Low cost GNSS instruments for monitoring applications using Galileo

Low-cost multi-frequency GNSS receivers have recently become a viable alternative to geodetic-grade instrumentation for deformation and displacement monitoring applications. Among current GNSS constellations, Galileo offers specific advantages for such applications, including signal authentication through the Open Service Navigation Message Authentication (OSNMA), which enables navigation message authentication and increases the reliability of GNSS-based monitoring system. This study investigates the capability of low-cost GNSS instrumentation to detect millimetric displacements by using only Galileo observations. A dedicated experimental test network composed of five sites was established, where low-cost and geodetic-grade receivers operated simultaneously under identical conditions. At the central monitoring site, controlled three-dimensional displacements were imposed using a calibrated triaxial translation sledge. Three low-cost antennas with similar electronic electrical characteristics but different costs were tested in combination with a dual-frequency u-blox receiver. The collected datasets were processed on a daily basis using both Precise Point Positioning (PPP) and relative positioning approach, relying exclusively on Galileo E1 and E5a signals. The results demonstrate that low-cost GNSS systems can achieve coordinate repeatability comparable to geodetic-grade solutions, particularly for horizontal components. Millimetric horizontal displacements (≥ 2.5 mm) are reliably detected in PPP, while relative positioning enables detection down to 1 mm for short baselines (100 m). Vertical displacement sensitivity is more dependent on antenna quality, highlighting the critical role of antenna design. Overall, the results confirm that low-cost Galileo-based GNSS systems represent a reliable and cost-effective solution for long-term displacement monitoring applications, provided that appropriate antenna choice and processing strategies are adopted.