Short answer
A permanently-installed GNSS receiver streaming raw measurements 24/7. CORS networks are the backbone of RTK and network-RTK services, geodetic monitoring, and post-processed precise positioning. Typical inter-station spacing is 50–100 km for regional RTK, 200–300 km for national geodetic networks.
Detailed explanation
A CORS station consists of a survey-grade GNSS antenna (typically a 3D choke ring on a stable monument), a multi-frequency multi-constellation receiver, a stable AC + UPS power supply, and a continuous internet uplink streaming RTCM-3 or RINEX data. Stations log every measurement at 1 Hz or higher and feed it to network operators that produce RTK / NRTK corrections, datum monitoring, post-processed PPP services, and geodetic research.
CORS networks underpin almost every commercial RTK service: state DOTs run them for transportation, surveyors run them for cadastral work, IGS runs the global network for geodesy. Inter-station spacing depends on application — 50–100 km for regional RTK (so any rover is within usable baseline of three stations), 200–300 km for national geodetic frame realisation, 5,000+ km for IGS global tracking.
Antenna selection for CORS is the single most consequential equipment choice — the antenna stays in service for 10–20 years, and any phase-centre drift accumulates into a measurable position bias. The IGS and NGS publish antenna calibration files (igs14.atx, then ATX files) that absolute-calibrate each tested model to within fractions of a millimetre.
GNSource sells choke-ring and multi-band geodetic antennas designed for CORS-class deployment. The TDXL-CA341 is the flagship: 30,000+ hour MTBF, ±1 mm phase centre across full multi-constellation bands, environmental qualification covering salt spray, vibration, lightning, and 30-year-design-life materials.
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High-Precision GNSS Measurement
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Open the toolRelated terms
RTK
A differential GNSS technique using carrier-phase measurements from a known base station to give a moving rover centimetre-level (typically 1–3 cm) horizontal accuracy in real time. The dominant high-precision GNSS technique for cadastral surveying, machine control, and precision agriculture.
PPP
A precise GNSS positioning technique using globally-broadcast precise orbit, clock, and atmospheric corrections to deliver decimetre-to-centimetre accuracy with a single receiver — no local base station required. Convergence times of 10–60 minutes for cm-level; instant for decimetre via PPP-RTK.
Phase center
The apparent electrical centre of an antenna — the point from which signal range is effectively measured by a GNSS receiver. Phase-centre stability (the variation in this point as the signal arrival angle changes) is the single most important parameter for survey-grade and geodetic antennas.
Choke ring antenna
A geodetic GNSS antenna with concentric corrugated grooves around the radiating element that absorb low-elevation signal reflections. Provides the best multipath rejection and most stable phase centre of any commercial GNSS antenna, at the cost of bulk and weight (typical 380 mm diameter, 5–10 kg).