Large-Scale 3D Baseline Measurement Based on Phase-Stabilized GNSS-Over-Fiber System

Multi-antenna GNSS-over-fiber system is considered an effective solution for three-dimension (3D) baseline measurement. By precisely determining the transmission time delays between the antennas and the receiver, the vertical precision can be improved based on the single difference (SD) model. This method, however, would encounter problems if the baseline is too long, since a high precision measurement of the time delay of a long fiber link is usually time-consuming. Here, we propose and demonstrate a high-speed phase-stabilized GNSS-over-fiber system for large-scale 3D baseline measurement. A relatively slow but accurate time delay measurement module is used to calibrate the link delay, then a fast active compensation device is employed to keep the time delay constant. If the delay variation exceeds the compensation range, the time delay measurement module would measure the link delay again and bias the active compensation device at a new operating state. In a proof-of-concept experiment, the precision of the 3D baseline measurement obtained by the proposed system with a 20-km optical fiber is around 2.82 mm thanks to the rigid active compensation and the high-precision time delay measurement. If the active compensation device is disabled, the vertical precision of the baseline measurement obtained would be degraded from 2.82 mm to 16.46 mm in 10 minutes.