CORS Networks
Continuously Operating Reference Stations
Continuously Operating Reference Station (CORS) networks are modern, high-precision geodetic infrastructures used for accurate positioning. They consist of a network of permanently installed reference stations that operate continuously, collecting data from Global Navigation Satellite Systems (GNSS) and providing correction data to users, enabling significantly higher positioning accuracy. CORS networks are widely used in geodesy, surveying, mapping, construction, geodynamics, and any application requiring precise positioning.
The operation of CORS networks is based on GNSS technology. CORS stations are equipped with multi-frequency GNSS receivers capable of tracking signals from one or more GNSS constellations simultaneously, increasing both the accuracy and reliability of positioning measurements.
A typical CORS station consists of several key components. It includes a high-precision geodetic GNSS antenna mounted on a stable monument to ensure long-term positional stability. The antenna is connected to a GNSS receiver that continuously records satellite observations. The station also includes data logging and storage equipment, communication systems for transmitting data over the internet, and a reliable power supply for uninterrupted operation.
The main advantage of a CORS station is that it operates at a location with precisely known coordinates. As the station receives GNSS signals, it computes its position. Since its true coordinates are already known, the difference between the calculated position and the known position represents the error affecting the satellite observations. Based on this difference, the station computes correction data to compensate for the various error sources affecting GNSS measurements.
These errors mainly originate from the Earth's atmosphere, satellite orbit inaccuracies, and clock errors in both satellites and receivers. CORS stations therefore calculate corrections related to the ionosphere, troposphere, satellite orbits, and clock biases. These corrections are transmitted to network users and are applied to significantly improve positioning accuracy.
There are two primary methods of using data from a CORS network. The first is real-time positioning, using techniques such as Real-Time Kinematic (RTK) and Network RTK (NRTK). In this case, the user operates a GNSS receiver in the field that connects to the CORS network via the internet and receives correction data in real time. This method typically achieves positioning accuracy of 1–3 cm.
The second method is Post-Processed Kinematic (PPK) positioning. In this workflow, the user collects GNSS observations in the field using their own receiver and later downloads observation data from a CORS station. The datasets are processed afterward using specialized software, allowing even higher positioning accuracy, which can reach the millimeter level.
CORS stations generally operate as part of a larger network. These networks simultaneously process observations from multiple reference stations and generate regional error models covering an entire geographical area. As a result, they provide more accurate corrections than those generated by a single reference station. Such networks often implement techniques such as Virtual Reference Stations (VRS), enabling users to receive correction data specifically optimized for their location.
The positioning accuracy achieved through a CORS network is significantly higher than that of a standalone GNSS receiver because the network continuously processes observations from multiple permanently installed reference stations distributed throughout a geographical region. For example, a standalone GNSS receiver typically provides an accuracy of approximately 3 to 10 meters. Differential GNSS corrections improve this to approximately 1 to 3 meters, while RTK positioning achieves centimeter-level accuracy. With post-processing techniques such as PPK, positioning accuracy can be improved further to the millimeter level.
Tersus PNW is an advanced CORS network management and high-precision positioning software platform independently developed by Tersus GNSS, incorporating optimized positioning algorithms. The software efficiently models errors caused by the ionosphere, troposphere, and satellite orbits, accurately computing the correction data transmitted to GNSS rovers. This enables receivers to achieve rapid real-time positioning with centimeter-level accuracy. The reliability and stability of Tersus PNW have been demonstrated through the operation of large-scale CORS networks, making it a dependable solution for high-precision applications including surveying, geodesy, deformation monitoring, and other positioning-critical projects.