NVI provides support services to the Goddard VLBI group - a key component of the International VLBI Service for Astrometry and Geodesy (IVS). VLBI - very-long-baseline interferometry - is a type of astronomical interferometry used in radio astronomy. The Goddard group is the IVS Coordinating Center and an IVS Analysis Center. Two NVI staff are members of the IVS directing board, and several staff serve on various IVS working groups. The expertise of NVI staff include expertise includes physics, remote sensing, radio astronomy, geodesy, geophysics, atmospheric sciences, mathematics, computer system, telecommunications and networking. The VLBI measurement technique provides extraordinarily precise measurements of distances between VLBI telescopes, and was the first technique to measure contempoary tectonic plate motion in the 1980s. VLBI also measures the orientation of the Earth's spin axis (the "North Pole") and the rate of rotation of the Earth. Application of this technique has allowed the observation of important scientific phenomena, including the detection of El Nino and La Nina effects. Under a contract with the United States Naval Observatory, NVI provides support for the Washington Correlator. This is one of 3 major geodetic VLBI correlators, and is responsible for processing roughly half of all geodetic VLBI sessions. VLBI is the only technique that can measure changes in the Length of Day and nutation parameters, and plays an important role in measuring other components of Earth Orientation. These parameters are crucial to maintaining the orbit of satellites, including the GPS system, and in performing Deep Space Navigation. Under a separate contract with USNO, NVI provides support services to Naval Observatory Astrometry group. NVI has had shorter term contracts with a variety of customers including JPL, Honeywell, Raytheon, NICT (Japan).
