Very Long Baseline Interferometry (VLBI),

The primary mission of NOAA’s National Geodetic Survey (NGS) is to define, maintain, and provide access to the National Spatial Reference System (NSRS). The NSRS is the basis for all civilian positioning applications in the United States. The geometric component (latitude, longitude, and ellipsoid height) of the NSRS is defined using space-geodetic techniques and is accessed via Continuously Operating Reference Stations (CORS) that track Global Navigation Satellite System (GNSS) signals. The CORS provide data continuously, and when combined with their NSRS coordinates, permit users to position their points of interest rapidly and precisely. A modern, high-accuracy NSRS is achieved by connections to the global framework of the International Terrestrial Reference Frame (ITRF). The ITRF is realized through a combination of space-geodetic techniques including: GNSS