GNSS-Over-Fiber Sensing System for High Precision 3D Nodal Displacement and Vibration Detection

Aiming at realizing comprehensive structural health monitoring, a GNSS (Global Navigation Satellite System) over fiber sensing approach is presented and experimentally demonstrated to achieve 3D nodal displacement and vibration detection simultaneously. GNSS signals from multi-antennas are transferred to a receiver based on an optical fiber link, also used as distributed sensing fiber. Broadband linear frequency-modulated (LFM) probe light with high linearity is generated based on electro-optic modulation to probe distributed vibrations and monitor the transmission time delay along the whole fiber with high precision. The spectral components generated by vibrations are detected using the cross-correlation method to achieve distributed vibration sensing. In addition, with the assistance of high-precision hardware-delay measurement, the variation of transmission time delay can be obtained, improving the precision of 3D displacement measurement in the GNSS-over-fiber architecture. In the proof-of-concept experiment, a 3D baseline can be obtained with the precision of 2.8, 3.6, and 2.0 mm, while vibrations with frequencies of 40 kHz, 80 kHz, and 100 kHz along 250 m fiber are successfully detected with a spatial resolution of 1 m.