Real Time Global Navigation Satellite System

Monitoring Ground Displacement in Dams, Levees, and Soft Ground Using GNSS with Sub-Centimeter Accuracy

To monitor ground displacement in structures such as dams, levees, or areas with soft ground, high-precision GNSS (Global Navigation Satellite System) techniques can be employed. These methods are capable of detecting movements with an accuracy of less than 1 cm, particularly when combined with post-processing.

High-Precision GNSS Equipment

Use dual-frequency (L1/L2 or L1/L5) GNSS receivers and geodetic-grade antennas capable of tracking signals from multiple satellite constellations (e.g., GPS, GLONASS, Galileo, BeiDou). These receivers are typically installed on fixed monitoring points across the structure.

Static GNSS Surveying

For the highest accuracy, static GNSS surveying is used. This involves collecting raw satellite data over extended observation periods (often from 30 minutes to several hours, depending on baseline length and required accuracy).

Reference Stations

Establish a nearby reference station with known coordinates (either from an existing continuously operating reference station (CORS) or a dedicated base station). The relative position between the reference and the monitoring points is calculated to eliminate common errors (e.g., atmospheric delay, satellite clock errors).

Post-Processing

Post-processing software (e.g., open-source tools like RTKLIB) is used to analyze the collected raw data. Differential GNSS or precise point positioning (PPP) methods can be applied depending on the availability of correction data.
- Differential GNSS(DGNSS/RTK) : Provides high relative accuracy by processing data from both the base and rover stations.
- PPP : Uses precise satellite orbit and clock information to determine absolute positions with high accuracy, often used when no nearby base station is available.

Displacement Analysis

By comparing the processed coordinates over time, it is possible to detect and quantify ground movements. These can be monitored in 3D (horizontal and vertical displacements). The sub-centimeter level of precision allows for early detection of structural deformations or potential failures.

Applications

The Geovan GNSS technique is widely used in :

• Deformation monitoring of embankment dams and levees
• Settlement analysis of soft ground or reclaimed land
• Long-term structural health monitoring of critical infrastructure