Experimental research on the shallow ambient noise using a single optical fiber vector hydrophone

An optical fiber vector hydrophone consists of a three-component optical fiber accelerometer and an omnidirectional pressure hydrophone. It can be used to measure both the scalar and vector components of the ambient noise simultaneously. In order to analyze the characteristics of the ambient vector noise field in shallow water, a sea trial was carried out in the South China Sea in July 2012. The spectra of the ambient noise collected in rainy and sunny weather are compared. The rainfall increases the spectral levels of both scalar and vector components. In addition, the horizontal directionality of the ambient noise is estimated by vector beamforming at four different frequencies of 200, 800, 1000 and 1600 Hz. The estimation results show that the anisotropy of the ambient noise increases with frequency. What´s more, the ambient noise is dominant from the open sea in sunny weather, but dominant from all directions in rainy weather. Based on the horizontal directionality of the ambient noise, the theoretical signal-to-noise ratio gains of the X-channel and Y-channel are calculated and compared with the experimental results.