Characterization of a global navigation satellite system's vertical measurement system for sea state monitoring

This study investigates the effectiveness of Global Navigation Satellite System (GNSS) signals for measuring vertical displacement (or heave) in dry conditions, using a controlled pendulum to create a wave-like motion. The experiment was conducted using three GNSS receivers operating in different measurement modes: Single Point (SP), Differential GNSS (DGNSS), and Real Time Kinematics (RTK). An Inertial Navigation System (INS), with high precision for navigation applications, was previously verified, then used as a reference in the experiment. The vertical motion, or heave, was obtained from the three receivers, considering the position measurements or by integrating the velocity measurements over time. Results indicate that GNSS velocity measurements are effective, but precision is limited by sensor characteristics. The RTK mode provided the highest accuracy, with a deviation of 2.5 % from the reference signal, followed by DGNSS at 3.5 %, and SP mode at 4 %. Altitude-based heave estimations showed similar trends, with RTK being the most accurate. However, signal loss in the RTK mode poses challenges in the management of measurement data, impacting measurement stability. The findings suggest that, while GNSS-based heave estimation is feasible, improvements in velocity precision and correction signal reliability are necessary for enhanced accuracy. This study provides insights into GNSS-based motion measurement techniques, highlighting their potential and limitations in marine applications.