI Fits into NASA

The GSFC VLBI group is part of NASA's Goddard Space Flight Center:

==> + NASA's Goddard Space Flight Center
==> ==> + Sciences and Exploration Directorate (SED), Code 600
==> ==> ==> + Solar System Exploration Division (SSED), Code 690
==> ==> ==> ==> + Planetary Geodynamics Laboratory, Code 698
==> ==> ==> ==> ==> GSFC VLBI group


The GSFC VLBI group studies the Earth and coordinates the international study of the Earth using the geodetic technique of VLBI. The GSFC VLBI group also supports general solar system exploration by providing data that missions (e.g., Cassini-Huygens and the Phoenix Mars Lander) use in calculating their flight paths.

The group is composed of GSFC civil servants, who oversee the group, and employees from three contractor companies:
  • NVI, Inc.
    • technique improvement research
    • software development (Field System, SKED, Calc/Solve)
    • data analysis
    • IVS Coordinating Center operations
    • IVS network support
  • Raytheon ITSS
    • network support
  • ITT Corp — Information Systems
    • manages the Goddard Geophysical and Astronomical Observatory
    • operates the Kokee Park Geophysical Observatory
    • supports masers and receivers


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