A Continuously Operating Reference Station (CORS) is a permanently installed, precisely surveyed GNSS ground station that operates around the clock to collect and distribute satellite navigation data. These stations form the backbone infrastructure enabling high-precision GNSS positioning services including Real-Time Kinematic (RTK), Network RTK, Precise Point Positioning (PPP), and post-processed positioning solutions used across surveying, mapping, agriculture, construction, and autonomous systems industries.

Each CORS installation consists of a geodetic-grade GNSS receiver connected to a high-quality antenna mounted on a stable, precisely surveyed monument. The station’s coordinates are determined through rigorous surveying techniques and are defined within established reference frames such as the International Terrestrial Reference Frame (ITRF) or regional datums like NAD83. Because the station’s true position is known with millimeter-level certainty, any discrepancy between this known position and the position calculated from satellite signals reveals the combined errors affecting GNSS observations at that location and time.

CORS stations serve two primary functions in precision GNSS applications. First, they generate correction data that dramatically improves positioning accuracy for nearby GNSS users. By comparing calculated positions against precisely known coordinates, CORS stations quantify errors from atmospheric delays, satellite clock and orbit inaccuracies, and other sources, then transmit these corrections to rovers via internet (NTRIP), radio, or satellite links. Second, CORS stations archive raw observation data that enables post-processed positioning workflows, allowing users to achieve centimeter-level accuracy hours or days after data collection.

Government agencies operate extensive CORS networks that often provide free public access to correction data and archived observations. In the United States, the National Geodetic Survey coordinates the National CORS Network with over 2,000 stations. Similar networks exist worldwide, including EUREF in Europe and GEONET in Japan. Commercial CORS networks operated by private companies supplement government infrastructure, often providing value-added services including real-time correction streaming, quality monitoring, and customer support for professional users.