|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
VLBI brochure .
Where VLBI Fits into NASA
The GSFC VLBI group is part of NASA's Goddard Space Flight Center:
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
- ITT Corp Information Systems
- manages the Goddard Geophysical and Astronomical Observatory
- operates the Kokee Park Geophysical Observatory
- supports masers and receivers