How GNSS Displacement Monitoring Stations Achieve Millimeter-Level Deformation Detection

By utilizing differential positioning and choke-ring antennas to suppress multipath errors, GNSS displacement monitoring stations can provide stable, millimeter-level 3D coordinate data—even during long-term, unattended operation in the field—thereby offering a continuous and reliable basis for assessing engineering safety.

In the field of engineering safety monitoring, the primary requirements for displacement data are high precision and continuity. The effectiveness of GNSS displacement monitoring stations in applications such as dams, bridges, and landslide-prone areas stems from their ability to elevate satellite positioning from "meter-level navigation" to "millimeter-level observation." In static differential mode, these systems can achieve a horizontal precision of ±(2.5 mm + 1 ppm) and a vertical precision of ±(5 mm + 1 ppm)—a level of accuracy sufficient to detect subtle changes that are invisible to the naked eye but may signal potential structural risks. Achieving this level of precision depends on the equipment's capacity to control error sources, with antenna design playing a critical role.

Multipath effects are a common source of interference in GNSS monitoring. When satellite signals reflect off the ground or nearby structures before reaching the antenna, they interfere with the direct signals, leading to inaccuracies in coordinate calculations. Choke-ring antennas, combined with magnetic wave-absorbing materials, help suppress these reflected signals, making the antenna less sensitive to interference arriving from low-elevation angles. For monitoring stations installed on dam crests or bridge abutments—where complex surrounding surfaces often cause significant signal reflection—this design is essential for ensuring that the collected data remains clean and usable. Furthermore, the equipment supports RTCM3 differential data input; when used in conjunction with a reference station or a network-based RTK service, it can further mitigate common error sources, such as ionospheric delays and satellite orbital errors.

Another challenge for long-term field deployment is ensuring reliable communication and data processing. Some monitoring sites are located in remote areas with unstable 4G coverage; relying solely on cloud-based processing could lead to data loss if the network link is interrupted. To address this, the equipment supports the Modbus-RTU communication protocol and features edge-based offline processing capabilities, allowing for local calculation of displacement—including both vertical and horizontal components. This means that even if network connectivity is temporarily lost, raw observations and calculated results are retained locally on the device and can be transmitted once communication is restored, thereby reducing the risk of data gaps. The device operates within a temperature range of -40°C to +85°C and a humidity range of 0% to 95% RH (non-condensing), making it well-suited for the climatic conditions typical of most field monitoring sites in China.

In terms of installation, the unit—measuring 360 mm in diameter and 163 mm in height—is relatively compact and easy to transport and deploy; however, the stability of the mounting base requires special attention. GNSS monitoring is highly sensitive to the stability of the antenna phase center; even the slightest vibration in a mounting pole or concrete pier will be interpreted by the processing software as a displacement signal. In practice, the device should be secured to a concrete pier or a similarly stable structure, with the antenna positioned to ensure a clear field of view, free from obstructions or surfaces that could cause strong signal reflections. While these installation details may seem elementary, they are critical in determining whether the resulting data can be reliably used to assess trends.

Regarding data integration, the device supports both the Modbus-RTU protocol and the RTCM3 standard, facilitating its incorporation into existing monitoring systems. Whether connecting to a PLC environment or a cloud-based platform, this protocol compatibility minimizes the need for additional development. For water conservancy or transportation projects that already have safety monitoring systems in place, new GNSS stations can be integrated without requiring an overhaul of the existing architecture; data can simply be fed into the established database and early-warning workflows. The true value of monitoring lies not in individual readings, but in the accumulation and comparison of data over long time series. If displacement trends begin to accelerate or shift direction abruptly, the system can provide timely alerts, allowing for on-site verification and intervention. This, in essence, is the role of a GNSS displacement monitoring station within the engineering safety chain: it does not replace human judgment, but rather provides the high-density data support necessary to inform such judgments.